casting is to serve, or how it is to be treated: in such a case he is
guided partly by his knowledge of the use of such patterns, and a
consideration of being on the safe side. The form shown in Fig. 2773
would suggest itself as being a very ready method of making the pattern;
by coring out the hole, it can be made parallel, which the drawing seems
to require. The advantage of leaving the hole parallel is that less
metal will require to be left for boring in case it should be necessary;
because, if the hole is made taper, the largest end of the bore will
require to have the proper amount of allowance to leave metal sufficient
to allow the hole to be bored out true, and the smaller end would,
therefore, have more than the necessary amount; while just the least
taper given to the exterior would enable the moulder to withdraw the
pattern from the mould. Made in this way, it would be moulded as shown
in Fig. 2774, with the flange uppermost, because almost the whole of the
pattern would be imbedded in the lower part of the flask, the top core
print being all that would be contained in the cope; and even this may
be omitted if the hole requires to be bored, since the lower core print
will hold the core sufficiently secure in small work, unless the core is
required to be very true. The parting of the mould (at C D, Fig. 2774)
being level with the top face of the flange, much taper should be given
to the top print (as shown in Fig. 2773), so that the cope may be lifted
off easily. Were this, however, the only reason, we might make the top
print like the bottom one, providing we left it on loose, or made it
part from the pattern and adjust to its place on the pattern by a taper
pin; but another advantage is gained by well tapering the top print, in
that it necessitates the tapering of the core print at that end; so
that, when the two parts of the mould are being put together, that is to
say, when the cope is being put in place, if the core has not been
placed quite upright, its tapered end may still arrive and adjust itself
in the conical impression, and thus correct any slight error of position
of the core. The size of the core print should be, at the part next the
pattern, the size of the core required; for if the extremities are made
of the size of the core, and the taper or draft is in excess, there will
be left a useless space around the core print, as shown at A B in Fig.
2774, into which space the metal will flow, producing on the casting,
around the hole and projecting from the end face, a useless web, which
is called a fin, which will of course require to be dressed off the
casting.
[Illustration: Fig. 2772.]
"We will now suppose that our piece, when cast, is to be turned under
the flange and along the outside of the hub or body, and that the hole
also is to be bored. In this case the pattern made as above would still
be good, but could be much more easily made and moulded if it has to
leave its own core, its shape being as shown in Fig. 2775; because the
trouble of making a core is obviated, and the core is sure to be in the
centre of the casting, which it seldom is when a core is used. We must,
however, allow more taper or draft to a hole in a pattern than is
necessary on the outside; about one-sixteenth inch on the diameter for
every inch of height on work of moderate size is sufficient. The
allowance for boring should be one-sixteenth inch at the large end of
the hole, provided the diameter of the hole is not more than five or six
inches, slightly exceeding this amount as the diameter increases;
whereas, if the pattern had been made with core prints, an allowance of
one-eighth inch for small, and three-sixteenths inch for larger work
would be required. These are the advantages due to making the pattern
leave its own core. We have still to bear in mind, however, that, if the
casting require a parallel hole, a core must be used; and furthermore,
if the hole is a long one, we have the following considerations: The
separate dry sand core is stronger, and therefore better adapted to
cases where the length of the hole greatly exceeds the diameter. Then
again, if the hole require to be bored parallel, it can be more readily
done if the hole is cast parallel, because there will be less metal to
cut out. The casting also will be lighter, entailing less cost, provided
it has to be paid for by the pound, as is usually the case. The moulder
is given more work by making the core; but the saving in metal, and in
turning, more than compensates for this, provided the length of the hole
is greater than the diameter of the bore.
"Let it now be required that the casting is to be finished all over. It
would, in that case, be preferred that if the casting should contain any
blow or air holes, they should not be on the outside face of the flange,
and this will necessitate that the piece be moulded the reverse way to
that shown in Fig. 2773: that is to say, it must be moulded as shown in
Fig. 2776, with the flange downwards; for it may be here noted that the
soundest part of a casting is always that at the bottom of the mould;
and furthermore, the metal there is more dense, heavier, and stronger
than it is at the top, for the reason that the air or gas, which does
not escape from the mould, leaves holes in the top of the casting or as
near to the top as they can, by reason of the shape of the casting,
rise. The bottom metal also has the weight of the metal above it,
compressing it, and making an appreciable difference in its density. It
must, therefore, be remembered that faces requiring to be particularly
sound should be cast downwards, or at least as near the bottom of the
mould as they conveniently can. Following this principle, our gland will
require to be moulded as shown in Fig. 2777, P P representing the line
of the parting of the mould; so that, when the cope is lifted off, the
loose hub A will rise with it, leaving the flange imbedded in the lower
half of the mould. It is evident that in this case the pattern must be
made, as shown in Fig. 2776, the body and core prints being in one piece
and the flange in another, fitting easily on to a parallel part on one
end, and adjoining the core print, as shown at A. For glands of moderate
size, this method is usually adopted, and it answers very well for short
pieces; but in cases where the length of the body approaches, say, three
diameters, the horizontal position is the best, and the pattern should
be made as shown in Figs. 2778, 2779, or 2780. Even in short pieces,
when the internal diameter approaches that of the external, this plan is
the best, because it is difficult for the moulder to tell when his core
is accurately set in position.
[Illustration: Fig. 2780.]
"For a pattern to be moulded horizontally, Fig. 2780 shows the best
style in which it can be made. Its diameters are turned parallel; the
required draft is given by making the rim of the flange a little thinner
than at the hub, and by making the end faces of the hub and the core
prints slightly rounding. If the hub is very small, as, say, a half-inch
or less, and the flange does not much exceed it, the pattern may be made
solid, as shown in Fig. 2778; but if the hub be small and the flange
large, it should be made as shown in Fig. 2776.
[Illustration: _VOL. II._ =EXAMPLE IN PATTERN WORK.= _PLATE XIV._
Fig. 2773.
Fig. 2774.
Fig. 2775.
Fig. 2776.
Fig. 2777.
Fig. 2778.
Fig. 2779.]
"To construct the pattern shown in Fig. 2773, we proceed as follows:
From a piece of plank we saw off a piece of wood a little larger and
thicker than the required flange, and turn it up between the lathe
centres, using a pattern makers' contraction rule, which has its
measurements larger than the actual standard ones in the proportion of
one-eighth inch per foot: so that a foot on the contraction rule is
12-1/8 standard inches, and an inch is 1-1/96 standard inches. The
reason for this is, that when the metal is poured into the mould, it is
expanded by heat; and as it cools it contracts, and a casting is,
therefore, when cold, always smaller than the size of the mould in which
it was made. Brass castings are generally said to be smaller than the
patterns in the proportion of one-eighth inch per foot, and cast-iron
castings one-tenth inch per foot; and so, to avoid frequent calculations
and possible errors, the contraction rule has the necessary allowance in
every division of the foot and of the inch. It is not, however, to be
supposed that the possession of such a rule renders it possible for the
pattern-maker to discard all further considerations upon the contraction
of the casting; because there are others continually stepping in. Such,
for example, is the fact that the contraction will not be equal all
over, but will be the greatest in those parts where the casting contains
the greatest body of metal.
"In the smaller sizes of patterns, such as those of 6 inches and less in
diameter, there is another and a more important matter requiring
attention, which is, that after a moulder has imbedded the pattern in
the sand, and has rammed the sand closely around it, it is held firmly
by the sand and must be loosened before it can be extracted from the
mould. To loosen it, the moulder drives into the exposed surface of the
pattern a pointed piece of steel wire, which he then strikes on all
sides, causing the pattern to compress the sand away from the sides of
the pattern in all directions; and as a result, the mould is larger than
the pattern. In many kinds of work, this fact may be and is disregarded,
but where accuracy is concerned, it is of great importance, especially
in the matter of our example (brasses for journals), for they can be
chipped and filed to fit their places much more rapidly than they can be
planed, and it is necessary to have the castings as nearly of the
correct conformation as possible. In cases where it is necessary to have
the castings of the correct size without any work done to them, the
shake of the pattern in the sand is of the utmost importance. If it is
required to cast a piece of iron 3 inches long and 1 inch square,
supposing the pattern were made to correct measure by the contraction
rule, the moulder, by rapping the pattern (as the loosening it in the
mould is termed) would, by increasing the size of the mould above that
of the pattern, cause the casting to be larger than the pattern; that is
to say, it would be longer and broader, and therefore, in those two
directions, considerably above the proper size, since even the pattern
was too large to the amount allowed for contraction. The depth, however,
would be of correct size, because the loosening process or rapping does
not drive the pattern any deeper in the mould. It follows that, to
obtain a casting of as nearly the correct size as possible, the pattern
must be made less in width and in length than the proper size, to the
amount of the rapping; and to insure that the moulder shall always put
the pattern in the sand with the same side uppermost, the word "top"
should be painted on the face intended to lie uppermost in the mould.
The amount to be allowed for the rapping depends upon the size of the
pattern, and somewhat upon the moulder, since some moulders rap the
patterns more than others; hence, where a great number of castings of
accurate size are required, it is best to have two or three castings
made, and alter the pattern as the average casting indicates. For
castings of about 1 inch in size, the patterns may be made 1/32 inch too
narrow and the same amount too short; but for sizes above 6 inches,
allowance for rapping may be disregarded.
"In patterns for small cast gears, the rapping is of the utmost
consequence. Suppose, for instance, we have six rollers of 2 inches
diameter requiring to be connected together by pinions, and to have
contact one with the other all along the rollers; if we disregard the
allowance for rapping, the pinions will be too thick, and we shall
require to file them down, entailing a great deal of labor and time,
besides the rapid destruction of files.
[Illustration: Fig. 2781.]
[Illustration: Fig. 2782.]
"Let it be required to cast a pillow block to contain a babbitt-metal
bearing. In this case there requires to be a cavity to receive and hold
the babbitt metal. This is provided by casting ridges of metal around
the edges of the bearing, as shown in Fig. 2781, at D E and on each side
at F, the pieces D E may be made solid with the pattern, but those for
the sides must be removable, having dovetails as at _c_ _c_ to hold them
in position while being moulded, or in place of the dovetails, wires as
at F F may be employed, in either case the pattern would be extracted
from the mould, leaving the side strips to be removed afterwards. If,
instead of a pillow block, a bracket or frame, such as in Fig. 2782,
were required, it must be moulded in the direction of the arrow, and in
that event it would be desirable to core out the journal bearing. This
would be accomplished by providing a core print to block up the whole
opening B. A suitable core box for the bearing would be as in Fig. 2783.
The core print must project below the casting so as to form in the
mould a core print for the core, and it is obvious that the core itself
must be made of increased depth to the amount allowed for core print;
hence the end piece B, Fig. 2783, is increased in thickness to the
amount allowed for core print."
[Illustration: Fig. 2783.]
Patterns for cylindrical bodies, especially those that are hollow and
thin, are constructed in pieces by a process termed "building up." The
pieces are usually segments of circles, and the manner of marking them
is as follows:--
[Illustration: Fig. 2784.]
[Illustration: Fig. 2785.]
[Illustration: Fig. 2786.]
[Illustration: Fig. 2787.]
Let it be required to make a pattern for a flanged pulley, such as shown
in section in Fig. 2784. It would be constructed in two halves composed
of a number of courses as from 1 to 8, and each course would be composed
of segments of the form shown in Fig. 2785. The length of the arc of
these segments must be such that it will require a certain number of
these to complete the circle of that part of the cylinder which the
segment is to form; and the manner of accomplishing this is shown in
Fig. 2786, in which the circle C is of the diameter of the outside,
while circle D is that of the outside of the pulley proper, circle E is
of the diameter of the inside of the pulley rim. These circles are
divided into as many equal divisions as there are to be segments in the
circumference; hence the number of divisions determines the length of
arc of the segments. Thus A would be a segment for the body of the
pulley, and F a segment for the rim. A template is then made of each one
of these segments, as at A and F. This template must be made slightly
larger in every direction than the respective divisions, to allow for
the stuff that will be turned off in truing the pattern in the lathe and
in jointing the segments to one another during the building. The
templates are employed to mark out on the board which should first be
planed to the required thickness. This will be a trifle thicker than the
course so as to allow for truing the surface of each finished course in
the lathe. The courses are best built up on the chuck of the lathe on
which they are to be turned, and a saving in time will be effected if
there are two chucks, so that a course on one half of the pattern may be
built up while the glue of another course on the other half is drying.
On the lathe chuck, and directly beneath, where the joints of the
segments will come, pieces of paper as at _a_, _c_, _e_, _g_, Fig. 2787,
and if the segments are long ones, intermediate pieces of paper, as _b_,
_d_, _f_, _h_, will be necessary. The radial edges of the segments are
trimmed on what is termed a shooting board, which is a device such as
shown in Fig. 2788, in which A is a piece of board on which is fastened
the piece B. S is a piece projecting above B, and is provided to rest
the segment S´ against, the flat surface of the latter lying on the
board B. It is thus held in a fixed position, ready to have its edges E
planed, the whole being laid upon the bench against the bench stop G.
If, however, it is more convenient to rest the shooting board across the
bench, a piece C may be fastened beneath A, so as to come against the
edge of the bench as in Fig. 2789, in which T is the bench. The plane is
laid with its side on A as in Fig. 2790, so that the surface of A acts
as a guide, keeping the edge of the plane vertical, and thus planing the
edges of the segment square. The plane is operated by hand in the usual
manner (save that it lies on its side), taking its cut most off the
outside or inside of the edge of the segment S´, according as the
position of the latter is varied. In some of the shooting boards
manufactured by tool makers, the height of B from A is adjustable, so
that all parts of the plane blade edge may be used, which saves
grinding, since only that part of the edge that is used dulls. Also
there is provided means whereby the required lateral position of the
segment may be adjusted; such a device is shown at P, Fig. 2788, which
is a plate having a slot through it, through which passes the thumb
screw V, which screws into S. Hence the plate may be adjusted so that
when one end of the segment rests against the end of S, and the other
against the end of P, its edge E will be in the proper position to be
planed to correct angle by the plane, whose line of action is in this
case rendered positive by means of a slide on the plane, acting in a
groove in the base A.
[Illustration: Fig. 2788.]
[Illustration: Fig. 2789.]
[Illustration: Fig. 2790.]
The first segment is glued to the pieces of paper on the chuck, as shown
in Fig. 2787, S´ representing the segment. A second segment is then
added, being set fair to the pencil circle O, and jointed and glued both
to the chuck and to the ends of the first segments. Successive segments
are added until the whole circle or course is completed, and when dry
the radial face of this course is turned in the lathe so as to be true,
flat, and of the required thickness, and the diameter is trued. The
second course may then be added, but the joints at the ends of the
segments should not come over those of the first course, but in the
middle as shown by the dotted line. The ends of the segments should be
made to bed properly against each other, and glue should be applied to
the joint between the two courses and at the ends. By adding the
successive courses the whole may be built up on the chuck ready to
receive the arms. As each segment is added it should be clamped or
weighted to press it firmly to its seat and press out the excess of
glue.
If the pattern consists of two, or say three, courses, the glue will be
sufficient to hold it to the chuck while turning, but if there are more
courses a screw should be inserted through the chuck and into each
segment of the first course. The cylinder must then be turned inside and
out ready to receive the spokes. These are made of pieces equal in
length to the internal diameter of the rim, or a trifle longer, so that
the ends may be let into the rim. A line is then marked along the edge
of the rim, dividing its thickness into two divisions, and in the centre
of the length a recess should be cut out from the face to the line, the
width of the recess equalling the width of the arm, so that one arm will
let into the other, forming a cross, of which the flat surfaces lie in
the same plane. This cross is let into the rim of the wheel and fixed
temporarily with brads. The lathe may then be started and the centre of
the arms (and therefore that of the cylinder or pulley) be found by a
pencil point moved until it marks a point and not a circle when the
lathe revolves. The arms may then be marked to shape and a recess turned
at their centre to receive the hub. The arms being marked to their
respective places and their outside faces being marked with a pencil so
that they may be replaced in the same position in the wheel, they may be
removed and shaped to the required dimensions and form, and then
replaced and glued to the rim.
If the wheel is to have six arms they may be constructed as follows:--
Instead of taking two pieces of the diameter of the rim, as in the case
of four arms, three pieces are necessary, and in this case the thickness
of the edge of each piece is divided by two marked lines which will
divide the thickness of the edge into three equal divisions, as shown by
the dotted lines 1 and 2 in Fig. 2791, which will divide the thickness
of the edge into three equal divisions of thickness. From the centre of
the lengths of each of the three pieces we mark on the flat face a
circle whose diameter will equal the width on the flat face of the
pieces themselves.
With an angle square having its adjustable blade set to an angle of 60°,
and set so that the back is fair with the edge of the piece, and one
edge coincident with the perimeter of the circle, lines tangent to the
circle and crossing each other are drawn on the pieces A C. On the piece
B four of such tangent lines (two on each side) must be drawn. The piece
A is recessed between one pair of tangent lines to the depth of the
second lines on its edge, or, in other words, to a depth of two-thirds
its thickness, and between the other pair to a depth of one-third, as
shown, the two-thirds at D, the one-third at E. The piece D must be
recessed between its tangents on each side to a depth of one-third its
thickness, as denoted at F F, while on C the whole space between the
tangent lines must be recessed to a depth equal to two-thirds its
thickness, as shown at G. The pieces may then be put together so that
the two diametrically opposite arms will be in one piece. If an odd
number of arms is employed this form of construction cannot be followed;
hence each spoke will be a separate piece, extending from the rim to the
centre and jointed at the latter, as in Fig. 2792, which is for five
arms.
For this construction draw a circle _c_, Fig. 2792, and divide it into
as many equal points of division as there are to be arms in the wheel.
From these points of division draw lines to the centre, and these lines
will show the required bevel at the end of each spoke, as shown in the
figure. The ends should be verified for bevel by striking from the
common centre a second circle, as D; and measuring if the arms are
equidistant, measured at the circle and from the edge of the arm to that
of the next, finished along the full length. When fitted, corrected,
glued and dry, the spokes may be let into the wheel and a recess turned
into the centre to receive the hub.
The rim and all parts that can be got at may then be turned in the
lathe, the pattern then being reversed in the lathe to turn the inside
of the rim, or the other side of the spokes, when the job will be
complete. When, however, the rim is to be a very thin one, it may be
necessary to fasten the segments together at the ends by other means as
well as glue, hence a saw-cut may be made in each end, and a tongue
inserted.
[Illustration: Fig. 2791.]
[Illustration: Fig. 2792.]
It is obvious that each half of the pattern is constructed by similar
segments, the line of parting being through the centre of the arms, as
at A B, in Fig. 2791. To keep the two halves coincident when in the
mould, pins are inserted in the rim and arms of one half, fitting
closely into holes provided in the other half.
To construct a pattern for a pipe, the pattern would be made in two
halves, and constructed of what are termed staves, that is, pieces of
wood running lengthways of the pipe. The number of these staves is
optional, save that it must be even, so that each half pattern will
contain an equal number.
[Illustration: Fig. 2793.]
Let it be required to make a pattern for a pipe 18 inches in diameter,
and to be 1 inch thick. Draw the line A B, Fig. 2793, and from a point
on it, as C, draw a semicircle A B, equal in diameter to the diameter of
the outside of the pipe. Also the circle D E F, equal to the diameter of
the inside of the pipe, and these will represent an end view of the
pipe. Divide these semicircles into as many equal divisions as it is
decided to have staves in the half pattern--as 1, 2, 3, 4, 5, 6; and
from one of these divisions make a template as denoted by the oblique
lines at 2, leaving it slightly larger than the division, to allow stuff
to work on in fitting the staves, &c.
[Illustration: Fig. 2794.]
Now, when the staves are cut out it is necessary to have some kind of a
frame or support to hold them while jointing them; hence, draw also from
the points of division, as D, E, F, the lines _a_, _b_, _c_, _d_, _e_,
_f_, and these will form the sides of a half-disk polygon, whose
diameter is from D to F. A sufficient number of these polygonal
half-disks are cut out to stand about two feet apart along the whole
length of the pipe, as in Fig. 2794, and on these, temporarily fastened
to the board B, the staves are jointed and fastened together by glue
while each stave is held to its place on each half-disk by a screw. The
top stave may be put on first, as it will act as a stay to the
half-disks. If the pipe is so long that it is composed of more than two
pieces, the end pieces should be put on first, and the intervening space
filled up last, which enables the ends to abut firmly. The second half
may be added to the first one, putting a piece of paper between the
edges of the two to prevent their sticking together.
If the pipe has a bend, it is built up separately, instead of being
formed of staves, the process being as follows:--
[Illustration: Fig. 2795.]
[Illustration: Fig. 2796.]
In Fig. 2795 let B represent the centre of the bend curve, the line C
representing one end, G the other end, H the inner and J the outer arc
of the bend. Let it be determined to build up the bend in five pieces,
as shown at 1, 2, 3, 4, 5, which represents an end view of the half
pattern. Templates are then made for each of the pieces 1, 2, &c., being
formed as denoted by the oblique lines, whose dimensions slightly exceed
the half circle E of the pattern, to allow wood for dressing up. To find
the curve for these pieces, set the compasses to a radius from B to the
outer corner of piece 1, and draw the arc K. Set the compasses to the
radius from B to the inner corner of piece 1, and draw the arc L, and
the space between these two arcs, which space is marked 1 T, is a
template for the curve of piece 1. By a similar process applied to
pieces 2, 3, 4 and 5 similar templates for their respective curves are
obtained; and selecting timber of a proper thickness, we mark out the
respective curves from these templates, which may be of thin board or of
stiff paper. In putting these pieces together the lower ones are set to
lines forming a plan of the bend, being set a little outside the lines
to allow wood for truing the pieces to shape after they are put
together. The lower pieces are temporarily fixed to the board on which
the plan is marked, and the upper ones fastened to the lower by glue,
the joint surfaces of each line being planed true previous to being
glued. It is a great assistance, however, to cut out two half circles,
representing the ends of the pipe, and to place them on the board to
build upon. When a bend of this kind occurs in a covering for a pipe
that is exposed to view, it is necessary, for the sake of appearance, to
have the pieces composing the bend to correspond with those on the
straight part of the pipe, as shown in Fig. 2796. The part A would be
got out in staves, as described for the pattern of a pipe. The bend B
would be also got out as described for that figure for a bend, save that
the number of staves for the bend would equal the number on the pipe.
But in this case each stave should be fitted to its fellow by pins, or
its edge fitting into dowels on the edge of its fellow; thus one edge of
a stave would have the dowels and the other the pins; the whole, when
finished, being bound together by metal bands, as shown in the figure.
[Illustration: Fig. 2797.]
The patterns for a globe valve, such as shown in section in Fig. 2797,
would be made as follows (which is taken from "The Pattern Makers'
Assistant"):--
[Illustration: Fig. 2798.]
[Illustration: Fig. 2799.]
"The flanges vary in shape; but as a rule small valves are provided with
hexagons and large ones with round flanges suitable for bolting to
similar flanges to make joints. For small valves, say up to 2 inches,
the pattern is usually made with the hexagons cut out of the solid, but
for sizes above that, they should be made in separate pieces, as shown
in Fig. 2798, and screwed to the pattern, so that in case of necessity
they may be removed, and flanges substituted in their stead. In Fig.
2799, we have a perspective view of the finished pattern; and Fig. 2800
represents the pattern as prepared, ready to receive a flange or hexagon
as may be required. A globe valve pattern should be made in halves, as
shown in Fig. 2801, the parting line of the two halves being denoted by
A B. To make this pattern, we first prepare two pieces of wood so large
that, when pegged together, the ball or body of the pattern can be
turned out of them, and long enough not only to reach from P to P, in
Fig. 2799, but also to allow an excess by means of which the two pieces
may be glued or otherwise fixed together. These two pieces we plane to
an equal thickness, and then peg them to retain them in a fixed
position, taking care, however, that the pegs do not occur where the
screws to hold the flanges will require to be. We also place two pegs
within a short distance of what will be the ends of the pattern when the
excess in length referred to is turned off. We next prepare, in the same
way, two more pieces, to form the two halves of the branch, shown at B,
in Fig. 2801, for which, however, one peg only will be necessary. These
pieces must be somewhat wider than the size of the required hexagon
across the corners, that is, supposing the hexagon is to be solid with
the branch; otherwise we must make them a little wider than the diameter
of the hub of the flange, or of the round part of the hexagonal pieces.
Their lengths must be such as to afford a good portion to be let into
the ball or body of the pattern (as shown by the dotted lines in Fig.
2800), which is necessary to give sufficient strength. The two pieces
must be firmly fixed together, and then turned in the lathe.
[Illustration: Fig. 2800.]
[Illustration: Fig. 2801.]
[Illustration: Fig. 2802.]
"During the early stages of the turning, or, in other words, during the
roughing out, we must occasionally stop the lathe and examine the flat
places on the body; for unless these places disappear evenly, the work
is not true, and one half will be thicker than the other, so that the
joint of the pattern will not be in the middle. It was to insure this
that the pieces were directed to be planed of equal thickness, since, if
such is the case, and the flat sides disappear equally and
simultaneously during the turning, the joint or parting of the pattern
is sure to be central. If the lathe centres are not exactly true in the
joint of the two pieces, they may be made so by tapping the work on the
side having the narrowest flat place, the process being continued and
the work being trued with the turning tool at each trial until the flat
places become equal. By this means, we insure, without much trouble, two
exact halves in the pattern, which is very important in a globe valve
pattern on account of the branch and other parts, not to mention the
moulding. Having turned the body of the pattern to the requisite
outline, and made, while in the lathe, a fine line around the centre of
the ball where the centre of the branch is to come, as shown in Fig.
2800 by the line A, we make a prick point (with a scriber) at each
crossing of the line A and the joint or parting of the pattern. We then
mount the body upon a lathe chuck, in the manner shown in Fig. 2802. A
point centre should be placed in the lathe and should come exactly even
with the line A. In Fig. 2802, V V are two [V]-blocks made to receive
the core prints. These [V]s are screwed to the lathe chuck, and the
pattern is held to them by two thin straps of iron, placed over the core
prints and fastened to the [V]s by screws. If the chuck and centre point
run true, the [V]-blocks are of equal height, and the core prints are
equal in diameter, the prick point opposite to the one placed to the
centre point will run quite true; and we may face off the ball or body
to the required diameter of branch, and bore the recess to receive the
same. We make the holes in the flanges of the same size as the core
prints; but we should not check in the print, because, if a flange with
a different length of hub were substituted, it would be a disadvantage.
To obtain the half flanges, we take a chuck and face it off true in the
lathe; then, with a fine scriber point, we mark the centre while the
chuck is revolving. We then stop the lathe, and, placing a straight-edge
to intersect the chuck centre, we draw a straight line across the chuck
face. We then take two pieces suitable for the half flanges, and plane
up one flat side and one edge of each piece. If the flanges are not
large ones, they may be planed all at once in a long strip. We place the
pieces in pairs, and mark on each pair a circle a little larger than the
required finished size of flange. We then fix each pair to the chuck,
with the planed faces against the chuck, and the planed edges placed in
contact, their joint coming exactly even with the straight line marked
on the chuck face, and we may then turn them as though they were made in
one piece and to the requisite size.
[Illustration: Fig. 2803.]
"In Fig. 2803 we have a representation of one half of a suitable core
box, the other half being exactly the same, with the exception that the
position of the internal partition is reversed. To get out this core
box, we plane up two pieces of exactly the same size and length as the
pattern, and of such width and thickness as will give sufficient
strength around the sphere, allowing space for the third opening. After
pegging these two pieces together, we gauge, on the joint face of each,
lines representing the centres of the openings and the centre of the
sphere. We then chuck them (separately) in the lathe, and turn out the
half sphere. We next place the two halves together, and chuck the block
so formed in the three positions necessary to bore out the openings; or
if preferred, we may pare them out. The partition (A, in Fig. 2803)
follows the roundness of the centre hole, and is on that account more
difficult to extract from the core than if it were straight and
vertical. When, however, the partitions are of this curved form, the
pieces of which they are formed are composed of metal, brass being
generally preferred. Patterns have in this case to be made wherefrom to
cast these pieces, and they may be made as follows: First, two half
pieces are turned; each is then cut away so as to leave the shape as
shown at A in the same figure, and is then fitted into the spherical
recess in the core box, letting each down until both are nearly but not
quite level. The two wing pieces are then fastened on, and this pattern
is complete. When the pieces are cast, they must be filed to fit the
core box, and finished off level with its joint face, a small hole being
drilled in the centre, and a pin being driven through the piece and into
the box to steady the corners. We then saw the pieces in halves with a
very fine saw.
[Illustration: Fig. 2804.]
"If the partition, instead of following the roundness of the valve seat,
is made straight, the construction of the core box is much more simple.
In this case, a zigzag mortice is made clear through each half of the
box, its size and shape being that of the required partition. Fig. 2804
represents a half-core box of this kind. A piece of wood A is fixed, as
shown, to the partition, to enable the core maker to draw it out before
removing the core from the box. The mortice for the partition should be
turned out before the half-spherical recess, the mortice being
temporarily plugged with wood to render easy the operation of turning.
[Illustration: Fig. 2805.]
"In very large valves (say 10 or 12 inches) a half-core box is generally
made to serve by fitting the two half partitions, shown at A, in Fig.
2803, to a half-core box, and keeping them in position by means of pegs,
a half-core being made first with one and then one with the other in the
core box. It is often necessary to form a raised seat in the body of an
angle valve, such as shown in Fig. 2805, which represents a section of
such a body. It is shown with flanged openings, though in small valves
hexagons to receive a wrench would be substituted.
[Illustration: Fig. 2806.]
[Illustration: Fig. 2807.]
"Fig. 2806 is a plan of half the core box necessary for forming the
raised seat. From this construction, it will be seen that the large
core, though solid with the branch core, is not solid with that forming
the hole in the seat and the part below it; therefore the core prints on
the body pattern must be left extra long to give sufficient support in
the mould for the overhanging cores. The loose round plug P, is made of
the size of the outside of the seat and fitted to the box. The part
outside the box is a roughly shaped handle to draw it out by. The
diminished part D is a print, and into the impression left by it is
inserted the core made in box shown in Fig. 2807. The print D is of the
same diameter as the hole in the seat; and the print on the pattern is
of the size of the increased diameter below the seat. Large angle valves
are made with half a core box by making a branch opening in the box
right and left, a semicircular plug being provided. Two half-cores are
made with the plug, first in one and then in the other branch opening.
The plug P should be in this case only half round."
[Illustration: Fig. 2808.]
For finding the lengths of the sides of regular polygons, scales, such
as shown in Figs. 2808 and 2809, may be used, the construction being as
follows:--
[Illustration: Fig. 2809.]
Draw a horizontal line O P, Fig. 2809, and at a right angle to it the
line O B. Divide these two into inches and eighths of an inch, and draw
lines meeting the corresponding divisions on O P, O B. From the point O
draw the following lines: A line at 55-1/2 degrees from line O P, which
is to serve for polygons having 9 sides; a line at 52-1/2 degrees to
serve for polygons having 8 sides; a line at 49 degrees for polygons
having 7 sides; a line at 45 degrees for 6 sides; a line at 40 degrees
for polygons having 5 sides. It may be added, however, that additional
lines may be drawn at the requisite angle for any other number of sides.
The application of the scale is as follows:--
The point O represents the centre of the polygon; hence from O to the
requisite line of division on O B represents the radius of the work.
From the line O B to the diagonal line (measured along the necessary
horizontal line of division) is shown the length of a side of the
polygon. From the point O, measured along the line having the requisite
degrees of angle, to the horizontal line denoting the radius of the
work, gives the diameter across corners of the polygon. The diameter
across the flats of a square being given, its diameter across corners
will be represented by the length of a line drawn from the necessary
line of division on O B to the corresponding line of division on O P. A
cylindrical body is to have six sides, its diameter being 2 inches, what
will be the length of each side? Now, the radius of the 2-inch circle of
the body is 1 inch; hence, find the figure 1 on line O B and measure
along the corresponding horizontal line the distance from the 1 to the
line of 45 degrees, as denoted by the thickened line.
A body has six sides, each side measuring an inch in length, what is its
diameter across corners? Find a horizontal line that measures an inch
from its intersection of the line O B to the line of 45 degrees, and
along this latter to the point O is one-half the diameter across
corners.
_Example 3._--It is desired to find the diameter across corners of a
square whose side is to measure 3 inches. Measure the distance from the
3 on line O P to the 3 on line O B, which will give the required
diameter across corners.
This scale lacks, however, one element, in that the diameter across the
flats of a regular polygon being given, it will not give the diameter
across the corners. This, however, we may obtain by a somewhat similar
construction. Thus, in Fig. 2808, draw the line O B, and divide it into
inches and parts of an inch. From these points of division draw
horizontal lines; from the point O draw the following lines and at the
following angles from the horizontal line O P:--
A line at 75° for polygons having 12 sides.
" 72° " 10 "
" 67-1/2° " 8 "
" 60° " 6 "
From the point O to the numerals denoting the radius of the polygon is
the radius across the flats, while from point O to the horizontal line
drawn from those numerals is the radius across corners of the polygon.
A hexagon measures 2 inches across the flats, what is its diameter
measured across the corners? Now, from point O to the horizontal line
marked 1 inch, measured along the line of 60 degrees, is 1-5/32 inches;
hence the hexagon measures twice that, or 2-5/16 inches across corners.
The proof of the construction is shown in the figure, the hexagon and
other polygons being marked for clearness of illustration.
[Illustration: Fig. 2810.]
[Illustration: Fig. 2811.]
Let it be required to make a pattern for a section of pipe such as shown
in section and in plan in Fig. 2810, which is from "The Pattern Maker's
Assistant." This pattern would be made to mould, as shown in the
section, lying horizontally, and must therefore be made in two halves,
the line of joint for the two halves being along A B in Fig. 2811.
"The body A and the branch B would be made separate from the flanges,
and would be reduced in diameter at the ends to receive them. To form A,
take two pieces of timber, say three inches longer than the length of A,
including the core prints, and measuring a little more than half the
diameter of the pipe one way, and a little larger than the full diameter
of the pipe the other way, and glue them together at the ends for a
distance of 1-1/2 inches, which will serve to hold them while turning
them in the lathe.
"The pieces may then be turned in the lathe to the required diameter.
During this turning, however, it is essential to insure that the joint
of the two pieces be exactly in the centre, otherwise one half of the
pattern will be (when the halves are separated) thicker than the other.
"The ends are then turned down to receive the flanges, the reduced
diameter being necessary so as to leave a shoulder for the flanges to
abut against to keep them true, or at a right angle to the axial line of
the body. The branch is turned up in the same way, and the flanges are
then turned and put on.
"The end of the branch may be cut to fit the circumference of the body
as follows:--
"Set a bevel square to an angle of 45°. Take the halves of the branch
apart, and rest the stock or back of the bevel against the end face, and
let the blade lie on the joint face, and mark two lines A B in Fig.
2812, which lines must just meet in the centre of the branch at the end.
Cut away the angular pieces C and D down to the lines A B. This
performed on each half will leave them when given a quarter turn as
shown in Fig. 2812, and the curve shown by the junction of the
horizontal with the vertical shading lines is the curve for the end;
hence the surface covered with the horizontal lines requires to be cut
away.
[Illustration: Fig. 2812.]
"When this is done on both halves the branch will fit to the body, as
shown in Fig. 2813, in which A is the body and B C the two half
branches. For a temporary pattern the branch may be fastened to the body
with a few screws; but for a permanent pattern it should be glued also,
which is done as follows:--
[Illustration: Fig. 2813.]
[Illustration: Fig. 2814.]
[Illustration: Fig. 2815.]
"Lay one half of the body A, Fig. 2813, on a board, with the flange
overhanging to be out of the way, and clamp it there; lay the branch
also on the board, and draw it firmly up to the body by clamps, while
also clamping it flat down to the board, as shown in Fig. 2814. This
will insure that the joint faces are true with one another, that is, lie
in the same plane. Paper should, however, be placed between the joint
faces and the board to prevent them from becoming glued to the board,
and the edges, therefore, from breaking away. The second half can be put
together as the first one, paper being put between the two to prevent
them from being glued together; and to further strengthen the joint, let
into each half a piece of hard wood P, Fig. 2815, and put in the screw
shown at A.
"Suppose now that the diameter of the branch had been smaller than that
of the body of the pattern, then the length of curve necessary on the
branch end to let it abut fairly against the cylindrical pattern body
may be found as follows:--
[Illustration: Fig. 2816.]
[Illustration: Fig. 2817.]
[Illustration: Fig. 2818.]
"Draw on a piece of board the line A B, Fig. 2816, and from any point C
mark a semicircle equal in radius to that of the radius of the body of
the pattern, draw the line E parallel to A B, and distant from it to an
amount equal to the radius of the branch, then from the junction of E
with the semicircle as at D, mark the line F at a right angle to A B.
Let it now be noted that the semicircle A G represents half the pattern
body, and E D F B the branch; hence from F to G is the length of the
branch end that will require to be curved to fit the circumference of
the body, while it is also the length to be added to the distance the
branch requires to stand out from the body. To draw the curve on the end
D F G of the branch the gauge or marking instrument, shown in Fig. 2817,
is employed. The branch P is placed in [V]-blocks (Fig. 2818), resting
upon a plane surface. The gauge consists of a stand E carrying a
vertical bar A; upon A is the closely fitting cross-tube carrying the
arm C, which in turn carries the marking pointer D, which is set distant
from the centre of the bar A to the amount of the radius of the piece of
work or the cylinder is to fit against.
[Illustration: Fig. 2819.]
"If the branch required to stand at an angle to the body, as in Fig.
2819, the marking may be performed by the same gauge and in the same
manner, but the axial line of the branch must be set, when marking one
side, at an acute angle to the axial line of A, and at an obtuse angle
to A when turned over to mark the other side, which may be done in each
case by raising one of the [V]-blocks until the branch lies in either
case at the same angle to A as it will require to stand to the body on
which it is to fit.
"When the body is much larger in diameter than the branch, a hole may be
bored in the former to receive the end of the latter, by giving to the
branch end a stem, as in Fig. 2820, and then cutting in the body a
recess for the branch end and its additional stem. This recess may be
cut out in the lathe, chucking the body as in Fig. 2821.
[Illustration: Fig. 2820.]
[Illustration: Fig. 2821.]
"Should it occur that one end of the [T] is of larger diameter than the
other, one chucking [V] must be deeper than the other, and we may find
their respective depths by the following process:--
[Illustration: Fig. 2822.]
"Draw line A B, Fig. 2822, which line represents the chuck face. Let
point C represent the centre of the lathe. Mark line C E and set a pair
of compasses to the radius of the body of the pattern at the centre of
the branch location. Then take a radius from C and about 1/16 inch up
from line A B, and with this radius we mark on the line C E the point E.
From this centre we mark the two arcs having radii corresponding to the
unequal diameters of the pattern at the location where the chucking
[V]'s are to be placed. We then draw tangent lines to each of these
arcs, and thus obtain the correct depth of [V] necessary to hold the
axial line of the pattern parallel to the lathe chuck.
[Illustration: Fig. 2823.]
"The core box would, unless the pattern were a small one, be built up in
courses, as shown in Fig. 2823. The box would be drawn in plan, and end
and side views drawn as shown, so as to draw in the half circle
representing the bore of the half-core box and mark off the courses as
from 1 to 6. These courses need not be of equal or of any particular
thickness, but may suit that of any suitable timber at hand. Courses 1
and 2 should extend over the whole outline of the box, while the pieces
3 and 4 are made in width to suit the curvature of the core as shown,
and to extend the full length of the box. The pieces 7, 8, 9, and 10 are
of the length of the branch, and are made in width to suit the curvature
of the branch core. If the branch core were a short one it could be cut
out of the solid; but in any event, the grain of the wood should be as
shown, and the holding pieces at G and H should be employed."
CHAPTER XXXV.--WOOD WORKING MACHINERY.
The machines employed in wood working may be divided into 7 classes as
follows:
1. Those driving circular saws.
2. Those driving ribbon or band saws.
3. Those driving boring or piercing tools.
4. Those employing knives having straight edges for surfacing purposes
and cutting the work to thickness.
5. Those employing knives or cutters for producing irregular surfaces
upon the edges of the work.
6. Those employed to produce irregular surfaces on the broad surface of
work.
7. Those employed to finish surfaces after they have been acted upon by
the ordinary steel cutting tools.
CIRCULAR SAWS.
[Illustration: Fig. 3078.]
The thicknesses of circular saws is designated in terms of the
Birmingham wire gauge, whose numbers and thicknesses are shown in Fig.
3078, where a Birmingham wire gauge is shown lying upon two circular
saws, which show the various shapes of teeth employed upon saws used for
different purposes.
The teeth numbered 1 are for large saws, as 36 inches in diameter, to be
used on hard wood. Numbers 2 and 5 are for soft wood and a quick feed.
Numbers 3 and 4 are for slabbing or converting round logs into square
timber. Number 6 is for quick feeds in large log sawing. Numbers 7, 8, 9
and 10 are for bench saws, or, in other words, saws fed by hand or
self-feeding saws. Number 8 is known as the "London Tooth," because of
being used in London, England, on hard and expensive woods. Number 9 is
the regular rip-saw tooth for soft woods. Number 10 is the Scotch gullet
tooth. Number 11 is for either cross-cutting or rip sawing by circular
saws used on soft woods. Number 12, is for large cross-cut saws; the
flat place at the bottom of the tooth prevents the teeth from being
unnecessarily deep and weak. Number 13 is for cross-cutting purposes
generally. Number 14 is for rip sawing on saws of small diameter. It is
also used for tortoise-shell, having in that case a bevel or fleam on
the front face, and no set to the teeth.
The following table gives the ordinary diameters and thicknesses of
circular saws and the diameters of the mandrel hole:
---------+------------+-------------------
Diameter.| Thickness. | Size Mandrel Hole.
---------+------------+-------------------
4 inch.| 19 gauge. | 3/4
5 " | 19 " | 3/4
6 " | 18 " | 3/4
7 " | 18 " | 3/4
8 " | 18 " | 7/8
9 " | 17 " | 7/8
10 " | 16 " | 1
12 " | 15 " | 1
14 " | 14 " | 1-1/8
16 " | 14 " | 1-1/8
18 " | 13 " | 1-1/4
20 " | 13 " | 1-5/16
22 " | 12 " | 1-5/16
24 " | 11 " | 1-3/8
26 " | 11 " | 1-3/8
28 " | 10 " | 1-1/2
30 " | 10 " | 1-1/2
32 " | 10 " | 1-5/8
34 " | 9 " | 1-5/8
36 " | 9 " | 1-5/8
38 " | 8 " | 1-5/8
40 " | 8 " | 2
42 " | 8 " | 2
44 " | 7 " | 2
46 " | 7 " | 2
48 " | 7 " | 2
50 " | 7 " | 2
52 " | 6 " | 2
54 " | 6 " | 2
56 " | 6 " | 2
58 " | 6 " | 2
60 " | 5 " | 2
62 " | 5 " | 2
64 " | 5 " | 2
66 " | 5 " | 2
68 " | 5 " | 2
70 " | 4 " | 2
72 " | 4 " | 2
---------+------------+-------------------
Circular saws are sometimes hollow ground or ground thinner at the eye
than at the rim, to make them clear in the saw kerf or slot with as
little set as possible, and therefore produce smooth work while
diminishing the liability of the saw to become heated, which would
impair its tension. They are also made thicker for a certain portion of
the diameter and then bevelled off to the rim.
This is permissible when the work is thin enough to be easily opened
from the log by means of a spreader or piece that opens out the sawn
piece and prevents it binding against the saw.
The shingle saw, shown in Fig. 3079, is an example of this kind, the saw
bolting to a disc or flange by means of countersink screws.
The concave saw shown in Fig. 3080, is employed for barrel heads. The
three pieces for a barrel head are clamped together and fed in a
circular path, so that the saw cuts out the head at the same time that
it bevels the edge.
The advantage of the circular saw lies mainly in the rapidity of its
action, whether used for ripping or cross-cutting purposes. In order,
however, that it may perform a maximum of duty, it is necessary that the
teeth be of the proper shape for the work, that they have the proper
amount of set, that they be kept sharp, and that the tension of the saw
is uniform throughout when running at its working speed.
[Illustration: Fig. 3079.]
[Illustration: Fig. 3080.]
The centrifugal force created by the great speed of a circular saw is
found to be sufficient to cause it to stretch and expand in diameter.
This causes the saw to run unsteadily unless it is hammered in such a
way as to have it rim bound when at rest, leaving the stretching caused
by the centrifugal force to expand the saw and make its tension equal
throughout. The saw obviously stretches least at the eye, and the most
at its circumference, because the velocity of the circumference is the
greatest, and the amount of stretch from the centrifugal force is
therefore the greatest.
It is obvious that the amount of centrifugal force created will depend
upon the speed of the saw, and it therefore follows that the hammering
must be regulated to suit the speed at which the saw is to run when
doing cutting duty, and in this the saw hammerer is guided solely by
experience.
A circular saw may have its tension altered and impaired from several
causes as follows:
1. From the saw becoming heated, which may occur from the arbor running
hot in its bearings, or from the work not being fed in proper line with
the saw.
2. From the reduction in diameter of the saw by frequent resharpening of
the saw, this reduction diminishing the amount of centrifugal force
generated by the saw, and therefore acting to cause the saw to become
loose at the eye.
3. From the saw teeth being allowed to get too dull before being
sharpened, which may cause the saw teeth to heat, and thus destroy the
tension.
4. From stiffening the plate at the throats of the teeth when gumming
the saw, an effect that is aggravated by using a dull punch.
5. From the saw teeth having insufficient set, and thus causing the saw
to heat.
The methods of discovering the errors of tension in a saw, and the
process of hammering to correct them, have already been explained with
reference to the use of the hammer on pages from 68 to 70 of volume 2 of
this work.
Before hanging a saw on a mandrel, it is necessary to know that the
mandrel itself runs true in its bearings or boxes. In a new machine this
may be assumed to be the case, but it is better to know that it is so,
because if the mandrel does not run true several very improper
conditions are set up. First, the saw will run out of true
circumferentially, and therefore out of balance, and the high side of
the saw will be called upon to do more cutting duty than the low side.
Second, the centrifugal force will be greatest on the high side, and the
saw will be stiffer, thus setting up an unequal degree of tension.
Third, the saw will run out of true sideways, cutting a wider kerf than
it should, thus wasting timber while requiring more power to drive.
The collar on the saw arbor should be slightly hollow, so that the saw
will be gripped around the outer edge of the collar, and the arbor or
mandrel should be level so that the saw will stand plumb. The boxes or
bearings of the arbor should be an easy working fit to the journals, and
there should be little, or what is better, no end play of the arbor in
its bearings.
If a saw arbor becomes heated enough to impair the tension of the saw,
it has been hot enough to impair its own truth, and should be examined
and trued if necessary.
The most important point in this respect is that the face of the collar
against which the saw is clamped should run true, bearing in mind that
if it is one hundredth of an inch out of true in a diameter of, say 3
inches, it becomes twenty hundredths or one-fifth of an inch at the
circumference of a saw that is 60 inches in diameter.
In cases of necessity, a saw that wabbles from the collar face of the
mandrel running out of true, may be set true by means of the insertion
of pieces of paper placed between the saw and the face of the collar.
The first thing to do in testing the saw is to take up the end motion of
the saw arbor, or if this cannot be done, then a pointed piece of iron
or wood should be pressed on the end of the mandrel so as to keep it
from moving endways while the saw is being tested.
The saw should be revolved slowly, and a piece of chalk held in the
cleft of a piece of wood should be slowly advanced until it meets some
part of the face of the saw just below the bottom of the saw teeth.
As soon as the chalk has touched and the saw has made one or two
revolutions the chalk should be moved a trifle farther on from the
teeth, and another mark made, and then moved on again, and so on, care
being taken to notice how much space there is between the high and low
sides of the saw. It will be found, however, that the shorter the chalk
marks are the more the saw is out of true.
A more correct method is to chalk the face of the saw and use a pointed
piece of iron wire of about one-quarter inch in diameter, but in any
case the saw should only be touched lightly.
The pieces of paper should be portions of rings or segments, and should
extend an equal distance below the circumference of the collar, because
the same thickness of paper will alter the saw more in proportion, as it
is inserted farther in toward the eye of the saw.
If it should happen that two thicknesses of paper are necessary to true
the saw, one should be made about half the length of the other, and the
long one may extend farther in toward the eye of the saw. Thus one ring
of paper may be an inch deep and the other one-half inch deep.
If but one piece of thin paper is needed, it may be simply a straight
piece inserted half way down the collar and trimmed off level with the
collar. In placing the paper, the middle of its length should be on that
side of the saw that is diametrically opposite to the marks left by the
chalk on the face of the saw.
When the saw is trued and is started it will be loose on the outside,
but as its speed increases it should stiffen up so as to run true and
steadily when running at its working speed.
If the saw is to be tried by actual work, it must be borne in mind that
the tension of the saw must be right for its speed when in actual use,
and not when running idle. If the machine has belt power enough to
maintain the same speed whether the saw is cutting at its usual rate of
feed, or whether it is running idle, the tension will not be altered by
putting on the feed, but if the saw has been hammered to run at the full
speed of the machine when not cutting and the feed is heavy enough to
slacken the speed, then the tension of the saw will not be correct for
its working speed.
[Illustration: Fig. 3081.]
The eyes of small saws are either made to fit the mandrel an easy
sliding fit, or else the mandrel is provided with cones to accommodate
various sizes of holes, an ordinary construction being shown in Fig.
3081, in which A is the saw arbor, fast on which is the collar B, S
representing a section of the saw, W a washer or loose collar, and N the
nut for tightening up W. The cone _c_ is screwed upon A and passed
through the saw until it just fills the hole, and thus holds the saw
true.
In putting on the saw, it should be passed up to the collar, and _c_
screwed home until it binds in the saw eye with enough force to bring
the threads of _c_ fairly in contact with those on the mandrel A, but if
screwed home too tightly it may spring the saw, especially if the saw is
a very thin one.
As _c_ must be removed from the arbor or mandrel every time the saw is
changed, the wear on its thread is great, and in time it becomes loose,
which impairs its accuracy.
[Illustration: Fig. 3082.]
This objection is overcome in the construction shown in Fig. 3082, which
is that employed by the S. A. Woods Machine Company. It is seen in the
figure that the cone _c_ fits externally in a recess in the collar B,
and at the coned end also upon the plain part _e_ of the arbor. The cone
is hollow and receives a spiral spring _s_, S. When the saw is put on it
first meets _c_, and as nut N is screwed up, the saw S and cone are
forced along arbor _e_ until the saw meets the face of B, and the
clamping takes place. The strength of the spring _s_ is sufficient to
hold the saw true, and as the motion of cone _c_ is in this case but a
very little, therefore its wear is but little, which makes this a
durable and handy device, while the saw cannot be sprung from
over-pressure of the cone. Circular saws of large diameter, as from 40
inches upwards, are made a fair sliding fit upon their arbors or
mandrels, and are provided with two diametrically opposite pins that are
fast in the arbor collar.
The pins should be on diametrically opposite sides of the arbor, and an
easy sliding fit to the holes in the saw, but they should not bind
tight. Both pins should bear against the holes in the saw, and if both
the pins and the holes in the saw are properly located, the saw will
pass up to the collar with either side against the arbor collar, or in
other words, the saw may be turned around upon the arbor.
If the pins, or either of them, bind in the holes of the saw, and the
latter is forced on the arbor, it will spring the saw out of true, and
when this is the case care should be taken in making the correction to
discover whether it is the pins or the holes in the saw that are wrongly
located. If it is the pins, the error will show the same whichever side
of the saw is placed next to the arbor collar, while if the error is in
the holes, the error will show differently when the saw is reversed on
the arbor.
When a saw becomes worn, and its teeth require sharpening, the first
thing to do is to _joint_ it, that is to say, bring down all its teeth
to the same height, which may be done by holding an emery block or file
against it while the saw is running, care being taken to hold the block
or file firmly, and to continue the process until the tops of the teeth
run true.
The next operation is to gum and sharpen the teeth. Gumming a saw is
cutting out the throats, or gullets between the teeth, so as to maintain
the height of the tooth, and it follows that on saws that have sharp
gullets (or in other words, saws in which the back of one tooth and the
face of the next tooth join in a sharp corner), the sharpening process
with the file may be made to also perform the gumming.
In the case of teeth of coarse pitch, however, this would entail too
much labor in filing, and furthermore, as the height of the teeth
increases with the pitch or distance apart of the teeth of circular
saws, and as the higher the tooth the weaker it is, therefore coarse
pitched teeth are given round gullets so as to strengthen them as much
as possible. The gumming of a saw should always be performed before the
sharpening, and the sharpening before the setting.
When the sharpening is to be done with the file, the cutting strokes of
the file should be in the same direction as the teeth lean for the set,
as this leaves a sharper cutting edge, and it follows that the proper
plan is to file every other tooth first, going all around the saw, and
to then turn the saw around in the vise, and file the remaining teeth.
The height of the teeth and the diameter of the saw will be best
maintained by filing the front face of the tooth to bring it up to an
edge, but in filing the front face the spacing of the teeth should be
kept as even as possible.
If the front face has been filed until a tooth is as widely spaced as
those already filed, and the edge is not brought up sharp, then the edge
may be brought up by filing the back of the tooth.
[Illustration: Fig. 3083.]
A saw gumming, gulleting or chambering machine to be operated by hand,
and constructed by Henry Disston & Sons, is illustrated in Fig. 3083. It
consists of a frame spanning the saw, and having screws B B, B B, to
adjust to the saw thickness; 4 and 5 are two saw teeth, and 6 the
cutter, K is a wheel for the feed screw G, and C and D gauges for
regulating position and depth of the gulleting.
The cutter 6 is driven or revolved by means of the handles H H, but an
important point in the construction is, that a pawl and ratchet wheel is
used to drive the cutter, so that if the handles H H were revolved in
the wrong direction, the cutter would not be revolved. This saves the
cutter teeth from breakage. The machine is operated as follows:
Run the cutter back by means of screw G as far as necessary, then place
the machine on the saw, with the cutter close up in the chamber of the
tooth to be gummed.
If the teeth are regular and the same distance apart, start the cutter
in any chamber; but if they are irregular, make them even by commencing
in the smallest space. After gumming the saw a few times the teeth must
become regular. F is a set-screw to regulate the depth of gullet. Fasten
the machine to the saw by means of the screws B B, and proceed to gum
the first tooth, one of the points of the star being struck at each
revolution by a projection on the handle, steadily feeding the cutter
until arrested by set-screw F. Remove the machine to the next tooth
towards you, after having run the cutter back, and proceed as before
until the whole of the teeth are gummed.
The cutter is so arranged as to slide on its axis, and when one portion
becomes dull, remove a washer from back to front, and thus present a new
sharp cutting surface; and so continue changing the washers until the
whole face of the cutter becomes dull.
Set is given to saw teeth in two ways: first, by what is called _spring
set_, which is applied to thin saws and to cross-cut saws; and second,
_swage set_, which is given to thick saws and to inserted teeth. Spring
set consists of bending the teeth sideways so as to cause the saw to cut
a passageway or _kerf_, as it is termed, wide enough to permit the saw
to pass through the timber without rubbing on its sides.
Swage set consists of upsetting the point of the tooth with a swage,
thus spreading it out equally on both sides of the body of the saw
plate, as shown at A, Fig. 3084.
The set of the teeth, whether given by swaging or upsetting, or by
spring set, should be equal throughout the saw, so that each tooth may
have its proper share, and no more, of duty to perform.
If spring set is employed, it should not extend down more than half the
depth of the teeth, and this point is one of considerable importance for
the following reasons. The harder the saw is left in the tempering the
easier the teeth will break, but the longer they will keep sharp. Now a
tooth that is hard enough to break if it is attempted to carry the set
down to the root or bottom, will set safely if the set is given to it
for one-half its depth only.
If a saw is to be sharpened by filing, it should be made as hard as it
can be to file properly, even at the expense of rapidly wearing out the
file, because the difference in the amount of work the saw will do
without getting dull enough to require resharpening is far more than
enough to pay the extra cost of files.
Circular saws with inserted teeth are made of thicker plate than solid
saws of corresponding diameters, which is necessary in order that they
may securely hold the teeth. The principal difference in the various
forms of inserted teeth lies in the method of locking or securing the
teeth in the saw.
Figs. 3084 and 3085 represent the chisel tooth saws of R. Hoe and
Company. The No. 2 tooth is that used on gang edging machines and for
bench work. No. 3 tooth is that used in miscellaneous sawing, for hard
woods and for frozen lumber. No. 4 is the shape used in the soft and
pitchy woods of southern and tropical countries.
The method of inserting the teeth is shown in Fig. 3084 on the left, the
pin wrench being shown in position to move the socket whose projection
at C carries the tooth D home to its seat and locks it there.
The sockets for the numbers 3 and 4 tooth are, it is seen, provided with
a split, which gives to them a certain amount of elasticity that
prevents the sockets from getting loose.
Swing-frame saws are made in various forms, generally for cross-cutting
purposes or cutting pieces to length.
[Illustration: Fig. 3084.]
[Illustration: Fig. 3085.]
[Illustration: Fig. 3086.]
Fig. 3086 represents a swing-frame saw that is mounted over a work
bench, and can therefore be used without necessitating carrying the work
from the bench. It consists essentially of a frame pivoted at the upper
end to the pulley shaft and carrying below a circular saw driven by
belt over pulleys on the upper shaft and the saw arbor. In this machine
the iron hubs carrying the frame have sockets fitting over the outer
diameter of the hanger hubs, so that the frame hangs upon those hubs and
not upon the pulley shaft. The advantage of this plan is that the frame
joint is relieved of the wear which would ensue were it hung upon the
revolving spindle, while at the same time the movement of the joint is
so small as to induce a minimum of abrasion. To counterbalance the frame
while it is placed out of the perpendicular, there is provided a
compensating weight as shown in the engraving.
[Illustration: Fig. 3087.]
Fig. 3087 represents an example of that class of cutting-off saw bench
in which the length of the work is determined by the width apart of the
saws.
This machine is constructed by Trevor and Company, and is designed for
cutting barrel staves to exact and uniform lengths.
[Illustration: Fig. 3088.]
The stave is laid upon the bars of the upright swing-frame (which is
pivoted at its lower end), and the latter is vibrated by hand, which may
obviously be done both easily and quickly on account of the lightness of
the swing-frame and its vertical position. A dimension sawing machine,
by G. Richards and Company, is shown in Fig. 3088. This machine is
designed for general fine work, such as pattern making, and its general
features are as follows:
It carries two saws (a cross-cut and a rip-saw), mounted on a frame that
can be quickly revolved by a worm and worm wheel to bring either saw
into position as may be required.
There is a fixed table and adjustable fence on one side of the saw, and
a movable table and fence on the other.
The saws are ground thin at the centre, as shown in Fig. 3089, so that
but little or no set need be given to the saw teeth; hence the cutting
edges of the teeth are more substantial and true, and as a result the
work is cut very smoothly, and if the machine is kept in thoroughly good
order, the sandpaper may follow the saw.
In Fig. 3088, A is a substantial box frame, to which is bolted the fixed
table T. T´ is the movable table which runs on rollers, and is guided by
the [/\] slideway at _e_. This table the workman pushes to and fro by
hand, the work being adjusted upon the table or to the fence, as the
case may be. At W is the wheel for swinging the frame to bring the
required saw into position.
[Illustration: _VOL. II._ =DIMENSION SAWING MACHINE.= _PLATE XVIII._
Fig. 3089.]
In Fig. 3089 the worm gear for swinging the saws into position is shown,
and also a sectional view of one saw arbor and of the movable table. A
is the main frame, and _f_ the disc frame carrying the two saw arbors.
The disc _d_ is turned to fit a seating formed in the base, while the
other end of the disc frame fits through a substantial bearing B; W´ is
the worm wheel, and W´´ the worm for swinging the disc frame. The worm
teeth fit closely to the worm wheel teeth, and backlash or play is
prevented by means of the spring bearing shown at D, the spiral springs
forcing the worm teeth into the worm wheel teeth. Thus _a_ is the
bearing for the worm carried in the box _c_, upon which is the spiral
spring whose tension is regulated by the screw _g_.
The end of the worm is therefore held in a swivel joint that causes it
to operate very easily.
[Illustration: Fig. 3090.]
Fence F, Fig. 3088 is for slitting, and is made to swing back for bevel
cutting, while F´ is for cross cutting, and is adjustable for angle
cutting. Fence F is fitted to a plate P, Fig. 3090, which rests on the
table top, and also rests on the long slide _g_. This slide fits in a
beveled way _h_, and contains a [_|_] groove. A tongue likewise beveled
fits in the top of this groove, the tongue being permanently fast to the
fence plate. The [_|_] bolt passes through the tongue and fence plate,
having at its upper end a milled or knurled thumb wheel R, which when
tightened up fastens the fence plate and the slide together.
Upon slacking the thumb wheel R, the fence plate and [_|_] bolt may be
readily shifted, setting the fence as near to gauge as possible by hand,
and the thumb wheel is then tightened, and the slide (which carries the
fence bodily with it) is adjusted by means of the hand wheel H and its
screw which threads into a lug from the table.
The fence F is pivoted to plate P at _p_, and the angling link which
holds it in position is secured by a hand nut M.
The front journal of the saw arbor has a double cone, and by means of
the nuts _n n´_, Fig. 3089, can be regulated for fit independently of
the back bearing and journal, the latter being also coned and capable of
independent adjustment by means of the adjustment nuts _m m´_.
The countershaft for driving the saw arbors is below the machine, so
that the saw that is not in use remains stationary.
[Illustration: Fig. 3091.]
Examples of the work done on this machine are shown in Fig. 3091, the
various sections shown being produced by the vertical movement of the
saw through the table and the cross movement of the fence. For example,
for cutting out a core box, such as shown at 6, small grooves are cut
through to remove the bulk of the wood, and the saw marks at the bottom
of each saw cut serve as gauge lines for the workman in finishing the
circular bore with the gouge, etc.
An example in which the table is fixed to the frame and the saw is
adjusted for height above the table is shown in Fig. 3092. The saw arbor
is here carried in a frame that is pivoted at one end to the main frame,
while at the other end is a handle through which passes a locking screw
for securing that end of the saw arbor frame to the arc slot shown on
the main frame.
[Illustration: Fig. 3092.]
In a more expensive form of this machine an adjusting screw is used for
regulating the height of the saw, and an iron table is employed instead
of a wooden one.
[Illustration: Fig. 3093.]
A double saw machine constructed by P. Pryibil is shown in Fig. 3093. In
this machine each saw is carried in separate frames, that are pivoted at
one end to the main frame and secured at the other to segments, so that
either saw may be elevated to the required distance above the work
table.
One saw is for ripping and the other for cross cutting, and the arbor of
the latter is provided with an adjusting screw operated by the hand
wheel shown on the right hand of the machine.
As the saws are on independent arbors, they can be speeded differently
to suit different saw diameters, which is an advantage because, as
machines of this class are for the lighter classes of work, the ripping
saw will rarely be required for work of more than about 3 or 4 inches
thick, and a rip saw of large diameter is not therefore necessary.
The cross cut saw however requires to be of larger diameter, as its work
includes cross cutting up to 8 or 10 inches diameter, and the saw being
larger does not require so high a speed of revolution.
Both saws are provided with ripping gauges and with right and left hand
mitre fences, adapted to the application of either short or long work,
and provided with length gauges.
[Illustration: Fig. 3094.]
Fig. 3094 illustrates the various gauges in place upon the table of a
machine. The table is provided with a slideway, or slot, on each side of
the saw, and parallel with it, and also with a slideway at one side of
the table. In the figure, the mitre gauge, or gauge for sawing at an
angle, is shown in two positions.
The gauge A A A is for cutting work to length, and for cropping the ends
at the same time, an extension frame being used, as shown for unusually
long work.
[Illustration: Fig. 3095.]
[Illustration: Fig. 3096.]
Fig. 3095 illustrates the method of employment of the mitre gauge. The
pointer is set to the degree of angle the work is to be cut to, and is
fastened to its adjusted position by the set screw H. The stop is set to
the required length, and the work is held by hand against the face of
the gauge, and at the same time endways against the stop, and the gauge
is then moved along the slot, feeding the work to the saw. When the work
is sawn and is to be withdrawn, care must be taken to keep the work
fair, both against the gauge and against the stop.
[Illustration: Fig. 3097.]
Figs. 3096 and 3097 show the application of the gauges for cropping off
the ends of work and cutting it to exact length. There are two stops, S
and T, each of which is secured in position by a set screw, and has a
tongue that may be thrown over, as occasion may require--thus, suppose
it is desired to merely crop off the end of the work--and both stops may
be set for the work to rest against as in Fig. 3096, and the end of the
work may be cut off or cropped to square it or remove a defective part.
Stop S may then be thrown over as in Fig. 3097, and the squared or
cropped end of the work rested against stop T, to gauge the length to
which the work will be cut. This is a simple and convenient method of
cropping and gauging.
[Illustration: Fig. 3098.]
Fig. 3098 represents a circular saw machine, constructed by the Egan
Company, in which the table is carried on a vertical slide, and may be
raised or lowered by means of the hand-wheel, bevel gears, and screw
shown, and may be set at any required angle to the saw for cutting
bevels.
The saw arbor or mandrel is carried by the main frame, and is therefore
rigidly held.
The fences can be used on either side of the saw, which is very
convenient when the table sets out of the level.
BEVEL SAWING MACHINE OR COMBINATION MITRE SAWING MACHINE.
In this machine, which is shown in Figs. 3099, 3100, and 3101, the
construction permits of the saw being set so as to revolve at other than
a right angle to the work table, which is rigidly secured to the frame
of the machine.
This machine is constructed by J. S. Graham & Company, and its action
may be understood from the following:
Fig. 3099 is a general view, while Figs. 3100 and 3101, are sectional
views of the machine.
The table is firmly bolted to the frame, and is fitted with the
necessary groove slides and fences for rip sawing and cross cutting. It
is also provided with a removable piece, which allows the use of
wabbling saws, dado heads, etc.
[Illustration: Fig. 3099.]
[Illustration: Fig. 3100.]
The sides of this machine A, A, Fig. 3099, are cast with an extension
for countershaft. Referring now to Figs. 3100 and 3101, the upright
piece I, I, with arms B B, and G, G, is bolted to the frame as shown.
The arbor frame M, M, is gibbed to T, T, by the circular piece U, and is
moved to any angle by the hand wheel Z, which operates the worm W, which
in turn moves the arbor frame M, M. This arrangement does not require
any locking device to hold the saw in position. As the centre upon which
the arbor swings is in the intersection of the planes of the saw and
table top, the opening in the table needs not be larger than for the
ordinary saw. When cutting a mitre the saw takes the position J, Fig.
3101. When cutting at a right angle the saw takes the position J´ and
the arbor takes the position P´ N´.
[Illustration: Fig. 3101.]
The saw arbor can be raised and lowered by the use of the hand wheel
which operates the screw _b_ (Fig. 3100.)
There is an accurate index located in front of the machine in sight of
the operator, marked from 0 to 45°.
The iron table is of one piece 4 feet by 3 feet and fitted with the
necessary groove slides for ripping and cross cutting gauges. It is also
provided with removable piece E, Fig. 3101, allowing the use of dado
head, etc. The table is provided with a bevel slitting gauge S´, and
cross cut or mitering gauge X´, Fig. 3099, which in connection with the
angular adjustment of the saw enables the operator to get every
conceivable plain or double mitre ever required. The pulleys A´, B´, are
made wide to allow the belt to travel as the saw is inclined. The pulley
B´ takes up the slack of the belt. The countershaft and tightener are a
part of the machine and can be run wherever a belt can be brought to
them.
ROLL FEED CIRCULAR SAWS.
Figs. from 3102 to 3105 represent a roll feed circular saw, by J.
Richards.
Fig. 3102 is a side elevation, Fig. 3103 a plan, and Fig. 3104 a
cross-sectional view through the rolls.
In Fig. 3102, P is the saw-driving pulley, T a stand for carrying the
saw guides _a_, _b_, _c_, _d_, which are adjustable for height by means
of the arm whose set screw is shown at U; at W is the spreader for
opening out the board after it has been cut by the saw, and thus prevent
its binding against the saw and heating it.
The construction of the feed motion is shown in Figs. 3103, 3104, and
3105.
On the saw arbor is the feed cone C, Fig. 3103 having four steps so as
to give four rates of feed. This cone connects by belt to feed cone D,
whose shaft drives feed pulley E, which drives F by belt connection. F
drives two worms shown by dotted lines at H and I, and these drive the
worm wheels which drive the feed rolls, one of these worm wheels being
shown at K, in the side view, Fig. 3102.
The feed roll L (Fig. 3103) is supplemented by a fence or gauge face P,
which guides the work closer up to the saw than would be possible with a
roll, and a supplemental roll is provided at M, thus affording a guiding
surface for the work from M to the end of P. The stand for guide roll L
fits in a slideway, and is adjustable along it by means of the screw S.
Similarly the stand for roll N is fed along its slideway by screw R.
There are three separate sets of saw guides, all of which are shown in
the plan view Fig. 3103, and of these the top ones, _a_, _b_, _c_, _d_,
_e_, _f_, _g_, and _h_ are adjustable by nuts. The front ones, _l_, _m_,
_n_, _o_, _p_, _q_, and the back ones, _i_, _j_, _k_, and _r_, _s_, _t_,
are adjustable by means of the wedges _w_. At Z is a wedge for adjusting
the spreader W so as to keep it close to the saw whatever the diameter
of the latter may be.
[Illustration: Fig. 3102.]
[Illustration: Fig. 3103.]
Fig. 3105 is an end view of the machine showing the feed worms H and I,
and the belt tightener V, which is carried on the arm _u_ on whose shaft
is the weight _y_, attached to which is the handle X.
[Illustration: Fig. 3104.]
[Illustration: Fig. 3105.]
SEGMENTAL CIRCULAR SAWS.
[Illustration: Fig. 3106.]
A segmental circular saw is one in which the saw is composed of segments
secured by screws to a disc, the construction being such as shown in
Fig. 3106, in which A is the saw arbor, D the disc, and E, F, G, H, I,
J, etc., the segments.
The segments are made of varying thicknesses at the cutting edge, and
are tapered for a distance for from 6 to 8 inches inwards from the teeth
points. Thus in the figure there is shown at P an edge view of a
segment, from _a_ to _b_ being parallel, and from _b_ to _c_ being
ground off taper.
The segments are held to the disc by the two sets of screws, R, S, and
are further secured at their edges by pieces of copper, as shown at W.
Between the edges of the segments there is left a space or opening of
about 1/16 inch, which is necessary to insure that the segments shall
not bind together edgeways, as that might prevent their seating fairly
against the face of the disc D.
The seats for these pieces of copper are shaped as shown in the face
views at W, and in the edge views at W´, the mouth of the slot being
widened on each side, so that riveting up the pieces of copper will
prevent the segments from moving sideways.
In fitting in these pieces of copper, it is essential to take care that
they do not completely fill the slots, but leave a small opening at each
end of the slot, as at _f_ and _g_ in the figure, and in order to do
this the copper must be left about 1/8 inch narrower than the width of
the slot.
If the copper is, in riveting up, brought to bear against the end of the
slot, it will twist the segments out of line one with the other, causing
the saw to drag, cut roughly and produce bad work.
[Illustration: Fig. 3107.]
[Illustration: Fig. 3108.]
Figs. 3107 and 3108 represent portions of segmental saws for cutting
veneering. In some of these saws the screw holes are so arranged that
the segments can be moved out to maintain the diameter of the saw as it
wears.
GANG EDGING MACHINES.
For dressing the edges of planks parallel and to width what are called
gang edgers or gang edging machines are employed.
A gang edger consists of an arbor driving two or more circular saws,
through which the boards to be edged are fed. Means are provided whereby
the distance apart of the saws may be rapidly adjusted while the saws
are in motion, so that if a board will not true up to a given width, the
saws may be set to cut it to a less one without delay.
[Illustration: Fig. 3109.]
Fig. 3109 represents a self-feeding gang edger, constructed by J. A. Fay
& Company, and in which the left-hand saw may be fixed at any required
position on the left-hand half of the saw arbor, while the two
right-hand ones may be adjusted independently along the arbor, while the
machine is running.
At the back of the saw is a feed roll, and above it a pressure roll,
whose pressure may be regulated by means of the weight and bar shown at
the back of the machine. The object of placing the feed and pressure
rolls at the back of the saws, is, that if a board is found to be too
narrow for the adjustment of the saws, it may be withdrawn without
stopping or reversing the machine, and the saws may be drawn together
sufficiently to suit the case.
Fig. 3110 is a plan and Fig. 3111 an edge view of the work table, and
show the means of adjusting the saws. A is the saw arbor, and 1, 2, 3,
the circular saws. Saw 1 is carried by the sleeve B, which is secured in
its adjusted position by the set screw C.
The mechanism for traversing saws 2 and 3 corresponds in design, and may
be described as follows:
The arbor A has a spline S to drive the sleeves D, D´, which hold the
saws and are carried by arms E, E´, which operate in slideways and have
racks F, F´, into which gear pinions whose shafts G, G´, are operated by
the hand wheels H, J.
It is obvious that by means of the hand wheels H, J, saws 2 and 3 may be
regulated both in their distances apart or in their distances from saw
1, while the machine is in full motion, the bushes or sleeves D and D´
being carried by and revolving in the slide pieces or sliding bearings E
and E´ respectively. Now suppose that E´ be moved to the left by hand
wheel J, until it abuts against the end of D, at the slide end, and a
further movement of D´ will also move D, causing it to operate its
pinion and revolve the hand wheel H, hence D and D´ may be
simultaneously moved without disturbing their distances apart by
operating hand wheel J. On the yoke above the saws is a coarse-figured
register plate to enable the setting of the saws to accurate widths
apart.
RACK FEED SAW BENCH.
This machine is employed for the purpose of reducing balks or logs into
planks of any thickness required. The machine is fixed on the floor of
the saw mill, all the gearing being underneath the floor, so that the
table may be set level with the floor, which is a great convenience when
heavy logs are to be operated upon. The machine consists of a
substantial bed plate or frame A, Fig. 3112, carrying the saw and the
feed works. The carriage runs on rollers, some of which are fixed to the
frame A, and others to the framing timbers B, which are long enough to
support the carriage throughout its full length, when the carriage is at
either end of its traverse.
[Illustration: Fig. 3110.]
[Illustration: Fig. 3111.]
The driving pulley for the saw arbor is shown at C, Fig. 3112, in dotted
lines and in Fig. 3113 in full lines. Upon the saw arbor is a cone
pulley D, Fig. 3113, for operating the carriage to the feed, the
construction being as follows:
Referring to Figs. 3112 and 3113, cone pulley D connects by a crossed
belt to cone pulley E, on whose shaft is a pulley _e_ which drives the
pulley F, on whose shaft is the pinion _f_, which drives the gear G. On
the same shaft as G is a pinion _g_, which drives the gear wheel H,
which engages the rack J, on the carriage, and feeds the carriage to the
cut. The diameters of pulleys E, F, and of _f_, G, and _g_, are
proportioned so as to reduce the speed of the cone pulley D, down to
that desirable for the carriage feed. But, as there are four steps on
the cones D, E, therefore there are four rates of cutting feed or
forward carriage traverse, which varies from 15 to 30 feet per minute.
The speed of the saw varies in practice, some running it as slow as
9,000 feet per minute at the periphery of the saw, and others running it
as high as 16,000 feet per minute. The latter speed however, is usually
obtained when the saws are packed with fibrous packing, which will be
explained presently.
The quick return motion for the carriage is obtained as follows:
Referring to Figs. 3113, and 3114, K is a fast and K´ a loose pulley on
the shaft _k_, and receiving motion by belt from a countershaft.
[Illustration: _VOL. II._ =RACK-FEED SAW BENCH.= _PLATE XIX._
Fig. 3112.]
The speed of the fast pulley K is such as to give a return motion to
the carriage of about 50 or 60 feet per minute, being about twice as
fast as the carriage feed motion.
We have now to explain the methods of putting the respective carriage
feed motions into and out of operation, and insuring that both shall not
be in gear at the same time.
[Illustration: Fig. 3113.]
Referring therefore to Figs. 3113 and 3114, suppose the carriage to have
completed a feed or cutting traverse, and the operator pushes with his
knee the lever or handle _h_, Fig. 3114, which revolves shaft _m_, on
which is an arm that moves the belt-shifting rod _n_, thus moving the
belt from fast pulley F to loose pulley F´, thus throwing the feed gear
out of engagement and causing the carriage to stop. He then presses down
the foot lever L, Fig. 3113, which operates the belt-shifting rod _p_,
Fig. 3114, and moves the belt from loose pulley K´, to fast pulley K,
which having a crossed belt, operates the pulley F in the reverse
direction and traverses the carriage backwards, or on the return motion.
Upon releasing the foot from the lever L, the weight W operates the foot
lever L, and the belt is re-shifted from fast pulley K to loose pulley
K´, and the carriage stops.
The carriage is formed of iron plates with an open space of about 1/2
inch between them, as shown in Fig. 3114, this space forming a race to
permit the carriage to travel past the saw. The only connection between
the two sections or parts of the table, is a wide plate at the rear end
which secures them together, and causes the lighter portion of the
table, which is merely driven by the friction of the rollers C, to
always travel with the lower or under portion, which is driven by the
rack J. In larger machines for the heaviest work, both sections are
driven by a rack motion.
The guide motion for the carriage is constructed as follows:
_a_, _a_, are brackets placed at intervals along the whole frame work.
These brackets support rollers _c_, which have flanges on them to
prevent any side motion of the carriage, the construction being most
clearly seen in Fig. 3113; _b_ being a bearing for the shaft _v_ of the
rollers. Each section of the carriage, it will be seen, has two ribs or
ways which rest on the rollers, which are arranged four on each shaft
_v_ (_i.e._ two for each section of the carriage).
The fence or gauge against which the face of the work runs is very
simply arranged as is shown in Figs. 3113, and 3114, being secured to
the shaft _q_, by a long bolt _t_, threaded into the top of the fence,
and at its lower end abutting against a shoe fitting partly around the
top of the shaft _q_. It is squared at the top to receive a wrench or
handle _u_, and it is obvious that unscrewing the handle releases the
fence from shaft _q_, so that the fence may be moved rapidly by hand
across the table to approximate the adjustment of the fence from the
saw. The fence having been thus approximately adjusted, and locked to
the shaft by means of the handle _u_, the final adjustment is made by
means of the hexagon nut _w_, on the bed of the shaft nut _x_, serving
as a lock nut, to hold _q_ in its adjusted position.
FIBROUS PACKING.--The fibrous packing before referred to is composed of
hemp, plaited in a four strand plait and inserted in an open-top trough,
along the sides of the saw for a distance about two inches less than the
radius of the smallest saw the machine uses.
[Illustration: Fig. 3114.]
This packing steadies and stiffens the saw, and also affords a means of
adjusting its tension, while the saw is running.
Suppose for example, that the saw is rim bound,[47] and the fibrous
packing may be rammed tightly to the saw, as near to the saw rim as
possible, and less tight as centre of the saw is approached.
[47] For the principles involved in hammering saws to equalize the
tension see page 69 (Vol. II.) _et seq._
This warms the saw, but makes it warmer at the circumference than at the
centre, expanding the circumference, and by equalizing the tension,
enables the saw to run straight.
[Illustration: Fig. 3115.]
When the packing is to be adjusted, the carriage is run out of the way,
and the packing operation is performed by hand, with a caulking tool.
The packing and its box, as applied to a rack saw bench is shown in Fig.
3115, by the dark rectangles. By thus packing the saw to guide it and
keep it straight, thinner saws may be used, saws 52 inches in diameter,
and having a thickness of but 7 or 8 gauge being commonly employed, and
in some cases of 9 gauge.
Saws that are thus packed, produce much smoother work.
The packing, it may be observed, is kept well lubricated with oil, and
the following is the method of adjusting it.
[Illustration: _VOL. II._ =PLANTATION SAW MILL.= _PLATE XX._
Fig. 3117.]
The side of the saw on which the operator stands is the last to be
packed, the packing on the other side being inserted so as bed fairly
but lightly against the saw, so as not to spring it, which may be tried
with a straight-edge. The packing on the other side is then inserted to
also bed fairly against the saw, without springing it, and the saw is
run until it gets as warm as it may, from the friction of the packing.
If, then, the saw flops from side to side, the outside (circumference)
is _loose_, and the packing is rammed together on both sides of the saw
and near the saw arbor or mandrel, care being taken that in ramming the
packing the saw is not unduly pressed on either side.
Expert sawyers generally change the packing when the saw is changed, and
thus keep for each saw its own packing. The slot or pocket in which the
packing lies is about 1-1/4 inches deep, and 1/2 inch wide.
[Illustration: Fig. 3116.]
In ordinary circular saw benches or machines the packing comes about up
to the level of the table, as shown in Fig. 3116, in which A is a hand
hole for putting in and lifting out the plate B, so as to put in or
remove the wooden pieces C, D, upon which the packing rests.
Fig. 3117 represents a saw mill constructed by the Lane & Bodley
Company. In this machine two circular saws are employed, the upper one
being of small diameter and revolving in the same direction as the log
feed. A is the driving pulley for the main saw arbor _a_, and B the
driving pulley for the upper saw arbor _b_. The carriage feed is
obtained by belt from cone pulley C to cone pulley D, on whose shaft is
a friction pulley _e_, which, for the feed motion, is moved by lever E
into driving contact with pulley F, whose shaft drives the pinion G,
which gears with the rack of the carriage. The three steps on the cones
C, D, give three rates of feed, and a quick return motion is given to
the carriage by engaging the friction pulley with a wheel not shown in
the engraving.
The log to be sawn rests upon the slideway S S´, and is secured thereon
by the dogs J, J, which are capable of sliding up or down upon the heads
H, H´. When the handles K are raised the slides carrying dogs J are free
to be moved up and down H, H´, whereas when handles K are depressed the
dogs J are locked and hold the log. The operation is to raise the dog
slides to the top of H, H´, set the log up to the faces of H, H´, and
then by raising handles K, let the dog slides fall, their weight forcing
the dogs into the log, and the depression of K locks the dog slides upon
H, H´, respectively.
The log feed is obtained from the lever L, which operates the ratchet
wheel T, which drives bevel gears V and W, which operate the screws that
slide the heads H, and H´, along the slideways S and S´.
Three rates of log feed are obtained by regulating the amount of motion
that can be given to the lever L, the construction being as follows:
In the lever L is a slot in which a stop _r_ can be secured at different
heights, and the piece M has four notches. The limit to which L can be
moved to the left is until it comes against the stop _x_, but the limit
to which it can be moved to the right is governed by the height of the
stop _r_ in the slot in L. If stop _r_ is set at its highest position in
the slot, L can be moved to the right until the stop _r_ meets the right
hand step on the circumference of M, and a maximum of log feed is given.
TUBULAR SAW MACHINE.
[Illustration: Fig. 3118.]
Fig. 3118 represents a tubular saw machine. The saw runs in fixed
bearings, the work feeding on the table B, running on ways on A. The
work is here obviously sawn to a curve corresponding to that of the
circumference of the saw.
CROSS CUTTING OR GAINING MACHINE.
In Figs. 3119 and 3120 is represented a machine constructed for either
cross cutting or gaining, the gaining head shown on the machine being
replaced by a cross-cut saw when cutting off is to be done.
[Illustration: Fig. 3119.]
It consists of a vertical column or standard, upon the face of which a
slideway A for the arm B, on which is a slideway C, along which the head
for carrying the saw arbor traverses.
When the saw is to be used, the carriage or work table must be locked in
position and adjusted so that the saw will come fair in the groove,
provided in the table, but it is not necessary to dog or fasten the work
to the table, because the saw itself draws the work over fair against
the fence.
When the machine is used for gaining, the work must be dogged fast to
the table, so that the work and table may be moved accurately together
and the widths apart of the gains kept accurate.
Joshua Oldham's combination saw for grooving or gaining is shown in Fig.
3121. It consists of two outside saws, such as shown at the top of the
figure, and having spur teeth between the ordinary cutting teeth. The
tops of the spur or cross-cutting teeth are a little higher than the
other teeth, so that they sever the fiber before the ordinary teeth
attempt to remove it, and thus produce very smooth work. The inside
pieces, shown at the bottom of the figure, go between the two outside
saws, if necessary, to make up the required width of gain. They are made
1/8 inch thick, with an odd one 1/16 inch thick, and will thus make
gains advancing in widths by sixteenths of an inch.
SCROLL SAWING MACHINES.
The scroll sawing machine derives its name from the fact that it is
particularly fitted for sawing scroll or curved work by reason of the
saw (which is a ribbon of steel with the teeth cut on one edge) being
very narrow.
The principal points in a scroll sawing machine are to have the saw held
under as nearly equal tension as possible throughout the whole of the
stroke; to render the machine readily adjustable for different lengths
or sizes of saws, to provide it with means of taking up lost motion, and
to avoid vibration when the machine is at work.
A scroll sawing machine constructed by the Egan Company is shown in Fig.
3122, a sectional view of the saw straining mechanism being shown in
Fig. 3123. A, A, is a casting having slides for the head B, which is
adjustable upon A to suit different lengths of saws, and is secured in
its adjusted position by the bolt C and nut D. To the ends of the
springs S, a strip or band of leather is secured, the other end passing
around the small step F of a roller R, and being secured thereto. The
roller R is so supported that it may rise and fall with the strokes of
the saw. A second leather band G is secured at T, passes over the large
step of R, and at its lower end hooks to the saw, which is strained by
the springs S. This reduces the motion of the springs, and thus serves
to equalize their pressure throughout the saw stroke.
The lower end of the saw is gripped in a slide or cross-head that is
driven by the connecting rod and crank motion shown in the general view
Fig. 3122. The lever shown at the foot of the machine moves the belt to
the fast or loose pulley to start or stop the machine, and operates a
brake to stop the machine quickly.
[Illustration: _VOL. II._ =GAINING OR GROOVING MACHINE.= _PLATE XXI._
Fig. 3120.
Fig. 3121.]
Fig. 3124 represents a scroll saw constructed by H. L. Beach. This
machine is provided with a tilting table, which can be set at any angle
up to 39 degrees, either to the right or left, the exact angle being
indicated by a graduated arc.
[Illustration: Fig. 3122.]
[Illustration: Fig. 3123.]
[Illustration: Fig. 3124.]
The straining device, including the springs, air pump, guide-ways,
cross-head and steel bearing, are all attached to the vertical tubular
shaft, which is secured to the heavy cast back support by the box E and
eccentric lever F. By raising the lever F, the shaft, being balanced, is
free to move up or down to suit any length of saw.
At the same time, the steel bearing L forms a support for the back and
sides of the saw, and can be raised or lowered to suit any thickness of
work.
The under guide-ways are so constructed that their expansion by
tightening does not tighten the cross-head. Instead of the ordinary
tight and loose pulleys, the crank shaft carries a friction pulley and
combination brake by which the saw is stopped or started instantly, by a
single motion of the foot.
This leaves the hands entirely free, and saves considerable time in
stopping and starting.
The lower end of the saw is held by a steel clamp; when the saw breaks
it can be used again by filing a notch. Both ends of the saw are
arranged to take up lost motion and wear.
Any desired strain from 10 to 75 pounds can be given to the saw, and the
strain is equal at all points of the stroke.
BAND SAWING MACHINES.
[Illustration: Fig. 3125.]
The simplest form of band sawing machine is that in which the work is
fed to the saw by hand, a machine of this class, constructed by J. A.
Fay & Co., being shown in Fig. 3125. It consists of a standard or frame
A, carrying the saw-driving wheel B, and the upper wheel C, the saw
being strained upon these two wheels. The lower wheel runs in fixed
bearings, while the bearing of the upper wheel is carried in a slide
provided in the frame, being operated in the slide by a screw, whose
hand wheel is shown at E, so that it may be suited for different lengths
of saws.
The bearing of the upper wheel is so arranged that the tension placed on
the saw may be governed by a weighted lever F, which enables the upper
bearing to lower slightly, so that if a chip should fall between the saw
and the lower wheel, it may not overstrain, and therefore break the saw.
At J, is a bar carrying a guide G, which sustains the saw against the
pressure of the cut, a similar guide being placed below the table T, at
G´. This latter guide is fixed in position, whereas the upper one, G, is
adjustable for height from the work table, so that it may be set close
to the top of the work, let the height of the latter be what it may. G´´
is a guide and shield for the saw at the back of the machine, and H is a
shield to prevent accident to the workman, in case the saw should break.
Band saws are ribbons of steel, brazed together at their ends and having
their teeth provided on one edge. The widths of band saws vary from 1/16
inch to 8 inches, and their thicknesses from gauge 18 to 22 gauge,
according to width.
The advantage of the band saw lies in that it may be run at high
velocity, may be made thin, and its cutting action is continuous.
As a band saw is weak, it is desirable to have the teeth as short as
possible and leave enough room for the sawdust, so that it shall not
pack in the teeth.
[Illustration: Fig. 3126.]
In a circular saw, the centrifugal force acts to throw the sawdust out,
while in a frame saw, the backward motion of the saw acts to clear the
teeth of the dust, whereas in a band saw the dust is apt to pack in the
teeth while they are passing through the work. The remedy is to space
the teeth widely, thus giving room for the dust without having a deep
tooth, an ordinary form of tooth being shown in Fig. 3126.
[Illustration: Fig. 3127.]
A stronger form of tooth is shown in Fig. 3127, the tooth gullets being
well rounded out, and the teeth shallow at the back, while having ample
room in front for the dust.
In determining the shapes of the teeth of band saws, we have the
following considerations:
[Illustration: Fig. 3128.]
One of the principal objects is to have the back edge of the saw bear as
little as possible upon the saw guide, and as the feed tends to force
that edge against the guide, we must so shape the teeth as to relieve
the back guide as much as the circumstances will permit. This may be
done by giving to the front faces of the teeth as much rake as the
nature of the work will permit. Thus, in Fig. 3128, it will be seen that
from the front rake, or _hook_ of the teeth, as it is commonly called,
there is a tendency for the cut to pull the saw forward, this tendency
being caused by the pressure, on the teeth in the direction of the
arrows, and obviously acting to prevent the saw from being forced
against the back guide.
For sawing soft woods, such as pine, the teeth may be given a maximum of
front rake or hook, whereas for hard woods, the front faces must be made
to stand at very nearly a right angle to the length of the blade, and
the feed must therefore be lighter, in order to relieve the back edge of
the saw from excessive contact with the back guide, which would not
only rapidly wear the guide, but acts to crystallize the edge of the saw
and cause it to break.
[Illustration: Fig. 3129.]
The set of the teeth of band saws is given in two ways, _i. e._ by
spring set, which consists of bending each alternate tooth sideways, as
in Fig. 3129, or by swage set (upsetting or spreading the points of all
the teeth), a plan that may be followed with advantage for all saws
thicker than about 20 gauge.
Spring set is given either by bending, or by hammer blows, and swage set
either by blows or by compression. In spring set, each tooth cuts on one
side, and there is consequently a pressure tending to bend the tooth
sideways, and break it at the root, whereas in spread set, the tooth
cuts on both sides equally. As the front faces of band saw teeth are
filed straight across, as in Fig. 3129, and are not given any fleam for
any kind of woodwork, the set, whether spring or a spread, should be
equal in amount for every tooth, and the pitch and depth of the teeth
should be exactly alike, so that no one tooth will take more than its
proper share of the cut.
The bend or set of the tooth in spring set saws, should not extend more
than half way down the depth of the tooth, which will make the set more
uniform and save tooth breakage, it being borne in mind, that a tooth
hard enough to break if the set extends down to the root, will set
easily if it extends half way down only, and that a saw may be soft
enough to file, and of a proper temper, and yet break if the spring set
is attempted to be carried too far down the tooth.
[Illustration: Fig. 3130.]
If as in the case of fine pitched teeth, the teeth are filed with a
triangular or _three_ square file but little front rake or hook can be
given, without pitching the teeth widely. This is shown in Fig. 3130, in
which S, is the section of a saw, and F, a section of a three square
file. The front faces have no rake, and the file is shown as acting on
both faces.
[Illustration: Fig. 3131.]
In Fig. 3131, we have the same pitch of teeth, but as the file is canted
over, so as to give front rake or hook to the tooth, the tooth depth is
reduced, and there is insufficient room for the sawdust. In order,
therefore, to give to the teeth front rake, and maintain their depth
while keeping the pitch fine, some other than a three square file must
be used.
The principal defect of the band saw is its liability to break,
especially in band saws of much width, as say 3 inches and over. A saw
that is 6 inches wide will ordinarily break by the time it has worn down
to a width of 4 inches. Now for heavy sawing it is necessary that wide
saws be used, in order to get sufficient driving power without
over-straining the saw.
[Illustration: Fig. 3132.]
The causes of this saw breakage are as follows:
In order that the saw may be regulated to run on the required part of
the upper wheel, and lead true to the lower wheel, it is necessary that
the upper wheel be canted out of the vertical, and band sawing machines
are provided with means by which this may be done. If the upper wheel
were set level, as in Fig. 3132, the saw itself would be held out of
level, and the toothed edge would be more tightly strained than the back
edge. Furthermore the middle of the saw cannot bed itself perfectly to
the wheel. Furthermore, the velocity of the toothed edge would be
greater than that of the back edge because of its running in a circle of
larger diameter when passing over the wheels.
[Illustration: Fig. 3133.]
This is to some extent remedied by setting the wheel out of the
vertical, as in Fig. 3133, in which case the two edges will be more
equally strained, and have a more equal velocity while passing over the
wheels.
[Illustration: Fig. 3134.]
There will still however, be an unequal strain or tension across the
saw width, and it is found that unless the saw is made what is known as
loose,[48] it is liable to break, and will not produce good work. It is
to be observed however, that the above may be to a great extent, and
possibly altogether, overcome by means of having the rim face of the
wheel, or of both wheels, curved or crowned in their widths, so that the
saw will be in contact with the face of the wheel, nearly equally across
the full saw width. This would also cause the saw to run in the middle
of the wheel width, and thus enable the alignment of the saw to be made
without requiring the upper wheel to be set out of level.
[48] See page 69, Vol. II., for what is technically known as looseness
in a saw.
RE-SAWING BAND SAW MACHINE.
A re-sawing machine is one used to cut lumber (that has already been
sawn) into thinner boards. Fig. 3134 represents a band saw machine,
constructed by P. Pryibil, having a self-acting feed motion, consisting
of four feed rolls, all of which are driven, and two small idle rolls,
which are so arranged as to guide the last end of the stuff or work
after it has left the driven rolls.
Four rates of feed are provided, and the upper wheel can be set at the
required angle from a perpendicular while the machine is in motion.
The upper guide wheel, and the mechanism by which it is carried, is
counterbalanced by a weight that hangs within the column or main frame,
and is therefore out of sight.
[Illustration: Fig. 3135.]
The construction of the parts by means of which the upper wheel is
adjusted in height to regulate the tension of the saw, and which also
cants the wheel out of the vertical, is shown in Fig. 3135, which
represents a portion of the main frame or column, on which is a slideway
B, for the slide C, which carries the bearing for the upper wheel.
The method of moving the slide C for moving the upper wheel to adjust
the saw tension is as follows:
By means of the handle H and the worm and worm wheel at W, the shaft S
is revolved. The upper end of S is threaded into the nut N, which is
capable of end motion in its bearing at _e_, and which abuts against the
lever L, the latter abutting against the end of the screw M, and acting
at its other end on the rubber cushion P. Now suppose that S be revolved
in the direction denoted by the arrow, and the effect will be to raise
the nut N. This effect will be transferred through the screw M to the
slide C, which will rise up on B, carrying with it the upper wheel
bearing and wheel.
When the upper wheel receives the strain of the saw, then the continued
revolution of shaft S will cause the nut N to lift endways in its
bearing _e_, the screw M acting as a fulcrum to cause the lever L to
compress the rubber cushion P. The amount of tension on the saw is
tested by springing it sideways with the hands. Now suppose the saw to
be properly strained, and that a piece or chip of wood accidentally gets
between the saw and the lower wheel, and the result will be that the
slide C will (from the extra strain caused by the chip) move down on its
slideway B, which it is capable of doing, because the long arm of the
lever L can move down, compressing P, and this will prevent the saw from
breaking.
To cant the wheel for leading the saw true to the lower wheel, the
following means are provided:
The upper wheel bearing rests on the fulcrum at _a_, and is guided
sideways by the screws _c_ and _d_. At _f_ is a stud threaded into the
bottom half of the upper wheel bearing, the wheels _g_ and _h_ threading
upon _f_. The weight of the upper saw wheel endeavors to lift the end J
of the wheel bearing, and wheel _h_ determines how much it shall do so,
while wheel _g_ acts as a check nut to lock the adjustment.
[Illustration: _VOL. II._ =BAND SAW WITH ADJUSTABLE FRAME.= _PLATE
XXII._
Fig. 3139.]
[Illustration: _VOL. II._ =BAND SAW MILL.= _PLATE XXIII._
Fig. 3140.
Fig. 3141.
Fig. 3142.]
The feed rolls are carried in slides which are operated in slideways by
means of screws, and the two back rolls, or those nearest to the column
are maintained vertical. The two front ones, however, are provided with
means by which they may adjust themselves to bear along the full depth
of the work, notwithstanding that it may be taper. The construction by
means of which this is accomplished is shown in Figs. 3136 and 3137, in
which A is front and B a back feed roll. The bearings of feed roll A
abut against rubber cushions C, C, whose amount of compression is
regulated by the set screws D, D.
[Illustration: Fig. 3136.]
[Illustration: Fig. 3137.]
[Illustration: Fig. 3138.]
The construction of the saw guides is shown in Fig. 3138, which is a
plan view partly in section. S S are hardened steel plates set up to the
saw by means of studs whose nuts are shown at N N. W is a friction wheel
which supports the saw against the thrust caused by the work feeding to
the saw. The adjustment of the wheel W to the saw is obtained by means
of the wheel H.
The hand wheel H operates the screw _r_ _r_, that adjusts the wheel W to
the saw, the wheel J serving to lock the screw in its adjusted position.
Fig. 3139 represents Worssam's band saw machine, in which the standard
may be set at any required angle for cutting bevels.
When the work is heavy and not easily handled it is preferable to set
the standard and saw at the required angle, rather than to set the table
at an angle and have the saw remain vertical. In Worssam's machine this
is accomplished as follows:
A is the main frame carrying the work table T, and having circular
guideways B, B´, which carry the standard C having guide C´ for working
in the circular guideways B, B´.
The saw-driving wheel D, is carried in bearings provided in C, and,
therefore moves when the standard C is moved.
At the upper end of C, is the slide E, which carries the bearing for the
upper wheel F, this slide being adjusted to regulate the saw tension by
the hand wheel O, whose screw threads into a nut in the slide E. H
carries the front guide G, for the saw, the back guide G´ being carried
by a bracket bolted to C. The back guide is fixed in position, but the
front one is adjustable to suit the height of the work by raising or
lowering it.
The means for setting the saw at the required angle to the work table
are as follows:
At the back of the standard C is a rack J, whose pitch line is an arc of
a circle of which the axis of the guideway C´ is the centre.
Into the rack J fits the worm wheel K, at the bottom of the shaft of
which is a pair of bevel gear wheels L, which are operated by the hand
wheel M.
A band saw machine constructed by Messrs. London, Berry & Orton, is
shown by Figs. 3140, 3141 and 3142, in plate XXIII. The saw-driving
wheel D, has wrought iron arms turned true and screwed into the wheel
hub. The wooden segments have their grain lengthways of the rim, and
between them are placed pieces of soft wood with the grain across the
rim. This acts to keep the joints tight, notwithstanding the expansion
and contraction of the wood.
The upper wheel is adjusted for straining the saw, and for leading the
saw true, by the following construction. It is carried in a U-shaped
frame F, which is pivoted at _y_ to a slide that is gibbed to the main
frame, and by operating the screw shown at X, the frame F is set to the
required level.
To regulate the tension of the saw, the hand wheel K is operated, which
drives the pair of bevel gears J and I, the latter of which operates the
threaded shaft H, whose upper end G connects with the slide which
carries F. Within G is a spring to act as a cushion to the slide, and
thus prevent saw breakage should a chip pass between the saw and its
driving wheel.
The saw guide frame is secured to the main frame at _m´_, _m´_. Upon the
face of _m_, is a slideway for the saw guide arm _n_, which may thus be
adjusted as closely to the upper face of the work as possible.
The weight of arm _n_ is counterbalanced by a rope passing over the
pulley V, and supporting the counterbalance weight _w_. The feed motion
is constructed as follows:
On the same shaft as the main fast and loose pulleys A, B, is the feed
pulley L, which by belt connection drives pulley M, which is on the
shaft W, upon which is a friction disc N, by means of which the rate of
feed is regulated. The feed disc N drives the wheel O; the degree of
contact between these two (N and O) is regulated by means of the weight
T, on the lever U.
On the same shaft as the friction wheel O, is a pinion driving the gear
X, which is on the same shaft as the pinion Y, which drives the two
gears Y´ and Y´´.
Referring now to Fig. 3142, gear Y´ drives the pair of bevel gears Z and
Z´, for the feed roll _e_, and the pair of bevel gears shown at Z´´, the
feed roll _f_. The gear Y´´ drives similar gearing for the feed rolls
_e´_ and _f´_, seen in the plan Fig. 3140.
Referring now to the plan Fig. 3140, and the side elevation, Fig. 3142,
the feed roll _f_ is carried in a frame _g_, which is fitted on the
slideway _d_, _d_, and receives a screw _i_, upon which is a hand wheel
_h_; at the back of this wheel is the lever _j_, which is weighted as
shown, so that the force with which feed roll _f_ grips the work is
determined by the weighted lever _j_, and may be varied to suit the
nature of the work by moving the weight along _j_.