the top of D, and being secured in its adjusted position by the screw I.
The work should obviously be set so that its upper face lies horizontal,
and is fed to the wheel by moving shoe C by hand along bar B, the long
bearing keeping C steady, and the lightness of the moving parts making
the feeding more sensitive than it would be were it required to move bar
B.
The tooth being ground is held by hand against the gauge G in Fig. 1994,
as was described with reference to that figure, and the reamer,
therefore, in the case of having spiral grooves, revolves upon its
centre while being fed to the emery wheel.
For tapers that are beyond the capacity of this device, and also for
holding cutters to have their face teeth ground, the device shown in
Fig. 2000 is employed. Upon the slide F is fixed knee K (the
corresponding parts to which are seen in the general view, Fig. 1992),
whose disk face at R is graduated as shown. Piece S is pivoted by a pin
passing through the hub of K and having a nut T to secure it in its
adjusted position. S is bored to receive the cutter arbor H, and is
split through so that by means of the screw at V the arbor may be
gripped and locked in S. The stud W for holding the gauge G passes into
a bore in the bracket X, and is secured therein by the screw at Y, the
lugs through which Y passes being split through into the bore for W. As
shown in the figure, the arbor H is set for grinding the side teeth of
the cutter, but it is obvious that S being pivoted to K may be swung out
of the vertical and to any required angle, so as to bring the face of
the tooth that is to be ground horizontally beneath the emery wheel, as
shown in Fig. 2001, which represents an angular cutter in position. We
have now to consider the adjustment of the cutter to the emery wheel,
necessary in order that the cutting edges may be given the necessary
clearance.
First, then, suppose in Fig. 2002 that the line A A represents the line
of centres of the emery-wheel spindle and the cutter arbor, and if the
front face B of the tooth be set coincident with this line, as in the
figure, then the top of the tooth partaking of the curvature of the
wheel that grinds it would have its heel C the highest; hence the edge
at B could not cut.
If, however, the line A A in Fig. 2003, still representing the line of
centres, we so set the gauge (G, Fig. 1994) that the heel C of the
tooth comes up to line A A, then the curvature of the emery wheel would
give clearance to the heel C, and therefore a cutting edge to face B of
the tooth.
[Illustration: Fig. 2000.]
[Illustration: Fig. 2001.]
[Illustration: Fig. 2002.]
The amount of clearance that may be given in this way is limited by the
spacing of the teeth and the diameter of the emery wheel, as is seen
from Fig. 2004, it being obvious that when tooth A is being ground the
emery wheel must clear the rear tooth B or it will grind its edge off,
and it is obvious that the smaller the emery-wheel diameter the more the
tooth to be ground may be set in advance of the line of centres of the
wheel and spindle. It may be pointed out, however, that there are two
methods of adjusting the cutter to the wheel.
In Fig. 2005, for example, let A A represent the line of centres of the
cutter and the wheel, and line B the plane of the front face of the
tooth being ground; and in Fig. 2006 let line A represent a vertical
line from the axis of the wheel, and B a vertical line passing through
the axis of the cutter, the tooth edge C occupying the same position in
both figures. Now suppose we employ cutting edge C as a centre and swing
the cutter until its axis or centre moves along the arc D to the dot E,
and it is evident that during this motion the heel of the tooth will
have approached the axis of the emery wheel and that more clearance will
therefore have been given to the cutting edge C.
The actual curve of the top face, as C, Fig. 2007, of the tooth T will
remain the same in either case, but its position with relation to the
front face will be altered. As this curve is greater in proportion as
the diameter of the emery wheel is diminished, and as the curvature
weakens the cutting edge of the tooth, it is obviously desirable to
employ a wheel of as large a diameter as possible.
To eliminate this curvature it would appear that the position of the
emery wheel might be reversed, as in Fig. 2008, but as the emery wheel
would wear only where in contact with the tooth, it would gradually
assume the shape in Fig. 2009, there being a shoulder at S that would
destroy the cutting edge of the tooth.
This may to a great extent be remedied by presenting the cutter
diagonally to the wheel, as in Fig. 2010, employing a wheel so thin that
the whole of its face will cross the tooth top during a revolution. Or
if the side faces of the wheel be recessed, leaving only a narrow
annular grinding ring at the circumference, the wheel might be mounted
as in Fig. 2011, thus making the top of the tooth quite flat. It may be
observed, however, that the usual plan is to revolve the wheel at a
right angle to the work axis, as was shown in Fig. 1994.
[Illustration: Fig. 2003.]
[Illustration: Fig. 2004.]
[Illustration: Fig. 2005.]
[Illustration: Fig. 2006.]
[Illustration: Fig. 2007.]
[Illustration: Fig. 2008.]
[Illustration: Fig. 2009.]
[Illustration: Fig. 2010.]
[Illustration: Fig. 2011.]
In grinding cutters having their teeth a right-hand spiral, care must be
taken that in grinding one tooth the emery wheel does not touch the
cutting edge of the next tooth.
Thus in Fig. 2013 it is seen that the corner C of the emery wheel is
closer than corner D, and being at the back of the wheel and out of
sight it is apt to touch at C unless a thin emery wheel be used.
In a left-hand spiral, Fig. 2012, it is the corner D that is apt to
touch the next tooth, the liability obviously being greatest in cutters
of large diameter.
The emery wheel should be of a grade of not less than 60 or more than
70. If it is too coarse it leaves a rough edge, which may, however, be
smoothed with an oilstone slip. If the wheel is too fine it is apt to
_burn_ the cutter, or in other words, to soften the cutting edge, which
may be known by a fine blue burr that may be seen on the front face of
the tooth, the metal along this line being softened.
The diameter of the wheel may be larger for small cutters than for large
ones, since the teeth of small cutters clear the wheel better. The
larger the wheel the less the curvature on the top of the tooth.
[Illustration: Fig. 2012.]
[Illustration: Fig. 2013.]
For general work a diameter of 2-1/2 inches will serve well, the
thickness being about 5/16 inch or 3/8 inch. The speed of a wheel of
this diameter varies in practice from 3,000 to 4,500 revolutions per
minute, but either too fast or too slow a speed will cause the wheel to
burn the cutter, and the same thing will occur if the cutter is fed too
fast to the wheel, or if too deep a cut is taken. The finishing cut
should obviously be very small in amount, especially in cutters of large
diameter, for otherwise the wear in the diameter of the wheel will
sensibly affect the teeth height, those last ground being the highest.
CHAPTER XXIII.--EMERY WHEELS AND GRINDING MACHINERY.
EMERY WHEELS AND GRINDING.--Emery grinding operations may be divided
into four classes as follow:--
1st. Tool or cutter grinding, in which the emery wheel is used to
sharpen tools which, from their shape, were formerly softened and
sharpened by the file, already largely treated in the preceding chapter.
2nd. Cylindrical grinding, in which both the work and the emery wheel
are revolved, as has been explained with reference to grinding-lathes.
3rd. Flat surface grinding, in which the emery wheel takes the place of
the ordinary steel cutting tool; and
4th. Surface grinding, in which the object is to remove metal or to
smoothen surfaces.
The distinctive feature of the various makes of solid emery wheels lies
in the material used to cement the emery together, and much thought and
experiment are now directed to the end of discovering some cementing
substance which will completely meet all the requisite qualifications.
Such a material must bind the emery together with sufficient strength to
withstand the centrifugal force due to the high speeds at which these
wheels must be run to work economically; and it must neither soften by
heat nor become brittle by cold. It must not be so hard as to project
above the surface of the wheel; or in other words, it should wear away
about as fast as does the emery. It must be capable of being mixed
uniformly throughout the emery, so that the wheel may be uniform in
strength, texture, and density. It must be of a nature that will not
spread over the surface of the emery, or combine with the cuttings and
form a glaze on the wheel, which will prevent it from cutting. This
glazing is, in fact, one of the most serious difficulties to be
encountered in the use of emery wheels for grinding purposes, while it
is a requisite for polishing uses, as will be explained farther on. Many
of the experiments to prevent glazing have been in the direction of
discovering a cement which would wear away under about the same amount
of duty as is necessary to wear away the cutting angles of the grains of
emery, thus allowing the emery to become detached from the wheel, rather
than to remain upon it in a glazed condition.
With the same grade of emery the wheel will cut more freely and glaze
less in proportion as the cementing material leaves the wheel softer,
but the softer the wheel the more rapidly it will wear away; indeed it
is the dislodgement of the emery points as soon as they have become
dulled that produces freedom from glazing. It may be remarked, however,
that the nature of the material operated upon has a good deal to do with
the glazing; thus wrought iron will glaze a wheel more quickly than
hardened steel, and brass more quickly than wrought iron, while on the
other hand soft cast iron has less tendency than either of them to
glaze. Glazing occurs more readily in all cases upon fine than upon
coarse wheels. Glazing is more apt to occur as the work is pressed more
firmly to the wheel, and with broad and flat surfaces rather than with
cylindrical ones. An excellent material for removing the glaze from an
emery wheel is a piece of ordinary pumice stone.
The principal cements used in the manufacture of emery wheels are as
follows, each representing the cement for one make of wheel:--
1. Hard rubber. 2. Chemical charcoal (leather cut down by acid and used
to prevent shrinkage), and glue. 3. Oxychloride of zinc. 4. Shellac. 5.
Linseed oil and litharge. 6. Silicate of soda and chloride of calcium.
7. Celluloid. 8. Oxychloride of magnesium. 9. Infusoria. 10. Ordinary
glue.
The vitrified emery wheel is made with a cement which contracts slightly
while cooling, leaving small pores or cells through which water,
introduced at the centre, is thrown (by centrifugal force) to the
surface. This causes, when the wheel is rotating, a constant flow of
water from the centre to the surface, carrying off the cuttings and the
detached emery.
In order that an emery wheel shall run true with its bore it must fit
the driving spindle, and in order that it may do this closely the wheel
bore is sometimes filled with lead, the latter being bored out to fit
the spindle. If the bore of the emery wheel itself were made a tight fit
to the spindle it would abrade the spindle in being put on, and the
pressure of the fit if any would tend to split the wheel. A common
method of securing emery wheels to their spindles is to fill the bore of
the wheel with lead, and bore it out to fit the spindle of the emery
grinding machine. The flanges between which the wheel is held are
recessed so as to grip the wheel at and near their perimeters only.
Between the flange and the wheel a thin disk of sheet-rubber is
sometimes used to afford a good bedding for the flange.
The forms of the perimeters of emery wheels are conformed to suit the
form of the work to be ground, and it is found that from the great
strength of the emery wheel it can be used to a degree of thinness that
cannot be approached in any kind of grinding stone. For instance,
vulcanite emery wheels 18 inches in diameter and having 3/16 inch
thickness, or face as it is commonly termed, are not unfrequently used
at a speed of some 5,000 feet of circumferential feet per minute,
whereas it would be altogether impracticable to use a grindstone of such
size and shape, because the side pressure would break it, no matter at
what speed it were run. Indeed, in the superior strength of the emery
wheels of the smaller sizes lies their main advantage, because they can
be made to suit narrow curvatures, sweeps, recesses, &c., and run at any
requisite speed under 5,000 feet per minute, and with considerable
pressure upon either their circumferential or radial faces.
GRADES OF COARSENESS OR FINENESS OF EMERY WHEELS.--Emery is found in the
form of rock, and is crushed into the various grades of fineness. The
crushing is done either between rollers or by means of stamps, the
latter, however, leaves the corners of the grains the sharpest, and
hence the best for cutting, though not for polishing purposes. The
grades of emery are determined by passing the crushed rock through
sieves or wire cloths having from eight to ninety wires to the inch;
thus, emery that will pass through a sieve of sixty wires to the inch is
called No. 60 grade.
The finest grade obtained from the manufactory is that which floats in
the atmosphere of the stamping room, and is deposited on the beams and
shelves, from where it is occasionally collected. Washed emery is used
by plate-glass workers, opticians, and others that require a greater
degree of fineness than can be obtained by the sieve.
The numbers representing the grades of emery run from 8 to 120, and the
degree of smoothness of surface they leave may be compared to that left
by files as follows:
8 and 10 represent the cut of a wood rasp
16 " 20 " " coarse rough file
24 " 30 " " ordinary rough file
36 " 40 " " bastard "
46 " 60 " " second cut "
70 " 80 " " smooth "
90 " 100 " " superfine "
120, F & FF " " dead smooth "
The F and FF emery is flour emery which has been washed to purify it.
The following are the kinds of wheel suitable for the respective
purposes named:--
Kind of work. Kind of wheel.
For rough grinding, such as on the edges of iron }
or steel plates, for removing the protuberances on } Coarse grain and
castings or on narrow surfaces where rough grinding } hard texture.
is sufficient. }
For narrow surfaces, such as moulding knives, lathe } Medium grain and
tools, saw gumming, &c. } hard texture.
For free cutting without gumming on broad surfaces } Medium grain and
on iron, steel, or brass. } soft texture.
For grinding fine tools, such as milling machine }
cutters, or for work in which the duty is not great } Fine grain and
while the wheel requires to keep its shape and keep } soft texture.
true. }
For smooth grinding on soft metals, as cast iron } Fine grain and
and brass. } hard texture.
[Illustration: Fig. 2014.]
When the work is presented to the wheel unguided, the wheel wears out of
true, because the work can follow the wheel, hence it becomes necessary
to true the wheel occasionally. This can be done by a tool such as in
Fig. 2014, which is applied by hand on the hand rest, and corresponds to
the tool shown in Fig. 2061 for grindstones, or by the use of a diamond
set in a tool to be held by hand or in a slide rest. The diamond
produces the most true and smooth work, but the cut of the wheel is at
first impaired by the action of the diamond, which is not the case with
the tool in Fig. 2014.
Corundum is a mineral similar to emery, and corundum wheels are made and
used in the same manner as emery wheels. Their cutting qualifications
are, however, superior to those of the emery wheel, both cutting more
freely and being more durable with less liability to glaze.
SPEEDS FOR EMERY WHEELS.--The speed at which an emery wheel may be run
without danger of bursting varies according to the thickness or breadth
of face of the wheel, as well as according to the quality of the
cementing material and excellence of manufacture. Hence, although a
majority of manufacturers recommend a speed of about 5,000
circumferential feet per minute, that speed may be largely exceeded in
some cases, while it would be positively dangerous in others. It is, in
fact, impracticable in the operations of the workshop to maintain a
stated circumferential speed, because that would entail a constant
increase of revolutions to compensate for the wear in the diameter of
the wheel. Suppose, for example, that a wheel when new is a foot in
diameter: a speed of about 1,600 revolutions per minute would equal
about 5,000 circumferential feet; whereas, when worn down to 2 inches in
diameter, the revolutions would require, to maintain the same
circumferential speed, to be about 9,500 per minute, entailing so many
changes of pulleys and counter-shafting as to be impracticable. In
practice, therefore, a uniform circumferential speed does not exist, the
usual plan adopted being to run the large-sized wheels, when new, at
about the speed recommended by the manufacturer of the kind of wheel
used, and to make such changes in the speed of the wheel during wear as
can be accomplished by changing the belt upon a three-stepped cone
pulley, and perhaps one, or at most two, changes of pulley upon the
counter-shaft. It is sometimes practicable to use wheels of a certain
diameter upon machines speeded to suit that diameter, and to transfer
them to faster speeded machines as they diminish in diameter. Even by
this plan, however, only an approximation to a uniform speed can in most
cases be obtained, because as a rule certain machines are adapted to
certain work, and the breadth of face and form of the edge of the emery
wheel are very often made to suit that particular work. Furthermore, a
new wheel is generally purchased of such a size, form, and grade of
emery as are demanded by the work it is intended at first to perform.
Neither is it, as a rule, practicable to transfer the work with the
diametrically reduced wheel to the lighter and faster-speeded grinding
machine. So that, while it is desirable to run all emery wheels as fast
as their composition will with safety admit, yet there are practical
objections to running small wheels at a rate of speed sufficient to make
their circumferential velocities equal to those of large wheels. The
speeds recommended for the various kinds of wheels now in use vary from
about 2,700 to 5,600 circumferential feet per minute; but the speeds
obtaining in workshops average between 2,000 and 4,000 feet for wheels 3
inches and less in diameter, and from about 3,000 to 5,600 feet for
wheels above 12 inches in diameter. Wheels above 15 inches in diameter,
and of ample breadth of face, are not unfrequently run at much greater
velocities.
On account of the high velocity at which emery wheels operate, it is
necessary that they be very accurately balanced, otherwise the unequal
centrifugal motion causes them to vibrate very rapidly, every vibration
leaving its mark upon the work.
The method of balancing adopted by one firm is as follows: The arbors
are of cast iron, and are cast standing vertical so as to induce equal
density in the metal, it having been found that if the arbors were cast
horizontally the lower part of the metal would from the weight of the
molten metal be more dense than that at the top of the casting. In
casting the arbors upright, the difference in the density of metal
simply causes one end of the arbor to be more dense than the other, and
the difference being at a right angle to the plane of revolution has no
tendency to cause vibration. The driving pulleys are cast horizontal to
obtain equal density, and after being turned are carefully balanced. The
driving pulleys are held to the arbors by being bored a driving fit, and
are driven on so as to avoid the use of keys, which would throw the
wheels out of balance.
The centrepiece and flange to hold the wheel to the arbor are turned and
balanced. The nut to hold the wheel is a round one, which is easier to
balance than a hexagon nut. After the centrepiece is put on the arbor,
the whole is tried for balance, and corrected if necessary. The pulley
is then put on and the whole is again balanced, and so on, the arbor
being balanced after each piece is added, so that while each piece is
balanced of itself the whole is balanced after the addition of each
separate piece.
[Illustration: Fig. 2015.]
[Illustration: Fig. 2016.]
The emery or corundum wheel is then put on the arbor and tried for being
in balance. The method of correcting the balance of the wheel is as
follows: The arbor with the wheel on is placed in the lathe, the wheel
turned true with a diamond tool (the wheel revolving at a comparatively
slow speed). The arbor is then revolved at its proper speed (5,000
circumferential feet per minute), and a point applied to just meet the
circumference will touch the wheel where it is heaviest, leaving a line
as shown in Fig. 2015 at A. The centre of the arbor is then moved over
towards this line as shown in Fig. 2016, in which W is the wheel, the
location of the line A (marked as above) being as denoted by the arc A,
and C represents the arbor whose centre is moved over towards the arc A.
When therefore the arbor is again put in the lathe, it will run out of
true by reason of the centre at one end having been altered. A cut is
taken down that radial face of the wheel which faces the end of the
arbor that has had its centre moved so that the wheel is turned thinner
where the mark (A, Fig. 2016) is. The amount of cut to be taken off is a
matter of judgment and trial, since it must be just sufficient to
compensate for the greater density of the wheel on that side. This
greater density, be it noted, occurs from the difficulty in mixing the
corundum or other abrasive grains with the cementing material with
entire uniformity throughout the mass.
By this method of balancing, the wheel will remain in true balance
notwithstanding its wear, because the balancing proceeds equally from
the perimeter towards the centre of the wheel.
[Illustration: Fig. 2017.]
EMERY GRINDING MACHINES. (For grinding-lathes and roll grinding, see
article on Lathes.)--Fig. 2017 represents Brown & Sharpe's grinding
machine. The bed, the table, and the cross-feed motion of this machine
closely resemble those of the planing machine, but its work is far more
smoothly and accurately done than can be performed in a planing machine.
The table traverses to and fro, accurately guided in ways, and the
revolving emery wheel takes the place of the ordinary cutting tool,
being carried in a sliding head upon a cross slide or cross bar. The
drum for driving the emery wheel is at the back of the machine, as shown
in the cut.
[Illustration: Fig. 2018.]
The vertical feed motion for adjusting the depth of cut of the emery
wheel is capable of very minute adjustment, thus avoiding a difficulty
commonly experienced in iron planing machines on account of the
coarseness of feed-screw pitch, which coarseness is necessary to insure
their durability. The means by which this capability of minute
adjustment is effected is shown in Fig. 2018, in which D is the cross
head of the machine and C the sliding head having the arm C´, which
provides at B a pivot for the wheel-carrying arm A. F is a stud fast in
C and carrying E, which forms the nut for the feed screw. Outside this
nut is the spiral spring S, whose force steadies the upper end of A.
Now suppose the feed wheel G be operated a full rotation, and the
motion of that end of A will be that due to the pitch of the feed screw,
but the motion at the centre H of the emery wheel will be the pitch of
the screw divided by the difference between the length from the centre
of H to the centre of the feed screw, and that from the centre of H to
the centre of B. But even this diminished motion at H is still further
reduced, so far as the depth of cut put on is concerned, because the
motion of H is not directly vertical but an arc P, of which B is the
centre.
The standards carrying the cross slide are segments of a circle struck
from the centre of the driving drum, which is necessary to enable the
raising and lowering of the cross slide, and maintain a uniform tension
on the belt driving the emery wheel without employing an idler wheel or
belt tightener.
[Illustration: Fig. 2019.]
Fig. 2019 represents Wm. Sellers & Co.'s drill-grinding machine, in
which the drill is held in a chuck operated by the hand wheel A. The
jaws of the chuck grip the drill at the outer corners of the cutting
edge as shown in Fig. 2020, and so as to grind the point of the drill
central to those corners. In order to give to the cutting edges a
suitable degree of clearance in their lengths, and to allow for the
difference in thickness at their points between large and small drills,
the following construction is employed.
[Illustration: Fig. 2020.]
Fig. 2020 represents the jaws J J holding on the left a small, and on
the right a large drill. The line of motion of the right-hand jaw in
opening and closing to grip the drill is along the line _r_, while that
of the left-hand is along the line _p_ _p_, the centre upon which the
chuck is revolved to grind the drill being denoted by the small circle
at S. _x´_ represents the centre line of the large drill when held in
the chuck, and it is seen that the action of the jaws in closing upon
small drills is to lift the drill point closer to the centre S upon
which the chuck revolves (the cutting edge being ground to be on the
line _y´_ _y´_). The reason for this peculiar and simple but exceedingly
ingenious construction is, as before remarked, to maintain the cutting
edge in its proper relation to the thickness of the drill point (which
thickness varies in different diameters of drills), and to maintain a
proper degree of clearance at every point along the length of the
cutting edge. In other drill grinding machines the drill when rotated to
grind the clearance is moved on the axis A A in Fig. 2022 as a centre of
motion, and as this line is parallel to the face of the emery wheel it
follows that if the drill were given a full revolution its circumference
would be ground to a cylinder as shown in Fig. 2021 by the dotted lines.
In this machine the drill is rocked on the line B, Fig. 2023, as a
centre of motion, this line corresponding to the axis of the shaft of
lever F in Fig. 2019 upon which the chuck swings, and to the line B in
Fig. 2024. As a result the surface is ground to the form of a cone as
denoted by the dotted lines in Fig. 2024. The results of the two systems
are shown in Figs. 2025 and 2026, which represent the conical holes made
by a drill.
[Illustration: Fig. 2021.]
[Illustration: Fig. 2022.]
[Illustration: Fig. 2023.]
[Illustration: Fig. 2024.]
In Fig. 2025 a cylinder R is shown lying in a conical recess, and end
views of the cylinder are shown at V and W. Now suppose the line of
contact of the roll or cylinder upon the recess represents the cutting
edge of the drill, and that we consider the clearance at the outer end,
and at that part that in revolving would describe the circle Q, and on
referring to circle V and the outer circle of the recess, and also to
circles W and Q, it is seen that there is more clearance for V than
there is for W, and that the clearance of the latter would be still less
if Q were of smaller diameter, and it follows that the clearance is less
in proportion as the point of the drill is approached. In determining
the amount of clearance, therefore, we are compelled to make it
sufficient for the point of the drill, and this under this system of
grinding is excessive for the outer diameter of the drill, causing it to
dull quickly, it being borne in mind that as the outer corner of the
cutting edge of a drill describes the largest circle of any point of the
cutting edge it obviously performs the most cutting duty in removing
metal, and furthermore revolves at the highest rate of cutting speed,
both of which cause it to dull the most rapidly. In Fig. 2026 we have a
cone R lying in the coned recess, an end view of the cone being shown at
V and W, and if we again consider the line of contact of the cone on the
recess to represent the cutting edge and the circumferential surface of
the cone as the end surface of the drill, we observe in the end views V
and W that the clearance is equal for the two positions, or by varying
the degree of taper of the cone we may regulate the amount of clearance
at will. It is found preferable, however, to give more clearance as the
point of the drill is approached so as to increase the cutting capacity;
hence, in this case, the outer corner of the drill has the least
clearance, which greatly increases its endurance for the reasons already
mentioned, and which were further pointed out in the remarks upon
drilling in the lathe. There remains, however, an additional advantage
in this method of grinding which may be pointed out, inasmuch as that
the clearance produced by the method shown in Fig. 2019, while capable
of being governed from end to end of the cutting edge, yet increases as
the heel of the _land_ is approached, making the central cutting edge
(C, Fig. 2028) more curved in its length so that it approaches the form
of cutting edge of the fiddle drill and this enhances its cutting
capability.
[Illustration: Fig. 2025.]
Referring again to the general view of the machine in Fig. 2019, the
chuck is supported or carried by the shaft having the ball lever F,
which is clearly seen in the rear view, Fig. 2027, and the rod carrying
the sleeve B (which holds the centre for supporting the shank end of the
drill) is secured to the back of the chuck, as seen in the same figure.
When, therefore, lever F is moved over, the drill is moved through an
arc of a circle of which the axis of the shaft of F is the centre, and
this it is that gives clearance to the cutting edge of the drill.
The drill being chucked, the emery wheel is brought up to it by means of
the hand wheel E, which moves the frame C laterally, the grinding being
done by the side face of the emery wheel. On the same shaft as E is a
lever which may be used in connection with the stop or pin (against
which it is shown lying) to enable an adjustment of the depth of cut
taken by the wheel separately when grinding each lip, and yet to permit
both cutting edges of the drill to be gauged to the same length.
Suppose, for example, that the point of a drill has been broken so that
it requires several cuts or traverses of the emery wheel to bring it up
to a point again; then when this has been done on one cutting edge the
lever may be set to the stop, so that when the grinding of the second
cutting edge has proceeded until the lever meets the stop both edges
will be known to be ground of the same length, and will, therefore,
perform equal cutting duty when at work.
The depth of cut being adjusted, the lever D is operated to pass the
side face of the emery wheel back and forth along the cutting edge of
the drill, this lever rocking the frame C on which the emery wheel is
mounted back and forth in a line parallel to the cutting edge of the
drill. Different angles of one cutting edge of the drill to the other
are obtained by swivelling the frame carrying the shaft of lever F. The
emery wheel is cased in except at a small opening where it operates upon
the drill, and may, therefore, be liberally supplied with water without
the latter splashing over. Water is continuously supplied to the emery
wheel by an endless belt pump, which also delivers water on the end of
the drill, enabling heavy grinding cuts to be taken without danger of
softening the drill at the cutting edge, which is otherwise apt to
occur. The following is the method of operating the machine: Open the
jaws of the chuck by means of the hand wheel A, insert the drill from
the back of the chuck towards the face of the stone, letting the end of
the drill rest on the lower jaw, with the cutting edge just touching the
end stop; close the jaws temporarily, while the back centre B is run up
and clamped; then release the jaws, hold the drill back against the back
centre B with the left hand, at the same time rotating hard against the
two side stops on the jaws; then tightly closing the jaws, clamp the
drill by means of the hand wheel A, using the right hand for this
purpose. Throw ball-handle F part way back, and by means of hand wheel E
feed up the stone until it just touches the drill. Bring ball-handle F
forward and give additional feed; pass the stone over the face of the
drill, back and forth, by lever D, moving ball-handle F back a little
between each two cuts. This slices off the stock to be removed; then
when entirely over the face of the lip being ground, hold lever D
stationary, and rotate the drill against the stone by means of
ball-handle F. By this means a heavy slicing cut can be taken and a
final smooth finish obtained without any risk of drawing the temper of
the drill.
When one lip has been thus formed, slack up the jaws of the chuck, turn
the drill half around, pressing its lips as before against the side
stops on jaws, and at the same time be sure to hold the drill firmly
back against the back centre B (pay no attention to the end stop, which
is only used in locating the drill endways in the first setting),
tighten chuck, and grind the second lip without any readjustment of the
stone. The lips will then be of equal length. During all these
manipulations the stop that is arranged in connection with hand wheel E
can be slack, and may rest against the pin in the bed made to receive
it.
[Illustration: Fig. 2026.]
Fig. 2027 represents a rear view of the machine, at which there is an
attachment for thinning the point of the drill, which is advantageous
for the following reasons. In Fig. 2028 we have a side and an end view
of a twist drill, and it can be shown that the angular piece of cutting
edge C that connects the two edges A and B cannot be given sufficient
angle to make it efficient as a cutting edge without giving clearance
and angle excessive to the edges A and B.
In Fig. 2029 we may consider the angle of the cutting edge at the corner
H and at the points F and G. First, then, it is obvious that the front
face for the point H is represented by the line H _h_, that for F by
line F _f_, and that for G by G _g_, and it appears that on account of
the spiral of the flute the front face has less angle to the drill axis
as the point of the drill is approached.
[Illustration: Fig. 2027.]
Considering the end of the drill, therefore, as a cutting wedge, and
considering the cutting edge at the two points C and E, in Fig. 2030,
the end face being at the same angle, we see that the point C has the
angle A and point E the angle B; at the drill point there will be still
less cutting angle, and it has, therefore, the least cutting capacity.
To remedy this the attachment shown in the figure is employed,
consisting of a frame or head carrying a thin emery wheel, and capable
of adjustment to any angle to suit the degree of spiral of the drill
flute.
[Illustration: Fig. 2028.]
By means of this emery wheel a groove is cut in the flute at the point
of the drill, as shown in Fig. 2031, at A and B, thus reducing the
length of C, and therefore increasing the cutting capacity and
correspondingly facilitating the feed of the drill. It is found, indeed,
that by this means the drill will perform 15 per cent. more duty.
[Illustration: Fig. 2029.]
[Illustration: Fig. 2030.]
[Illustration: Fig. 2031.]
It is obvious, however, that as the thickness of drills at the point
increases in proportion to the diameter of the drill, this improvement
is of greater advantage with large than with small drills. The reason
for augmenting the thickness at the centre with the drill diameter is
that the pressure of the cut acts to unwind the spiral of the drill, and
if the drill were sufficiently weak at its axis this unwinding would
occur, sensibly enlarging the diameter of hole drilled, more especially
when the drill became partly dulled and the resistance of the cut
increased. By means of the small grooves A and B, however, the point is
thinned while the strength of the drill is left unimpaired.
[Illustration: _VOL. II._ =EMERY GRINDING MACHINERY.= _PLATE IV._
Fig. 2032.
Fig. 2033.]
Fig. 2032 represents Brown & Sharpe's surfacing grinder, designed to
produce true and smooth surfaces by grinding instead of by filing. In
truing surfaces with a file a great part of the operator's time is
occupied in testing the work for parallelism, and applying it to the
surface plate to test its flatness or truth, whereas in a machine of
this kind both the parallelism and the truth of the work are effected by
the accurate guiding of the machine table in its guideways. Furthermore,
a high order of skill is essential to the production of work by filing
that shall equal for parallelism and truth work that is much more easily
operated upon in the machine. The machine is provided with two feed
motions, the first of which is in a line parallel with the axis of the
emery wheel driving spindle, and is communicated (by means of the small
hand wheel on the right) to the lower table, which moves in [V]-guides
provided upon the base plate of the machine. Upon this lower, and what
may be termed cross-feed table slides, in suitable guideways, the
work-holding or upper table, which is operated (by the large hand wheel)
to traverse the work back and forth beneath the grinding wheel. Both
these feed motions are operated by hand, automatic feed motions being
unnecessary for work of the size intended to be operated upon in this
machine. The grinding wheel spindle is carried in a bearing carried in a
vertical slide, and is fed to its depth of cut by means of the vertical
feed screw and hand wheel shown. The spindle passes through the bearing
and carries a pulley at the back of the machine, which pulley is driven
by a belt passing over idler pulleys at the back of the machine, by
means of which the tension of the driving belt may be regulated.
Fig. 2033 represents The Tanite Co.'s machine for surface grinding such
work as locomotive guide bars. The emery wheel N is mounted beneath a
table T, whose upper surface is planed true, and which has two
cylindrical stems C D fitting into the bored guides E. The stems are
threaded at their lower ends to receive a screw, on the lower end of
which is a bevel-gear F meshing into a similar gear G on the shaft
actuated by the hand wheel W, hence by operating W the height of the
table face may be adjusted to suit the diameter of the wheel.
The surface to be ground is laid upon the face of the table, and the
operator moves it by hand, slowly passing it over the emery wheel, which
projects slightly through the opening shown through the centre of the
table. The operator stands at the end of the machine so as to be within
reach of the wheel, and the direction of rotation is towards him, so
that the work requires to be pushed to the cut and is not liable to be
pulled too quickly across the table by the emery wheel.
[Illustration: Fig. 2034.]
Fig. 2034 represents an emery grinding machine for grinding the bores of
railroad car axle-boxes. The circumference of the emery wheel is dressed
to the curvature of the box bore by a diamond tool A which swings on a
centre in its frame, and can be adjusted to any arc. Once set, it can
only turn the prescribed arc with accuracy. In order to avoid the
necessity of the foreman having to set the tool, a gauge is also
furnished. This consists of a spindle adjustable with a nut in such a
way that its two points rest in the centres on which the diamond tool
revolves. It is only necessary for a disk B turned accurately to the
diameter of the bearing, to be prepared, and this the apprentice can
place on the spindle, adjust the latter, and screw down the diamond tool
until it touches the periphery of the disk. A nut is then fastened on
the diamond tool, and the frame is lifted on the ways beneath the wheel,
when the moving of the handle turns the face of the wheel to the exact
circle desired.
To adjust the brass in the chuck C, it is first set on the axle D. The
chuck is then placed on frame E, in such a way that the [V]s fit. Handle
F then moves a cam that clamps the brass between the jaws G, one set of
which swings on a pivot at H. The brass is thus adjusted in such a
manner that, despite the imperfections in moulding, it is ground
accurately with the least removal of metal. The chuck C fits into planed
guides on the table I, and is thus brought in exact line with the motion
of the wheel. The crank J serves to move the table to and fro on the
rods K, and the table also rises and falls on planed ways, being pressed
up by springs. The hand wheel gives vertical adjustment to the whole bed
by means of a chain beneath it. There is a pulley by which a suction
fan, to remove dust, &c., may be driven. The machine is capable of
fitting from 150 to 500 car brasses per day.
[Illustration: Fig. 2035.]
Fig. 2035 represents an emery planing machine. The emery wheel, which
takes the place of the cutting tool of an ordinary shaping machine, is
upon a spindle driven by the pulley A upon the spindle B, which is
traversed endways by means of the connecting rod which is actuated by a
crank E driven by the cone pulley C. The work-holding table G is
traversed by the handle K or automatically through wheel H, which
through suitable gearing drives the spindle I. The blower or fan is to
draw off the cuttings and emery. It is obvious that any of the usual
forms of work-holding devices may be employed.
[Illustration: Fig. 2036.]
Fig. 2036 represents an ordinary form of emery grinding machine for
general purposes. A represents the frame affording journal bearing for
the driving spindle driven by the cone pulley P, having the fast flanges
_f_ and collars C, which are screwed up to hold the emery wheel by the
nut N, the direction of spindle rotation being denoted by the arrows.
The thread at the end K of the spindle must be a right-hand one, and
that at the other end L must be a left-hand, so that the resistance
against the nut shall in both cases be in a direction to screw the nuts
up and cause them to bind or grip the wheels more firmly, and not
unscrew and release the wheels. Upon the frame A are the lugs D to carry
the hand rests R and S, which are adjustable, and are secured in their
adjusted position by the handle nuts E. The rest S is of the same form
and construction as a lathe hand rest, while that at R is angular, to
support the tool while applying it to the side as well as to the
circumference of the wheel.
Fig. 2037 represents a machine for grinding the knives for wood-planing
machines, and having a hand feed only. It consists of an emery wheel
mounted upon a spindle and with a slide rest in front of it. Mounted on
the slide rest is a frame for holding the knife, and a set-screw for
adjusting the angle of the knife to the wheel. The slide rest is
traversed by means of the hand wheel operating a pinion in the rack
shown.
Fig. 2038 represents a swing frame for carrying and driving an emery
wheel to be used on the surfaces of castings, its construction
permitting it to be moved about the casting to dress its surface. The
overhead countershaft carries the grooved driving wheel A. At B is a
vertical shaft pivoted at I by the forked bearing which swings upon the
countershaft. The fork L at the lower end of shaft B carries a shaft on
which is the fork C´, C having journal bearing on it, and the driving
pulley J. Fork D has journal bearing on the same shaft as pulley J, and
is fast upon the rod or arm E, which affords journal bearing to the
emery wheel K on a shaft having handles H H. Motion to the emery wheel
is conveyed through the belts F and G. To counterbalance the frame the
weight W is employed, permitting the frame to be readily swung. The
upper fork carrying B, being pivoted to the shaft of A, permits B to
swing to any required position. The pivot at I permits B to rotate in a
vertical plane; the pivot of C´ C at D affords vertical movement to E;
the pivot at D allows E to rotate about its own axis, hence the wheel K
can be moved about laterally, raised, lowered, or have its plane of
revolution varied at will by simply swinging the handles H H to the
required plane. The emery-wheel shaft is pivoted upon the fork carrying
it, so that the emery wheel can be turned to stand in a horizontal plane
if desired.
[Illustration: Fig. 2037.]
Fig. 2039 represents an emery belt machine, in which the belt runs
vertically and its tension is adjusted by the idler pulley shown at the
top of the frame.
[Illustration: Fig. 2038.]
It is obvious that if a piece of work, as A in Fig. 2040, be held
steadily upon the rest R, its end will be ground to the curvature of the
emery wheel W, and that if it be required to grind the surface flat the
piece must be raised and lowered as denoted by the dotted lines, the
amount of this motion being determined by the thickness of the piece.
Furthermore, if the piece of work be of a less width than the thickness
of the wheel, as in the top view in Fig. 2041, the work A will wear a
groove on the wheel, and its side edges will therefore become rounded
off unless it be given sufficient motion in the direction of D and E to
cause it to traverse across the full width of the wheel face, and as
this motion would require to be simultaneous with the vertical motion
explained with reference to Fig. 2040, it is not practicable to grind
true level surfaces upon the perimeter of the wheel. As the sides of the
wheel are flat, however, it is self-suggestive to apply the work to the
side faces. But in this case, also, that part of the wheel surface that
performs grinding duty will gradually wear away, leaving a shoulder or
projecting surface upon the wheel.
Suppose, for example, that in Fig. 2042 the duty has been confined to
that part of the wheel face from A to the perimeter and the wheel would
wear as shown, the result being the same whether the width or distance
from the shoulder A to the perimeter of the wheel represents the width
of the work held steadily against the wheel or the traverse of a
narrower piece of work.
This difficulty may be overcome by recessing the wheel face, as in Fig.
2043, in which the wheel is shown in section.
In some cases, as for grinding the knives for wood-working machines,
hollow cylindrical wheels, such as in Fig. 2044. are used, the duty
being performed on the end face B B of the wheel, and the work being
traversed in the direction of the arrows. The wheel is here gripped
between the flange F and the collar C, which fits accurately to the end
of the driving spindle S, so as to be held true, and secured by screws
passing through C and into F, or the end of S may be threaded to receive
a nut to screw against C.
The circumferential surface of a wheel may be employed to grind a flat
surface, providing that the work be traversed to the wheel, as in the
side view in Fig. 2045. In this case, however, the cut must be taken
while the work P is travelling in the direction denoted by the arrow J,
and no cutting must be done while the work is travelling back in the
direction of K. After the work has traversed back in the direction of K,
and is clear of the wheel, the cut is carried farther across the work by
moving or feeding the work in the direction of the arrow in the front
view, Fig. 2046. In this case the whole surface of the work passes
beneath the wheel thickness, and the wheel face wears parallel to the
wheel axis, producing a true plane (supposing the work to be moved in
straight lines), save in so far as it may have been affected by the
reduction of the diameter of the emery wheel from wear, which is not
found sufficient to be of practical importance. If the whole surface of
the work does not pass across or beneath the wheel thickness the wheel
face may wear taper. Suppose, for example, that in Fig. 2047, P is a
piece of work requiring to have produced in it a groove whose bottom is
to be parallel to the lower surface F. Then the upper work surface being
taper the thick side A would wear away the side B of the wheel, and the
groove ground would not be parallel to F.
[Illustration: Fig. 2039.]
[Illustration: Fig. 2040.]
[Illustration: Fig. 2041.]
[Illustration: Fig. 2042.]
[Illustration: Fig. 2043.]
[Illustration: Fig. 2044.]
Another method of grinding flat surfaces is to mount the emery wheel
beneath a table T in Fig. 2048, letting the top of the wheel emerge
through an opening in the table, and sliding the work upon the trued
upper surface of the table. The surface of the table thus becomes a
guide for the work. To obtain true work in this way, however, it is
necessary that the cut taken by the emery wheel be a very light one, as
will be perceived from the following considerations.
[Illustration: Fig. 2045.]
[Illustration: Fig. 2046.]
[Illustration: Fig. 2047.]
In Fig. 2049 T represents a table and B a guide bar thereon. The depth
of cut taken will be equal to the height the emery wheel projects above
the surface A of the table, hence when the bar has been moved nearly
half-way across the table its surface will be as in Fig. 2050, the bar
occupying the position shown in Fig. 2051. Now the part of the bar that
has passed over the table will not rest upon it as is shown in Fig.
2051. When the bar has passed over the emery wheel more than half of the
bar length, its end F, Fig. 2052, will fall to meet the half D of the
table, and end E will lift from the half C of the table, causing the bar
surface to be ground rounding in its length. If, however, the cut taken
be a very light one the surface may be ground practically true, because
the bar will bend of its own weight and lap down to fit the table at
both ends. Furthermore it will be noted that in the case of a large
surface in which the wheel might sensibly wear in diameter before it had
operated over the whole of the work surface, the table may be lowered or
the wheel may be raised (according to the construction of the machine),
to offset the wear of the wheel, or rather to take it up as it were.
[Illustration: Fig. 2048.]
[Illustration: Fig. 2049.]
[Illustration: Fig. 2050.]
POLISHING WHEELS.--For polishing purposes as distinguished from that of
grinding, various forms of polishing wheels are employed. For the
rougher class of polishing, wooden wheels covered with leather coated
with fine emery that is allowed to glaze are employed. For a finer
degree of polish the wheels are covered with lead to which various
polishing materials are occasionally applied, while for the finest
polishing rag or buff wheels are the best. Wooden polishing wheels are
built up of sections of soft wood fastened together by gluing, and with
wooden pegs in place of nails or screws.
[Illustration: Fig. 2051.]
[Illustration: Fig. 2052.]
[Illustration: Fig. 2053.]
[Illustration: Fig. 2054.]
[Illustration: Fig. 2055.]
The joints of the sections or segments are broken--that is to say,
suppose in Fig. 2053 that 1, 2, 3, &c., up to 6, represent the joints of
the six sections of wood forming one layer of the wheel, the next six
sections would have their joints come at the dotted lines A, B, C, &c.,
up to F. To prevent them from warping after being made into a wheel it
is advisable to cut out the sections somewhere near the size in the
rough and allow them to lie a day or two before planing them up and
fitting them together; the object being to allow any warping that may
take place to do so before the pieces are worked up into the wheel,
because if the warping takes place afterwards it will be apt to throw
the wheel out of true, whereas it is necessary that these wheels be very
true, not only so that they may not prove destructive to their shaft
bearings, but that they may run steady, and not shake or terrible, and
because the work can be made much more true and smooth with a true than
with an untrue wheel. Only one layer of segments should be put on in one
day, and they should be put on as quickly as possible after the glue is
applied, so that the latter shall not get cold. So soon as each segment
is put into its place it should be clamped firmly to its seat and driven
firmly up to the joint of the next one, and when the layer is completed
it should be left clamped all night to dry. In the morning one clamp
should be removed, and that section fastened by boring small holes and
driving therein round and slightly tapered soft-wood pegs of about 1/4
inch diameter. The whole of the sections being pegged the next layer of
segments may be added, and so on until the required width of wheel is
attained. The whole wheel should then be kept two days before it is
turned, and as little as possible should be taken off in the turning
process. The circumferential surface should be turned slightly rounding
across its width, and as smoothly as possible. It is practicable to
proceed with the construction of the wheel without waiting between the
various operations so long as here advised, but the wheel will in that
case be more apt to get, in time, out of true. To cover the
circumference of the wheel sole leather is used, its thickness being
about 1/4 inch; it should be put on soft and not hardened by hammering
at all, and with the flesh side to the wood. The joint of the leather
should not be made straight but diagonal with the wheel face, the
leather at the edge of the joint being chamfered off, as shown in Fig.
2054 at A, and the joint made diagonal, as shown in Fig. 2055 at A.
If the leather were put on with a square butt joint there would likely
be a crease in the joint, and the emery or other polishing material
would then strike the work with a blow, as well as presenting a keener
cutting edge, which would make marks in the work no matter what pains
might be taken to prevent it. This, indeed, is found to occur to a
slight extent upon very fine polishing, even when the joint of the
leather is made as above; and the means taken to obviate it is to not
put any polishing material on the immediate joint and to wipe off any
that may get there, leaving 1/10 inch clear of polishing material. It is
obvious that in fastening the wheel to its shaft it should be put on so
that it will run in the direction of the arrow, providing the operator
works with the wheel running from him, as is usually the case with large
wheels, that is to say, wheels over 18 inches in diameter. In any event,
however, the wheel should be put on so that the action of the work is to
smooth the edge of the leather joint down upon the wheel, and not catch
against the edge of the joint, which would tend to rough it up and tear
it apart. The leather should be glued to the wheel, which may be
slightly soaked first in hot water. The glue should be applied very hot,
and the leather applied quickly and bound tightly to the wheel with a
band. One end of the leather may be first glued to the wheel and
fastened with a few tacks to hold it while it is stretched tightly round
the wheel; the leather itself should be softened by an application of
hot water, but not too much should be applied. After the leather is
glued to the wheel it is fastened with soft wooden pegs, about 3/16 inch
in diameter, driven through the leather into the wood and cut off
slightly below the surface of the leather.
[Illustration: Fig. 2056.]
[Illustration: Fig. 2057.]
Wheels of this kind are sometimes made as large as 5 or 6 feet in
diameter, in which case the truth of the wheel may be preserved by
letting in a wrought-iron ring, as shown in Fig. 2056, fastening the
rings with wood screws. The wheels thus constructed are covered with
emery of grades varying from No. 60 to 120, and flour emery. The coarser
grades perform considerable cutting duty as well as polishing. The
manner of putting the emery, and fastening it, upon the wheel is as
follows:--The face of the wheel is well supplied with hot glue of the
best quality, and some roll the wheel in the emery, in which case the
emery does not adhere so well to the leather as it does when the
operation is performed as follows:--Let the wheel either remain in its
place upon the shaft, or else rest it upon a round mandrel, so that the
wheel can revolve upon the same. Then apply the hot glue to about a foot
of the circumference of the wheel, and cover it as quickly as possible
with the emery. Then take a piece of board about 3/4 inch thick and 28
inches long, the width being somewhat greater than that of the polishing
wheel, and placing the flat face of the board upon the circumferential
surface of the wheel, work it by hand, and under as much pressure as
possible, back and forth, so that each end will alternately approach the
circumference of the wheel, as illustrated in Fig. 2057, the movement
being indicated by the dotted lines. By adopting this method the whole
pressure placed upon the board is brought to bear upon a small area of
the emery and leather, and the two hold much more firmly together than
would be the case if the circumference of the wheel were glued and then
rolled in a trough of emery, because the time occupied in spreading the
glue evenly and properly over the whole wheel surface would permit it to
cool before receiving the emery, whereas it is essential that the glue
be hot so that it may conform itself to the shape of the grains of emery
and hold them firmly.
The speed at which such wheels are used is about 7,000 feet per minute.
The finest of emery applied upon such wheels is used for cast iron,
wrought iron, and steel, to give to the work a good ordinary machine
finish; but if a high polish or glaze is required, the wheels are coated
with flour emery, and the wheel is made into a glaze-wheel by wearing
the emery down until it gets glazed, applying occasionally a little
grease to the surface of the wheel. Another kind of glaze-wheel is made
by covering the wooden wheel with a band of lead instead of a band of
leather, and then applying to the lead surface a mixture of rouge,
crocus and wax, worn smooth by applying to it a piece of sheet steel or
a piece of flint-stone before applying the work. Others add to this
composition a little Vienna lime. For flat surfaces, or those requiring
to have the corners or edges kept sharp, it is imperative that such
wheels as above described--that is to say, those having an unyielding
surface--be used; but where such a consideration does not exist, brush
and rag wheels may be used. In Europe comparatively large flat surfaces
requiring a high polish are finished upon wooden wheels made of soft
wood and not emeried, the polishing material employed being Vienna lime.
The lime for ordinary use is mixed with water, and is applied by an
assistant on the opposite side of the wheel to the operator. For
superfine surfaces the Vienna lime is mixed with alcohol, which
increases its efficiency; and here it may be as well to note that Vienna
lime rapidly deteriorates from exposure to the air, so that it should be
kept as little exposed as possible.
BRUSH-WHEELS.--These are polishing wheels of wood with a hair brush
provided around the circumference. These wheels are excellent
appliances, whether employed upon iron, steel, or brass. Their sizes run
from 1-1/2 inch to about 8 inches in diameter, and the hair of the brush
should not exceed from 1 to 1-1/4 inches in length. The speed at which
they should be run is about 2,500 for the largest, and up to 4,500
revolutions per minute for the smaller sizes. In ordinary grinding and
polishing practice in the United States, brush wheels are used with
Vienna lime in all cases in which the lime is used by itself--that is to
say, unmixed with wax, crocus, or rouge, or a mixture of the same. In
watchmaking, however, and for other purposes in which the truth of the
work is an important element, Vienna lime is applied to wooden or even
metal, such as steel, polishing wheels, which are in this latter case
always of small diameter. An excellent polishing composition is formed
of water 1 gill, sperm oil 3 drops, and sufficient Vienna lime to well
whiten the mixture. The brush may be let run dry during the final
finishing. For polishing articles of intricate shape, brush wheels are
superior to all others. If the articles to be polished are of iron, or
steel, the first stage of the process is performed with a mixture of oil
and emery, Vienna lime being used for final finishing only. The wheels
to which Vienna lime is applied should not be used with any other
polishing material, and should be kept covered when not in use, so as to
keep them free from dust.
For brass work, brush wheels are used with crocus, with rouge, or with a
mixture of the two, with sufficient water, and sometimes with oil, to
cause the material to hold to the brush and not fly off from the
centrifugal force. For very fine brass polishing, the first stages are
performed with powdered pumice-stone mixed with sufficient oil to hold
it together. This material has considerable cutting qualifications. The
next process is with rouge and crocus mixed, and for very fine finishing
rotten-stone.
Solid leather wheels are much used by brass-finishers. The wheels are
made of walrus hide glued together in disks, so as to obtain the
necessary thickness of wheel. The disks are clamped between pieces of
board so soon as the glue is applied, so as to make a good joint, and
also keep the wheel flat and prevent it from warping during the drying
process. Such wheels may be run at a velocity of 8,000 feet per minute,
and with any of the polishing materials already referred to. After the
wheel is made and placed upon its spindle or mandrel it may be turned
true with ordinary wood-turning tools--and it may here be remarked that
rag wheels may be trued in the same way. The spongy nature of these
wheels renders them very efficient for polishing purposes, for the
following reasons: The polishing materials become imbedded in the
leather and are retained, and become mixed and glazed with a fine film
of the material being polished, which film possesses the very highest
polishing qualifications. These walrus wheels may be used with pumice,
crocus, rouge, or Vienna lime, according to the requirements of the
case, or even with a mixture of flour emery and oil; and they possess
the advantage of being less harsh than leather or lead-covered wheels,
while they are more effectual than the latter, and will answer very well
for flat surfaces.
Rag polishing wheels are formed of disks of rags, either woollen or
strong cotton, placed loosely side by side, and clamped together upon
the mandrel at the centre only. Their sizes range usually from 4 to 8
inches in diameter, and they are run at a speed of about 7,000 feet per
minute. They assume a disk form when in motion from the centrifugal
force generated from the great speed of rotation. They are used for the
fine polishing only, and not upon work requiring the surfaces to be kept
very flat or the corners very sharp. For use upon steel or iron, they
are supplied with a polishing material composed of Vienna lime 3 parts,
crocus 3 parts, beeswax 3 parts, boiled up together, allowed to cool
off, and then cut into cakes. These cakes are dipped in oil at the end,
which is then applied to the rag wheel occasionally during the polishing
process. For brass-work, an excellent polishing composition is composed
of crocus 2 parts, wax 1 part, rouge 1/8 part, the wax being melted, and
the ingredients thoroughly mixed. This mixture gives to the metal a rich
color. It is dipped in oil and then applied to the rag wheel. It may be
used to polish fine nickel-plating, for which purpose it is an excellent
material. Nickel-plated articles having sharp corners should be polished
with fine rouge mixed with clear water and a drop of oil, the mixture
being applied to the rag wheel with the finger of the operator. Any of
the compositions of rouge, crocus, and rotten-stone may be used for
brass, copper, or nickel-plated work upon rag wheels, while for iron or
steel work the same materials, separate or in combination, may be used,
though they are greatly improved by the addition of Vienna lime. When,
however, either of these materials is used singly, it should be applied
to the rag wheels with a brush; and if it is used dry, it must be at a
greatly reduced speed for the wheel, which is sometimes resorted to for
very fine polishing.
[Illustration: Fig. 2058.]
Fig. 2058 represents a polishing device used to polish the surface of
engravers' plates. It consists of a spindle D, carried in bearings B,
and, having no collars, it is capable of end motion through those
bearings. The spindle is pressed downward by a spring A, carrying at its
end a piece C, which is capped to receive the end of the spindle D and
the piece E which threads into the spindle, thus making a sort of
universal joint. The spindle D is run by the pulley P, and carries a
piece of stone S, the work W resting upon the plate or table T. The
stone being set to one side of the centre of the spindle, each part of
its surface describes a circle, the centre of which is outside of the
stone, thus making the effectiveness of the centre of the stone greater
by increase of motion. To raise the stone from the work the spindle is
raised by means of the chord F, or the table T may have a simple lever
motion. The work is moved about and around and beneath the revolving
stone. Water, oil, benzine or alcohol is used to keep the stone clear
and wash away the cuttings. The device saves a good deal of hand work in
the preparatory stages of grinding, although it can be used only with
soft stones.
GRINDSTONES AND TOOL GRINDING.--The general characteristics of
grindstones are as follow:--
For rapid grinding a coarse and an open grit is the most effective. The
harder the grit the more durable the stone, but the liability of the
stone to become coated or glazed with particles of the metal ground from
the work is increased. With a given degree of coarseness a soft grit
stone will grind a smoother surface than a hard grit one.
The finer the grit the smoother the surface it will grind. In all
stones, however, it is of prime importance that the texture be even
throughout the stone, because the soft or open-grained part will wear
more rapidly than the close or hard grained. All grindstones are softer
when water-soaked than when dry, and will cut more freely, because the
water washes away the particles of metal ground from the work, and
prevents them from glazing the stone. It follows from this, however,
that a stone should not be allowed to rest overnight with its lower part
resting in water, as the wear of the stone will be unequal until such
time as it has become equally saturated. Furthermore the balance of the
stone is destroyed, and if run at a maximum speed, as in the case of
stones used to grind up large edge tools, the unbalanced centrifugal
force generated on the water-soaked side may cause the stone to burst.
The following stones are suitable for the class of work named:--
FOR GRINDING MACHINISTS' TOOLS.
----------------+-------------+-----------------+----------------
Name of stone. |Kind of grit.|Texture of stone.|Color of stone.
----------------+-------------+-----------------+----------------
Nova Scotia. |All kinds, |All kinds, from |Blue or
|from finest |hardest to |yellowish grey.
|to coarsest. |softest. |
| | |
Bay Chaleur |Medium to |Soft and sharp. |Uniformly light
(New Brunswick).|finest. | |blue.
| | |
Liverpool or |Medium to |Soft, with sharp |Reddish.
Melling. |fine. |grit. |
----------------+-------------+-----------------+----------------
FOR WOOD-WORKING TOOLS.
----------------+-------------+-----------------+----------------
Name of stone. |Kind of grit.|Texture of stone.|Color of stone.
----------------+-------------+-----------------+----------------
Wickersly. |Medium to |Very soft. |Greyish yellow.
|fine. | |
| | |
Liverpool or |Medium to |Soft, with sharp |Reddish.
Melling. |fine. |grit. |
| | |
Bay Chaleur |Medium to |Soft and sharp. |Uniform light
(New Brunswick).|finest. | |blue.
| | |
Huron, Michigan.|Fine. |Soft and sharp. |Uniform light
| | |blue.
----------------+-------------+-----------------+----------------
FOR GRINDING BROAD SURFACES, AS SAWS OR IRON PLATES.
----------------+-------------+-----------------+----------------
Name of stone. |Kind of grit.|Texture of stone.| Color of stone.
----------------+-------------+-----------------+----------------
Newcastle. |Coarse to |The hard ones. |Yellow.
|medium. | |
| | |
Independence. |Coarse. |Hard to medium. |Greyish white.
| | |
Massillon. |Coarse. |Hard to medium. |Yellowish white.
----------------+-------------+-----------------+----------------
The flanges for grindstones should be trued on both faces, and should
pass easily over the grindstone shaft, and there should be between these
collars and the stone an elastic disk, as of wood or felt, which will
bed fully against the surface of the stone. It is preferable also if the
under faces of these collars be recessed to within an inch of their
perimeters so as to confine the grip to the outer edges of the faces.
The process of grinding large surfaces is entirely distinct from that of
small ones, because of the difficulty in the former of getting rid of
the cuttings. As an illustration of this point it may be remarked that a
stone that has become dulled and glazed from operating upon a broad area
of surface, as say a large plate, may be both cleaned of the cuttings
and sharpened by grinding upon it a roller of, say, 1 or 1-1/4 inches in
diameter. This roller is laid across the "horn" or rut of the stone, and
pressed firmly against it, the bar being allowed to slowly rotate. What
is commonly termed grinding is the class of grinding that is followed as
a trade, such as file grinding, saw grinding, plate grinding, edge tool
and cutlery grinding. In all this class of grinding the speeds of the
stones is very much greater than for machine-shop tool grinding. For all
the above, save cutlery grinding, the stones when new are of a diameter
from 5 to 8 feet, and of a width of from 8 to 15 inches. The stones used
by cutlers are about 15 inches in diameter, and from 1/2 inch to 3
inches thick. The average speed of grindstones in workshops may be given
as follows:--
Circumferential speed
of stone.
For grinding machinists' tools, about 900 feet per minute.
" carpenters' " 600 "
The speeds of stones for file grinding and other similar rapid grinding
is thus given in the "Grinders' List."
Diameter of
stone.
Revolutions
ft. in. per minute.
8 0 135
7 6 144
7 0 151
6 6 166
6 0 180
5 6 196
5 0 216
4 6 240
4 0 270
3 6 308
3 0 360
These speeds are obviously obtained by reducing the diameter of the
pulley on the grindstone shaft each time the stone has worn down 6
inches less in diameter, and give a uniform velocity of stone if the 8
feet stone be driven with a pulley 32 inches in diameter. Each shift (or
change of pulley) giving a pulley 2 inches less in diameter.
The following table (from the _Mechanical World_) is for the diameter of
stones and the number of revolutions they should run per minute (not to
be exceeded), with the diameter of change or shift pulleys required,
varying each shift or change 2-1/2 inches, 2-1/4 inches, or 2 inches in
diameter for each reduction of 6 inches in the diameter of the stone:--
+-------------+-------------+-----------------------------+
| | | Shift of pulleys in inches. |
| Diameter of | Revolutions +---------+---------+---------+
| stone. | per minute. | 2-1/2 | 2-1/4 | 2 |
+-------------+-------------+---------+---------+---------+
| ft. in. | | | | |
| 8 0 | 135 | 40 | 36 | 32 |
| 7 6 | 144 | 37-1/2 | 33-3/4 | 30 |
| 7 0 | 154 | 35 | 31-1/2 | 28 |
| 6 6 | 166 | 32-1/2 | 29-1/4 | 26 |
| 6 0 | 180 | 30 | 27 | 24 |
| 5 6 | 196 | 27-1/2 | 24-3/4 | 22 |
| 5 0 | 216 | 25 | 22-1/2 | 20 |
| 4 6 | 240 | 22-1/2 | 20-1/4 | 18 |
| 4 0 | 270 | 20 | 18 | 16 |
| 3 6 | 308 | 17-1/2 | 15-3/4 | 14 |
| 3 0 | 360 | 15 | 13-1/2 | 12 |
+-------------+-------------+---------+---------+---------+
| 1 | 2 | 3 | 4 | 5 |
+-------------+-------------+---------+---------+---------+
"Columns 3, 4, and 5 are given to show that if you start an 8 feet stone
with, say, a countershaft pulley driving a 40 inch pulley on the
grindstone spindle, and the stone makes the right number (135) of
revolutions per minute, the reduction in the diameter of the pulley on
the grinding-stone spindle, when the stone has been reduced 6 inches in
diameter, will require to be also reduced 2-1/2 inches in diameter, or
to shift from 40 inches to 37-1/2 inches, and so on similarly for
columns 4 and 5. Any other suitable dimensions of pulley may be used for
the stone when 8 feet in diameter, but the number of inches in each
shift named, in order to be correct, will have to be proportional to the
number of revolutions the stone should run, as given in column 2 of the
table."
[Illustration: Fig. 2059.]
[Illustration: Fig. 2060.]
In all grinding operations it is necessary that the stone should run
true. This is sometimes accomplished by so mounting the stones in their
frames that their perimeters touch at the back of each stone, one stone
running slightly faster than the other. Or sometimes the work is placed
between the two stones, as in Fig. 2059, which represents a plan
frequently used to grind circular saws; _c_ in the figure represents the
grinding-stone and _a_ the saw. Long saws are mounted vertically as in
Fig. 2060, _a_ representing a frame to which the upper end of the saw is
attached and driven by a disk crank and connecting rod as shown, the two
stones _c_ _e_ may, in this case, be of equal diameter.
[Illustration: Fig. 2061.]
Fig. 2061 represents a grindstone truing device (for tool-grinding
stones) in which a series of serrated disks are employed in place on a
threaded roll. The disks are fed to the stone by the hand wheel and
screw, and are traversed back and forth across the stone face by means
of the lever handle shown.
The fast running grindstones used for heavy and coarse grinding are
trued by a process known as hacking. The high spots of the stone are
marked by holding a piece of coal to the stone while it revolves slowly,
and a tool similar to an adze is used to cut or chop indentations in the
stone. The highest spots will be most plainly marked by the coal, and
the hacking is spaced closer together in these places, the hacking marks
crossing each other and varying in depth to suit, obviously being
deepest where the marks are blackest. The hacking also sharpens the
stone. To prevent the stone from wearing uneven across its face the file
grinder mounts the stone in a very ingenious manner, causing it to
traverse automatically, back and forth, while rotating.
[Illustration: Fig. 2062.]
This device is shown in Fig. 2062, in which A represents the grindstone
spindle having journal bearing at B B, but as there are no collars on
the journals, A can move endwise through B B. Fast to A are the collars
C and C´ (sometimes the face of the pulley hub is made to serve instead
of C´); S is a sleeve fitting easily to A, and containing a return
groove, as shown; D is a fixed arm carrying a pin which projects down
into the groove of S, as shown; P is the pulley driving A, and W W are
suspended weights. The operation is self-acting, as follows: The shaft
revolving causes the sleeve to revolve by friction, and the pin causes
the sleeve to move endwise; its end face abutting against the face of
the collar on one side, or the face of the pulley on the other side, as
the case may be, causing the shaft to travel in that lateral direction.
When the pin has arrived at the end of the groove, the stone ceases
lateral motion (there being left a little play between the faces of the
sleeve and of the collar and pulley face for this special purpose),
while the cam travels in the opposite lateral direction, getting fairly
in motion until it strikes the face, when it slowly crowds the face
over. In travelling to the right it crowds against the face of the
collar C´, and in traveling to the left, as shown in the figure, against
the face of the collar C. The swing thus given to the stone is a slow
and very regular one, the motion exciting surprise from its simplicity
and effectiveness, especially when it is considered that the friction of
the rotation of a shaft about 2-1/2 inches diameter in a smooth hole
about 6 inches long is all that is relied upon to swing a ponderous
stone.
The following are the considerations that determine in grinding tools or
pieces held by the hands to the grindstone. Upon the edge of a tool that
last receives the action of the stone there is formed what is termed a
feather-edge, which consists of a fine web of metal that bends as the
tool is ground, and does not become detached from the tool in the
grinding. The amount or length of this feather-edge increases as the
work is thinner, and is greater in soft than in hardened steel. It also
increases as the tool or piece is pressed more firmly to the stone.
To prevent its formation on such tools as plane blades or others having
thin edges, the tool is held as at G in Fig. 2063, the top of the stone
running towards the workman, and the tool is held lightly to the stone
during the latter part of the grinding operation. With the tool held on
the other side of the stone as at C, and pressed heavily to the stone, a
feather-edge extending as long as from D to E may be formed if the tool
has a moderate degree only of temper, as, say, tempered to a dark
purple. The feather-edge breaks off when the tool is put to work, or
when it is applied to an oil-stone, leaving a flat place instead of a
sharp cutting edge. In well-hardened and massive tools, such as the
majority of lathe tools, the amount of feather-edge is very small and of
little moment, but in thin tapered edges, even in well-hardened tools,
it is a matter of importance.
After a tool is ground it is often necessary to remove the feather-edge
without having recourse to an oil stone. This may be accomplished by
pressing the edge into a piece of wood lengthways with the grain of the
wood, and while holding the cutting edge parallel with the line of
motion, draw it towards you and along the grain of the wood, which
removes the feather-edge without breaking it off low down, as would be
the case if the length of the cutting edge stood at a right angle to the
line of motion.
The positions in which to hold cutting tools while grinding them are as
follows: The bottom faces of lathe tools and the end faces of tools such
as scrapers should be ground with the tool laid upon the grindstone rest
as in Fig. 2064, the stone running in the direction of the arrow. The
best position for thin work as blades is at F providing the stone runs
true, for otherwise the tool edge will be liable to catch in the stone.
With an untrue stone the position shown in Fig. 2065 is the best, the
blade being slowly reciprocated across the face of the stone.
If the facet requires to be ground rounding and not flat the position at
C, Fig. 2064, is the best, the work being moved to produce the roundness
of surface. If the tool is to be ground hollow or somewhat to the
curvature of the stone, as in Fig. 2066, the curve being from _b_ to
_c_, the position at B is the best. At position D the tool cannot be
held steadily; hence, that position is altogether unsuitable for tool
grinding purposes.
For grinding the top faces of lathe or planer tools or other similar
shaped pieces that must be held with their length at a right angle (or
thereabouts) to the plane of the rotation of the stone, the tool is held
in the hands, and the hands are supported by the grindstone rest as in
Fig. 2067, the fingers being so placed that should the tool catch in the
stone it will slip from between the fingers and not carry them down with
it upon the tool rest.
Tools to be ground to a sharp point should be ground at the back of the
stone, that is to say, with the top of the stone running away from the
operator, and the point should be slowly moved across the width of the
stone to prevent wearing grooves in its surface.
To produce a finer edge than is possible with the grindstone, the
oil-stone is brought into requisition, the shape of the oil-stone being
varied to suit the shape of the tool. Three kinds of oilstone are in
general use, Turkey stone, Arkansas stone, and Washita stone, the latter
being softer and of inferior quality to the two former. The best quality
of Arkansas stone is of a milky white color, of very fine and even
grain, and very hard, being impervious to a file; but there are softer
grades. An oil-stone should be of even grain throughout, so that it may
wear even throughout, and produce a smooth and unscored edge. Arkansas
stone is rarely obtainable in lengths above 6 inches, on account of the
presence of fine seams of hard quartz, which wears less than the stone,
and forms a projection that scores the cutting edge of the tool, and the
same applies to the Turkey stones.
For tools fully hardened and not tempered the hardest oilstones are
best; but for tools that are tempered, as tools for woodwork, a softer
grade of stone is preferable, since it will cut the most free.
When an oil-stone has worn out of shape it may be dressed on a
grindstone; but if a flat surface is required it is best to true it by a
piece of coarse sand-paper laid upon a flat true surface.
The action of an oil-stone is to smooth the surfaces; but while doing
this the oil-stone itself forms what is termed a wire-edge, which
resembles a feather-edge, except that it is smoother and more
continuous. It is caused by the weak edge of the blade giving way under
the pressure with which it is held to the stone. To reduce the wire-edge
as much as possible the tool is pressed very lightly to the oil-stone
during the latter part of the stoning, and is frequently turned over. If
the motion of the tool upon the oil-stone is parallel with the line of
cutting edge, the wire-edge will be greater than if the line of motion
were at a right angle to it.
Again, the strokes performed while the cutting edge is advancing upon
the oil-stone produce less wire-edge than the return strokes, hence the
finishing process consists of a few light strokes upon one and then upon
the other facet repeated several times. Now let it be observed that, the
wire-edge will never be turned toward the facet last oil-stoned, and
cannot be obviated by the most delicate use of the stone; but after the
stoning proper is finished, the operator will lay one facet quite level
with the face of the stone, and then give to the blade, under a very
light pressure, forward diagonal motion, and then perform the same
operation with the other facet upon the stone, the last facet operated
upon being usually the straight and not the bevelled one. To still
further reduce the wire-edge for very fine work, the operator sometimes
uses a piece of leather belt, either glued to a piece of wood, as upon
the lid of the oil-stone box, or some attach it at each end to
projecting pieces of wood, while yet others lap the tool upon the palm
of the hand. In giving an edge to a razor, the process may be carried
forward in the usual way by means of straps, the first strokes being
long ones made under a slight pressure, the strokes getting shorter and
the pressure lighter as the process proceeds, until at last the motion
and contact are scarcely perceptible.
[Illustration: Fig. 2068.]
When, as in the case of plane blades and carpenters' chisels, the area
of face is large, it is advantageous to grind the face somewhat concave,
as in Fig. 2068, so that the heel and the point only of the tool has
contact with the oil-stone, thus reducing the area to be stoned and
steadying the tool, because, the area being small, the heel as well as
the edge may be allowed to rest upon the oil-stone without unduly
prolonging the stoning operation.
[Illustration: _VOL. II._ =GRINDSTONE GRINDING.= _PLATE V._
Fig. 2063.
Fig. 2064.
Fig. 2065.
Fig. 2066.
Fig. 2067.]
[Illustration: _VOL. II._ =FULL AUTOMATIC GEAR CUTTER.= _PLATE VI._
Fig. 2069.
Fig. 2070.]
CHAPTER XXIV.--GEAR-CUTTING MACHINES.
[Illustration: Fig. 2071.]
The Brainard automatic gear cutter, Figs. 2069, 2070, 2071 and 2072 is
arranged to cut spur, bevel, and worm-wheels, and is of that class where
the manipulations required in gear cutting are all performed by the
machine itself, thus dispensing with the care of an attendant except to
place the wheels in position and set the machine for the proper depth
and length of cut. The manner in which these results are accomplished
will be seen from the following description, reference being had to the
engravings. The wheel to be cut (_a_, Fig. 2070) is held upon a mandrel
_b_ fitted to the spindle _c_, which is mounted in firm bearings upon a
column or standard _d_. To the face of the standard is gibbed a sliding
knee _e_. Upon this knee is placed the cutter slide _f_, which is
arranged to be inclined for bevel-gear cutting, and to be swung aside in
cutting worm-wheels. Rotary cutters are carried on arbors fitted to the
cutting spindle (_g_, Fig. 2071). Power for driving the cutter is
applied to the pulley _h_, mounted upon the cutter spindle.
The cutter slide _f_ is operated through the medium of a screw and
bevel-gears from a shaft _h_^{1}, which is arranged to revolve
alternately in opposite directions from a continuous motion of the
driving cone pulley _t_, receiving, motion from the feed pulley _i_,
through the means of a swinging arm, carrying a receiving pulley and
cone as is shown in Fig. 2069.
The method of obtaining these opposite motions of the shaft _h_^{1} will
be seen in Fig. 2071. To the block _h_^{2} which supports the shaft
_h_^{1} is secured a gear _h_^{3}, which engages with a pinion _h_^{4}
mounted loosely on the cone pulley _i_^{1}. Side by side with this gear
is placed a second gear _h_^{5} also engaging with the pinion _h_^{4}
and having one tooth less than the gear _h_^{3}. This gear is mounted
loosely on the shaft _h_^{1} and is sleeved through the block _h_^{2},
and to it is secured a ratchet clutch _j_.
This arrangement produces a motion analogous to that of worm gearing;
the revolution of the cone _i_^{1} carrying the pinion _h_^{4}, causes
the gear _h_^{5} to be moved in the opposite direction to that of the
cone _i_^{1}, and at a speed of one tooth for each revolution of the
cone. The cone _i_^{1} carries on its outer end a second clutch _j_^{1}.
The shaft _h_^{1} is made hollow, and two clutches are secured to a rod
playing loosely on the hollow shaft, and arranged to be engaged
alternately with the clutches _j_ and _j_^{1}. This engagement is
effected by means of a bell crank _k_, operated by a shipper rod _k_^{1}
on which adjustable dogs are placed, arranged to be operated by the
cutter slide _f_.
This arrangement of feed shipping motion is very positive in its action,
and allows of a very quick return of the cutter slide. The parts are so
proportioned that the slide returns thirty-three times as fast as the
forward motion, and yet on the very fastest speeds there is no
perceptible jar of the parts. The entire mechanism can be disconnected
from the feed screw, when desired, by disengaging the clutch _j_^{3} on
the feed screw. The means employed for spacing the wheel blank are shown
in Figs. 2070 and 2072. At the rear end of the spindle _c_ is secured a
worm-wheel _l_. This worm-wheel is made in two parts screwed firmly
together. By this construction the wheel is made very accurately. The
screw holes in the ring _l_^{1} are slightly elliptic. After the wheel
has been hobbed out the position of the ring is changed and the wheel
re-hobbed, and so on until the teeth will match perfectly in any
position of the ring, when the ring is pinned and screwed on
permanently. This wheel is driven by a worm _m_ in connection with
change gearing _m_^{1}, _m_^{2}, in such a way that one turn of the
shaft _m_^{3} serves for all divisions. To the shaft _m_^{3} is secured
a graduated plate _o_, to which is secured a latch plate _o_^{1} by
means of a [T]-slot and bolts. The latch plate _o_^{1} is secured in
this manner in order that the plate _o_ may be turned any desired amount
of "set over" in bevel-gear cutting, without disturbing the change
gearing or latch. This dividing mechanism is driven by an independent
belt from the countershaft to the pulley P, which is secured to a pinion
P^{1}, running loose on a stud. The pinion P^{1} engages with a gear
P^{2} mounted loosely on the shaft _m_^{3}. This gear is made to drive
the latch plate _o_^{1} at the proper time by means of friction plates,
which are set to the required tension by check nuts. The latch plate
_o_^{1} is held by a spring latch _v_, which is secured to an arm
_v_^{1} mounted loosely on a stud. The arm _v_^{1} is moved by a disk
_v_^{2} carrying a secondary latch _v_^{3}. This secondary latch _v_^{3}
has on one side a roll which engages with a fixed cam _v_^{4} which
trips the latch _v_^{3} from its connection with the arm _v_^{1}, thus
allowing the spring on the latch _v_ to return it to its seat in the
latch plate _o_^{1}.
The disk _v_^{2} is moved by a steel ribbon (S, Fig. 2070) which is
connected to a pair of plates, _t_ _t_^{1}, held together by a [T]-slot
and bolts, and mounted loosely upon the carriage which carries the
cutter slide _f_. The object of the double plates is to take up the
slack ribbon, in any required position of the carriage, on the knee _e_.
To the inside plate _t_^{1} is connected a shipper rod _t_^{2}, which
carries a dog and is operated by the return motion of the cutter slide
_f_. A spiral spring coiled on the stud supporting the disk _v_^{2}
returns the disk to its original position on the forward motion of the
cutter slide _f_ and reseats the secondary latch _v_^{3} in its seat in
the arm _v_^{1}. This arrangement of dividing mechanism requiring but
one turn of the shaft _m_^{3} possesses some very decided advantages
over the ordinary way of simple gearing and multiplied turns. The latch
_v_ is tripped immediately after leaving its seat in the plate _o_^{1},
and is returned by its spring against the periphery of the plate, and is
surely seated by means of a lip on the upper side of the plate. Should
it, however, fail by reason of any accident no harm will be done as the
gear will be correctly spaced whenever the latch is seated, only one or
more spaces will have been missed. Another advantage is that the feed
gear can be disconnected and the latch withdrawn, thus allowing the gear
to be revolved for the purpose of examination without any necessity for
remembering the exact number of turns. When the latch is again seated
the gear will be always properly spaced.
[Illustration: Fig. 2072.]
Fig. 2073 represents the same machine made half automatic, or in other
words the feed is automatic, but when the cut is through, the worm that
actuates the feed is thrown out of gear by a catch which lets the box or
bearing at the left hand of the worm shaft drop vertically, this catch
being operated by a stop on the side of the cutter slide. The method of
arranging the feed mechanism so that it shall remain undisturbed, and
require no alteration or adjustment at whatever height the knee carrying
the cutter slide may be, is substantially the same as that already
described with reference to the universal milling machine in Fig. 1893,
while the dividing mechanism and other general features are the same as
in the full automatic, with the exception of the mechanism for operating
the cutter during the return stroke, and operating the dividing
mechanism, both of which operations are done by hand in the
half-automatic machine.
Fig. 2074 represents a Whitworth machine in which the cutter is carried
in a vertical spindle carried in a sliding head. A is the driving
pulley, B a pair of bevel-gears, and C a pinion driving the cutter
spindle D, the cutter being at E. The cutter spindle has journal bearing
at each end in arms upon the sliding head F, which is operated along the
slideway of H by the gear-wheel G, receiving motion from the worm at C;
at K is the index wheel, the wheel to be cut being carried on its shaft
at M. The head N, carrying the index-wheel shaft, may be moved along the
bed on which it slides by the handle P, which operates a screw within
the bed, and engaging a nut on the under side of N. The worm for the
worm-wheel K is carried beneath the wheel by a bracket from N, and being
on a splined shaft moves with N. P is the handle for the divisions, the
latter being obtained by means of change wheels at J, which connect with
the worm shaft. By employing change gears the handle P makes a complete
turn for any division, and is locked in a recess, which determines when
an exact turn has been made. The range of a machine of this design is
very great, because of the length of the bed on which the head N slides,
which may be longer than would be practical if it stood upright.
Fig. 2075 represents a gear planing machine, shown with a bevel-gear in
place. The main spindle is horizontal upon a fixed head, and has its
dividing mechanism at the back of the machine. A single pointed tool is
used in a slide rest, operated (by crank motion) upon the horizontal
slideway shown, which may be set at any required angle for bevel-wheels.
The cut is carried from the point to the flank of the tooth, and is put
on by a rod and ratchet motion, the rod striking against the stop seen
beneath the cross slide for the slide rest, and on the side of the
horizontal slideway.
Figs. 2076, 2077, 2078, 2079, 2080, 2081, and 2082 represent different
views of a gear-cutting machine, which consists of a bed plate A A,
Figs. 2077, 2078, and 2079, having an extension at end A^{2}, to support
the hollow cylindrical column A^{3}, which carries an overhead shaft
_a_, at one end of which is a four-step cone A^{3}, for driving the
cutter feed motions. At the other end are the tight and loose pulleys
for driving this shaft, upon which is also a series of grooved pulleys
_a_^{5}, arranged in the form of a cone. The object of this is to drive
the cutter. At the base of the column A^{3} is a corresponding series of
grooved pulleys, also arranged in the form of a cone _a_^{6}. A round
belt is employed. The shaft on which _a_^{6} is placed extends through
the column, and on its opposite end a grooved pulley is also placed.
This serves to drive a belt which, passing over a series of idle
pulleys, as will be seen by reference to Figs. 2076 and 2077, drives the
rotary cutter.
The wheel to be cut is carried as follows: Upon the bed-plate of the
machine is placed a head B, Fig. 2078, corresponding to the headstock of
a lathe, opposite which is a head B´, answering to the tailstock of a
lathe. These two carry a mandrel D, to which is fastened a face-plate D´
against which the work is chucked. At the end of D´´ is fixed, in the
usual manner, the worm-wheel for the dividing mechanism. The cutting
arbor is held in a head that is carried in a cross slide C^{2}, Fig.
2077, this cross slide being a carriage that may be fed along the side
extension of the bed, which is broken off in the plan view of the
machine, Fig. 2078. The two slides thus provided in this machine form in
effect a longitudinal and cross feed, answering to the feeds of a lathe
carriage and tool rest.
[Illustration: _VOL. II._ =GEAR-CUTTING MACHINES.= _PLATE VII._
Fig. 2074.
Fig. 2075.]
The cutter head M, Fig. 2077, is composed of two parts, C and M.
Provision is made to swing the head in two directions, one of which is
noted by the plain arrow and the other by the feathered arrow in the
engravings. Between the two the cutter arbor, it will be perceived, may
be set at an angle in whatever direction the nature of the work may
require. Referring to Figs. 2076 and 2077, it will be seen that the
cutter-driver mechanism operates as follows: The tight pulley _a_^{1},
driven in the direction noted by the arrow, turns the cone _a_^{6} which
drives the pulley _b_. The belt from _b_ passes over grooved idlers,
_b_^{1}, _b_^{2}, _b_^{3}, &c., to the grooved pulley _b_^{8}, which is
fast on its shaft and drives a train of gearing that operates the cutter
arbor, the train being best shown in Fig. 2077. The train of gearing
thus driven is composed of gears _c_^{1}, _c_^{2} and _c_^{5}, the
latter being on the cutter arbor. The object of this arrangement is to
obtain a high belt velocity. It will be seen that all these gears have
their teeth at an angle to their axes, a feature that has been
introduced to obtain smoothness of action. To maintain equal tension of
belt at whatever angle the cutter may be set, the idle pulley _b_^{2}
acts as a belt tightener, being carried by the rods _t_ and _t_^{1}.
[Illustration: Fig. 2073.]
Referring now to the feed motions, the machine is provided with a quick
return for the cutter, the mechanism of which is as follows: The cone
pulley _a_^{4}, Fig. 2077, is mounted upon a driver shaft _d_, Fig.
2079. Upon this shaft are two loose bevelled pinions _d_^{2} _d_^{4},
between which, and splined to the shaft, is a clutch _f_. For the feed
traverse the clutch _f_ is moved to engage with the pinion D^{4}, while
for the quick return it engages with _d_^{2}. This device corresponds to
the old-style quick-return motion used in some of the heavy English
planing machines. The clutch _f_ is operated by a rod _l´_, and drives
the bevelled pinions _d_^{2} _d_^{4} by friction. The hub of the clutch
is coned to fit a coned recess in the hubs of the two pinions. A pair of
gears, _d_^{6} _d_^{7}, transmit the motion of _d_^{5} to the shaft
_d_^{1}, on the end of which is the pinion _e_^{1}, Motion is conveyed
from this pinion to the feed-screw _e_, Fig. 2081, by the intermediate
gears e^{2}, _e_^{3}, _e_^{4} and _e_^{5}, and also by the helical
pinions _e_^{6} and _e_^{7}, the latter two being also shown in Fig.
2081.
Referring to the dividing mechanism, E, Fig. 2077, is an index-wheel
operated by a worm. E^{1} is an arm with a locking tongue. Motion from E
is conveyed to the shaft _g_ through a swing-frame, shown in dotted
lines in Fig. 2077, and a train of gears _g_^{2}, _g_^{3}, _g_^{4},
_g_^{5}, _g_^{6}. On shaft _g_, Fig. 2078, is a pair of angular-toothed
beveled pinions, _h_^{1} _h_^{2}, and on shaft _h_, Fig. 2080, is a
pinion _h_^{3}, driving a pinion _h_^{4}, which in turn drives pinions
_i_ _i_^{1}. The latter drive the worm H´ which operates the wheel H.
The two shafts carrying _i_ _i_^{1} are supported by a piece F, the arm
of which appears in section. This is fixed on the large toothed wheel G,
indicated by the dotted lines in the same figure. The piece F above
referred to is not fully shown in the engraving, portions of it having
been omitted in order to show the mechanism previously mentioned. The
wheel H is mounted on shaft D´´, and is used to revolve the face plate
D´, all as shown in Fig. 2078. The wheels _g_^{2} _g_^{3} are change
wheels, whose relative diameters determine the number of turns the wheel
E must make for a given pitch. The arm E^{1}, Fig. 2077, is provided
with a spring to hold the index pin into the notch of the index wheel.
From this description it is obvious that when the number of the teeth of
the wheel to be cut is a multiple of that of the wheel H, the number of
turns to be given to the tangent screw H´, Fig. 2080, is exactly
determined by the ratio existing between these two numbers. On the other
hand, where the number of teeth required is not a multiple of the teeth
in the wheel H, the number of turns to be given to the screw will be
equal to _n_ plus a fraction. In the first case, if all the intermediate
gears between the dividing apparatus and the tangent screw are arranged
to transmit to the former a number of definite turns, it will suffice to
make the crank describe the number of turns indicated by the ratio the
wheel E bears to the worm-wheel. In the second case, in order to give
the tangent screw _n_ turns plus a fraction by giving the crank _n_ +
turns, it is necessary to employ several wheels, for which the ratio
must be calculated. If the division so obtained is not an exact divisor
of the number of teeth of the wheel H, it is necessary that one of the
wheels forming the combination shall have a number of teeth which is a
multiple of the division mentioned.
[Illustration: Fig. 2076.]
Another consideration with reference to the number of turns to be given
to the crank of the dividing apparatus is mentioned in the inventor's
description of this machine. The smaller the number the greater will be
the chance of error in the result; for example, if it be supposed that a
division corresponding to one turn of the tangent screw is to be made,
if only one turn of the crank is made, the play unavoidable where easy
movement is secured will be repeated and multiplied in the same way that
an error is produced after a certain number of divisions. If, on the
contrary, the mechanism be arranged so that the number of turns of the
crank is multiplied in obtaining one turn of the tangent screw, the
error will be appreciably reduced. It is therefore recommended by the
designer of this machine to arrange the train of gears so as to give a
certain number of full turns to the crank in all cases. If, after having
cut the teeth in the blank, it is desirable to go over them again, it is
simply necessary to turn the screw _j_ which engages with the gear-wheel
J^{1}.
The next feature to be described is the adjustment of the cutter. In
some cases it is necessary to incline the cutter in such a way that the
axis of the shaft carrying it forms a certain angle with the vertical.
This is the case in cutting angle teeth, as shown in Fig. 2076. In order
to produce the necessary angle for such teeth, it is only necessary to
turn the worm _k_ that engages with the worm-wheel _k_^{1}, Fig. 2077.
This wheel is fast on to the piece M, and the latter, when set to the
desired inclination, is kept in place by means of bolts O, Figs. 2077
and 2081. In some cases it is necessary to incline the cutter in such a
way that the axis of the shaft that carries it does not cease to be in
a vertical plane perpendicular to the shaft D, this being the case as
illustrated in Fig. 2082. In order to obtain this obliquity the small
shaft _m_ is turned, and the movement so obtained is transmitted by
means of two small pinions _m_^{2} _m_^{3} to the shaft carrying at its
extremity the screw _n´_. This screw gears with the segment _n´´_. The
latter is fixed to a piece J, furnished with bearings for the reception
of the shaft that drives the cutter spindle, which is adjusted endways
by means of the nuts shown.
[Illustration: Fig. 2077.]
If it is desired to produce a wheel with angle teeth it is necessary,
after having arranged the cutter as shown in Fig. 2076, and while the
forward motion of the carriage takes place, that the wheel R shall turn
with a slow, regular movement until the tooth operated upon is finished.
After this the tool retraces its path at a somewhat higher speed. This
automatic motion is obtained from a shaft (Fig. 2076), on which are
placed the pinions _e_^{2} _e_^{3}. This shaft carries a third pinion
_p_^{2}, which, by means of one or more pairs of wheels mounted two by
two on a swinging frame _p_, as shown by _p_^{3} _p_^{4} _p_^{5}, turns
the shaft _p´_ (Fig. 2080), which carries at one of its extremities the
wheel _p_^{5} and at the other the screw _h_^{3}. This screw, by proper
intermediates, operates the toothed wheel G, Fig. 2080, which in its
rotation carries along the piece F, with all the parts supported by it.
In this movement the pinion _h_^{3} does not turn, nor does the second
pinion _h_^{4}, which slides on the former. The screw H´ slightly turns
the large wheel H, which, as previously mentioned, is mounted on the
shaft D, Fig. 2078. When the special tooth operated upon is finished the
movement is reversed by operating the lever _l_. The table and the wheel
R, Fig. 2077, then move in the opposite direction. When the original
position is reached by the cutter, the reversing lever is thrown out of
gear; the handle E´ is then used so as to effect the proper division,
and the machine is again started.
As has been shown, only a small portion of the circumference of the
wheel G is subjected to wear. In this way it would be possible to limit
the operation of cutting the teeth to a certain length of arc only. In
that case, however, considerable wear would be produced; for this reason
the constructor has preferred to provide the whole circumference with
teeth, in order to change the working point from time to time, so as to
distribute the wear. In order to permit this displacement it is
necessary to disengage the worm K (Fig. 2076), which is accomplished by
turning the hand wheel _v_, mounted on the shaft _v´_, Fig. 2078. This
shaft carries at each extremity small pinions, _v_^{2}, _v_^{3}, gearing
with other pinions fixed at the extremity of each of the supports of the
shaft _p´_.
[Illustration: Fig. 2078.]
[Illustration: Fig. 2079.]
[Illustration: Fig. 2080.]
In order to make the operation of this machine better understood, we
will conclude our description by some practical examples of the
calculations required in making helical teeth. It will be observed that
the two small movements necessary in cutting an angle tooth in a given
inclination are obtained first by the screw _e_, Fig. 2077, feeding the
cutter head, and second by the tangent screw K, Fig. 2076, that governs
the rotary motion of the wheel G, and consequently of the shaft D,
carrying the face plate and the blank to be cut. The second wheel H,
mounted on this shaft, is driven by the endless screw H´, Fig. 2080, the
supports of which are fixed on the wheel G. It will be observed at the
same time that the speed of the screw _e_ acting upon the tool holder is
the same as that of the shaft carrying the wheels _e_^{2} _e_^{3} and
_p_^{2}, since the wheels _e_^{4} _e_^{5} _e_^{6} _e_^{7} have the same
number of teeth. It is obvious, therefore, that that ratio of speed
which will exist between the tangent screw K and the shaft of wheels
_e_^{2} _e_^{3} and _p_^{2} will have to be the same as that between the
driving screw _e_ of the cutter head and the tangent screw K.
Consequently, the combinations of wheels that connect this tangent screw
K to the shaft _e_^{2} _e_^{3} and _p_^{2} will produce the same effect
as if they were connected directly with the feed screw _e_. This being
established, the general formulæ determining the gearing to be employed
in order to produce helical teeth inclined at a certain angle are
obtained in the following manner: It should here be observed that the
teeth produced will be what in the United States are called angle teeth,
corresponding, however, so nearly to the helix as to be considered
helical. Suppose that the number of teeth in the wheel G is 300, and
that the pitch of the driving screw of the cutter head is 5 mm., using
for convenience the French system of measurements. Let _x_/_y_ be the
ratio of the four wheels that it is necessary to mount. Let M designate
the degrees of inclination of the teeth. Let P equal the pitch of the
desired helix, and D the diameter of the wheel to be operated upon. We
then have cotan. M = P/(D × 3.14), from which we find P = cotan. M × D ×
3.14, and in order to make the cutter head run over a distance
corresponding to this pitch, the driving screw _e_ must make a number of
turns equal to
cotan. M × D × 3.141
--------------------
5
But while the cutter head passes over a distance equal to the pitch,
the wheel G makes one turn and the tangent screw 300 turns;
consequently, the ratio to be established between the speed of the
tangent screw and between that of the screw driving the carriage will be
represented by
_x_ 1500
--- = --------------------
_y_ cotan. M × D × 3.141
[Illustration: Fig. 2081.]
[Illustration: Fig. 2082.]
Thus, for a wheel with a diameter of 1.75 inches, the machine ought to
have an inclination of 15° to the primitive circumference, and we would
have, for the ratio to be established between the tangent screw and the
driving screw,
_x_ 1500 1500
--- = ------------------------- = --------
_y_ cotan. 15° × 1.75 × 3.141 20.51778
It should be remarked that, according as the angle should be either to
right or to left, one or two intermediate pieces are placed on the
swing-frame, the slide of which is nearly horizontal. The speed of the
driving shaft, supported by the column mentioned in introductory
remarks, is 120 revolutions; that of cutter equals from 20 to 30
revolutions; that of screw of cutter head, advance from 1 to 42
revolutions, return from 7 to 66 revolutions.
CHAPTER XXV.--VICE WORK.
Vice work may be said to include all those operations performed by the
machinist that are not included in the work done by machine tools. In
England vice work is divided into two distinct classes, viz., fitting
and erecting. The fitter fits the work together after it has been
operated upon by the lathe planer and other machine tools, and the
erector receives the work from the fitter and erects it in place upon
the engine or machine. Fitting requires more skill than turning, and
erecting still more than fitting, but it is at the same time to be
observed that the operations of the erector includes a great many of
those of the fitter. In treating of the subjects of vice work and
erecting, it appears to the author desirable to treat at the same time
of some operations that are not usually included in those trades,
because they are performed with tools similar to those used by the
fitter, and may be treated equally as well in this way as in any other,
while a knowledge of them cannot fail to be of great service to both the
fitter and erector. Among the operations here referred to are some of
the uses of the hammer; such, for example, as in straightening metal
plates.
The vice used by the machinist varies both in construction and size
according to the class of work it is to hold. For ordinary work the vice
may possess the conveniences of swiveling and a quick return motion, but
when heavy chipping constitutes a large proportion of the work to be
done the legged vice is preferable.
The height of vice jaws from the floor is usually greater for very small
work than for the ordinary work of the machine shop, because the work
needs to be more clearly observed without compelling the operator to
stoop to examine it. The gripping surfaces of vice jaws are usually made
to meet a little the closest at the top, so as to grip the work close to
the top and enable work cut off with a chisel to be cut clean and level
with the jaws.
[Illustration: Fig. 2083.]
The jaws of the wood-worker's vice are made then as in Fig. 2083, and
reach higher above the screw than the vices used for iron work, because
the work is often of considerable depth, and being light will not lie
still of its own weight, as is the case with iron.
[Illustration: Fig. 2084.]
An example of the ordinary vice of the machine shop is shown in Fig.
2084, which represents partly in section a patent swivel vice. A is the
jaw in one piece with the body of the vice, and B is the movable jaw,
being the one nearest to the operator. The movable jaw is allowed to
slide freely through the fixed one (being pushed or pulled by hand), or
is drawn upon and grips the work by operating the handle or lever H. The
means of accomplishing this result are as follows: As shown in the cut,
B is free to be moved in or out, but if H be pulled away from the vice,
the shoulder C, meeting the shoulder _n_, will move the toggle G, and
this, through the medium of G´, moves the tooth bar _t_, so as to engage
with the teeth on the side of the movable jaw bar shown at T. As soon as
the teeth _t_ meet the teeth T the two travel together, and the jaw B
closes on and grips the work. But as the motion is small in amount, the
jaw B should be placed so to nearly or quite touch the work before H is
operated. To unloose the work, the handle H is operated in an opposite
direction, and the hook M meets _m_ and pulls _t_ to the position shown.
The spring S operates upon a hook at U, to engage the teeth _t_, with
the rack T, as soon as the handle H is moved in the tightening
direction. The vice grips with great force, because during the
tightening the toggle, G is nearly straight, and its movement less than
would be the case with a screw-vice having the ordinary pitch of thread
and under an equal amount of handle movement.
[Illustration: Fig. 2085.]
In this vice the fixed jaw is made to fasten permanently to the work
bench, but in others having a similar tightening mechanism the fixed jaw
is so attached to the bench as to allow of being swivelled. The method
of accomplishing this is shown in Fig. 2085, in which S is the foot of
the vice bored conical to receive a cone on the casting R, which is
fastened to the bench B. W is a washer and H the double arm nut.
Loosening this nut permits of the vice being rotated upon R.
When handle H is operated to release the movable jaw it can be moved
rapidly to open and receive the work, and to close upon the work, when
by a second handle movement the work can be gripped, the operation being
much quicker than when the movable jaw is traversed by a screw and nut.
In this vice the gripping surface of the jaws are always parallel one to
the other, and attachments are employed to grip taper work as wedges.
[Illustration: Fig. 2086.]
[Illustration: Fig. 2087.]
In Fig. 2086 is represented a patent adjustable jaw vice, which is also
shown in Fig. 2087 with the adjustable jaw removed and upside down. From
the construction it is apparent that the groove G, being an arc of a
circle of which C is the centre, the jaw is, as it were, pivoted
horizontally, and can swing so as to let the plane of the jaw surfaces
conform to the plane of the work; hence a wedge can be gripped all along
the length enveloped by the jaws, and not at one corner or end only.
When the pin A is inserted the jaw stands fixed parallel to the sliding
jaw. The pin A engages in a ratchet in the base below it to secure the
back vice jaw in position when it is set to any required angle.
A second convenience in this vice is that the whole vice can be
swivelled upon the base that bolts to the bench, which is provided with
a central hole and annular groove into which the base of the field jaw
pivots; at B is a spring pin passing into holes in the bench plate, so
that by lifting the pin B, the whole vice can be swung or rotated upon
the base or bench plate, until the pin B falls into another hole in the
base plate, which is provided with eight of these holes. The movable jaw
is here operated by a screw and nut.
[Illustration: Fig. 2088.]
Fig. 2088 represents a form of leg vice for heavy work. In the ordinary
forms of this class of vice the two gripping surfaces of the jaws, only
stand parallel and vertical when at one position, because the movable
leg is pivoted at P; but in that shown in the figure the movable jaw is
supported by the arm A, passing through the fixed leg L, which carries a
nut N. A screw S, having journal bearing in the movable leg, screws
through the nut N, and is connected to the upper screw by the chain C,
which passes around a chain wheel provided on each screw, so that the
movable leg moves in an upright position and the jaw faces stand
parallel, no matter what the width of the work. This is a very
substantial method of obtaining a desirable and important object, and
greatly enhances the gripping capability of the vice. Fig. 2089
represents a sectional view of another patent vice. A is the sliding and
B the fixed jaw. P is the bed plate carrying the steel rack plate H.
Attached to each side of the base of the handle is a disk. These disks
are carried on the outer end of the movable jaw A, and are held in place
by the friction straps T, adjusted by the screws S. On the radial face
of the disk is the pin K, which, when the handle or lever is lifted or
raised, depresses the end of lever J, which at its other end raises the
clutch G, disengaging the same from the rack H, as shown in the
engraving. The jaw A is thus free to be moved by hand, so as to have
contact with the work. To tighten the vice the handle is depressed,
whereon K releases J and the latter permits the toothed clutch G to
engage with the teeth of H. At the same time the bar D, which is pivoted
to the disks, is drawn outward. The end of the bar D, meeting the
surface of the lug shown on A, acts (in conjunction with the toothed
clutch H) as a toggle fulcrum from which the disks may force the movable
jaw to grip the work.
[Illustration: Fig. 2089.]
This action may be more minutely described as follows: The end _d_ of D
is pivoted upon the disks, as shown; hence when the handle is depressed
the effort of the end _d_ is to move to the right, but D being fixed at
the other end the pressure is exerted to force the movable jaw to the
left, and therefore upon the work. The amount of jaw movement due to the
depression of the handle is such that if that jaw is pushed near or
close to the work the handle will stand about vertical downward when the
vice firmly grips the work.
For vices whose jaws cannot be swiveled horizontally to enable them to
conform to taper work, attachments for the jaws are sometimes provided,
these attachments having the necessary swiveling feature. So likewise
for gripping pipes, and similar purposes, attachments are made having
circular recesses to receive the pipes.
[Illustration: Fig. 2090.]
[Illustration: Fig. 2091.]
To prevent the vice jaws from damaging the work surface, and also to
hold some kinds of work more firmly, various forms of clamps, or
coverings for the vice jaws are used. Thus Figs. 2090 and 2091 represent
clamps for holding round or square pins. In the former the grooves pass
entirely through the clamp jaws, so as to receive long pieces of wire,
while in the latter the recesses are short, so as to form an abutment
for the end of the pins, and act as a gauge in filing or cutting them
off to length.
[Illustration: Fig. 2092.]
An excellent form of pin clamp is shown in Fig. 2092, the spring bow at
the bottom acting to hold the jaws open and force the faces against the
vice jaws when the latter are opened. The flanges at B B rest upon the
tops of the vice jaws; hence it will be seen that the clamp is not
liable to fall off when the vice is opened to receive the work, which is
placed either in the hole at A or that at B, as may be most desirable.
[Illustration: Fig. 2093.]
Fig. 2093 shows such a clamp holding a screw, the clamp jaws being
forced against the screw by the vice jaw pressure, when the vice jaws
are opened the spring of the bow will cause the clamp jaws to open and
release the screw.
Clamps such as shown in Figs. 2090 and 2091, but without the pin holes,
are also provided, being made one pair of copper and another of lead,
the latter being preferable for highly finished work. As the filings are
apt to imbed in the copper, and, furthermore, as the copper gradually
hardens upon its surface, the copper clamps require to be annealed
occasionally, which may be done by heating them to a low red heat and
dipping them in water. Lead clamps will hold small work very firmly, and
are absolutely essential for triangular or other finished work having
sharp corners, and also for highly finished cylindrical work, which may
be held in them sufficiently firmly to be clipped without suffering
damage from the vice jaws. A piece of thick leather, such as sole
leather, also forms a very good clamp for finished work, but to prevent
its falling off the vice jaws it is necessary to cut it nearly through
on the outside and at the bent corner.
The hammer in some form or other is used in almost all kinds of
mechanical manipulation, and in each of these applications it assumes a
form varied to suit the nature of its duty, and of the material to be
operated upon. In the machine shop it is used to drive, to stretch, and
to straighten.
The most skilful of these operations are those involving stretching
operations, as saw and plate straightening, examples of which will be
given.
In using a hammer to drive, the weight and velocity of the hammer head
are the main considerations. For example, the force of a blow delivered
by a hammer weighing 1 lb., and travelling 40 feet in a second, will be
equal to that weighing 2 lbs, and travelling 20 feet in a second; but
the mechanical effects will be different. If received on the same area
of impact the effects will sink deeper into the metal with the greater
velocity, and they will extend to a less radius surrounding the area of
impact. Thus in driving out a key that is fast in its seat, a quick blow
is more effective than a slow one, both being assumed to have at the
moment of impact an equal amount of mechanical force stored up in them.
On the other hand, for riveting the reverse will be the case. In the
stretching processes the hammer requires to fall with as dead a blow as
possible. Thus the hammer handle is, for saw stretching, placed at such
an angle to the length of the hammer that the latter stands about
vertical when the blow is delivered. In straightening, the blow is
varied to accommodate the nature of the work; thus a short crook or bend
would be best straightened by a quick blow with a light hammer, and a
long one by a slower blow with a heavier hammer, which would cause the
effects of the blow to affect a greater radius around the part receiving
the impact.
As an example of the difference in mechanical effect between a number of
blows aggregating a given amount of energy and a single blow having an
equal amount of energy, suppose the case of a key requiring a given
amount of power to start it from its seat, and every blow delivered upon
it with insufficient force to loosen its hold simply tends to swell and
rivet it more firmly in the keyway.
Probably the most expert use of the hammer is required in the
straightening of engravers' plates, as bank-note plates; and next to
this comes the ornamental repoussé work of the manufacturing jeweller.
The most expert hammer process of the machine shop is that of
straightening rifle barrels and straightening saws and sheet metal
plates.
In straightening rifle barrels, the operator is guided as to the
straightness as follows: A black line is drawn across a piece of glass
elevated to the light, and the straightener looks through the bore at
this line, which throws a dark line of shadow along the rifle bore. If
this line appears straight while the barrel is rotated the bore is
straight; but if the line waves the barrel requires straightening, the
judgment of the operator being relied upon to determine the amount of
the error, its location, and the force and nature of the blow necessary
to rectify it.
The following information on the duration of a blow is taken from
_Engineering_, the results having been obtained from some experiments by
Mr. Robert Sabine. These experiments, which were intended as preliminary
to a more extended inquiry, were made with a view to find approximately
how the duration of a blow varied with the weight of the hammer, its
velocity of descent, and with the materials. An iron ball weighing 1/4
lb. was suspended by a fine wire from an insulated support upon the
ceiling; so that when it hung vertically it just grazed the vertical
face of an ordinary blacksmith's anvil placed upon its side on a table.
By raising the ball and letting it swing against the face of the anvil a
blow of varying force could be struck. On rebounding, the ball was
arrested whilst the excursion of the galvanometer needle was observed.
By measuring the angle through which the ball was separated, its
vertical fall and final velocity could be easily deduced. In this way
the greatest vertical height from which the iron ball was let fall on to
the face of the iron anvil was 4 ft., the least about 1/80 inch. Six
readings were taken for each height, and they were invariably found to
agree amongst each other. The averages only are given in the following
records:
Vertical fall Duration of contact
in inches. in seconds.
48 0.00008
36 0.00008
28 0.00008
17 0.00009
9-1/4 0.00010
4 0.00011
1 0.00013
0-1/4 0.00016
0-1/16 0.00018
0-1/32 0.00021
0-1/80 0.00030
From this it would appear that when the velocity of a blow is increased,
the duration is decreased within a certain limit; but that it reaches a
minimum. The velocity of impact in the first experiment was about sixty
times as great as in the last one; but the duration of the blow appears
to be reduced only to about one-fourth of the time. The blows given by
two hammers of different weights were compared. No. 1 weighed 4 ozs.,
No. 2 weighed only 2-1/4 ozs. The durations of the blows were as
follows:
+----------------+---------------------------+
| | Duration of contact. |
| Vertical fall. +-------------+-------------+
| | Ball No. 1. | Ball No. 2. |
+----------------+-------------+-------------+
| inch. | seconds. | seconds. |
| 1 | 0.000135 | 0.000098 |
| 4 | 0.000096 | 0.000083 |
+----------------+-------------+-------------+
It appears from this that a heavier hammer of the same material gives a
longer duration of blow.
In the course of these experiments it was observed that the ball after
striking the anvil rebounded irregularly, sometimes to a greater, at
others to a less height, and that some relation appeared to exist
between the heights to which the ball rebounded and the excursions of
the galvanometer needle due to the residue of the charge.
In the next series, therefore, the rebounds of the iron ball from the
iron anvil were measured and recorded, from which it appeared that when
the rebound was greater the duration of contact was shorter, and _vice
versâ_.
+----------------+-------------------+-------------------+
| Vertical fall. | Vertical rebound. | Duration of blow. |
+----------------+-------------------+-------------------+
| inch. | inch. | seconds. |
| 6 | 2 | 0.000120 |
| 6 | 2-1/2 | 0.000111 |
| 6 | 3-1/4 | 0.000101 |
| 6 | 3-1/2 | 0.000091 |
| 14-1/2 | 3-1/4 | 0.000106 |
| 14-1/2 | 4-1/2 | 0.000103 |
| 14-1/2 | 5-1/4 | 0.000095 |
| 14-1/2 | 6-1/2 | 0.000086 |
| 25 | 7-3/4 | 0.000096 |
| 25 | 8-1/4 | 0.000091 |
| 25 | 9-1/2 | 0.000086 |
| 25 | 12 | 0.000078 |
+----------------+-------------------+-------------------+
The explanation of this is probably that when the energy of the blow is
expended in bruising or permanently altering the form of the hammer or
anvil by which the contact of the two is prolonged, it has less energy
left to enable it to rebound, and _vice versâ_. Substituting a brass
anvil and brass ball, it was found that the blow was duller, the rebound
much less, and the duration contact nearly three times as great as when
the iron ball and anvil were used.
+----------------+-------------------+----------------------+
| Vertical fall. | Vertical rebound. | Duration of contact. |
+----------------+-------------------+----------------------+
| inch. | inch. | seconds. |
| 1-3/4 | 0-1/3 | 0.00036 |
| 6 | 1 | 0.00033 |
| 14-1/2 | 1-1/2 | 0.00026 |
| 25 | 2 | 0.00027 |
+----------------+-------------------+----------------------+
This series also shows the longer duration of the blow when its velocity
is small. Using a brass anvil and iron ball the duration of the blow was
greater than when both were of iron, but less than when both were of
brass.
+----------------+-------------------+----------------------+
| Vertical fall. | Vertical rebound. | Duration of contact. |
+----------------+-------------------+----------------------+
| inch. | inch. | seconds. |
| 1-3/4 | 0-1/8 | 0.00021 |
| 6 | 0-1/2 | 0.00018 |
| 14-1/2 | 1-1/3 | 0.00015 |
| 25 | 2 | 0.00014 |
+----------------+-------------------+----------------------+
Striking the brass anvil with a common hammer, the duration of the blow
appeared shorter when struck sharply.
Duration of contact.
seconds.
Moderate blow 0.00027
Harder blow 0.00019
Striking the blacksmith's anvil with a common carpenter's hammer, the
duration appeared to be nearly constant.
Duration of contact.
seconds.
Moderate blow 0.00011
Harder blow 0.00010
It was, of course, necessary to allow in each case the hammer to rebound
freely, and not to prevent it doing so by continuing to exert any
pressure at the instant of the blow. When this condition was observed,
it was invariably found that the harder and sharper the blow the shorter
was its duration. It was also noticed that whenever the anvil gave out a
sharp ringing sound, the duration of the blow was much shorter than when
the sound was dull.
A very slight error would be introduced by reason of thermo-currents set
up between the metals at the moment of the blow. By reversing the
direction of charge of the accumulator, however, the effect from this
cause was found to be quite inappreciable.
[Illustration: Fig. 2094.]
[Illustration: Fig. 2095.]
[Illustration: Fig. 2096.]
[Illustration: Fig. 2097.]
[Illustration: Fig. 2098.]