shown in Figs. 2094, 2095 and 2096, and varies in weight from about
1-3/4 lbs. for heavy chipping to about 1/2 lb. for light work, the
handle being about 15 inches long for the heavy, and about 10 or 12 for
the light business. The round face is usually somewhat convex on its
surface with its edge slightly rounded or beveled. The pane or pene A,
Fig. 2097, is usually made in European practice to stand at a right
angle to the axis of the handle as shown, while in the United States it
is usually made to stand parallel with the handle as in Fig. 2096. The
face end is sometimes given taper as in Figs. 2094 and 2095, and at
others parallel as in Figs. 2097 and 2098, or nearly so. The pene is
mostly used for riveting purposes, and it is obvious that with the pene
at a right angle to the handle axis as in Fig. 2097, it will not matter
whether the pene meets the work quite fair or not, especially as the
pene is made slightly curved in its length, and it is easier to hold the
hammer level sideways than it is to hold it so true lengthways that the
pene, when forward, as in Fig. 2096, will meet the work fair.
[Illustration: Fig. 2099.]
[Illustration: Fig. 2100.]
[Illustration: Fig. 2101.]
The proper shape for the eye of a hammer is that shown in Figs. 2099 and
2100, a representing the top of the hammer. The two sides of the eye are
rounded out from the centre towards each end, while the ends of the eye
are made parallel. The form of the eye as viewed from the top A is as
shown in Fig. 2102, while Fig. 2101 represents a view from the bottom B.
The handle is fitted a driving fit and is driven in from side B, and is
shaped as in Figs. 2103 and 2104 which are side and edge views.
From C to D the handle fills the eye, but from D to E it fills the eye
lengthways only of the oval. A saw-slot, to receive a wedge, is cut in
the handle, as shown in Fig. 2104. The wedge is best made of soft wood,
which will compress and conform itself to the shape of the slot. To
drive the handle into the eye, preparatory to wedging it permanently, it
should be placed in the eye held vertically, with the tool head hanging
downward, and the upper end struck with a mallet or hammer, which is
better than resting the tool head on a block. The wedge should be made
longer than will fill the slot, so that its upper end may project well,
and the protruding part, which may split or bulge in the driving, may be
cut off after the wedge is driven home.
[Illustration: Fig. 2102.]
[Illustration: Fig. 2103.]
The wedge should be driven first with a mallet and finally with a
hammer. After every few blows on the wedge, the tool should be suspended
by the handle and the end of the latter struck to keep the handle firmly
home in the eye. This is necessary, because driving the wedge in is apt
to drive the handle partly out of the eye.
[Illustration: Fig. 2104.]
[Illustration: Fig. 2105.]
The width of the wedge should equal the full length of the oval at the
top of the eye, so that one wedge will spread the handle out to
completely fill the eye, as shown in Fig. 2105. Metal wedges are not so
good as wooden ones, because they have less elasticity and do not so
readily conform to the shape of the saw-slot, for which reasons they are
more apt to get loose. The taper on the wedge should be regulated to
suit the amount of taper in the eye, while the thickness of the wedge
should be sufficiently in excess of the width of the saw-cut, added to
the taper in the eye, that there will be no danger of the end of the
wedge meeting the bottom of the saw-slot.
[Illustration: Fig. 2106.]
By this method, the tool handle is locked to the tool eye by being
spread at each end of the same. If the top end of the tool eye were
rounded out both ways of the oval, two wedges would be required to
spread the handle end to fit the eye, one wedge standing at a right
angle to the other. In this case, one wedge may be of wood and one of
metal, the one standing across the width of the oval usually being the
metal one. The thin edge of the metal wedge is by some twisted, as shown
by Fig. 2106, which causes the wedge to become somewhat locked when
driven in.
In fitting the handle, care must be taken that its oval is made to stand
true with the oval of the tool eye. Especially is this necessary in the
case of a hammer. Suppose, for example, that in Fig. 2107 the length of
the oval of the handle lies in the plane A B, while that of the eye lies
in the plane C D, then the face of the hammer will meet the work on one
side, and the hammer will wear on one side, as shown in figure at E. If,
however, the eye is not true in the hammer, the handle must be fitted
true to the body of the hammer; that is to say, to the line C D. The
reason for this is that the hand naturally grasps the handle in such a
manner that the length of the oval of the handle lies in the plane of
the line of motion when striking a blow, and it is obvious that to
strike a fair blow the length of the hammer should also stand in the
plane of motion.
[Illustration: Fig. 2107.]
The handle should also stand at a right angle to the plane of the length
of the hammer head, viewed from the side elevation, as shown in Fig.
2108, in which the dotted line is the plane of the hammer's length,
while B represents a line at a right angle to A, and should, therefore,
represent the axial line of the hammer handle. But suppose the handle
stood as denoted by the dotted line C, then the face of the hammer would
wear to one side, as shown in the figure at D.
In the operation of straightening iron or steel plates by hammer blows,
the process when correctly carried out is one of liberating the strains
(whose existence throws the plate out of a true plane) by stretching
those parts that are unduly contracted. Every hammer blow should,
therefore, be directed towards this end, for one misdirected blow
entails the delivery of many others to correct its evil influence;
hence, if several of such misdirected blows are given, the plate will
have upon it a great many more hammer marks, or "hammer sinks" or chops,
as they are sometimes termed, than are necessary. As a result, not only
will the painter (in fine work) be given extra trouble in stopping the
hollows to make a smooth surface, but the following evil will result:
Every blow struck by the hammer compresses and proportionately stiffens
the small surface upon which it is delivered, and creates a local
tension upon the surrounding metal. The misdirected blows then cause a
tension acting in opposition to the effect of the properly delivered
ones; and though the whole plate may be stiffened by the gross amount of
blows, yet there will be created local tensions in various parts of the
plate, rendering it very likely to spring or buckle out of truth again.
If, for example, we take a plate of iron and hammer it indiscriminately
all over its surface, we shall find it very difficult to straighten it
afterwards, not only on account of the foregoing reasons, but for the
additional and most important one that the effect of the straightening
blows will be less, on account of the hammered surface of the plate
offering increased resistance to the effects of each blow; and after the
plate is straightened, there will exist in it conflicting strains, an
equilibrium of which holds the plate straight, but the weakening of any
of which will cause the preponderance of the others to throw the plate
out of straight; for the effects of the blows cannot be permanent unless
the whole body of the iron is acted upon to an equal extent by the
hammer. Suppose, for example, that we take a flat plate, and deliver
upon it a series of blows round about its centre. The effect will be to
make it hollow on one side and rounding on the other, the effect of the
blows being, not only to indent the plate in the spots where they fell,
but to carry the whole body of the middle out of true; because, the area
of the iron being increased by the stretching effect of the blows, the
centre leaves the straight line to accommodate the increased area. Thus,
if we mark off a circle of, say, a foot in diameter, in the middle of a
plate, and hammer it so as to stretch it and increase its area 1/8 inch
each way, the form of the plate must alter to suit this added area, and
the form of a dish or curve is the only one it can assume.
[Illustration: Fig. 2108.]
The skilful workman, so soon as he has ascertained where the plate is
out of true, sets to work to stretch it, so as to draw the crooked place
straight, taking care that the shape and weight of the hammer and the
weight of the blows delivered shall bear a proper relation to the
thickness of the plate and the material of which it is composed. If it
is of consequence that the finished work shall bear no marks of the
hammering (as in the case of engravers' plates), an almost flat-faced
hammer is employed; but for other work the shapes, as well as the
weights, of the hammers vary.
[Illustration: Fig. 2109.]
[Illustration: Fig. 2110.]
[Illustration: Fig. 2111.]
Fig. 2109 represents what is called the long cross-face hammer, used in
saw straightening for the first part of the process which is called the
smithing. The face that is parallel to the handle is called the long
one, and the other is the cross-face. These faces are at a right angle
one to the other, so that without changing his position the operator may
strike blows that will be lengthways in one direction, as at A, in Fig.
2110, and by turning the other face towards the work he may strike a
second series standing as at B. Now, suppose we had a straight plate and
delivered these two series of blows upon it, and it will bend to the
shape shown in Fig. 2111, there being a straight wave at A, and another
across the plate at B, but rounded in its length, so that the plate will
be highest in the middle, or at C; if we turn the plate over and repeat
the blows against the same places, it will become flat again. Both faces
of this hammer are made alike, being rounded across the width and
slightly rounded in the length, the amount of this rounding in either
direction being important, because if the hammer leaves indentations, or
what are technically called "chops," they will appear after the saw has
been ground up, even though the marks themselves are ground out, because
in the grinding the hard skin of the plate is removed, and it goes back
to a certain, but minute, extent towards its original shape. This it
will do more in the spaces between the hammer blows than it will where
the blows actually fell, giving the surface a slightly waved appearance.
[Illustration: Fig. 2112.]
The amount of roundness across the face regulates the widths, and the
amount of roundness in the face length regulates the length of the
hammer marks under any given force of blow. As the thicker the plate the
more forcible the blow, therefore the larger the dimensions of the
hammer mark.
The twist hammer, shown in Fig. 2112, is used for precisely the same
purposes as the long cross-face, but on long and heavy saws or plates,
and for the following reasons, namely: When the operator is engaged in
straightening a short saw he can stand close to the spot he is
hammering, and the arm using the hammer may be well bent at the elbow,
which enables him to see the work plainly, and does not interfere with
the use of the hammer, while the shape of the smithing hammer enables
him to bend his elbow and still deliver the blows lengthways, in the
required direction. But when a long and heavy plate is to be
straightened, the end not on the anvil must be supported with the left
hand, and it stands so far away from the anvil that he could not bend
his elbow and still reach the anvil. With the twist hammer, however, he
can reach his arm out straight forward to the anvil, to reach the work
there, while still holding up the other end, which he could not do if
his elbow were bent. By turning the twist hammer over he can vary the
direction of the blow the same as with the long cross-face.
[Illustration: Fig. 2113.]
[Illustration: Fig. 2114.]
It is obvious that by slightly bending the elbow and turning either of
these hammers over the blows may be caused to be in any required
direction, as shown in Fig. 2113. These two hammers are used for the
straightening or smithing processes, and not to regulate the tension,
because the effects of their blows do not extend equally around the part
struck, but follow the form of the hammer marks, whose shapes are shown
in Fig. 2114, at A and B, the radiating lines denoting the directions in
which the effects extend; obviously the size of these marks depends upon
the shape of the hammer face and the force of the blow.
[Illustration: Fig. 2115.]
[Illustration: Fig. 2116.]
[Illustration: Fig. 2117.]
An inspection of hammered saw plates, however, will show that the marks
(which are scarcely visible, having a merely dulled surface), are
usually about one-half wider than the thickness of the plate, and about
four or five times as long as they are wide. Obviously, also, the
direction of the effects of a blow follow the direction in which the
hammer travels. If, for example, the long cross-face falls vertically
its effects will extend equally all around the hammer mark, as at A in
Fig. 2115, but if the hammer moved laterally to the left while falling
its blows would have more effect on the left-hand side of the mark as at
B, or if it moved away from the operator its effects would extend most
in front as at C, the amount increasing with the force of the blow, and
it may be remarked that quick blows are not used, because they would
produce indentations or chops; hence, the force of the blow is regulated
by the weight of the hammer rather than by the velocity it travels at.
On account of the oval shape of the blow delivered by the long
cross-face and by the twist hammers, the dog-head hammer, shown in Fig.
2116, is used to regulate the tension of the plate or saw, the effects
of its blow when delivered vertically being circular, as at A, in Fig.
2117; obviously, however, if in falling it moved vertically in the
direction of arrow C the effects would extend as at B. But while the
dog-head is used entirely for regulating the tension, it may also be
used for the same purposes as either the long cross-face or the twist
hammer, because the smith operates to equalize the tension at the same
time that he is taking down the lumps; hence he changes from one hammer
to the other in an instant, and if after regulating the tension with the
dog-head he should happen to require to do some smithing, before
regulating the tension in another, he would go right on with the
dog-head and do the intermediate smithing without changing to the
smithing hammer. Or, in some cases, he may use the long cross-face to
produce a similar effect to that of the dog-head, by letting the blows
cross each other, thus distributing the hammer's effects more equally
than if the blows all lay in one direction.
In circular saws, which usually run at high velocity, there is generated
a centrifugal force that is sufficient to actually stretch the saw and
make it of larger diameter. As the outer edge of the saw runs at a
greater velocity than the eye it stretches most, and therefore the
equality of tension throughout the saw is destroyed, the outer surface
becoming loose and causing the saw to wabble as it revolves, or to run
to one side if one side of the timber happens to be harder than the
other, as in the case of meeting the edge of a knot.
The amount of looseness obviously depends upon the amount the saw
expands from the centrifugal force, and this clearly depends upon the
speed the saw is to run at; so the saw straightener requires to know at
what speed the saw is to run, and, knowing this, he gives it more
tension at the outside than at the eye; or, in other words, while the
eye is the loosest, the tension gradually increases towards the
circumference, the amount of increase being such that when the saw is
running the centrifugal force, and consequent stretching of the saw,
will equalize the tension and cause the saw to run steadily.
If the eye of a circular saw is loose, or, in other words, if it is rim
bound when running, it will dish, as in Fig. 2118, and the rounded side
rubbing against the side of the saw slot or kerf, will cause the saw to
become heated and the eye to expand more than the outer edges, thus
increasing the dish. But if the saw strikes a knot on the hollow side it
may throw the dish over to the other side of the saw in an instant. The
remedy is to hammer the saw with the dog-head as shown in the figure,
not touching the eye, and letting the blows fall closer together
towards the circumference.
[Illustration: Fig. 2118.]
[Illustration: Fig. 2119.]
[Illustration: Fig. 2120.]
[Illustration: Fig. 2121.]
[Illustration: Fig. 2122.]
[Illustration: Fig. 2123.]
[Illustration: Fig. 2124.]
On the other hand, if the eye is tight and the circumference loose the
saw will flop from side to side as it runs, and the remedy is to stretch
it round about the eye, letting the blows fall wider apart as the outer
edge of the saw is approached. The combinations of tight and loose
places may be so numerous in circular saws that as the smith proceeds in
testing with the straight-edge he marks them, drawing a circular mark,
as at G, in Fig. 2119, to denote loose, and the zig-zag marks to
indicate tight places. To cite some practical examples of the principles
here laid down, suppose we have in Fig. 2120 a plate with a kink or bend
in the edge, and as this would stiffen the plate there, it would be
called a tight place. To take this out, the hammer marks would be
delivered on one side, radiating from the top of the convexity, as on
the left, and on the other as shown radiating from the other end of the
concavity, as on the right, the smithing hammer being used. This would
induce a tight place at A which would be removed by dog-head blows
delivered on both sides of the plate. Suppose we had a plate with a
loose place, as at G in Fig. 2121. We may take it out by long cross-face
blows, as at A and B, delivered on both sides of the plate, or we might
run the dog-head on both sides of the plate, both at A and at B, the
effect being in either case to stretch out the metal on both sides of
the loose place G, and pull it out. In doing this, however, we shall
have caused tight places at E and F, which we remove with dog-head
blows, as shown. If a plate had a simple bend in it, as in Fig. 2122,
hammer blows would first be delivered on one side, as at A, and on the
other side, as at B. A much more complicated case would be a loose place
at G, in Fig. 2123, with tight places at H, J, K, and L, for which the
hammer blows would be delivered as marked, and on both sides of the
plate. Another complicated case is given in Fig. 2124, G G being two
loose places, with tight places between them and on each side. In this
case, the hammering with the long cross-face would induce tight places
at D and E, requiring hammer blows as denoted by the marks.
[Illustration: Fig. 2125.]
[Illustration: _VOL. II._ =THE HAMMER AND ITS USES.= _PLATE VIII._
Fig. 2127.
Fig. 2128.
Fig. 2129.
Fig. 2130.
Fig. 2131.
Fig. 2132.
Fig. 2133.
Fig. 2134.]
The saw or plate straightener's anvil or block is about 12 by 18 inches
on its face, which must be very smooth and is slightly convex, because
it is necessary that the plate should be solid on the block, directly
beneath the part of its surface which is being hammered, otherwise the
effect of the blows will be entirely altered. If, for instance, A, in
Fig. 2125, represents the straightening block, and B a plate resting
thereon, then the blows struck upon the plate anywhere save over the
very edges of the anvil will have but little effect, because of the
spring and rebound of the plate; and the effect of the blow will be
distributed over a large area of the metal, tending to spring it rather
than give it a permanent set. If the blow is a quick one, it may indeed
indent the plate without having any straightening effect. On the other
hand, by stretching the skin on the upper side of the plate, it will
actually, under a succession of blows, become more bent. In fact, to use
a straightening block, so large in proportion to the size of the plate
that the latter cannot be adjusted so that the part of the plate struck
lies solid on the block, renders all the principles above explained
almost valueless, and is a process of pounding, in a promiscuous way,
productive of hammer marks, and altogether fatal to the production of
true work.
[Illustration: Fig. 2126.]
To straighten the plate shown in Fig. 2125, we place it upon the anvil,
as shown in Fig. 2126, striking blows as denoted at A, and placing but a
very small portion of the plate over the anvil at first; and as it is
straightened, we pass it gradually farther over the anvil, taking care
that it is not, at any part of the process, placed so far over the anvil
as to drum, which will always take place if the part of the plate struck
does not bed, under the force of the blow, well upon the anvil.
The methods employed to discover in what parts a plate requires
stretching, in order to straighten it and to equalize its tension, are
as follow: Suppose we have a plate, say 18 inches by 24, and having a
thickness of 19 gauge, and we rest one end of it upon the block and
support the other end in the left hand, as shown in Fig. 2127; then with
the right hand we exert a sudden pressure in the middle of the plate;
and quickly releasing this pressure, we watch where its bending movement
takes place. If it occurs most at the outer edges, it proves that the
plate is contracted in the middle; while, if the centre of the plate
moves the most, it demonstrates that it is expanded in the middle. And
the same rule applies to any part of the plate. This way of testing may
be implicitly relied upon for all plates or sheets thin enough to be
sprung by hand pressure.
Another plan, applicable for either thick or thin plates, and used
conjointly with the first named, is to stand the plate on edge with the
light in front, as in Fig. 2128; we then cast one eye along the face of
the plate upon which the light falls, and any unevenness will be made
plainly visible by the shadows upon the surface of the plate. The eye
should also be cast along the edges to note any twist or locate any
kinks.
We may take a thin piece of plate in the hands, and if it is loose in
the middle and we lay a straight-edge upon its upper surface, and try to
bend the middle of the plate downward with the fingers, it will go down
under the finger pressure, the straight-edge showing a hollow place in
the middle; and the same thing will occur if the straight-edge be tried
with either side of the plate uppermost. But if the piece be tight in
the middle and we test with the fingers and straight-edge in the same
way, the middle instead of bending downwards, appears to rise up, the
straight-edge showing it to be rounded. In the first case the middle
moves because it is loose, and in the second the edges move because they
are loose.
Fig. 2129 represents a plate for a circular saw that is loose in the
middle, and if we bend the middle down it will become concave on the
top, as shown in the figure. But if it were tight in the middle and
loose at the outer edge, it would become, under the same pressure,
convex on the top, as in Fig. 2130, and here again the part that is
loose moves the most.
In thin saws, such as hand saws, the workman takes the saw in his hands,
as in Fig. 2131, and bends it up and down so that by close observation
he may see where it moves the most, and then discover the loose places,
or he may watch for the tight places, since these are the places he must
attack.
[Illustration: Fig. 2135.]
The sledge hammer used by the machinist is usually made in one of the
two forms shown in Figs. 2132 and 2133, the latter being the most
serviceable because it has two faces which may be used for driving
purposes, which is the only use the machinist has for the sledge hammer.
The coppersmith varies the shape of his hammer faces to suit the nature
of the work, thus Fig. 2134 represents a coppersmith's hammer, its two
faces being of different sizes and of different curvature, and both
being used to form convex surfaces having different degrees of
curvature, it being noted that the curvature of the hammer face is
always less than that of the work. In other forms of coppersmith's
hammers there are two penes and no face, one being at a right angle to
the other, as in Fig. 2135, the penes being rounded as in the figure, or
sometimes square.
[Illustration: Fig. 2136.]
Fig. 2136 represents a coppersmith's hammer with a square nosed pene,
which is sometimes made to stand at a right angle to the handle as in
the figure, and at others parallel to it.
[Illustration: Fig. 2137.]
Fig. 2137 represents the file cutter's hammer, whose handle is at the
angle shown because the chisel is held at an angle, the point or cutting
edge being nearest to the workman; hence if the handle were at a right
angle to the hammer length his arm would require to be considerably
elevated in order to let the hammer face fall fair on the chisel head,
whereas by setting the handle at the angle shown the arm need not be
elevated, and the blow may be given by a movement of the wrist.
[Illustration: Fig. 2138.]
[Illustration: Fig. 2139.]
Figs. 2138 and 2139 represent hammers used by boiler-makers for riveting
boiler seams. The faces are made small so that if the blows are properly
directed the edge of the face will not meet the boiler plate and indent
it. These hammers are made long and narrow so that the weight may lie in
the same direction as the hammer travels in when delivering the blow,
and thus cause the effects of the hammer blows to penetrate deeper than
if the hammer was wider.
In the cooper's hammer, shown in Fig. 2140, the face extends flush up to
the head, thus enabling it to strike a hoop upon a barrel without
danger of the extreme end or top of the hammer meeting the barrel, and
preventing the hammer face from meeting the edge of the barrel hoop when
driving it on the barrel. The face is square and its front edge
therefore a straight line, which is necessary on account of the circular
shape of the hoop of the barrel.
[Illustration: Fig. 2140.]
[Illustration: Fig. 2141.]
The mallet is made in various forms to suit the nature of the work and
the tools it is to be used upon. Thus the carpenter's mallet is a
rectangular block, such as shown in Fig. 2141. It is composed of wood,
because the carpenter's tools are held in wooden handles, and a metal
hammer would split them in course of time. It is rectangular in shape so
that it may be applied to tools held in a corner of the work, where a
round mallet could not, if of sufficient diameter, give the necessary
weight. For such carpenters' or wood-workers' tools as are for heavy
duty, and the tools for which have ferrules at the head of their handles
to prevent them from splitting, the mallet is made cylindrical or round,
as it is termed, and has an iron band at each end to prevent the face
from spreading or splitting.
The stonemason's mallet is also of wood, and is disk-shaped, with the
handle in the centre, the circumferential surface forming the face. The
reason for this is that his tools are of steel and have no handles;
hence if the blow continually fell on the same part or spot of the
mallet face it would sink or indent holes in it, which is prevented by
utilising the whole circumference of the mallet for the face.
An excellent mallet for the machinist's use, for driving finished work
without damaging it, is formed of raw hide secured in a metal eye that
receives the handle. Or for the same purpose a lead hammer is used,
being especially serviceable for setting work in machines.
What is known as pening, or paning, consists of hammering the skin of
metal to stretch it on the side that is hammered. It may be employed
either to bend or to straighten. Suppose, for example, we have a piece
of metal that is bent to a half circle, and if we take a light hammer
and hammer it on the concave side and all over its surface the piece
will straighten out to an amount depending on the amount of pening. Or
if he hammers the convex side the piece will bend to a smaller circle.
The principle involved is, that if one side of a piece is elongated and
the other remains of its original length, the only shape it can assume
to accommodate or permit the elongation is that of a curve of which the
convex side is the longest. It follows, therefore, that the hammer blows
must in pening be sufficiently light to condense or stretch the metal on
one side only of the metal, and not forcible enough to effect it all
through.
In order to accomplish this stretching as rapidly as possible it is
necessary to use a light hammer, with sufficient force to be expended in
condensing the metal at its surface, and to so form the hammer that it
shall expend its force upon the work with a dead blow, that is, with as
little rebound as possible. These results are best accomplished with a
ball pened hammer, such as shown in Fig. 2108 and weighing about 1/2 lb.
The blows should fall dead; that is, the hammer should fall, to a great
extent, by its own weight, the number rather than the force of the blows
being depended upon; hence, the hammer marks will not be deep. This is
of especial importance when pening has to be performed upon finished
work, because, if the marks sink deeply, proportionately more grinding
or filing is required to efface them; and for this reason the force of
the blows should be as near equal as possible. Another and a more
important reason, however, is that the effect of the pening does not
penetrate deeply; and if much of the pened surface is removed, the
effects of the pening will be also removed. The work should not be
rested upon metal, but upon wood.
[Illustration: Fig. 2142.]
[Illustration: Fig. 2143.]
The following are examples of pening. Fig. 2142 represents a shaft bent
as shown, the arms being too wide at A, which may be corrected by pening
at B. If the error was in the arms themselves and not in the stem, the
side faces of the arms would require to be pened. Thus in Fig. 2143 the
distance A is too short, and the pening must be at B C.
[Illustration: Fig. 2144.]
Fig. 2144 represents a strap requiring to be closed across A, the pening
being at C or D. But as pening at D would bend the crown and unpair the
bed of the brasses, it is preferable to pene at C. In either case the
jaws will close as denoted by the dotted lines.
Fig. 2145 represents another common form of connecting rod strap, and in
this case the pening may be most quickly and effectively done at the
crown as denoted by the dots; and as this would alter the inside curve,
the brass or box fitting into it must be refitted. In case the pening
should be overdone it is better to modify it by filing away some of the
pened surface.
Cast iron is more rapidly affected by pening than either wrought iron or
steel. One of the most useful applications of pening is in the case of
moulding patterns, which in time may become warped from the rapping of
the pattern in the mould, and this warping may be corrected by judicious
pening, or suppose that a number of plates, such as represented in Fig.
2146, having been cast, it is found that the ends of the tongues A B
curl up when cooling in the mould, then the tongues may be pened as at C
D, throwing them down to the requisite amount, and thus moulding the
pattern to accommodate the curling in cooling.
[Illustration: Fig. 2145.]
[Illustration: Fig. 2146.]
The riveting usually performed by the machinist is generally upon cold
metal. The blows in this case should fall dead and the riveting be
performed with a view to stretching the metal uniformly and evenly over
the surface to be riveted.
[Illustration: Fig. 2147.]
[Illustration: Fig. 2148.]
An excellent example of cold riveting is given in the crank pin P in
Figs. 2147 and 2148. C is the crank (both being shown in section). The
end of the pin should be recessed as shown at A, so that it may be the
more readily riveted outward to fill the countersink shown in the crank
at B, B. The crank-pin is rested upon a piece of copper D interposed
between it and the iron block E to prevent damage to the finished face
of the crank-pin.
The riveting blows should be given with a ball-faced hammer, and
delivered with a view to stretch the whole end face of the crank-pin
evenly. Otherwise the riveted surface will be apt to split as shown.
This usually occurs from not riveting the area at and near the
circumference sufficiently, although it may occur from riveting that
part of the area too much. The line of travel of the hammer should not
be directly vertical, but somewhat lateral in a direction from the
centre towards the circumference. If the countersink is a deep one, it
is desirable to leave the crank-pin sufficiently too long, so that after
the riveting has proceeded some time the surface of the metal which has
become condensed and crystallized from the direct impact of the hammer
blows, may be chipped away, leaving a surface that is swollen by the
riveting without being so much condensed. This enables a much greater
spreading of the metal without splitting it.
If in this class of work the riveted piece (as the crank-pin) is not
driven in very tight before riveting, the riveting blows will be apt to
jar the pin back. Hence, it is necessary to occasionally drive the pin
home. The riveting should proceed equally all over, as if one side be
riveted in advance of the other it tends to throw the pin out of true.
When, however, the riveting begins to bed the pin, four equidistant
places may be riveted home in advance so as to bring the pin home and
hold it firmly.
[Illustration: Fig. 2149.]
[Illustration: Fig. 2150.]
[Illustration: Fig. 2151.]
THE CHISEL.--The machinist's cold chisel is made from the two forms of
steel shown in Figs. 2149, 2150, and 2151, and of these the former is
preferable because it has two broad flats diametrally opposite and these
form a guide to the eye in holding the chisel on the grindstone, and aid
in grinding the facets that form the cutting edge true. Furthermore, as
the cutting edge is in the same plane as these flats they serve as a
guide to denote when the chisel edge lies parallel to the work surface,
which is necessary to produce true and smooth chipping.
The width of the chisel may be made greater, as in Figs. 2152 and 2153,
for brass or cast-iron work than for wrought iron or steel for the
following reasons. On account of the toughness and hardness of wrought
iron and steel the full force of a 1-3/4 lb. hammer, having a handle 13
inches long, may be used on a chisel about 7/8 inch wide without danger
of causing the metal to break out below the chipping line, but if such a
chisel be used with full force blows upon cast iron or brass the metal
is apt to break out in front of the chisel, the line of fracture often
passing below the level it is intended to chip down to. Hence if a
narrow chisel is used lighter blows must be delivered. But by using a
broader chisel the force of the blow is distributed over a longer length
of cutting edge, and full force blows may be used without danger of
breaking out the metal.
[Illustration: Fig. 2152.]
[Illustration: Fig. 2153.]
[Illustration: Fig. 2154.]
[Illustration: Fig. 2155.]
[Illustration: Fig. 2156.]
[Illustration: Fig. 2157.]
[Illustration: Fig. 2158.]
The cutting end of the chisel should be kept thin, as in that case it
cuts both easier and smoother. The total length of a chisel should not
when new exceed 8 inches, for if made longer it is not suitable for
heavy or smooth chipping, as it will bend and spring under heavy blows,
and cannot be held steadily. The forged part should not exceed about
2-1/2 or 3 inches in length, as a long taper greatly conduces to
springiness, whereas solidity is of great importance both to rapid and
smooth work. The facets forming the cutting edge should be straight in
their widths, as at B in Fig. 2154, and not rounded as at A, so that the
face next to the work may form a guide in holding the chisel at the
proper angle to maintain the depth of the cut. This angle depends upon
the nature of the material to be cut; the facets forming an angle one to
the other of about 65° for cast steel and about 50° for gun metal or
brass. The more acute these angles the nearer the body of the chisel
lies parallel with the work and the more effective the hammer blows.
Thus in Fig. 2155 chisel C is the position of the chisel for wrought
iron, and position D is for steel. The angles should always be made,
therefore, as acute as the hardness of the material will permit. If they
are too acute the cutting edge will be apt to bend in its length, while
if not sufficiently acute they will not cut keen enough; hence the
object is to make them as acute as possible without causing the cutting
edge to bend in its length. For copper and other soft metals the angle
may be about 30° or 35°, the chisel end being kept thin so that it may
not become wedged between the work and the chipping, which will bend but
little, and is, therefore, apt to grip the wedge end of the chisel. The
cutting edge should be slightly rounded in its length, which will
strengthen it and also enable a fine finishing clip to be taken off, as
in Fig. 2156, the width of the chip not extending fully across the
chisel width so that the corners are not under duty and are not,
therefore, liable to break, or dig in and prevent smooth chipping. In
some practice the edge is made straight in its length, as shown in Fig.
2149, which is permissible in heavy chipping when a cape chisel has been
used, but in any event an edge rounded in its length is preferable. If
the edge is hollow in its length, as shown in Fig. 2157, and magnified
in Fig. 2158, the chip acts as a wedge to force the corners outwards as
denoted by the arrows, causing them to break under a heavy cut, and,
furthermore, a smooth cut cannot be taken when the corners of the chisel
meet the work surface.
If the facets are ground under on one side, those on the other, as in
Fig. 2159, the edge will not be parallel with the flats of the chisel,
so that in holding it the flats will not form a guide to determine when
the edge lies parallel to the work surface as it should do. The edge
should also be at a right angle to the length of chisel, as denoted by
the lines, as in Fig. 2160, for if not at a right angle the chisel will
be apt to move sideways after each blow, and cannot be held steadily.
[Illustration: Fig. 2159.]
[Illustration: Fig. 2160.]
The chisel should be held as close to its head as possible, so that the
hand will steady the head as much as possible, and should be pushed
forward firmly and steadily to its cut, which will greatly facilitate
rapid and smooth chipping, and for wrought iron and copper it is found
better to occasionally moisten the chisel with oil or water, the former
being preferable.
[Illustration: Fig. 2161.]
Messrs Tangye, of Birmingham, have introduced the employment of chisel
holders, such as shown in Fig. 2161, the object being to fit to each
holder a number of short pieces of steel for chisels so that a number
can be ground or forged at one time; obviously chisels of different
shapes require different forms of handle.
[Illustration: Fig. 2162.]
[Illustration: Fig. 2163.]
[Illustration: Fig. 2164.]
When a heavy cut is to be taken the cape (Fig. 2162) chisel is used,
first to carry through grooves or channels, such as shown in Fig. 2176
at A, B, and C, the distance apart of these grooves being slightly less
than the width of the flat chisel, whose cut is shown partly carried
across at D in the figure. The width of a cape chisel should gradually
decrease from A to B in Fig. 2163, so that its side will be free in the
groove it cuts, and the chisel head will be free to be moved sideways,
and the direction of the groove may be governed thereby. If the chisel
end be made parallel, as at C in Fig. 2164, it will have no play in the
groove and the head cannot be moved; hence if the groove is started out
of line, as it is apt to be, it will continue so.
[Illustration: Fig. 2165.]
[Illustration: Fig. 2166.]
[Illustration: Fig. 2167.]
[Illustration: Fig. 2168.]
The round-nosed chisel, Figs. 2165 and 2166, may be straight from H
nearly to the point G, but should be bevelled at and near G, so that the
chisel head may be raised or lowered to govern the depth of the cut. Its
round nose should also be wider than the metal higher up, so that the
chisel head may be moved sideways to govern the direction of the cut as
in the cape chisel. The cow mouth chisel, Figs. 2167 and 2168, should be
bevelled from G to the point to enable the governing of the depth of
the cut, and should be of greater curvature than the corner it is to cut
out, so that its corners cannot wedge in the work.
[Illustration: Fig. 2169.]
[Illustration: Fig. 2170.]
The oil groove chisel, Figs. 2169 and 2170, should be wider at the
cutting edge than at A for reasons already stated, and of less curvature
than the bore of the brass or bearing it is to cut the oil groove in.
[Illustration: Fig. 2171.]
[Illustration: Fig. 2172.]
[Illustration: Fig. 2173.]
[Illustration: Fig. 2174.]
[Illustration: Fig. 2175.]
[Illustration: Fig. 2176.]
The diamond point chisel, Figs. 2171 and 2172, may be made in two ways.
First, as in Figs. 2173 and 2174, for shallow holes, and as in Figs.
2171 and 2172 for deep ones. In shallow holes the chisel can be leaned
over, as in Fig. 2176 at _y_, whereas in deep ones it must be held
straight so that the chisel body may not meet the other side of the
hole, slot, or keyway. The form shown in Fig. 2172 is the strongest,
because its point is brought into line with the body of the steel, as
shown by the line Q. The side chisel, Fig. 2175, for cutting out the
sides of keyways or slots, should be bevelled from W to the cutting edge
for the reasons already given, and straight from W to V, the line V W
projecting slightly above or beyond the body U. An application of the
cow mouth chisel is shown at L, and one of the side chisel is shown at Z
in Fig. 2176. All these chisels are tempered to a blue color.
The chisel that is driven by hammer blows may be said to be to some
extent a connecting link between the hammer and the cutting tool, the
main difference being that the chisel moves to the work, while the work
generally moves to the cutting tool. In many stone-dressing tools the
chisel and hammer are combined, inasmuch as that the end of the hammer
is chisel shaped; an example of this kind of tool being given in the
pick that flour millers use to dress their grinding stones. On the other
hand we may show the connection between the chisel and the cutting tool
by the fact that the wood-worker uses the chisel by driving it with a
mallet, and also by using it for a cutting tool for work driven in the
lathe. Indeed, we may take one of these carpenter's chisels and fasten
it to the revolving shaft of a wood-planing machine, and it becomes a
planing knife; or we may put it into a carpenter's hand plane, and by
pushing it to the work it becomes a plane blade. In each case it is
simply a wedge whose end is made more or less acute so as to make it as
sharp as possible, while still retaining strength enough to sever the
material it is to operate upon.
[Illustration: Fig. 2177.]
In whatever form we may apply this wedge, there are certain well-defined
mechanical principles that govern its use. Thus when we employ it as a
hand tool its direction of motion, under hammer blows, is governed by
the inclination of the face which meets the strongest side of the work,
while it is the weakest side of the material that moves the most to
admit the wedge and therefore becomes the chip, cutting, or shaving. In
Fig. 2177, for example, we have the carpenter's chisel operating at A
and B to cut out a recess or mortise, and it is seen that so long as the
face of the chisel that is next to the work is placed level with the
straight surface of the work the depth of cut will be equal; or in other
words, the line of motion of the chisel is that of the chisel face that
lies against the work. At C and D is a chisel with, in the one instance,
the straight, and in the other the bevelled face toward the work
surface. In both cases the cut would gradually deepen because the lower
surface of the chisel is not parallel to the face of the work.
If now we consider the extreme cutting edge of chisel or wedge-shaped
tools it will readily occur that but for the metal behind this fine edge
the shaving or cutting would come off in a straight ribbon, and that the
bend or curl that the cutting assumes increases with the angle of the
face of the wedge that meets the cutting, shaving, or chip.
[Illustration: Fig. 2178.]
I may, for example, take a piece of lead, and with a penknife held as at
A, Fig. 2178, cut off a curl bent to a large curve, but if I hold the
same knife as at B it will cause the shaving to curl up more. Now it has
taken some power to effect this extra bending or curling, and it is
therefore desirable to avoid it as far as possible. For the purpose of
distinction we may call that face of the chisel which meets the shaving
the top face, and that which lies next to the main body of the work the
bottom face. Now at whatever angle either face of the chisel may be to
the other, and in whatever way we present the chisel to the work, the
strength of the cutting edge depends upon the angle of the bottom face
to the line of motion of the chisel, and this is a principle that
applies to all tools embodying the wedge principle, whether they are
moved by a machine or by hand.
[Illustration: Fig. 2179.]
Thus, in Fig. 2179 we have placed the bottom face at an angle of 80° to
the line of tool motion, which is denoted by the arrow, and we at once
perceive its weakness. If the angle of the top face to the line of tool
motion is determined upon, we may therefore obtain the strongest cutting
edge in a hand-moved tool by causing the bottom angle to lie flat upon
the work surface.
[Illustration: Fig. 2180.]
But in tools driven by power, and therefore accurately guided in their
line of motion, it is preferable to let the bottom face clear the work
surface, save at the extreme cutting edge. The front face of the wedge
or tool is that which mainly determines its keenness, as may be seen
from Fig. 2180, in which we have the wedge or tool differently placed
with relation to the work, that in position A obviously being the
keenest and less liable to break from the strain of the cutting process.
[Illustration: Fig. 2181.]
If we now turn our attention to that class of chisel or wedge-shaped
tools in which the cutting edge is not a straight line, but may be
stepped or curved--as, for example, the carpenter's plane blade--we
shall find that so long as the blade stands at a right angle to the
surface it is operating upon, as in Fig. 2183 at B, the shape of surface
it cuts will exactly correspond to the shape of its cutting edge; but so
soon as the tool is inclined to its line of motion its cutting edge
will, if curved, produce a different degree of curvature on the work.
[Illustration: Fig. 2182.]
[Illustration: Fig. 2183.]
Suppose, for instance, that we have in the figure a piece of moulding M
and a plane blade B, and the length of the cutting edge is denoted by A,
Fig. 2182; now suppose that the blade is inclined to its line of motion
(as in the case of carpenters' planes) and stands at C, Fig. 2183: we
then find that the cutting edge must extend to the length or depth D,
and it is plain that the depth of the curve on the moulding is less than
the depth of the cutting edge that produces it; the radius E being less
than of D, so that if we place the cutter C upright on the moulding it
will appear as shown in Fig. 2181. If, therefore, we are required to
make a blade that will produce a given depth of moulding when moved in a
straight line and presented at a given angle to the work, we must find
out what shape the blade must be to produce the given shape of moulding,
which we may do as follows:
In Fig. 2184 let A be a section of the moulding, and if the blade or
knife is to stand perpendicular, as shown at B, Fig. 2183, and if it is
moved in a straight line in the direction of the length of the work,
then its shape would necessarily be that shown at B, Fig. 2184, or
merely the reverse of A. In the position mentioned it could be used only
as a sweep applicable to some few uses, but not adapted to cutting. To
become a cutting tool it must be inclined and stand at some angle of
less than 90° to its line of motion.
[Illustration: Fig. 2184.]
[Illustration: Fig. 2185.]
Thus in Fig. 2185 D B E represents the bottom of the moulding and line
of motion of the cutter, and A B the cutter perpendicular to it, the
highest point of the cutting edge, as _c_ of Fig. 2184, being at _c_,
Fig. 2185. The height or thickness of the moulding cut would be the
space between the lines E B D and _e_ _c_ _f_, but the cutter assuming
the position B C at an angle of 30° from A B, the point _c_ is brought
to _d_; consequently the highest line of the moulding would now be _g_
_d_ _h_, and its thickness less. This is further exhibited in Fig. 2186,
where _a_ represents the original depth section of Fig. 2184 that would
be formed by knife B of Fig. 2184 when standing perpendicular; and G
shows the depth with the same knife when placed as B C, Fig. 2185, or at
30° inclination, and H shows the depth that would be cut with the same
knife or cutter at 45°. It is now evident that every change in the
inclination of the same cutter would effect a change in the shape of
moulding which it cuts, and to produce a given style of moulding the
shape of the cutter must be decided by its inclination, or the angle at
which it is used.
[Illustration: Fig. 2186.]
[Illustration: Fig. 2187.]
The method of projecting a given section of moulding in order to exhibit
the form that the curve of the opening should assume on the face of the
knife, is shown in Fig. 2187. Upon a horizontal line A B C D draw a
section of the required style of moulding, as shown at A E B. To the
right of this draw a line, as F C, to meet the base line A B C D, and as
F C represents the cutter, it must stand at the same angle that the
proposed cutter is to have--in this particular example 30° from the
perpendicular. From the highest point of the section A E B draw a
horizontal line E G, meeting F C in G. From points G and C draw lines,
as C J and G H, of any convenient length, at right angles to F C. At any
distance from G H draw K L parallel to G H, and upon K L trace the
section of moulding A E B, as K M L. Draw lines from the extreme edges K
and L of K M L, as K N, L J, perpendicular to K L, cutting G H and
meeting C J at N and J. E G being parallel to A B C D, G will be the
point on the cutter where the top E of the moulding will come on the
highest point of the cutting edge, and C G will be the entire length of
cutting edge or height of opening measured on the face of the cutter F
C. C J being drawn from the lowest point C of the cutter and G H being
drawn from G, the highest cutting point, both lines at right angles to G
C, then their distance from each other, as P O, must obviously represent
the extreme height of opening in the cutter in its new position or front
view, and K L, representing the width of moulding transferred to N J by
the parallel lines K N and L J, will show the width of opening in the
cutter. Having now the height and width, it only remains to project an
indefinite number of points and trace the curve through them. Divide A B
into a number of parts, and to avoid confusion mark the points of
division thus obtained upon A B--1, 2, 3, 4, &c. Divide K L in an
exactly similar manner and into the same number of parts, and mark the
divisions I., II., III., IV., &c. Erect perpendiculars from points 1, 2,
3, 4, &c., meeting the curve A E B, and from the points thus found on A
E B draw horizontal lines to F C; from the termini of these horizontals
on F C draw the remaining lines parallel to and between G H and C J.
From the divisions _i._, _ii._, _iii._, _iv._, &c., on K L, let drop the
perpendiculars, cutting the other series of lines at right angles. A
point of the curve will then be at the intersection of the line from 1
on A B, with line I on K L; another at the intersection of the line
originating at 2 with that from II, and so on, and the proper curve is
found by tracing from N through the intersections to P, and from P to J.
Then K N being one side of the cutter and L J the other, N P J is the
curve that the opening or cutting edges must have to cut the profile A E
B, with the cutter set at F C, or 30°.
[Illustration: Fig. 2188.]
The same method is shown in Fig. 2188, except that in this case, instead
of dividing A B and K L, the divisions are made directly on the
peripheries A 6 B and K VI. L by stepping round with the dividers. The
cutter F C is shown in this case at an angle of 45°, in order that the
change in form which the curve assumes with the cutter at different
angles may be clearly seen by comparing the curve N P J of Fig. 2187
with the same in Fig. 2188. The two figures are similar in other
respects, and as the lettering is the same on each, the description of
Fig. 2187 will apply equally to Fig. 2188.
[Illustration: Fig. 2189.]
There remains one more case of cutters moving in right lines, and that
is where, besides having an inclination backward, as at F C, Fig. 2187,
making a vertical angle to the line of motion, they are placed at an
angle across the guiding piece also, or "skewing," thus making an angle
to the line of motion on a horizontal plane as well as on a vertical
one. Thus, suppose an ordinary carpenter's plane to have the cutter or
"iron" turned partly round and placed so that the cutting edge, instead
of lying at a right angle across the body, crosses it at some other
angle. Fig. 2189 represents an ordinary carpenter's plane with the blade
so placed. Here the edge, or rather side, D B, of the blade inclines
back at an angle, as A B D, which is 45° in this case, to the
perpendicular line A B on the side of the plane. For convenience call A
B D the vertical angle. The lower or cutting edge E B of the blade also
crosses the bottom of the plane at an angle E B C--30° in this
instance--to a line B C, crossing the bottom at right angles. Now, it is
evident that this latter angle E B C will influence the form of the
cutter, if, instead of being a flat plane, as represented for clearness
in Fig. 2189, it had a cutting edge of curved outline for cutting
mouldings or similar work. But in either case the angle that D B or one
side of the blade makes to E B, or the cutting edge--that is, the angle
D B E--must be found in order to cut off the blank for the cutter or
knife at the right "slant."
[Illustration: Fig. 2190.]
The method given in Figs. 2187 and 2188 of determining the form of
cutter to produce a moulding of given profile now undergoes a
modification where there are two angles to be taken into consideration
instead of one. As an example, suppose a cutter is required that is to
be fixed in such a position in its carrier or block that the handle A B
D, or "vertical angle," of Fig. 2189 is, say, 45°, and the angle E B C,
or "horizontal angle," of Fig. 2189 shall be 30°. Required the angle at
which the bottom of the blank for the cutter must be cut off; or the
angle that the side D B and lower edge B E of Fig. 2189 would make to
each other, measured on the face of the cutter, and required the outline
of cutting edge to be traced on the face of cutter to cut the section of
moulding A E B, Fig. 2190: draw a horizontal line, as A B C D, and erect
a perpendicular, as C R. From C draw C F, making an angle to C R equal
to the "vertical angle," or angle A B D, Fig. 2189, which is 45° in this
case. Draw a profile of the required moulding, as A E B, with its back A
B coincident to the horizontal line A B C D. Draw a horizontal line from
the highest point of the profile, as E, to meet F C in G. Draw parallel
lines C J and G H, from C and G respectively, of any convenient length
and making right angles to F C. At right angles to G H and C J, and
parallel to F C, draw K H J to represent one side or edge of the cutter,
but the angle of the lower end or angle D B E of Fig. 2189 must now be
determined; to do this, draw an indefinite horizontal line, A B C, Fig.
2191, and from any point, as B, drop a perpendicular B D; now, from B
set off on A B C the distance C _b_ of Fig. 2190, obtaining point E, and
from E extend a perpendicular above and below A B C, as F E H. From E on
E F set off distance G _b_ of Fig. 2190, obtaining J on E F. From B draw
a line, making the same angle to B D that the angle E B C is in Fig.
2189, or 30° in this case, and cutting E H in K. Set off distance E K
from E on A C, obtaining L; draw L J. Now, on Fig. 2190, with centre at
H, and radius L J of Fig. 2191, describe arc _w_ _x_, and from J as
centre, on Fig. 2190, and B K of Fig. 2191 as radius, describe arc _y_
_z_. Through the intersection _v_ of arcs _y_ _z_ and _w_ _x_, J L M
must be drawn, making the proper angle to the side J H K of the cutter;
this angle is 69° in this case, as found by construction. From H draw H
N parallel to J L, and from H draw H O at the same angle to H N that B K
is to B D, Fig. 2191, or angle E B C, Fig. 2189. Place a duplicate of A
E B, with its base coincident to H O and corner A at H, as H P R. From R
draw R N at right angles to H R and cutting H N at N; through N draw S N
L parallel to K H J. Then while K H J represents one edge of the cutter,
S N L will be the other, and J L the cutting edge before the opening is
cut out. Divide the curves E B and P R similarly, obtaining points 1, 2,
3, &c., and I., II., III., &c., respectively. From points 1, 2, 3, &c.,
lines are to be drawn parallel to E G, meeting G C, continued from G C
parallel to G H, and meeting H J, and from H J parallel to H N, meeting
N L. From points I., II., III., &c., lines are to be drawn perpendicular
to H R, meeting H N and continued from H N, parallel to H J, to J L,
thus intersecting the first series. Lines from points 1, 2, 3, &c., then
determine the height of different points of the curve, and those from
I., II., III., &c., their location laterally; hence, by tracing through
the intersections of 1 with I., 2 with II., &c., the curve H T L is
obtained. The two outside lines K H J and S N L may now represent the
edges of a piece of steel of which the cutter is to be made, and H T L
will be the contour of cutting edge that must be given it in order that
when, fixed for use at the angles named, it will form the required
moulding A E B.
[Illustration: Fig. 2191.]
[Illustration: Fig. 2192.]
If the chisel, knife, or cutter revolves in a circle, instead of in a
right or straight line, the problem is again different, and the shape of
cutting edge necessary to produce a given shape of moulding is again
altered. Let Fig. 2192, for example, represent the bar or head of a wood
moulding machine, the bar or head revolving in the direction of the
arrow, and the moulding being moved beneath it in a straight line
endways as denoted by the arrow at N.
In order that the nut that holds the cutter to the head may clear the
top of the moulding the highest cutting point of the cutter must not
come nearer to the corner of the head than 1/4 inch. This is shown in
the end view of a 2-1/2 inch cutter head in Fig. 2193, the circle B
representing the path of revolution of the nut. In larger heads the nut
will clear better.
Now we may consider that the cutter simply revolves about a circle whose
diameter is the largest that can be described on the end of the square
bar that drives it.
If, for instance, we look at the end of the bar as it is presented in
Fig. 2195, we see that the circle just fills the square, and that if we
cut off all four corners, leaving the bar round, as denoted by the
circle, the chisel will revolve in the same path as before. Now suppose
we place beneath the revolving chisel a piece of square timber, and
raise this timber while holding it horizontally, as would be done by
raising the work table. It will cut the work to the shape shown in the
two views in the figure, enabling us to observe the important point that
the only part of the work that the chisel has cut to its finished shape
is that which lies on the line A A. This line passes through the axis on
which the bar and cutter revolve, and represents the line of motion of
the work in feeding upward to the chisel.
If now we were to move the work endways upon the table, we should simply
cause the moulding to be finished to shape as it passes the line A;
because all the cutting is done before and up to the time that the
chisel edge reaches this line; or in other words, each part of the
chisel edge begins to cut as soon as it meets the moulding, and ceases
to cut as soon as it reaches this line. We may now draw this circle and
put on it a chisel in two positions, one at the time its lowest cutting
point is crossing the line A and the other at the time the highest point
on its cutting edge is passing the line, these positions being marked 1
and 2 in Fig. 2196; the depth of moulding to be cut being shown at S.
Now, since the chisel revolves on the centre of the circle, the path of
motion on its highest cutting point C will be as shown by the circle B,
and that of the lowest point or end E of its cutting edge will be that
of the circle D, while the depth of moulding it will cut is the distance
between C and E, measured along the line A A, this depth corresponding
to depth shown at S.
[Illustration: Fig. 2193.]
[Illustration: Fig. 2194.]
Clearly when the chisel has arrived at position 2, the moulding will be
finished to shape, and it is therefore plain that it takes a length of
cutter-edge from C to F to cut a moulding whose depth is S, or what is
the same thing, C E.
But to solve the question in this way, we require for every different
depth of moulding to make such a sketch, and the square bar that drives
the chisel is made in various sizes, each different size again altering
the length or depth of chisel edge necessary for a given depth of
moulding.
[Illustration: Fig. 2195.]
[Illustration: Fig. 2196.]
But we may carry the solution forward to the greatest simplicity for
each size of square bar, and for any depth of moulding that can be
dressed on that size of bar, by the following means:--In Fig. 2197 we
have the circle and the line A as before; the depth from C to E being
the greatest depth of moulding to which the square bar is intended to
drive the chisels; while point C is the nearest point to the square bar
at which the top of the moulding must be placed. Line _a_ represents a
chisel cutting at its highest point; line _b_ a chisel cutting the
moulding to final shape at 1/4 inch below C, on the line A; line _c_ a
chisel cutting the moulding to final shape at a distance of 1/2 inch
below point C and measured on the line A; lines _d_, _e_, _f_, _g_, _h_,
and _i_ represent similar chisel positions, the last meeting the point
E, which is the lowest point at which the chisel will cut. Suppose, now,
we set a pair of compasses one point at the centre A of the circle, and
strike the arc _j_; this arc will represent the path of motion of that
part of the chisel edge that would finish the moulding to shape at C;
similarly arc _k_ represents the path of motion of that part of the
chisel edge that cuts the moulding to final shape on the line A, and at
a distance of 1/4 inch below C, and so on until we come to arc _r_,
which represents the path of motion of the end of the chisel. All these
arcs are carried to meet the first chisel position C _a_, and from these
points of intersection with this line C _a_ we mark lines representing
those on a common measuring rule. The first of these from C we mark 1/4,
the next 1/2, the next 3/4, and so on to 2, these denoting the
measurement or depth of chisel necessary to cut the corresponding depth
of moulding. If, for example, we are asked to set a pair of compasses to
the depth of cutting edge necessary to cut a moulding that is an inch
deep, all we do is to set one leg of the compasses at C, and the other
at line 1 on the line C _a_; or if the moulding is to be 2 inches deep,
we set the compasses from C to 2 on line C _a_. We have here, in fact,
constructed a graduated scale that is destined to be found among the
tools of every workman who forms moulding cutters, and if we examine it
we shall find that the line that is marked 1/4 inch from C is not 1/4
inch but about 5/16 inch; its distance from C being the depth of chisel
edge necessary to cut a moulding that is 1/4 inch deep.
[Illustration: Fig. 2197.]
Again, the line marked 1 measures 1-3/16 inch from C, because it
requires a chisel edge 1-3/16 deep to cut a moulding that is one inch
deep. But if we measure from _c_ to the line marked 2 we find that it is
2-1/4 inches from C, and since it represents a chisel that will cut a
moulding two inches deep, we observe that the deeper the moulding is the
nearer the depth of cutting edge is to the depth of moulding it will
produce. This occurs because the longer the chisel the more nearly it
stands parallel to the line A, at the time when its point is crossing
the line A. Thus, line _i_ is more nearly parallel to A than line _a_
is, and our scale has taken this into account, for it has no two lines
equally spaced; thus, while that marked 1/4 is 5/16 inch distant from C,
that marked 1/2 is less than 5/16 inch distant from that marked 1/4, and
this continues so that the line marked 2 is but very little more than
1/4 inch from that marked 1-3/4. Having constructed such a scale we may
rub out the circle, the arcs, the line A, and all the lines except the
line from C to _a_ and its graduations, and we have a permanent scale
for any kind of moulding that can be brought to us.
If, for example, the moulding has the four steps or members _s_, _t_,
_u_, _v_, in the figure, each 1/2 inch deep, then we get the depth of
cutter edge for the first member _s_ on our scale, by measuring from _c_
to the line 1/2 on line C _a_. Now the next member _t_ extends from 1/2
to 1 on the moulding, and we get length of cutter edge necessary to
produce it from 1/2 to 1 on the scale. Member _u_ on the moulding
extends from 1 to 1-3/4; that is to say, its highest point is 1 inch and
its lowest 1-3/4 inch from the top of the moulding, and we get the
length for this member on a scale from the 1 to the 1-3/4; and so on for
any number of members.
After the depth of cutting edge for each member has thus been found, it
remains to find the exact curve of cutting edge for each step, and, in
doing this, the same scale may be used, saving much labor in this part
also of the process, especially where a new piece of moulding must be
inserted to repair part of an old piece that needs renewal in places
only, as is often the case in railroad cars.
In Fig. 2197A we have a scale or rule constructed upon the foregoing
principles, but marked to sixteenths, and it may now be shown that the
same scale may be used in finding the actual curve as well as the depth
of cutter edge necessary to produce the moulding of any member of it.
Let the lower curves _s_, _t_, for example, represent the moulding to be
produced, and the upper outline represent the blank piece of steel of
which the cutter is to be made, the edges C, D being placed in line one
with the other. We may then draw across both the moulding and the steel,
lines such as E E, F F, G G, H H, I I, J J, all these lines being
parallel to the edges C, D. To get the total depth of cutter edge for
the moulding we measure with a common measuring rule the total height of
the moulding, and supposing it to measure an inch, we set a pair of
compasses to an inch on our cutter scale, and with them mark from the
base _m_ of the steel, the line P giving total depth of cutter edge. We
next measure with a common rule the depth of member _s_ of the moulding,
and as it measures 1/2 inch we set the compasses to the 1/2 on the
cutter scale, and with these compasses mark from line _m_ line B,
showing the depth of member _s_. In order to find the exact curve for
each member, we have first to find a number of points in the curve and
then mark in the curve by hand, and it is for the purpose of finding
these points that the lines E E, F F, G G, H H, I I, J J, have been
drawn. These lines, it may be remembered, need not be equally spaced,
but they must be parallel, and as many of them may be used as
convenient, because the greater their number the more correctly the
curve can be drawn.
[Illustration: Fig. 2197A.]
[Illustration: Fig. 2198.]
[Illustration: Fig. 2199.]
The upper edge or base line, _m_ _m_, both of the steel and of the
drawing, is that from which all measurements are to be taken in finding
the points in the curve, which is done as follows: With an ordinary
measuring rule we measure on the moulding and from line _m_ _m_ of the
moulding as a base the length of the line F F below _m_ _m_, to the
curve, which in this case measures say 5/16 inch; we then set a pair of
compasses or compass calipers to the 5/16 on the cutter scale, and from
base _m_ _m_ on the cutter steel, mark, on line F F, an arc, and where
the arc cuts F F is one point in the curve.
Similarly we measure on the moulding, or drawing of the moulding, the
length of line G G from line _m_ _m_ to the moulding curve, and find
that it measures, say 7/16 inch, hence we mark from base line _m_ _m_ of
the steel, on line G G, arc V, distant 7/16 according to the cutter
scale. Similar measurements are taken at each vertical line of the
drawing which represents the moulding, and by means of the corresponding
divisions of the cutter scale, arcs are marked on the vertical lines on
the cutter steel, and where the arcs cut the vertical lines are points
in the curve, and through these points the curve may be drawn by hand.
We may make a cutter scale from an ordinary parallel rule, marking one
end to correct inches and the other end for a cutter scale. Measurements
from the moulding may then be made on one end of the rule; measurements
for the cutter may be taken from the other end of the rule, and the rule
may be used at the same time to draw the parallel lines E E, &c. Or, as
each size of cutter head requires a different cutter scale, we may make
a rule out of a piece of box or other close-grained wood, say 3/4 inch
square, using one side for each size of cutter head. One end of each
face of this rule may be marked in correct inches and parts of an inch
(the divisions being thirty-seconds of an inch), and the other end may
be marked as a cutter scale, the divisions being found as described with
reference to Fig. 2197.
An instrument, patented by R. Drummond, for finding the depth of cutting
edge and also for finding the curves, is shown in Figs. 2198 and 2199.
It consists essentially of a bar G bent at a right angle, thus making
two arms. Upon one arm is a slide W (best seen in Fig. 2199) secured by
a set-screw B, and having at A a pivot to carry a second bar H, which is
slotted throughout its length to permit bar G to slide freely through
it. Upon the other arm of G is a slide P secured by a set-screw C, and
carrying a compass point E. The bar H carries an adjustable slide Z
secured by a set-screw D and carrying the compass point F.
[Illustration: Fig. 2200.]
In using the instrument but three very simple operations are necessary.
First, the two slides W and P are set to the numerals on the bar, which
correspond to the size of the head on the moulding machine the cutter is
to be used upon; thus in Fig. 2199 they are shown set to numeral 2, as
they would be for a 2-inch cutter head. The instrument is next opened,
its two bars occupying the position shown in Fig. 2199, and the two
compass points are set to the height of the moulding or to any desired
member of it, as the case may be. The bars are then opened out into the
position shown in Fig. 2200, and the compass points at once give the
depth of cutter edge necessary to produce the required depth of
moulding.
It will be noted that the pivot A represents the centre upon which the
cutter revolves, and that while the face of the bar H corresponds to the
line of moulding formation answering to line A A in Fig. 2196, the face
of bar G corresponds to the face C F of the cutter in Fig. 2196; hence
the instrument simply represents a skeleton head and cutter, having
motions corresponding to those of an actual cutter head and cutter.
[Illustration: Fig. 2201.]
[Illustration: Fig. 2202.]
THE FILE.--The file is a piece of hardened steel having teeth produced
upon its surface by means of rows of chisel cuts which run more or less
diagonally across its width at an angle that is varied to suit the
nature of the material the file is to be used upon. The vertical
inclination of the tooth depends upon the inclination of the face of the
chisel with which it is cut, the two being equal, as is shown in Fig.
2201, which is an enlarged view of a chisel and some file teeth. In
order that the tops of the teeth shall be sharp, and not rounded or
curved, as in Fig. 2202, it is necessary that the edge of the chisel be
kept sharp, an end that is greatly aided by the improved form of chisel
shown in Fig. 2203. When a file possesses curved points, or caps, as
they are technically termed, a few strokes upon a narrow surface will
cause them to break off, reducing the depth of the teeth and causing the
cuttings to clog in them. If, however, the file is used upon a broad
surface these caps will remain, obviously impairing the cutting
qualifications of the file, even when new, and as they soon get dulled
the file loses its grip upon the work and becomes comparatively
valueless.
[Illustration: Fig. 2203.]
Files were, until the past few years, cut entirely by hand--file cutting
by machinery having previously been a wide field of mechanical
experiment and failure. Among the most prominent causes of failure was
that the teeth produced by the earlier machines were cut too regular,
both as to their spacing and their height; hence the points of the rear
teeth fell into the same channels as those in advance of them, thus
giving the tooth points too little opportunity to grip the work. This
also gives too broad a length of cutting edge and causes the file to
vibrate on the forward or cutting stroke, an action that is technically
known as chattering, and that obviously impairs its cutting capacity.
The greatest amount of duty is obtained from a file when the rear tooth
cuts off the projection left by the preceding one, because in that case
the duty of the tooth is confined to cutting off a projection that is
already weakened and partly separated from the main body by having the
metal cut away around its base. Workmen always practically recognise
this fact, and cause the file marks to cross each other after every few
strokes. In the machine-cut files made by The Nicholson File Co., the
teeth are arranged to attain this object by the following means:--1. The
rows of teeth are spaced progressively wider apart from the point
towards the middle of the file length by regular increments of spacing,
and progressively narrower from the middle toward the heel. 2. This
general law of the spacing is modified by introducing as the teeth are
cut an element of controllable irregularity in the spacing, which
irregularity is confined within certain limits, so that neither the
increment nor decrement of spacing is entirely regular. 3. In arranging
the teeth so that the successive rows shall not be exactly parallel one
to the other, the angle of inclination being reversed as necessity
requires. The irregularity of spacing, while sufficient to accomplish
the intended object, is not enough to practically vary the cut of the
file, or, in other words, it is insufficient to vary its degree of
coarseness or fineness to any observable extent. But it enables the file
to grip the work with as little pressure as possible, and enables the
teeth to cut easily without producing deep file marks or furrows.
Files and rasps have three distinguishing features: 1. Their length,
which is always measured exclusively of their tangs. 2. Their cut, which
relates not only to the character, but also to the relative degree of
coarseness of the teeth. 3. Their kind or name, which has reference to
the shape or style. In general, the length of files bears no fixed
proportion to either their width or thickness, even though of the same
kind. The tang is the spiked-shaped portion of the file prepared for the
reception of a handle, and in size and shape should always be
proportioned to the size of the file and to the work to be performed.
The heel is that part of the file to which the tang is affixed.
Of the cut of files we may say that it consists of three distinct forms;
viz.: "single cut," "double cut" and "rasp," which have different
degrees of coarseness, designated by terms as follows viz.:--
Single-cut. Double-cut. Rasp.
Rough Coarse Coarse
Coarse Bastard Bastard
Bastard Second-cut Second-cut
Second-cut Smooth Smooth
Smooth Dead-smooth
[Illustration: Fig. 2204.]
The terms "rough," "coarse," "bastard," "second-cut," "smooth" and
"dead-smooth," have reference only to the coarseness of the teeth, while
the terms "single-cut," "double-cut" and "rasp" have special reference
to the character of the teeth. The single-cut files (the coarser grades
of which are sometimes called "floats") are those in which the teeth are
unbroken, the blanks having had a single course of chisel-cuts across
their surface, arranged parallel to each other, but with a horizontal
obliquity to the central line, varying from 5° to 20° in different
files, according to requirements. Its several gradations of coarseness
are designated by the terms "rough," "coarse," "bastard," "second-cut"
and "smooth." The rough and coarse are adapted to files used upon soft
metals, as lead, pewter, &c., and, to some extent, upon wood. The
bastard and second-cut are applied principally upon files used to
sharpen the thin edges of saw teeth, which from their nature are very
destructive to the delicate points of double-cut files. The smooth is
seldom applied upon other than the round files and the backs of the
half-rounds. Fig. 2204 represents the cut of single-cut rough files,
their lengths ranging from 16 inches down to 4 inches. Fig. 2205 shows
the cut of the coarse, bastard, and second-cut, whose lengths also range
from 16 to 4 inches, and whose cut is also finer as the length
decreases. The float is used to some extent upon bone, horn, and ivory,
but principally by plumbers and workers in lead, pewter, and similar
soft metals. It will be seen that the teeth are nearly straight across
the file and are very open, both of these features being essential
requirements for files to be used on the above-named metals.
Double-cut files are those having two courses of chisel cuts crossing
each other. The first course is called the over cut, and has a
horizontal obliquity with the central line of the file, ranging from 35°
to 55°. The second course, which crosses the first, and in most double
cuts is finer, is called the up-cut, and has a horizontal obliquity
varying from 5° to 15°. These two courses fill the surface of the file
with teeth inclined toward its point, the points of which resemble
somewhat, when magnified, those of the diamond-shaped cutting tools in
general use. This form of cut is made in several gradations of
coarseness, which are designated by the terms "coarse," "bastard,"
"second-cut," "smooth" and "dead-smooth." Fig. 2206 represents the cut
of double-cut bastard files, from the 16 inch down to the 4 inch, and
Fig. 2207 the cut of the coarse, second-cut, and smooth. For very fine
finishing a still finer cut, called the dead-smooth, is made, being like
the smooth, but considerably finer. It is a superior file for finishing
work in the lathe, or for draw-filing machine work that is to be highly
finished. The double-cut is applied to most of the files used by the
machinist, and, in fact, to most of the larger number in general use.
For unusually fine work, tool-makers and watch-makers use the Swiss or
Groubet files--so called from their being made by M. Groubet, of
Switzerland. These files are double-cut, and their degree of coarseness
is denoted by number; thus, the coarsest is a bastard and the finest
number 8. The prominent characteristics of these files are their
exceedingly even curvature and straightness, and, in the finer grades,
the unusual fineness of the cut, which feels soft and velvety to the
touch. They are made in sizes ranging from 2 to 10 inches, and are
always double-cut.
[Illustration: Fig. 2205.]
[Illustration: Fig. 2206.]
[Illustration: Fig. 2207.]
Rasps differ from the single or double-cut files in that the teeth are
disconnected from each other, each tooth being made by a single-pointed
tool, denominated by file-makers a punch, the essential requirement
being that the teeth thus formed shall be so irregularly intermingled
as to produce, when put in use, the smoothest possible work consistent
with the number of teeth contained in the surface of the rasp. Rasps,
like files, have different degrees of coarseness, designated as
"coarse," "bastard," "second-cut" and "smooth." The character and
general coarseness of these cuts, as found in the different sizes, are
shown in Figs. 2208 and 2209. Generally speaking, the coarse teeth are
applied to rasps used by horseshoers, the bastard to those used by
carriage makers and wheelwrights, the second-cut to shoe-rasps, and the
smooth to the rasps used by cabinet-makers.
[Illustration: Fig. 2208.]
[Illustration: Fig. 2209.]
[Illustration: Fig. 2210.]
[Illustration: Fig. 2211.]
[Illustration: Fig. 2212.]
Figs. 2210, 2211 and 2212 are respectively coarse, bastard, and
finishing second-cut files, the first two being for brass.
Fig. 2210 represents a file open in both its over and up-cut, which is
not, therefore, expected to file fine, but fast, and is adapted for very
rough work on the softer metals, as in filing off sprues from brass and
bronze castings, filing the ends of rods, and work of a similar nature.
It is also, to some extent, used upon wood. The essential difference
between the bastard file shown in Fig. 2211 and that just described is
the degree of fineness of the up-cut, which is nearly straight across
the tool. This form of teeth, which may be applied to any of the finer
cuts, and upon any of the shapes usually made double-cut, is especially
adapted to finishing brass, bronze, copper and similar soft metals, and
is not so well adapted to the rougher work upon these metals as the
coarse brass file previously described. Fig. 2212 is a finishing file.
The first or over-cut in this case is very fine, and, contrary to the
general rule, has the least obliquity, while the up-cut has an unusual
obliquity, and is the coarser of the two cuts. The advantages in this
arrangement of the teeth are that the file will finish finer, and by
freeing itself from the filings is less liable to clog or pin than files
cut for general use. This form of cut is especially useful when a
considerable quantity of finishing of a light nature is required upon
steel or iron. It is not recommended for brass or the softer metals, nor
should it be made of a coarser grade than the second-cut.
The names of files are sometimes derived from the purpose for which they
are to be used. Thus, we have saw files, slitting files, warding files,
and cotter files. The term "warding" implies that the file is suitable
for use on the wards of keys, while "cotter" implies that it is suitable
for filing the slots for that class of key which the machinist terms a
cotter. In other cases files are named from their sections, as in the
case of "square," "round," "half-round," and "triangular," or
"three-square" files, as they are often termed.
The term "flat" may be considered strictly as meaning any file of
rectangular section whose width exceeds the thickness. Hence, "mill
files," "hand files," and "pillar files" all come under the head of flat
files, although each has its own distinguishing features. The general
form of the flat file is shown in Fig. 2213, while the cross-sections of
various quadrangular files are shown in Figs. from 2214 to 2218. From
these views it will be seen that the thicknesses gradually increase from
the mill to the square file. Mill files are slightly tapered from the
middle to the point both in their width and thickness. They are
single-cut, and are usually either bastard or second-cut, although they
are sometimes double-cut. Mill files of both cuts are principally used
for sharpening mill saws, mowing-machine knives and ploughs, and in some
machine shops for rough lathe work, and, to some extent, in finishing
composition brasswork. Mill sections are occasionally made blunt--that
is to say, their sectional shape is alike from end to end--in which case
they are mostly double-cut, and seldom less than 8 inches in length.
They are suitable for filing out keyways, mortises, &c., and for these
purposes should have at least one safe edge. A safe edge is one having
no teeth upon it, which allows the file to be used in a corner without
cutting more than one of the work surfaces. When the corner requires to
be very sharp it is preferable to take a file that has teeth upon its
edge and grind the teeth off, so as to bring the corner of the file up
sharp, which it will not be from the cutting, because the teeth do not
come fully up to a sharp corner.
[Illustration: Fig. 2213.]
[Illustration: Fig. 2214.]
[Illustration: Fig. 2215.]
[Illustration: Fig. 2216.]
[Illustration: Fig. 2217.]
Hand-files are tapered in thickness from their middle towards both the
point and the tang, and are, therefore, well curved or bellied on each
side. This fits them for the most accurate of work, on which account
they are generally preferred by expert workmen. They are nearly parallel
in width and have one safe edge and one edge cut single, while the face
is cut double. Hand-files are also made equaling, the term equaling
meaning that, although apparently blunt or of even thickness throughout
the length, yet, in fact, there is a slight curvature, due to the file
being thickest in the middle of its length. An equaling hand-file is
especially suitable for such purposes as filing out long keyways, in
which a great part of the file length is in action, and it can,
therefore, be easily pushed in a straight line.
The flat file, Fig. 2213, when 10 inches and under in length, is made
taper on both its sides and edges, from the middle to the front of the
file, and when longer than 10 inches they should be made full
taper--that is to say, the taper should extend from the middle toward
the heel, as well as toward the point. Flat files are usually
double-cut, the coarse-cut being used upon leather, wood, and the soft
metals. The flat bastard is that most commonly used, the flat
second-cut, smooth, and dead-smooth being used by machinists for
finishing purposes, the latter preceding the polishing processes.
Pillar files are tapered in thickness from the middle to each end; the
width is nearly parallel, and one of the edges is left safe. They are
double-cut, and, although not in general use, are especially adapted to
narrow work, such as in making rifles, locks, &c. The square file
ranges from 3 to 16 inches in length, and is made for general purposes
with considerable taper. It is usually double-cut, the bastard being the
principal cut, the second-cut and smooth being mainly used by the
machinist.
Square blunt files range from 10 to 20 inches in length, of the same
sectional sizes as the square taper, and are cut double, usually
bastard. For machinists' use, however, they are used in the second-cut
also, and are provided with sometimes one and sometimes two safe sides.
Square equalling files are in every respect like the square blunt,
except in the care taken to prepare a slight curve or belly in the
length of the file, which greatly enhances their value in filing out the
edges of keyways, splines, or mortises. The fault of the square blunt,
when used for fine, or true work, is that the heel, having no belly, is
apt to come into too prominent action.
[Illustration: Fig. 2218.]
Warding files, Fig. 2218, are made parallel in thickness, but are
considerably tapered on their edges. They range in size from 3 to 8
inches in length, progressing by half-inches in the sizes below 6
inches. They are cut double, and usually on both edges, and are mainly
used by locksmiths and jewellers, and to but a limited extent by
machinists. Some of the warding files are provided with teeth upon their
edges only, which are made quite rounding, the cut usually being
second-cut, single.
[Illustration: Fig. 2219.]
[Illustration: Fig. 2220.]
[Illustration: Fig. 2221.]
Files deriving their sections from the circle are shown from Figs. 2219
to 2222. "Round files" are circular in section, as shown in Fig. 2219,
their lengths ranging from 2 to 16 inches, and are usually of
considerable taper. The small bastards are mostly single-cut and the
larger sizes double-cut. The second-cuts and smooths are rarely
double-cut, except in some of the very large sizes. In imitation of
double-cut, however, they are sometimes made with the first, or overcut,
very open, called "hopped," which adds, however, but very little to the
cutting capacity of the file. The very small sizes--as, say, those of
one-quarter inch and less in diameter--are often called "rat-tailed"
files. For some classes of work--as for instance, the circular edges of
deep keyways--round, blunt files are used, their sizes running up to 18
and 20 inches, their principal cut being bastard and double.
The gulleting file is a round, blunt saw file, and, like most other
files for this purpose, is single-cut (except for a small space at the
point, which is left uncut). Its principal use is for extending the
gullet of what are known as gullet-tooth and briar-toothed saws.
Half-round files are of the cross-section shown in Fig. 2220, and
although their name implies a semicircle, yet, as generally made, their
curvature does not exceed the third part of a circle. They are made
taper; the bastard is usually double cut on both its sides; the
second-cut and smooth is double-cut on their flat sides, and single-cut
on the curve side, except occasionally in the larger sizes, when it is
double-cut or hopped. Half-round files for wood usually range in size
from 10 to 14 inches, and are of the same shape and taper as the regular
half-rounds. They are cut coarse and double, and are used by
wood-workers generally. Half-round rasps are also like the regular
half-round in shape, the sizes usually called for being 10, 12, and
14-inch. They are used principally by wheelwrights and carriage
builders, but are to some extent used by plumbers and marble workers.
[Illustration: Fig. 2222.]
Cabinet files are of the section shown in Fig. 2222, being both wider
and thinner than the half-rounds, the sectional curvature being somewhat
less than the fifth part of a circle. They are made taper from near the
middle to the point, while both the files and the rasps are made from 6
to 14 inches in length; 8, 10, and 12 inches are the sizes in most
common use. As usually known, the cabinet file is a bastard double-cut.
The cabinet rasp is punched smooth, and both the cabinet rasp and file
are rarely made of any other degree of coarseness. They are used by
cabinet, saddle-tree, pattern, and shoe-last makers, and also by
gunstockers and wood-workers generally.
[Illustration: Fig. 2223.]
Three-square files are made with equilateral triangular sections, as in
Fig. 2223. They are tapered to a small point with considerable curve,
and are double-cut. The larger sizes--say, from 10 to 14 inches--are
usually bastard, and are used to a considerable extent in rolling mills.
The smaller sizes are not unfrequently smooth or dead-smooth, and are
used in machine shops quite generally for filing interval angles more
acute than the rectangle, clearing out square corners, sharpening
cutters, &c. Three-square blued files of sizes from 3 to 6 inches are
sometimes made. They are mostly second-cut, or smooth and double-cut,
and are principally used in machine shops for filing up cutters for
working metals.
[Illustration: Fig. 2224.]
[Illustration: Fig. 2225.]
Cant files, whose cross-sections are shown in Fig. 2224, are usually
made blunt and double-cut, mostly bastard, on all three sides. These
sizes are usually 6, 8, and 10 inches. Lightning files are of the
cross-section shown in Fig. 2225, the term lightning being known
principally by those using the saws of this name, and to some extent by
those using other cross-cut, [M]-shaped saw teeth. The obtuse angle of
this file is five-canted, while the regular cant is hexagon or
six-canted, and it is found to be too obtuse for the purposes required
of the saw file. They are made blunt, and range in length from 4 to 12
inches, and are cut (except for a short space near the point) single on
their three sides.
[Illustration: Fig. 2226.]
[Illustration: Fig. 2227.]
[Illustration: Fig. 2228.]
Knife files are of the section shown in Fig. 2226, and rarely exceed 10
inches in length, the principal sizes being 4, 5, and 6-inch. They are
tapered, resembling somewhat the blade of a knife, and are cut double.
The very acute angle of the sides of this file makes it especially
useful in filing the inner angles of the rear and main springs of a
rifle lock and work of similar shape. These files are also made blunt.
Cross files (sometimes called double half-round or crossing files) are
of the section shown in Fig. 2227. They are mostly made to order, either
blunt or tapered, and usually double-cut. "Feather-edge" files (Fig.
2227) are but little used by the mechanics of this day. They were
formerly used in filing feather springs (as the rear spring of a gun
lock is sometimes called), and also the niches in currycombs, which led
them to be called by some currycomb files. The few files of this kind
which are now made are usually blunt and double-cut. Half-round "shoe
rasps" as generally made are of the cross-section shown in Fig. 2228,
their sizes ranging from 6 to 12 inches, while 8, 9, and 10 inch are the
most common. They are made parallel in width, but with their sides
slightly tapered from the middle; the ends are rounded and cut single;
the edges are safe or uncut, or if cut are usually made half-file and
half-rasp reversed (1/4 rasp and 3/4 file, while sometimes made, are the
exception). The file quarters are bastard double-cut, and the rasp
quarters second-cut. This form of shoe rasp is the one in general use at
this time, having almost entirely superseded the flat and swaged rasps
formerly in use.
[Illustration: Fig. 2229.]
Reaper files (B, Fig. 2229), so called from their use in sharpening the
knives of reaping and mowing machines, are of the cross-section shown.
They range in length from 7 to 10 inches, are slightly tapered, and are
cut single and on their sides only.
Tumbler files, whose cross-section is shown at A, Fig. 2229, were
formerly much used to file the tumblers of gun locks, but are now rarely
called for. They are taper and cut double. It will be seen, however,
that unless for some special purpose, the pitsaw round or half-round
file will be found to answer the same purpose as the tumbler file.
It is obvious that in the use of files the coarser cuts are for use when
it is required to remove a maximum quantity of material, and the finer
to produce a more smooth and true surface, and also that the form of
file selected is that which will best conform to the shape of the work,
or can be best admitted upon or into the work.
In selecting the length of the file, the size of the work and the
delicacy of the same are the determining considerations; thus, a 14-inch
file would be a clumsy tool upon a small piece of work, as, say, one
having an area of 1/2 inch square. In selecting the shape of the file
there are, however, other considerations than the shape of the work.
Among these considerations may be enumerated that, in proportion as the
number of teeth on any given file, performing cutting duty
simultaneously, is increased, the less metal will be taken off, because
the pressure on each tooth is reduced, and the file does not bite or
take hold of the work so well; hence it cuts smoother.
To fit the handles to small files, as 6-inch or less, it is simply
necessary to bore suitable-sized holes in the handles, and force in the
tang of the file. In doing this care should be taken to bore the hole
axially true with the handle, so that the latter may stand true with the
file, which greatly assists the production of true and rapid filing.
For larger files the handle should have a small hole bored up it as
before, the file tang should be made red hot (a piece of wet rag or
cotton waste being wrapped around the heel of the file, so that it shall
not get hot and be softened), and forced into the handle by hand, the
file and handle being rotated during the operation, and sighted to
insure that the handle is kept true with the centre line of the file. So
soon as the tang of the file has entered three-quarters or thereabouts
of its length it should be removed and gradually cooled by dipping in
water.
[Illustration: Fig. 2230.]
[Illustration: Fig. 2231.]
When the surface of the work is so large that the file handle would meet
the work before the point had reached fully across it, the raised handle
shown in Fig. 2230 is employed. The square end of the handle has a
dovetail groove into which the tang of the file is fitted. In the figure
the file is shown applied to a connecting rod end, and in such broad
surfaces it is especially necessary to vary the line of motion of the
file after every few strokes, so as to cause the file marks to cross and
recross, as shown in Fig. 2231.
The height at which work should be held to file it to the best advantage
depends entirely upon its size, the amount of metal to be filed off, and
the precision to which the filing requires to be executed.
Under ordinary conditions the work should stand about level with the
operator's elbow when he stands in position to file the work. This is
desirable so that the joint of the arm from the elbow to the wrist may
be in the same plane as the line of motion of the file, which will give
the workman the least fatigue. But when the work surface is very broad
it should be lower down, so that the operator may reach over all parts
of its surface. On the other hand, on very small round work, or work so
small as to require but one hand to hold the file, the work may be so
high as to require the operator to stoop but very little, in which case
the fatigue will be less, while the work will be more in sight, and can
be better scrutinized.
[Illustration: Fig. 2232.]
When the file is pushed endways it is termed cross-filing, and the teeth
cut on the forward or pushing stroke only, and in this case the file
should be held as in Fig. 2232, the end of the file handle abutting
against the palm of the right hand. But when the file is held in one
hand only, the forefinger may be placed uppermost, and either on the
file handle or on the file itself, as may be found most convenient. In
cross-filing the file should be relieved of cutting duty on the return
or back stroke, but should not be removed from the work surface.
For heavy cross-filing on iron or brass, a 15-inch file is sufficiently
large for any of the ordinary duty required by the machinist, and will
require all the pressure one man can put on it to enable it to cut
freely, and move at a suitable speed.
The workman should for heavy cross-filing stand well off or away from
the work so as to require to bend the body well forward. His feet should
in this case be spread apart so that when the pressure of the hands is
placed upon the file it will relieve the forward foot of a great part of
the weight of the workman's body, which will be thrown upon the file.
The rear foot operates during the forward stroke as a fulcrum, wherefrom
to push the file.
At each forward stroke the workman's body should move somewhat in unison
with the file; his arms being less extended than would otherwise be the
case, and the file being under more pressure and better control.
During the backward stroke the forward foot should again take the
workman's weight, while he recovers the upright position.
For less heavy filing and for smooth filing, the workman should stand
more nearly upright and nearer to the work.
The heavier the pressure (either in cross-filing or draw-filing), the
coarser the file cuts, and the more liable it is to pin and scratch.
In the case, however, of slim files, the pressure is apt to bend the
file, causing it to cut at the edges or ends only of the work, as shown
at A, in Fig. 2233. This may be avoided by holding the file as in the
figure, the pressure of the fingers in the direction of the arrows
causing the file to bend, and produce more straight work.
From the nature of the processes employed to cut the teeth of files,
they are unequal in height, and as the file in addition to this varies
in its straightness or warps in the process of hardening, it becomes
necessary in many cases to choose for certain work files whose shape is
best suited for it. Suppose, however, that files were produced whose
teeth or tops or points were equal in height from end to end of the
file, and it would be necessary for the workman to move the file in a
true straight line in order to file a straight surface. This the most
expert filers cannot accomplish. It is for this reason that hand files
are made as in Fig. 2234, being thickest in the middle M, and of a
curved taper both towards the point P and the heel H, so that when
applied to the work the file will bear on the work at A, Fig. 2235, and
be clear of it at B and C, which allows the file motion to deviate from
a straight line without cutting away the work too much at B and C. The
file curvature also enables any part of the file length to be brought
into contact with the work or with any required part of the surface of
the same, so as to locate or limit its action to any desired part.
If a bellied file (as this shape of file is sometimes termed) be moved
in a straight line it will file flat so long as it is moved to have
contact clear across the work, but if the file is concave in its length
it can only cut at that part which is in contact with the edge of the
work, and the latter must be filed convex.
[Illustration: Fig. 2233.]
It becomes obvious then that for flat work a bellied file must be used,
and that the belly should preferably be of even sweep from end to end.
But files, whatever their shape, and however evenly formed when soft,
warp (as already remarked) in the hardening process, sometimes having
crooks or bends in them, such as at E and D, in Fig. 2236. In such a
file the teeth at E would perform no duty unless upon work narrower than
the length of the concavity at E, while on the other side D, the extra
convexity would give the file great value for work, in which particular
spots only required to be filed, because the teeth at D could be brought
to bear on the required spot without fear of cutting elsewhere.
[Illustration: Fig. 2234.]
If, however, we have a taper flat file, such as in Fig. 2234, the
thickness being equal from H to M, and a curved taper from M to P only,
then it would be impossible to file flat unless only that part from M to
P be used, because the heel H would meet the work at the same time as M,
and it could not be known where the file would cut, more than that the
most prominent teeth would cut the most.
[Illustration: Fig. 2235.]
[Illustration: Fig. 2236.]
[Illustration: Fig. 2237.]
An excellent method of testing the truth of a file, and of finding its
high spots is to chalk a piece of board, press the file firmly to it and
take several strokes and the chalk will be transferred to the highest
parts of the file, showing very distinctly every hill and hollow in the
teeth, even on the finest of Groubet files, and it will be found from
this test that but very few of the best-made files are true, and that
very great care is necessary in selecting a file for flat and true work.
[Illustration: Fig. 2238.]
The curvature or belly on a file not only enables but few teeth to be
brought into action at any one turn, and thus cause it to cut more
freely; but it also enables all parts of the file length to be used and
worn equally. Thus in Fig. 2238 are shown two positions of a file, one
cutting at A and the other at B, these different locations being due to
different levels of the file which may be given by elevating or
depressing it at the handle end.
[Illustration: Fig. 2239.]
If a file is hollow in one side of its width, and rounding on the other,
as in Fig. 2239, the hollow side is unfit for any but the roughest of
work, since it will not file any kind of work true; but the rounded side
is very effective for flat surfaces, since the number of teeth in action
is more limited and their grip is therefore greater, while by canting
the file any part of its width may be brought into action. The rounded
side is especially advantageous for draw-filing (a process to be
hereafter explained).
In all cross-filing, whether performed to clean up a surface, remove a
maximum of metal, or prepare the work for draw-filing, or for reducing
the work to shape, the file should be given a slight lateral as well as
a forward motion, and it will be found that this lateral motion is more
effective if made from right to left, leaving the file marks in the
direction of marks B, in Fig. 2240, because the workman has more control
over the file (especially if a large one) than when the lateral motion
is from left to right; but this latter motion must be given occasionally
to prevent the file from cutting deep scratches, and to keep the file
surface true.
[Illustration: Fig. 2240.]
[Illustration: Fig. 2241.]
A new file should be used at first on broad surfaces so that the teeth
may not grip or bite the work so firmly that the strain will cause their
fine sharp edges to break off, which is apt to occur unless their edges
are slightly worn off. As a file becomes worn it may be used on narrower
work, because the narrower the surface the more readily the file will
bite. When a file is much worn, or when it is desired to remove a
quantity of metal as quickly as possible, the file may be used at
different angles upon the work, as shown in Fig. 2241, which by reducing
the number of teeth in action facilitates the cutting, but if this be
done with a new file it will break off the points of the teeth.
Cast iron, brass, and copper require a sharper file than do either steel
or wrought iron, hence for the first named metals (especially brass and
copper) new files are used, and these should not be used upon wrought
iron or steel until worn out for the above metals.
In the case of unusually hard cast iron or tempered steel a second-cut
file will cut more freely than a coarser grade.
Work to be draw-filed should first be cross-filed with smooth or at the
coarsest with second-cut files, so as to remove the scratches of the
bastard or rough file before the draw-filing, which should not be done
with a rough or bastard file.
Draw-filing consists in moving the file in a line at a right angle to
its length, the file being grasped at each end independently of its
handle, which may be removed from the file if it be in the way, as in
the case of files used on broad surfaces.
Draw-filing is employed for two purposes: first and most important, to
fit work more accurately than can be done by cross-filing, and secondly
to finish surfaces more smoothly, and lay the grain of the finish
lengthwise of the work. The greater accuracy of draw-filing occurs
because the high parts of the file can be selected and the file so
balanced that this high part covers the place on the work requiring to
be filed, while the strokes may be made to suit the length of the spot
to be filed.
In draw-filing the file can be moved more steadily than in cross-filing,
and will, therefore, rock so much less that even the novice can with
care produce very true work.
[Illustration: Fig. 2242.]
Suppose, for example, that a piece of work requires filing in the middle
of its length and half way along its width and half along its length,
and a well bellied file may be balanced upon C, Fig. 2242, and grasped
at its two ends A and B, and used with strokes of a sufficient length to
file half the work length as required.
In draw-filing the file should be pressed to the cut on the pushing
stroke only, and not on the return or pulling stroke.
Draw-filing produces with a given cut of file a smoother surface than
cross-filing, but it will not remove so much metal in a given time.
In draw-filing short strokes will produce better work than long ones,
because with the latter the file cuttings are apt to become locked in
the teeth of the file, and cut scratches in the work. This is called
_pinning_, and the pins cutting deeper than the file teeth produce the
scratches.
To avoid this pinning the file surface may be well chalked, which will
at the same time cause the file to cut smoother although not quite so
freely. It is necessary, however, to clean the file after every ten or
twelve draw-filing strokes so as to remove the filings. This removes the
chalk also, hence it requires occasional renewal. For this purpose lumps
of chalk are employed, but great care is necessary in its selection,
because it sometimes contains small pieces of flint or other stones, and
these score and greatly damage the file teeth.
To dislodge the chalk and filings the file surface may be rubbed two or
three strokes with the hand, and the file lightly tapped on the vice
back. But it will also be found necessary to occasionally clean the file
with a file-brush or file-card. The file-card is brushed across the
width of the file so that the wire may reach the bottoms of the rows of
teeth and clean them out.
[Illustration: Fig. 2243.]
If the pins have lodged too firmly in the teeth to be removed, the
scorer shown in Fig. 2243 is employed. This scorer is a piece of copper
or brass wire flattened out thin at the end E, which end is pressed
firmly to the file teeth and pushed across the width of the file. By
this means the thin edge becomes serrated, and the points of the teeth
forming the serrations pass down the bottoms of the rows of file teeth
and force out the pins. Here it may be remarked that pinning takes place
in cross-filing as well as in draw-filing, and is at all times
destructive to either good or quick work.
Oil is sometimes used to prevent pinning and produce a dead finish,
which will hide scratches, but it is much more dirty than chalk and no
more effective. Neither of these substances, however, is employed upon
cast iron, brass, copper, or other than the fibrous metals.
In removing the cross-file marks it will be found that the file will cut
more freely if it be slightly canted so that it cuts most at and near
the edge, as shown in Fig. 2244, the edge A B meeting the work, the file
stroke having progressed from C as shown. This is especially
advantageous if the metal be somewhat hard or have a hard skin upon it,
or in case of a hard spot, because it will enable the file to bite when,
if pressed flat upon the work, it would slip over it.
[Illustration: Fig. 2244.]
When draw-filing is resorted to, to obtain a very fine surface, to be
finished with emery paper and crocus cloth, it is best to reverse the
direction of the file strokes so as to cause the file marks to cross and
recross as shown in Fig. 2244, where the marks C cross those previously
made, which will not only produce smoother work, but it will partly
prevent the file from pinning. It will also be found that the
draw-filing will be smoother and pinning less liable to occur when the
file strokes cross the fibres or grain of the metal than when they are
parallel to that grain; hence when the finishing marks are to be left in
a line with the grain and a very smooth surface is required, the
draw-filing marks should, just before the final finishing, be across the
grain, the final finishing being with the grain simply to reverse the
direction of the marks.
Half-round files should be well curved in their lengths on the
half-round side, so that when applied to the work any part of the file's
length may be brought to bear upon the required spot on the work, as was
explained for the flat file, and shown in Fig. 2238. If the flat side is
straight or hollow in its length it is of little consequence, because it
can be used upon convex or upon narrow surfaces. The sweep or curve of
the file should in its cross-section always be less than the curve of
the work it is to operate upon, and the teeth should be brought up sharp
on the edges, and over the whole area of the half-round side, which is
in inferior files not always the case, because the rows of chisel cuts
are too far apart in the width of the file; hence, there is along the
length of the file between the rows of full teeth, rows that are not
brought fully up, which impair the cutting qualifications of the file.
[Illustration: Fig. 2245.]
[Illustration: Fig. 2246.]
[Illustration: Fig. 2247.]
In using a half-round file to cross file it should at each stroke be
swept first from right to left, and after a few strokes from left to
right, so that the file marks appear first as in Fig. 2245, running
somewhat diagonal from right to left, and then, when the side sweep of
the file is reversed in direction, the file marks will cross after the
manner shown exaggerated in Fig. 2247. Unless this is done, the curve
will be apt to have a wave in it as in Fig. 2246, or in large curves
there may be several waves, and the same thing may occur if the
direction of side sweep is not reversed sufficiently often. The file
should also be partly swept around the curve, so that if at the
beginning of a stroke it meets the work at the upper position in Fig.
2247, then at the end of the stroke it should be as at the lower one,
which will also prevent the formation of waves. The larger the curve the
less the amount of this sweep can be, the operator giving as much as
convenient for the size of curve being filed.
In draw-filing the file should be slightly rotated, so that if at the
beginning of a stroke it stands as at A, Fig. 2247, at the end of that
stroke it should stand as at position B, and it should at the same time
be given sufficient end motion, so as to cause the file marks to cross
as shown.
A round file should always be a little smaller at its greatest diameter
than the hole in the work. Before inserting it in the hole it should be
rotated in the fingers, and the eye cast along it, to select the part
having the most belly, which may then be brought to bear on the required
spot in the work, without filing any other place, and without filing
away the edges at the ends of the hole. For very accurate work it is
sometimes desirable to grind on a round file, a flat place forming a
safe edge. So likewise a safe edge flat file requires grinding on its
safe edge, because in cutting the teeth a burr is thrown over on the
safe edge, rendering it capable of scoring the work when filing close up
to a shoulder.
The work should be held as near down to the surface of the jaws of the
vice as will allow the required amount of metal to be filed off without
danger of the file teeth coming into contact with those jaws, and should
be placed so that the filing operation when finished shall be as near as
possible parallel with the top of the vice jaws. These jaws then serve
somewhat as a guide to the filing operation, showing where the metal
requires filing away.
For cutting steel that contains hard spots or places, a second-cut file
is more effective than a rough or bastard file.
Rough files are more suitable for soft metals, the bastard cut being
usually employed upon wrought iron, cast iron, and steel by the
machinist. But in any case the edge of the file is employed to remove
small spots that are excessively hard. The file should be clean and dry
to cut hard places or spots, and used with short strokes under a heavy
pressure, with a slow movement.
When a file has been used until its cutting edges have become too dull
for use, it may be to some extent resharpened by immersion in acid
solutions; but the degree of resharpening thus obtained has not proved
sufficient to bring this process into general or ordinary application;
hence, the files are either considered useless, or the teeth are ground
off and new ones formed by recutting them.
A recut file is of course thinned by the process, but if properly done
is nearly, if not quite, as serviceable as a new one, providing that in
grinding out the old teeth the file be ground properly true to curve;
but, unfortunately, this is rarely found to be the case.
An excellent method of resharpening files, and also of increasing the
bite of new files (which is an especial advantage for brass work), is by
the means of the sand blast. The process consists of injecting fine sand
against the backs of the teeth by means of a steam jet, and is
applicable to all files, from the rasp to the finest of Groubet files.
The action of the sand is to cut away the backs of the file teeth, thus
forming a straight bevel on the teeth back, and giving a new cutting
edge, and the process occupies from three to five minutes.
[Illustration: Fig. 2248.]
Fig. 2248 represents a machine constructed for this purpose. Steam is
conveyed by the piping to the nozzles A, A, which connect by rubber hose
H, H to sand pipe K, so that the steam jets passing through A, A carry
with them the mixture of quartz, sand, and water in the sand box. By
means of the overhead guide frame at D, E the file clamp C is caused to
travel when moved by hand in a straight line between the nozzles A, A in
the steam box, from which the expended sand and water flow down back to
the sand box. Thus both sides of the file are sharpened simultaneously,
and from the fixed angles of the nozzles and true horizontal motion of
the file the angles of all the teeth are equal and uniform.
To distribute the sharpening effects of the sand equally across the
width of the file, the carriage has lateral or side motion, as well as
endwise, and on the apparatus represented adjustable rollers regulate
this side movement. Having the two motions, any part of the file can be
presented to the blast.
The following is from _Engineering_:--"A comparative trial of the
cutting power of the sharpened files was lately made with the following
results: A piece of soft wrought iron was filed clean and weighed; 1200
strokes were made by a skilled workman with one side of a new 10-inch
bastard file, the iron was again weighed, and the loss noted. The other
side of this file was then subjected to the sand blast for five seconds,
and 1200 strokes were made with this sand-blasted side on the same piece
of iron, great care being taken to give strokes of equal length and
pressure in both cases. The iron was then weighed, and the loss found to
be double as much as in the first case.
"These operations were repeated many times, counting the strokes and
weighing the metal each time, and the quantity cut was found to
gradually become less for both sides as these became worn. When the
weight of metal cut away by 1200 strokes of the sand-blasted side was
found to be no greater than had been cut by the first 1200 strokes of
the ordinary side when quite new, a second sand blasting was applied to
it for 10 seconds, and in the next 1200 strokes its rate of cutting rose
to nearly its first figure. When the cut made by the ordinary side of
the file fell to about four-tenths of its cut when new, it was
considered by the workman as worn out, and a new file of the same size
and maker was used to continue the comparison with the one sand-blasted
side; 83 sets of 1200 strokes each and 13 sand-blastings were made on
the same side of this file, and in that time it cut as much metal as six
ordinary sides. In 99,600 strokes it cut away 14 ozs. avoirdupois of
wrought iron, and 16.4 ozs. of steel.
"With an equal number of strokes its average rate of cutting was, on
wrought iron, 50 per cent. greater than the average of the ordinary
sides, and on steel 20 per cent. greater. As the teeth became more worn,
the time of the application of the sand blast was lengthened up to one
minute. After the thirteenth re-sharpening its rate of cutting was
nine-tenths that of the ordinary side when quite new.
"When the teeth become so much worn that the sand blast ceases to
sharpen them effectively, the file can be recut in the usual way, and
each set of teeth can be made to do six times as much work as an
ordinary file, and to do it with less time and labor, because it is done
with edges constantly kept sharp. The time required to sharpen a
worn-out 14-inch bastard file is about four minutes, or proportionately
less if sharpened before being entirely worn out. Smooth files require
much less time. About 4 horse power of 60 lb. steam used during four
minutes, and one pint per minute of sand (passed through a No. 120
sieve), and the time of a boy are the elements of cost of the
operation."
RED MARKING OR MARKING.--This is a paint used by machinists to try the
fit of one piece to another, or to try the work by a test piece or
surface plate. It should be composed of dry Venetian red, mixed with
lubricating oil of any kind.
Instead of Venetian red, red lead is sometimes used for marking, but it
is too heavy and separates from the oil, and furthermore will not spread
either evenly or sufficiently thin, and is therefore much inferior to
Venetian red.
It is applied to the surface of the test piece or piece of work, and the
latter is brought to bear on the surface to be tested, so that it leaves
paint marks disclosing where the surfaces had contact, and therefore
what parts of the surface require removing in order to make the surfaces
have the desired degree of contact.
When either the test piece or the work can be put in motion while
testing, one piece is rubbed upon the other or passed along the same in
order that the bearing marks may receive the marking more readily and
show the bearing spots more plainly, the operation coming under the head
of fitting. When neither piece can be given motion, one is made to mark
the other by being struck with a mallet or hammer, or to avoid damage to
the work from the hammer blows, a piece of wood or copper is interposed.
This operation is termed "bedding."
[Illustration: _VOL. II._ =SCRAPERS AND SCRAPING.= _PLATE IX._
Fig. 2252.
Fig. 2253.
Fig. 2254.
Fig. 2255.
Fig. 2256.
Fig. 2257.
Fig. 2258.
Fig. 2259.
Fig. 2260.]
The thickness of the coating of marking varies with the kind of work,
the finer fit the work requires to be, the thinner the coat of marking.
Thus in chipping a thick coat is applied, for rough filing a thinner,
for smooth filing a still thinner coat, and so on, until for the finest
of work the coat is so thin as to be barely perceptible to the naked
eye. When either the work or the testing piece can be given motion and
the surfaces rubbed together, a thinner coat of marking may be used.
Marking is usually applied with a piece of rag doubled over and over,
and bound round with a piece of twine so as to form a kind of
paint-brush. This will give the surface a lighter and more evenly spread
coat than would be possible with a brush of any kind. For very fine
work red marking may be spread the lightest and the most even with the
palm of the hand, which will readily detect any grit, dirt, or other
foreign substance which the marking may contain from being left exposed.
[Illustration: Fig. 2249.]
[Illustration: Fig. 2250.]
THE HACK-SAW.--The hack-saw is employed by the machinist for severing
purposes, and also for sawing slots in the heads of screws. The blade
should be tightly strained in the frame, which will prevent saw
breakage. The ordinary method of doing this is to provide the end of the
saw frame with a sliding stud threaded at its end to receive a thumb
nut. The studs at each end of the blade should be squared where they
pass through the frame, as at A, B in Fig. 2249, so that the blade shall
not be permitted to twist. An improved form is shown in Fig. 2250, in
which the end E has a saw slot to receive the blade F. At the handle end
of the blade it is held by a stud sliding through the frame, being
squared at B; at C is a nut let into and screwed in the handle, and into
or through the nut is threaded the end of the stud, so that by rotating
the handle the blade is strained. The curve in the back at A gives a
little elasticity to it, and therefore a better strain to the blade. A
hack-saw should always be used with oil, which preserves the cutting
edge of the teeth.
In sharpening a hack-saw it is best to rest the smooth edge of the blade
on a piece of hard wood or a piece of lead, and spread the tops of the
teeth by light hammer blows, which serves a two-fold purpose, first it
thickens them and enables them to cut a groove wide enough to let the
blade pass freely through, and secondly it enables the teeth to be filed
up to a sharp cutting edge with less filing.
[Illustration: Fig. 2251.]
The screw-driver to be used in saw slots should have its end shaped as
at A in Fig. 2251, which will tend to prevent it from slipping out of
the saw slot, as it will be apt to do if wedge-shaped as at B, because
in that case the action of the torsional pressure or twist is to lift
the screw-driver out of the slot.
SCRAPERS AND SCRAPING.--The process of scraping is used by the machinist
to true work, and to increase the bearing area of surfaces, while the
brass finisher employs it to prepare surfaces for polishing, applying it
mainly to hollow corners and sweeps.
For scraping work to fit it together the flat scraper is used, ordinary
forms being shown in Figs. 2252 and 2256.
That shown in Fig. 2252 may be made of a flat smooth file, of about an
inch wide, and 3/16-inch thick, which is large enough for any kind of
work. Two opposite faces, one of which is shown at A, are ground beveled
so as to leave the end face B about 1/16-inch thick. This end face is
then ground square as denoted by the dotted lines, producing two cutting
edges of equal angles, and therefore equally keen. If it were attempted
to grind face B at an angle as denoted by the dotted lines G, in Fig.
2253, the lower edge H would cut too keenly, causing the scraper to
chatter and cut roughly, while the upper one I would not cut
sufficiently easily.
For very smooth work the scraper may be formed as in Fig. 2256, the
front face E being ground slightly out of square as shown, and the
bottom face F being given considerable angle to the body of the scraper.
For very rapid cutting, however, the front face E may be at an angle of
less than 90° to the top of the scraper.
The only objection to this form is that the eye lends no assistance in
bringing the edge fair with the work surface. The scraper should not
exceed about 6 inches in length, exclusive of the handle, for if longer
it will not cut well or smoothly, and its end face should be slightly
rounded as in Fig. 2254. Its facets should be ground square or straight
and carefully oil-stoned after the grinding, the oil-stoning process
being repeated for two or three resharpenings, after which it must be
reground upon the grindstone.
The scraper should be grasped very firmly in the hands, and held as in
Fig. 2255. It requires to be pressed hard to the work during the cutting
and lightly during the backward stroke.
The strokes should not exceed for the roughing courses, say, half an
inch in length, the first course leaving the work as represented in Fig.
2257.
The second course should be at a right angle to the first, leaving the
work as in Fig. 2258, and after these two courses the work should be
tested by surface plate, or with the part to which it is to fit, as the
case may be. Previous to the testing, however, the work must be
carefully wiped clean with old rag, as new rag or waste is apt to leave
ravelings behind. The surface plate should be given a light coat of red
marking, and then moved backward, forward, and sideways over the work,
or, if the work is small, it may be taken from the vice and rubbed upon
the surface plate, and the high spots upon the work will be shown very
plainly by the marks left by the plate. The harder the plate bears upon
the work the darker the marks will appear, so that the darkest parts
should be scraped the heaviest.
After applying the plate, the scraper may again be applied, the marks
being at an angle to the previous operation, the testing and marking by
the plate and scraping process being continued until the job is
complete, appearing as shown in Fig. 2259.
It will be noted that the scraper marks are much smaller and finer at
and during the last few scrapings; and it may be here remarked that the
scrapings are very light during the last few finishing processes.
The strokes of the scraper being made of a length about equal to the
acting width of its edge cuts, makes the scraper mark approximately
square, on which account it is sometimes termed "block" scraping. It
gives an excellent finish, while not sacrificing the truth of the work
to obtain the finish.
The scraper will not remove a quantity of metal so quickly as a file,
and on this account it is always preferable to surface the work with a
file before using the scraper, even though the work be well and smoothly
planed. Not until the file has almost entirely removed the planer marks,
and the surface plate shows the surface to be level and true, should the
scraper be brought into requisition, the first courses being applied
vigorously to break down the surface.
It would appear that scraping might be more quickly done by taking long
scraper strokes promiscuously over the work, but in this case the
bearing marks are not well defined and do not show plainly, which leads
to confusion and causes indecision as to where the most or heaviest
scraping requires to be done, whereas in the block scraping the marks
are clearly defined and the high patches or spots on the work show very
plainly, and the workman is able to proceed intelligently and with
precision.
Fig. 2260 represents a three-cornered or "three-square" scraper, which
is used principally upon hollow or very small flat surfaces. The
half-round scraper is employed upon holes, bores, or large concave
surfaces, such as brasses. Both these tools are for vice work, used in
the same manner as described for flat scrapers, while all scrapers cut
smoother when the edge is kept wetted with water, as is essential when
used upon wrought iron, copper, and steel.
HAND REAMERS OR RYMERS.--The hand reamer is employed for two purposes,
first, to make holes of standard diameter and smooth their walls, and
second, to bring holes in line one with the other.
[Illustration: Fig. 2261.]