Let it be required to cut a straight groove in the piece of brass _l_.

Wax it to the plate _p_ so that the axis of the required groove is over

the line traced on the plate. Now fix G in the tool-holder and replace

the pump-center by a rod D, the extremity of which is formed into a

cutter of a diameter equal to the width of the required groove; the

rod D should be fixed in the hollow arbor by a screw. It is then only

necessary to set the cutter in motion, forcing the piece _l_ against

the revolving cutter, until the requisite depth is attained. Then, by

making the tool-holder travel parallel to the face-plate, the groove

will be elongated until of the desired length.

=370.= The cutter may be of the form shown in Fig. 171, or it may be

as shown at _b_ in Fig. 172, since the movement is always in the same

direction. The cutting edges are each formed by two small inclined

faces, one pair of which is shown at _b_; they occupy half the diameter

of the cutter. At the back of this pair the cutter presents the

appearance of the lower half shown in the figure and _vice versa_.

It will be evident that the two sides of this cutter will act while its

motion is continuous in one direction.

Besides the numerous operations that can be performed on the lathe as

we have hitherto indicated, it may be employed, if divided on the head

stock, for tracing out angles, marking the crossings of a wheel, a

balance, etc., and for other purposes, many of which are referred to in

the course of this work.

PRODUCTION OF SCREW THREADS.

SCREW PLATES AND TAPS.

=371.= The lathes employed in the manufacture of screws are of two

kinds; those intended for polishing and, where necessary, modifying the

form of screw-heads, much used by watch examiners and repairers, and

those specially designed for cutting the threads, which are mainly in

use in factories.

Before discussing them, however, we will give some account of the

screw-plates and taps in ordinary use.

=372.= =Common Hand Screw-plates.= The use of these is much facilitated

by providing a second plate perforated with holes of such sizes that

a spindle which just passes into a hole of any given number will be

of the size most convenient for forming a screw in the hole of the

same number in the screw-plate. For a long time we have made use of

two Latard screw-plates so made that a rod which would enter one hole

without play was of the most convenient size for forming a screw in the

next smaller hole but one (thus the plate perforated with plain holes

can be replaced by a second screw-plate, or by using the successively

larger holes on a single plate as gauges).

[Illustration: _Fig. 173._]

In order to form a screw that is clean-cut and even, with the least

possible straining of the metal, the holes in the screw-plate should

have notches cut as shown at F, Fig. 173; they should be carefully

hardened and well polished on each side of the notch, and this system

is now even applied in the case of the smallest jewel screws.

=373.= =Screw Dies.= The ordinary plate, in which notches are not cut

at the sides, squeezes up and strains the metal. This effect is less

marked when separate dies are used, and disappears entirely if only

a small quantity of metal is removed at a time, and the cutting edges

of the dies are smooth and in good order. In addition to possessing

other advantages, this form of screw-plate enables us to obtain at

will screws of the same thread and different diameters or of the same

diameter and different threads. The dies must be carefully fitted to

the slides that receive them. Dies cannot be employed for cutting very

small screws.

=374.= =Fine-threaded Screw-plates.= At the present day these can

always be obtained at the material stores; but thirty years ago it was

not so, and the watchmaker was obliged to make them for himself. The

following method was adopted:

Take a screw formed with an ordinary plate, in which the thread is

broad as compared with the hollow. If the screw does not satisfy this

condition it must be modified thus:

Having ascertained that it runs true, and that it is larger than will

be ultimately required, insert it in a chuck in your lathe. The T-rest

must carry a smooth horizontal rod of hardened steel.

Rotating the screw, hold a slitting file in the hollow; the file

should fit into this hollow accurately, and should be smoothed on its

two sides, only cutting with one edge. The bar of hardened steel will

determine the depth to which the file is allowed to cut. By this means

a screw is obtained that has a thread thick at the bottom. With the

graver remove the top of this thread, round off its corners, and harden

the screw, filing three facets along its entire length, that make it

taper.

The tap, having been thus prepared, is employed for cutting a thread in

a piece of steel, not too thick, that has been previously annealed,

and in which a hole is drilled of the proper size. The thread of this

internal screw will be thin and the hollow proportionately broad.

The plate is now hammered cold with care until the thickness is so

far diminished that the thread and hollow are as nearly as possible

of equal thickness. Harden it and chamfer the ends of the hole with a

conical steel point and oilstone dust. Then clean it and cut a thread

on a piece of soft steel which may be formed into a tap.

If the operation has been properly conducted, this tap will satisfy

the prescribed conditions, and, when hardened, it is to be employed

to cut a thread in a second steel plate, which will be employed as

a screw-plate; for that first formed must, in consequence of the

hammering to which it was subjected, present irregularities in the

hole, and can only be used to cut one or two taps cautiously. It is

useless for making screws or tapping brass. (See also =378.=)

=375.= _To Clear a Stopped Hole in a Screw-Plate._ Drill a hole through

the center of the piece of metal that fills up the hole, taking care to

maintain it central, and to employ a drill that is sufficiently small

to avoid all risk of contact with the screw threads. Pass a broach

through this hole and, after tightening it with a few gentle blows

with the hammer, turn it in such a direction that it tends to unscrew

the broken screw, which will in nearly every case, be removed without

difficulty by this means.

TAPS.

=376.= Screw-cutting comprises two distinct operations—the formation of

a spiral thread on the circumference of a cylindrical spindle, and of a

spiral groove within a cylindrical hole to receive this thread.

Taps are made either by means of a screw-plate or in the lathe; we

shall presently refer to this second method. Every watchmaker may be

supposed to have received, early in his career, instruction as to the

cutting of a tap with a screw-plate. Great caution is necessary in the

hardening, for if the tap is not true or the metal burnt it will cut

badly and be apt to break. Taps are cleaned after hardening with a

piece of wood in the lathe or between two hard pieces of pith covered

with oilstone dust, and either three or four cutting facets may be

made. It is important to avoid the production of a burr in making these

facets; a good plan is to make them while the metal is still soft, and

to pass the tap through the plate subsequently, as a sharp cutting edge

is thereby produced. The facets should be carefully smoothed, and the

use of coarse rouge is an advantage.

A tap with three facets gives the cleanest cut and leaves the most

space to receive the metal that is removed, but with four facets the

roundness of the hole is more certain to be maintained.

[Illustration: _Fig. 174._]

We have seen taps formed as represented at M, Fig. 174, so that the

object in which a thread is being cut is loose at the part _o_, when

the direction of movement of the tap is reversed. They are also at

times made semi-cylindrical, as at G, and work well in the lathe for

tapping brass, but we have not tried this form with steel.

=377.= =To Cut a Tap when of Considerable Length.= The following

precautions must be observed in order to ensure that a long screw shall

be both round and true.

The steel must be of very goad quality, and loose dies should be used

in preference to a screw-plate. It is a good practice to employ two

pairs of dies (or even more); one to rough out the screw, leaving the

thread somewhat larger than it will finally be, and the other to finish

after having trued it, and even sometimes lightly turned the surface in

places. Very little metal must be removed at a time, the dies should

have sharp cutting edges, and a rather large number of threads.

A screw can be made in the ordinary manner in a screw-plate rather

larger than is required, then reduced to the requisite diameter, and

finished with a plate in which the holes are of the form shown at F,

Fig. 173, or in a screw-cutting lathe; in either case, however, care

must be taken to avoid straining the metal in its passage through the

first plate, on account of the tendency which it then possesses to

become distorted in the hardening.

If a micrometer screw is required, that is, a screw of absolutely

uniform pitch, it is necessary to apply to makers of astronomical and

other similar instruments of precision.

[Illustration: _Fig. 175._]

=378.= =To Cut a Screw of any Desired Pitch and Diameter.= Let it be

required to cut a thread on the stem B, Fig. 175, of any pre-determined

pitch that already exists in a screw-plate. Turn down the portion _d_

to such a diameter that a screw can be cut on it in this hole, and fit

two runners to the lathe of the form shown at G and H. The end of H

is drilled and tapped so that _d_ turns freely in it, and a hole is

drilled in G to receive the stem B freely, but without sensible play,

and a fine notch is cut at _a_.

It will be obvious that if now the ferrule _r_ is caused to rotate,

while a fine saw or file is inserted in the notch _a_, a screw will be

formed on B of the same pitch as that on _d_, although there may at the

same time be a very considerable difference in their diameters. This

method may be adopted in place of that explained in article =374= for

obtaining a fine-threaded screw.

=379.= =Left-handed Screw Taps.= The manner in which these are made in

the screw-cutting lathe will be subsequently explained; in its absence

the watchmaker may adopt one of the following methods:

[Illustration: _Fig. 176._]

_First method._ If, when an internal screw has been cut with a

right-handed tap, B, Fig. 176, it be required to tap a second hole in

the reverse direction, the following plan may be resorted to:

File the original tap B on two opposite sides, so as to give it the

flattened shape shown at A in the same figure. Insert the end into the

hole to be tapped and turn the tap to the left with the application of

considerable pressure, so as to force the tap to bite. When the tap has

been passed in and withdrawn there will be found to be a left-handed

thread cut in the hole. For, if the tap is turned towards the right,

the thread _f_ passes into the groove already formed by the thread _a_;

but, if turned towards the left, _f_ will originate a groove into which

_b_ will pass, traveling in an inverse direction to that previously

given to it.

The finer the thread of the screw, the better is the chance of success,

and with a wide thread it is often necessary to recommence two or three

times. If a plate or pair of dies be cut in this manner and hardened,

they will serve to cut an even left-handed tap.

[Illustration: _Fig. 177._]

_Second method._ Attach a comb to one or two sides of a cylinder, as

indicated at F, Fig. 177. This can be used to cut a thread in the

piece of metal S, that is either right or left-handed according to the

direction of rotation of F, sufficient pressure being at the same time

applied to force it into the plate. The pitch of the thread will depend

on the amount of pressure applied. This plan is only a modification

of the one described above, and, as in that case, success can only be

guaranteed when a means is adopted for securing a definite relative

amount of motion in F around its axis and S vertically.

[Illustration: _Fig. 178._]

_Third method._ A tap of unhardened steel is filed into a triangular

form, C, Fig. 178, and twisted so as to bring the angles _b_, _f_,

towards _a_, _d_, etc.; we thus obtain a tap which will serve,

throughout a certain portion of its length, to cut a left-handed

thread, but the part that is not so adapted, at the extremities, will

require to be removed before hardening.

[Illustration: _Fig. 179._]

=380.= _To Make a Left-handed Tap by Means of a Right-handed Tap._ A

portion of the right-handed tap is filed off on three faces to the

section shown at _b_, Fig. 179, and firmly set in the die _d_ so as to

be held in the frame for screw-cutting dies. A second die, _f_ made of

brass and having a semi-cylindrical recess opposite _b_ is fitted to

the frame. The diameter of this semi-cylinder should be the same as

that of the rod on which a left-handed thread is to be cut. Now grip

this rod as shown at _a_ by means of the screw _g_, so that it is held

between the die _f_ and the block _b_, and rotate the frame or the rod

_a_ towards the left; a spiral groove will thus be cut by the thread on

_b_. It is sometimes an advantage to cut this thread lengthwise in the

manner indicated at _b′_.

[Illustration: _Fig. 180._]

This method enables us to cut a given thread on a rod of any given

diameter. From an examination of Figs. 179 and 180, it will be seen

that a simple comb of the form of C or D, carefully made by hand

and fixed in the place of _b_, can be employed to cut a right or

left-handed thread on any given rod; it is advisable, however, that the

teeth of the comb be inclined to the axis of the screw, like the thread

of an ordinary tap, as otherwise the operation becomes more difficult

and success less certain.

[Illustration: _Fig. 181._]

The method may be simplified by taking a brass plate, D, Fig. 181, of

sufficient thickness, and firmly setting in it the right-handed tap,

_v_, having only filed away two opposite faces before hardening. The

rod to be tapped is then introduced with considerable pressure into

the hole _j_, and, if rotated towards the left, it will receive a

left-handed thread of the same pitch. The notch shown at _b′_, Fig.

179, will facilitate the operation, as a cutting action will take the

place of compression.

=381.= M. Gontard has suggested a modification of this arrangement,

which consists in forming the die _f_, Fig. 179, so that the original

right-handed tap can be embedded in a hole previously tapped in it and

filed away on the side towards _b_ so as to expose a cutting edge; and

he points out that, by suitably inclining the frame with reference to

the axis of the rod to be tapped, the appliance can be used to cut

a double or even a triple-threaded screw, right or left-handed. He

further draws attention to the fact that in a screw formed in this

manner the sides of the thread are smooth and polished, a condition

which cannot be secured when either a plate or dies are used.

=382.= =To Increase the Diameter of a Tap.= It sometimes happens that

a screw will not penetrate to a sufficient depth, or fits too tightly

into its hole, owing to the tap employed being of a less diameter,

either in consequence of the hardening, polishing or wear, or through

having been formed in a different screw-plate. In such a case the

following expedient may be resorted to:

[Illustration: _Fig. 182._]

Make a fresh tap in soft steel and file away two opposite sides so

as to give it the section shown at A or B, Fig. 182: after measuring

the diameter at several points in its length, hammer gently on the

flattened sides. With a little care and by using a micrometer at

intervals for testing the alteration in diameter, it will be found that

the required increase can be obtained without much difficulty. The tap

is then hardened and polished, etc.; indeed, it is best to make a fresh

tap.

METHODS OF TAPPING HOLES.

=383.= It is needless to refer to the method of tapping by hand, as it

is well known to all practical men.

=384.= =Tapping in the Lathe.= The plate of a watch is gripped in the

dogs of a face-plate, the hole to be tapped being centered by means of

the pump-center, which is then withdrawn, and a tap held to the hole;

the face-plate is then caused to rotate either by the hand resting

on its circumference, a slight backward motion being given after each

advance, or the motion may be continuous and be given by the wheel. In

the latter case, however, the tap must have a good cutting edge and

only be held in the hand with the degree of force required to make it

cut, so that it may rotate without breaking in case the resistance

opposed becomes too great. The tap may be steadied on the T-rest.

=385.= =To Tap with a Mainspring Winder.= The ordinary mainspring

winder will, if the click work is removed, be found very convenient

for tapping holes, and indeed, for forming the external thread on

screws. Having removed the winding arbor, replace it by a tap carefully

centered; then introduce its coned end into the hole in the plate,

which must be pressed forward while the handle is turned, a short

backward motion being given to it at frequent intervals. When the tap

is engaged sufficiently in the hole it is merely necessary to maintain

the plate at right angles without applying pressure.

=386.= =To Tap with a Bow.= Instead of the mainspring winder, one of

the small drill-stocks to be driven by a bow, consisting of an arbor,

with a coned hole at one end and ferrule at the other, supported in a

frame that is clamped in the vise, may be used. They are to be obtained

at any tool-shop.

The bow being on the ferrule and the tap properly centered in the

arbor, the hole is held against the coned end and the bow worked with

an alternate forward and backward movement; but if the tap has a good

cutting edge and the bow is strong (of steel or cane), a hole may be

tapped with a single stroke of the bow. After a few trials the method

will be found very easy and certain.

A regular and rather slow motion should be given to the bow, which

should be long and strong. It is well to ascertain the number of

revolutions of the ferrule that correspond to a stroke of the bow, so

as to ensure that the tap is not introduced to a greater depth than is

required. If it is desired that the screw work easily in the hole, the

tap should be moved several times backwards and forwards.

=387.= The little turns here referred to, some of which are perforated

throughout their entire length and others only at one end, are very

cheap and will often be found useful; they can be adapted to receive

drills, broaches, taps, etc.

=388.= =To Tap in an Ordinary Lathe.= In factories it is a common

practice to tap the holes in plates, etc., and even to cut the threads

of screws in a lathe specially arranged for the purpose. The tools

adapted for such work are of two kinds: in some the tap enters to the

required depth, when it is immediately arrested, disconnected, and then

rotated in an opposite direction; in others, the tap advances to a

definite point, and is immediately withdrawn. As a rule, however, the

tap remains stationary and the object is caused to rotate.

=389.= =Beillard Lathe for Tapping Screws.= The axis F M, Fig. 183, is

perforated throughout its length. At F, the screw-plate G is dovetailed

into it. The inner end of the hole in this plate is slightly coned to

facilitate the insertion of the brass wire D, and it must be exactly in

the axis of F M. A guide B sliding on two rods _c_, _c_, is traversed

by the rod D which can be clamped in it by the screw _a_.

By pushing D against the screw-plate at the same time that the handle

N is rotated, a thread will be traced on it and it will emerge at _k_.

When B has advanced to the point _m_, the screw _a_ is released, B is

drawn back, and _a_ again clamped.

[Illustration: _Fig. 183._]

When a long screw, such as X _x_ has to be tapped, the screw-plate

is fixed at _m_, and the guide B is fastened on to the portion X. Of

course the hole in the screw-plate must always be abundantly provided

with oil.

If the screw-plate F is replaced by a plate perforated with a round

or square hole, a drill, broach or tap may be substituted for _k_,

being clamped by the screw _h_, and the tool is at once available for

drilling, broaching or tapping any given hole.

RAPID MODE OF MAKING A SCREW.

=390.= The methods ordinarily adopted by watchmakers are too well

known to need description; we will therefore at once proceed to give a

special plan recommended by M. Vissiere.

An eccentric poppet-head with boring-plate, Fig. 185, is fitted to the

bed of the lathe, the eccentricity being such that the axis of the

centers is at the point _a_ on the circumference of the circle _a y_.

The conical hole, having a center at _a_, is cut away towards the rim

of the plate to the degree indicated in the figure, and its center is

so placed that the vertical line _f_ and the radius _d_ are inclined at

120°. The position of the T-rest is shown at _s_, and by bringing it

into actual contact with the disc the steadiness of both is increased.

The fixed headstock of the lathe is provided with a runner of the form

B, Fig. 184, terminating in a point _m_ at one end and a hollow cone or

funnel _n_ at the other end.

Having filed the ends of a rod T, of any required diameter, square

and fitted a ferrule, support it between the two cones, _a_ of the

boring-plate and _n_ of the runner. Near the end _a_ cut a hollow _r_

sufficiently small to allow the stem to pass through the notch in the

hole _a_, Fig. 185. After passing it through, the rod will be supported

as shown at H, Fig. 184, so that the rim _e i_ rests against the cone.

[Illustration: _Fig. 184._]

[Illustration: _Fig. 185._]

Further explanation is hardly necessary; after removing the portion _c

g_ with a graver, turn down to a point _p_. When making a screw, turn

out a second hollow _o o′_; it then only remains to turn off the disc

at the extremity, and the screw will be roughed out of the form _c p g

v_.

If it is preferred to work with a point at the left-hand end of B,

remove the rod after the point _v_ has been turned, replace _m_ B _n_

by a common runner, reverse B, and recommence the operation.

It would be difficult to devise a method for roughing out a screw

and making a point that would be more expeditious than the one here

described.

SCREW-HEAD TOOLS.

=391.= These are of various kinds: some work by hand and others by a

bow. The jaws are brought together sometimes by a sliding ring, and at

others by a milled head placed between them and rigidly attached to a

pin tapped with right and left-handed threads that engage in the jaws.

But neither of these plans is good; the screws are not held firmly and

they are rarely well centered; owing to the slight displacements of the

jaws.

[Illustration: _Fig. 186._]

A better plan is to arrange, either in the lathe or in the jaws of the

screw-head tool (when driven by a bow), a series of chucks of the form

shown at T, Fig. 186. They are easily made and tapped, the hole _i_

serving to remove the metal from the inner end of the hole that has

to be tapped; such chucks occupy very little space, and, if numbered

to correspond with the size of screw, any chuck required can be found

without trouble. If the hole becomes too large owing to frequent use,

a larger size of tap can be passed through the hole and its number

changed.

=392.= A set of such chucks is almost indispensable at the present day

to the watchmaker who wishes to repair watches well; for he rarely

makes his own screws, as they are to be obtained well made and very

cheap at the material dealers, whereby a great saving of time is

effected. But their heads are seldom of the proper size to fit the

original sinks, and by being provided with such a series of chucks the

watchmaker can at once overcome this difficulty, as he can turn the

heads down with a graver.

=393.= R, Fig. 187, is an arbor for a screw-head tool that is driven by

a bow, and is adapted to receive such chucks, or it can be used in an

ordinary lathe, _d_ being supported on a pointed center, and _g_ in a

boring-plate, Fig. 188, or in a cone-plate center.

=394.= In this form of screw-head tool the portion A is sometimes

perfectly cylindrical, so that the piece V can slide on to it, being

clamped by the screw _b_.

This tube V is cut away through about half its length with a notch, as

indicated in the figure; bent pieces of hardened steel _c_ and _n_ are

screwed to either side of the notch. Screws, _h_ and _f_, provided with

lock-nuts, determine the distance between these plates, and when V is

in position on A the ends of _c_, _n_, will rest on the screw-head,

leaving just sufficient space between them for inserting the file that

cuts the slit.

[Illustration: _Fig. 187._]

Hard steel caps of the form shown at M may also be fitted to A, a notch

being cut in them to receive the screw _b_. These will be found useful

as guides for filing or polishing screw-heads, or the ends of arbors

flat, reducing the heads of several screws to the same height, etc.

[Illustration: _Fig. 188._]

=395.= The tool for forming the U-spaces in a cylinder escape-wheel can

be easily be converted into a screw-head tool with laps. A glance at

Fig. 189 will at once make this evident. A number of chucks are adapted

to the arbor A, and in the tube _c c_ either a T-rest or a spindle

carrying a lap is fixed.

It will also serve as a tool for drilling; a drill-chuck with drill,

_f_, being adapted to A, and the object to be perforated at _b_

resting against a plate that projects at right angles from a slide _d

d_, which may be advanced by a screw _g_.

=396.= The modern watchmaker has so little call to cut screws that it

does not pay him to purchase a screw-cutting lathe; for a very small

sum he can have screws of any thread or diameter cut by those who make

a specialty of such work, always provided that he cannot find what is

wanted in the material stores. The same thing also applies to fuzees.

[Illustration: _Fig. 189._]

TOOLS FOR CUTTING AND ROUNDING-UP THE TEETH OF WHEELS.

WHEEL-CUTTING ENGINE.

=397.= The machine for dividing the circumference of a wheel, termed

the wheel-cutting engine, and one form of which is shown in Fig. 190,

is well known to nearly all workmen. The wheel is fixed to a chuck at B

by wax or screws, or by the pressure of a hollow cone or “sugar loaf”

of steel, to the apex of which pressure is applied by the arm D, or in

other ways. The wheel may be centered either by a pump-center within

the chuck or by an appliance such as is shown in Fig. 191, except that

the arm _b_ is curved and its index much longer. This little addition

may be fixed to the frame of the engine in any convenient position.

[Illustration: _Fig. 190._]

The chuck B that carries the wheel is rigidly connected with a large

brass plate A A, on which are concentric circles of divisions, and the

whole can be maintained stationary by setting the point of the index C

C in any desired hole on the division-plate. The cutter is carried on

an arbor (shown separate at L) between horizontal bearings in the frame

J, and is caused to revolve by means of the pulley K. The several parts

lettered E, F, G, H, are for bringing the cutter against the wheel and

modifying the direction in which it moves, so that the machine can

cut straight or inclined teeth, bevel or crown wheels, etc. It should

be added that the engine here represented is more complex than those

ordinarily used for cutting watch wheels, although the principle on

which it acts is the same.

The teeth may be cut by circular cutters of the nature of files, by a

small straight cutter, similar to those used in a slide-rest projecting

from a rotating axis, or by several such cutters mounted on a disc

which is caused to rotate. For the sake of distinction it will be well

to refer to the first of these as _file_ or _mill cutters_, while the

second and third may be termed respectively _single_ and _multiple

blade_ or _composite cutters_.

[Illustration: _Fig. 191._]

Watchmakers rarely possess a sufficiently large assortment of

file-cutters for making all the various forms of teeth that are met

with in horology; but this deficiency can be supplied by making them

for themselves to any required pattern in the manner subsequently

described.

=398.= _Observations._ The wheel-cutting engine in which the plate

is caused to rotate by means of a tangent screw is usually the most

accurate. If the pitch of the screw is fine it will give all the

subdivisions of a circle that are required for ordinary work, but it is

essential that a good form of counter be attached to the screw, and a

certain amount of calculation is always needful.

The engine that has a division-plate with conical holes arranged

concentrically over its surface is simpler and better adapted for rapid

work. The larger this plate, the greater is its chance of being correct

and, at the same time, it affords room for a larger number of divisions.

It is preferable that the cutter frame rise and fall in a vertical

dovetail, for when the arbor is carried in an H shaped arm pivoted on

two screws, the teeth are always slightly dished. The entire apparatus

should be somewhat heavily constructed and supported on a solid bed; so

as to prevent the vibration of the cutter-arbor from being distributed

over the entire machine.

The highest numbers on the plate should be used whenever it is

possible, so as to diminish the error due to irregularities in the

sub-division. For example, in cutting a wheel of 30 teeth, use the 90

or 120 circles, taking every third or fourth hole.

These remarks will probably be sufficient to enable any watchmaker who

possesses a wheel-cutting engine to employ it with success; we will,

however, add the description of a few appliances or processes that have

a bearing on this question.

=399.= =To Divide a Wheel so that it has one Tooth more or less than

any given number on the Division-plate.= It is to be observed that

neither this nor the following method is mathematically exact, but

if it is practiced with care and the division-plate is of sufficient

diameter, the error may as a rule be neglected.

[Illustration: _Fig. 192._]

Let P, Fig. 192, be a division plate that has a 30 circle, but not one

of 29 or 31 divisions. Divide the circumference of a disc _d_, seen on

edge, into a large number of parts in the engine, 360 for example, and

fix it to the end of the index, at the same time attaching a finger,

_i_, to the support _s_. Now advance the screw of the index through a

distance corresponding to the angle _l_ P _k_ included between the two

successive points of the 30-division circle. To measure this distance

a pointer should be previously fixed to the frame to correspond with

the middle point of a hole in the circle under consideration, and the

motion should be arrested when it coincides with the next succeeding

hole. Assume that this amount of displacement has required three

complete turns of the screw; 1,080 divisions on the disc have thus

passed under the finger _i_. Dividing this number by 31, we obtain

34.83.

After observing the division on _d_ that coincides with the pointer

_i_, cut the first space of the wheel; then cause 34.83 divisions to

pass under _i_, in such a direction that the plate is drawn with the

arrow, and transfer the index to the next hole of the circle, rotating

this time opposite to the arrow; the second space can now be cut, and

so on.

With a view to diminish errors arising from the omission of fractions,

since 31 does not divide evenly into 360, a number of multiples of the

number 34.83 should be determined. Thus 4 times 34.83 is 139.32, so

that, when the fourth space is cut, the pointer _i_ must be at this

number of divisions from its initial position.

The index should be so situated that, when half the arc _l k_ has been

traversed, as explained above, _s a_ is at right angles to the radius

P _r_ of the division-plate. If it is desired to move _d_ in a reverse

direction, it must be moved backwards to a considerable distance and

then forward up to the required point so as to avoid error due to

backlash. The screw of the index should fit the support s firmly and

without any shake.

=400.= =To Cut a Wheel with any Given Number of Teeth.= When the given

number does not occur on the division plate, proceed as follows: Take a

strip of metal, for example a pliant piece of soft steel, and cut in it

a series of equal and equidistant notches as shown at B, Fig. 193. Cut

the band to such a length that it has the same number of pairs of teeth

and spaces as the wheel is required to have teeth. Now turn a lead disc

of a diameter that the strip of metal will exactly enclose; fix this

strip round the circumference with pins, screws, or in any convenient

manner, as is shown at C. We thus obtain a temporary division plate

which can replace the permanent one or be attached to its upper or

under surface, and, when an index has been adapted to it, the wheel can

be divided into the requisite number of parts.

[Illustration: _Fig. 193._]

When employing an engine the division plate of which is worked by a

tangent screw, the above affords an easy means of making the divided

head for the screw with any desired number of divisions.

=401.= With a view to insure accuracy, it is advisable to employ a disc

of large diameter as the errors of division are thereby rendered less

important and the metallic blade can be made to lie closer to the rim.

The blade is subdivided by a saw to which a guide is attached as

indicated at H, Fig. 193, or the saw can with advantage be replaced

by a file that only cuts on its edge and not on either face, or by a

pair of mills or revolving cutters united together as shown at S. The

following plan, however, appears to be more expeditious and to involve

less trouble to ensure accuracy.

[Illustration: _Fig. 194._]

A hole _a_, Fig. 194 is drilled in a metallic band by means of

a semi-cylindrical drill fixed in the chuck of a lathe or in a

wheel-cutting engine, etc. It will be convenient if the drill can be

set vertical. Beneath it is a brass bed-plate in which are fixed two

pins equal in diameter to the hole _a_; this hole having been placed

over one pin _b_, the band is held firmly against the other, while the

second hole is drilled. This is then transferred to the pin, and so on.

In the absence of a suitable tool, a well made measure can be employed

for marking a series of points with the aid of an eyeglass; the holes

are then drilled with the bow or in any other manner.

=402.= =To Cut a Wheel, Ratchet or Pinion on an Ordinary Lathe.= When

only a moderate degree of accuracy is required, the ordinary lathe can

be adapted for cutting the teeth of minute wheels, ratchets, pinions,

etc., by making the following appliance:

The piece B, Fig. 195, provided with a stud at _p_, slides on two

horizontal and parallel cylindrical rods fixed to the slide C, or it

may move in a dovetail. The cannon _d_, carrying a ferrule _k_ and a

file-cutter _f_, rotates on the foot at _p_ without shake; and the cord

of a wheel or bow passes round _k_.

[Illustration: _Fig. 195._]

R, the wheel to be cut, is supported between the runners, the divided

plate V, which may even be an old wheel with the required number of

teeth, being fixed to the axis of R. V is held stationary during the

operation of cutting, by the index _l_. The mode of action hardly

requires explanation: while _f_ is rotating, advance B until it is

arrested by the stop _t_; then draw B back, advance _l_ to the next

division on the plate, and so on.

=403.= We have said enough on this subject to enable any watchmaker

to make such a tool, modifying it or completing it according to his

requirements. We would only remark that: (1) If a cannon of the form

_d_ is used, the stud should be diminished in diameter at its middle

part for about three-quarters of its length, so that friction occurs

only at extremities; and (2) if a wheel is used to rotate _k_, there

should be an idle pulley at _m_ supported on a fixed arm independent of

B, either attached to the lathe-bed or bench, or fixed in the vise, so

that the ferrule _k_ can move backwards or forwards without altering

the tension of the cord, in the manner indicated at Y.

=404.= =Wheel-cutting Arbor-chucks.= These appliances are specially

useful in making wheels that are required to be rigorously true, such,

for example, as escape wheels. The form is represented in Fig. 196.

It is simply the arbor of an ordinary lathe, formed in two pieces, _b

a_ and _b c_, the body _b d_ being very accurately fitted into the

conical hole in the plate of the wheel-cutting engine. If now a wheel

is fixed with wax on the extremity _z_ and turned in the lathe to the

required form, it is only necessary to unscrew _b c_ and introduce _b

d_ into the socket of the wheel-cutting engine; then having cut the

teeth, the piece _b c_ is replaced, and the whole is set in the lathe,

if required to test its truth, without the wheel having been displaced

from the chuck.

[Illustration: _Fig. 196._]

It will, of course, be evident that the two parts must be accurately

fitted together; the tapped hole and the screw must be true with the

axis. M. Millot, with whom we have seen this form of arbor in use, has

not been able to detect any eccentricity, although he often employs

them.

=405.= They might be formed in one piece, as _a d b_, with a point at

_p_. A boxwood ferrule is then fitted onto the portion _b d_, where it

is clamped by two screws, and these can be released when it is desired

to insert the chuck into the wheel-cutting engine. The points of these

screws should be received in recesses in order to avoid the production

of any roughness on the surface of _b d_.

Wheel-cutting engines have been made to receive these arbor-chucks

without removing the pulley. The point _c_ is placed in a hole and the

upper end is enclosed in a collar, which is tightened by means of a

screw.

The arbor used by M. Millot had a lantern chuck, and this is very

convenient in making objects that require to be measured during the

progress of the work.

=406.= =Modification of the Ordinary Arrangement for Holding the Wheel

While Cutting.= In the wheel-cutting engine as usually met with, the

wheel (when not mounted on an axis) is held against the chuck by a

hollow steel cone, on which presses an arm that slides on a vertical

pillar and can be clamped in any position. The hole at the end of this

arm does not always, therefore, correspond with the point of the cone,

and, as a consequence, the wheel often gets displaced during cutting.

This inconvenience can be avoided by adopting the following device,

which we have seen in use with several watchmakers.

[Illustration: _Fig. 197._]

The pillar with its sliding arm is replaced by an iron or steel piece

of the form G, Fig. 197. The point _a_ is received by the central

hole at the lower end of the division-plate axis, while the screw

_b_ presses on the point of the cone, clamping it firmly. Further

explanation seems unnecessary; we would only add that the piece G must

be made strong and perfectly rigid.

CUTTERS FOR FORMING THE TEETH OF BRASS WHEELS.

=407.= For making the teeth of the wheels of a train, a special form

of cutter, set to revolve on an axis, is employed, and it may be

constructed on either of three distinct systems.

[Illustration: _Fig. 198._]

[Illustration: _Fig. 199._]

(1) A single cutter mounted on an arbor, as at A, B, Figs. 198 and 199;

this may be termed a _single cutter_.

(2) A circular cutter, formed of a series of such single cutters, which

will be termed a _multiple blade_ or _composite cutter_. Two specimens

are shown at F, J, Fig. 200.

[Illustration: _Fig. 200._]

(3) The pinion, or steel wheel cutter or mill, formed of a single piece

of metal, as seen in Figs. 201, 202 and 203. These may be described as

_mill_ or _file cutters_.

=408.= =To Make a Single Cutter.= The form shown at A, Fig. 198, is

roughed out to as nearly as possible the required form in good steel.

Some makers, possessed of exceptional skill, make them entirely by

hand, and they make very beautiful teeth by this means; but as a rule

watchmakers cannot look for such success, so that it is better to

complete the formation of the cutter in a specially arranged tool.

[Illustration: _Fig. 201._]

[Illustration: _Fig. 202._]

The two sides may be made in the wheel-cutting engine, with the same

mill cutter, which is inclined when used to undercut the acting edge;

but this operation is not as easy as it appears at first sight, and the

watchmaker will find it to his advantage to make the following device:

[Illustration: _Fig. 203._]

A spindle, _b d_, Fig. 204, supported between the runners, _t_, _v_,

serves as an axis for the arm _f g h_, which is bent at _g_ so as to

afford a support to a conical cutter _a_, driven on the ferrule _c_.

The descent of this arm is limited by an adjustable stop, fixed to the

bed of the turns.

Having removed the T-rest, replace it by the rod N, to which the cutter

is clamped by a screw _k_, after being roughed out so as to reduce the

work required of the cutter.

Place N so that the conical cutter occupies the position indicated at

_z_, and, if a slight pressure be applied at _h_ while _a_ is caused

to revolve, both the straight and curved portion of the side will be

formed, and the side will, at the same time, be bevelled to an angle

corresponding with that of the cone. The curved portion of the side

will be more or less undercut, according as the arm _h_ is depressed

below the horizontal plane passing through the axis of the lathe. The

opposite side is formed by inverting the piece _f g h_.

[Illustration: _Fig. 204._]

In smoothing or polishing it is only requisite to replace the cutter by

a smooth conical roller, and to work as before.

=409.= The cutter is sometimes fixed in the arbor as shown in Fig. 198.

The arbor itself is thick and perforated with a round hole in which the

tail of the cutter accurately fits, a slight pressure applied by the

screw _m_ being sufficient to make it steady.

For cutting the escape-wheels of clocks the arbor should have a

velocity of about 200 turns a second.

M. Peupin, a skilful watchmaker who adopts the practice here given,

having observed that with a sharp cutting edge he did not obtain a

sufficiently smooth surface, succeeded in obviating the difficulty by

drawing a polisher with rouge along the cutting edge, maintaining it at

right angles to the plane of the cutter. This operation, if carefully

executed, will serve to remove the feather-edge, to make the edge

even and yet not dull, and to secure a highly polished cut surface.

The sides of the teeth will present a proportionately better surface,

according as the portion _c a_ (M, Fig. 198,) approximates towards the

dotted line _c d_.

His escape-wheel teeth are cut in successive stages. The last stroke of

the cutter is given by advancing it against the side of the wheel, so

that the cutter axis remains in the plane of the wheel.

=410.= =Triangular Cutters.= When a cylindrical or conical mill is

not available for finishing and sloping the sides of a cutter, it may

be replaced by a triangular cutter (T or C, Fig. 205,) and when the

application of much force is required there may be a pointed bearing;

but this is seldom necessary.

[Illustration: _Fig. 205._]

If carefully hardened and set, such a cutter gives a clean cut; of

course it will not act for as long a period as the conical form above

described, but this is of comparatively little importance, since the

blank cutters are always roughed out previously to nearly the requisite

shape.

=411.= =To Make Several Cutters at Once.= By adopting the following

method, it is possible to make several such cutters in one operation.

Turn a steel disc of the form of an ordinary mill cutter, as shown at

_l p_, Fig. 200. To finish it, giving the same curvature to the two

sides, take a piece of steel, C, and shape the corner _r_ to exactly

correspond with the side of the point or ogive of a tooth, bevelling

it so as to give a cutting edge at the upper surface; then harden and

smooth it with care. Having fixed it in position in the tool that

carries the arbor _a_ and the roughed out disc (whether this be the

lathe, wheel or pinion-cutting engine, or a special device) in the

required position, one side of the disc may be finished. The arbor _a_

is then reversed and the other side finished in the same manner, so

that both sides have the same curvature in opposite directions.

Of course the tool C may be advanced against _l p_, either sideways

from _r_ towards _l_, or radially in the direction _l p_, as is most

convenient. Or the tool might remain fixed and the disc advance against

it radially or laterally.

The traverse slide in a lathe is usually provided with a stop; it

would then be very easy to form one side of the disc in such a tool,

afterwards reversing the arbor and forming the other side.

If a very good cutting edge is desired, the sides should be smoothed

and, when the disc is completed, it may be divided into pieces

similar to B, Fig. 199, each of which will serve as a cutter. It will

be noticed that the acting edge is not undercut behind; it is thus

necessary to slope the cutter a little as shown at B, as otherwise the

rim will choke in the spaces of the wheel, straining it without cutting.

=412.= =Composite Cutter Formed of a Succession Of Single Cutters.= By

mounting a series of identical single cutters round the circumference

of a disc, a circular cutter can be formed in the manner indicated

in Fig. 206. The upper portion represents the arrangement of the

pieces while they are being turned, and the lower portion shows

their positions when the cutter is ready to be used. M. A. Croutte,

to whom we are indebted for several of the details here given, was

much surprised that this form of cutter is not better known, since it

possesses certain special advantages; we will summarize his remarks on

the subject.

[Illustration: _Fig. 206._]

The separate cutters _b_, _g_, etc., Fig. 206, are not undercut from

the acting edge backward; they are merely reversed, so that this

acting edge is towards the front, in other words it lies along the

radius. These separate pieces possess a special advantage in that they

can be used until the steel is quite worn out by the setting; in this

respect differing from the undercut cutters, for they are not altered

either in form or thickness by setting.

As a set-off against this important advantage, they are characterized

by the inconvenience of requiring that the two sides of the blade be

exactly in a plane at right angles to the axis, and that the slide

carrying the cutter-arbor shall move in a direction parallel to this

plane. And even when this double condition is satisfied, there will

be friction of the two sides above the dotted line _i j_, Fig. 199,

against the sides of the teeth; and if the above named conditions are

not satisfied, the cutter, being presented edgeways, will be choked

with brass, and the results will be unsatisfactory.

=413.= In order to ascertain whether such a fault exists, it is only

necessary to notice whether the cutter becomes brass-colored on one

side towards the point, and on the other more inwards, and the sides of

the teeth exhibit striæ or scores in opposite directions, as indicated

at E, Fig. 207. The white strip, 1, 1, corresponds to the bottom of a

space between two teeth; 2, 2, and 3, 3, the two sides of this space,

spread out like an open book.

[Illustration: _Fig. 207._]

By examining the marks with care, and noticing the direction in which

they are inclined, it will be possible to ascertain both whether the

separate cutters are out of place, and in which direction the arbor

should be moved in order to correct any error.

We must, then, repeat that all the cutters must satisfy this condition,

because if only one is wrong it will produce the scores here referred

to.

The necessity of these precautions in the use of such a composite

cutter, and the fact that the friction of the portion above the line _i

j_, Fig. 199, renders it difficult to obtain a polished cut (which is

essential for such delicate depths as those of watches), have doubtless

prevented its use becoming general. For work that is somewhat larger

or rough, it will be found to give satisfactory results and will last

longer than a single cutter. A lubricant, such as glycerine or oil,

should be applied to it.

=414.= =Composite Cutters with the Cutting Edges Undercut.= An old

Paris clockmaker, Brisson, used a cutter of the form F, Fig. 200, for

the teeth of his wheels. He undercut the two sides of the blades by

means of a small special tool. Strictly speaking, the operation can be

performed by hand.

In order to ensure that the curves that form the ogives of teeth are

alike on the two sides of a cutter, he made a series of templates or

standards of the form C, Fig. 206, in which were two holes, C and _c_,

of equal diameter. The upper one, which might be funnel-shaped so as to

give a cutting edge, was half cut away, and, after being hardened and

set, could be used to give a final stroke to the circumference of two

discs of equal diameter. These two discs, or one cut through a diameter

would suffice, having been brought by a file to the form H, and joined

as shown at _r s_, can be mounted eccentrically so as to present a

cutting edge to the roughed out cutter A; the two sides can thus be

made even. The disc may then be finished by cutting away the metal so

as to give the form shown at F, Fig. 200.

By the aid of the standards he could easily reproduce the same forms of

teeth when required.

Fig. 200 comprises, at J, a cutter for the teeth of watch wheels of

the form employed successfully by M. A. Phillippe. The figure will

explain itself.

We have known a Geneva wheel cutter who employed these composite

cutters with advantage in making duplex wheels. The principal

difficulty he experienced arose from the distortion of the metal in

hardening, because the acting portion naturally lengthened a little.

This form of composite cutter certainly demands careful workmanship,

but, if the construction, hardening and polishing are good, it will

produce fine work and will last a long time.

=415.= =General Observations on Cutting the Teeth of Brass Wheels with

a Single or Compound Cutter.= High-class English watches, the movements

for which are made at Prescot, in Lancashire, have the wheel teeth made

by a composite cutter after the wheels are riveted to their pinions. We

have remarked that these watches make less noise when running down than

those in which the teeth have been formed with a mill or continuous

action cutter.

Success in forming teeth with cutters depends mainly on the securing of

a good form as regards the cutting edge, and on its being maintained

in good condition; on the steadiness of the entire machine, so as to

avoid vibration; on the weight of the wheel, and on the velocity of

the cutter being sufficient. A cutter ought never to assume a brassy

color except when it requires setting; if it does so, and this is not

the case, it proves that the metal is being strained or scraped with

friction. The velocity must be very considerable; greater with a single

cutter than with one that is composite. The velocity is limited by that

point at which the heat generated would cause the oil to evaporate,

soften the cutter, distort, and sometimes even displace, the wheel

operated on. The engagement of the cutter with the metal must be very

slight, and should never be increased suddenly.

Attempts have been made to enclose the arbor bearings in horn, but it

is liable to be distorted by the heat.

Before dividing the disc into cutters it is essential that the two

edges be carefully smoothed, and this without their being distorted.

This can easily be done in an old depthing tool, using an arrangement

like that shown in Fig. 208. The lap must be of hard wood, and its

right-hand corner rounded off so as to resemble the side of a tooth;

it is set to engage with one side of the cutter. We say the right-hand

corner, because a lateral pressure can then be applied. It is important

that the surface as left by the graver be clean cut, because if the

smoothing is too much prolonged, it will deform the cutter.

[Illustration: _Fig. 208._]

=416.= In some factories it is usual to use discs about 2½ inches in

diameter, for cutting the teeth of brass wheels in timepieces. The

single cutters are arranged round the circumference as follows: One

forms a space between two teeth; the one immediately preceding forms

the right-hand side of the ogive, and that which follows forms the

left-hand side. By adopting such an arrangement of separate cutters, if

their side that lies against the disc is slightly inclined backwards it

is no longer necessary to bevel off the cutting edge.

MILL CUTTERS FOR STEEL.

=417.= =Pinions, Keyless Wheels, Etc.= The cutters that last for the

longest period when used for cutting steel are those formed like a

file; but a watchmaker is not always in a position to make them

himself; we will, therefore, here only speak of those he can make,

the description of the first few being taken from a work by M. A.

Phillippe, of Geneva, _Les montres sans clefs_ (keyless watches).

=418.= =Cutter for Forming the Inclined Teeth of Winding Pinions.=

Fig. 201 shows at S a section along the axis of such a cutter, and at

P a side view. When it is believed to be of the required form, rest

a piece of lead on the T-rest of the lathe and press it against the

rotating disc. The impression made in the lead will afford a means of

ascertaining both whether the form is correct, and whether the surfaces

are smooth enough. This last point is important.

The cutting edges are formed by merely making a number of notches

around the circumference with a tool for cutting ratchet teeth. Then

advance this ratchet cutter so that it may engage with the convex edge

of the cutter operated upon, and against the back of the teeth of this

cutter; the ratchet cutter is then in a position to form a second face,

_o i_, by which the teeth of the cutter are undercut at the back, but

in such a manner that a small flat surface _o a_ is left in order to

retain the form. When a cutter made in this way will no longer bite, it

may be set by passing a hard slip of whetstone over the faces of the

teeth.

The ratchet cutter employed for making this cutter should never be

pressed against it heavily.

=419.= =Cutter for Ordinary Wheel Teeth.= We will now pass to the

consideration of cutters for forming teeth of the usual shape, of

intermediate steel wheels, set-hands wheels, pinions, etc. They may be

made as follows:

The rim is indented with small fine ratchet teeth, _b d_, Fig. 202. Any

burr produced on the sides is then carefully removed, and the cutter is

placed in the wheel-cutting engine, and notches, _c_, _c′_, _c′′_,

_c′′′_, etc., are formed on either side with a flat square-edged

cutter of such a thickness that the circumference is about equally

divided into hollows and prominences. It is important to note that the

right side of the teeth must be but slightly roughed, not more than

is required in order to raise a slight burr, all that is necessary to

form the cutting edge of this portion of the disc. In roughing these

sides, at least one out of every two of the small ratchet teeth on the

circumference should be left untouched, so as to ensure the required

thickness being maintained.

The cutter shown in section and elevation at S and P, Fig. 201, might

be cut on the side _n_ in the manner here explained, and the convex

portion _k_ might be indented with a fine ratchet-toothed cutter,

carried in the hinged cutter-frame of the wheel-cutting engine. The

degree of penetration may be determined by fixing an ivory disc against

the cutter and concentric with it, the two differing in diameter by

the depth the cuts are to be made. The teeth will be rather too square

towards the circumference, but their form can be carefully corrected

by hand. It is obvious that the very greatest caution is necessary in

hardening cutters.

=420.= =Rose-Cutters or Forming Pinion Cutters.= As the edges of

pinion cutters are rounded, they can be made in the manner suggested

by Thevenin. Supporting the roughed out cutter in the cutter-frame of

a wheel-cutting engine, he fitted in the axis of the division-plate

a kind of rose-cutter, N, Fig. 205. Its extremity, _n_, instead of

being flat, is hollowed out as indicated by the dotted line, and,

by presenting the cutting edge thus obtained endwise to the grooved

edge of the cutter, the correct form can be given to it. With a

mushroom-headed piece of steel and oilstone dust, the cutting edge of

the rose-cutter can be made more or less acute by modifying the angle

of this steel lap.

=421.= =Other Forms of Pinion Cutter.= When a cutter is merely required

for a special piece of work, and not for continuous use, it will often

be sufficient to make it as shown at A, Fig. 203; this is made by

grooving the disc (_c_), or forming its edges as at _d_, after which

a series of teeth are cut on the periphery with a revolving cutter,

taking care to leave no more burr on one side than on the other. Then

pass a smooth worn file (or a worn flat cutter) over the faces of the

teeth, applying oil at the same time, so as to produce a slight burr

on the edges; if the file is not allowed to bite too much and is well

managed, these minute ridges will be uniform. After hardening, the

cutter is ready for use.

If the faces were smoothed without subsequently applying the file, the

cutter would not bite; for its action depends on the slight projection

of metal that corresponds to the file-cuts. The cutter is nothing more

than a circular file, with two cuts per tooth. If the corners are

turned over evenly by means of a very hard burnisher the same effect

will be produced; but this operation is delicate, as the amount of

metal turned over must be the same in every case.

When a cutter does not bite, it must be softened and restored to its

initial condition.

=422.= Or the following method may be adopted when it is required to

make a cutter for a special purpose.

Proceed at first in the manner just described, but the periphery is

divided into a greater number of teeth with a flat cutter, and to a

rather greater depth, as at E, Fig. 203. Bend backward each tooth to

a distance equal to about half a space by any convenient method; for

example, by a lever resting at the bottom of each space and pressing

against the corner of the tooth, etc. Before bending the first tooth

introduce a piece of brass into the space behind it, of a thickness

equal to about half this space, so as to avoid bending too far; for

succeeding teeth the thickness must be about equal to a space; thus E

will become E′. An inspection of Fig. 203 will suffice to make the

operation evident; it amounts to bending back a series of separate

cutters. The disc is then hardened, and the faces of the teeth are

smoothed when they do not cut well; or merely smooth those that are the

first to become dull.

It is important to employ soft steel that has previously been well

annealed.

=423.= =Cutter for Making Square Spaces.= The teeth of such a cutter

can be easily formed with a file, as shown at L, Fig. 209, the edge of

the cutter, _f_, being passed backwards and forwards in the direction

of the arrows, applying considerable pressure and at the same time

slowly rolling _f_ around. Or the cutter may be set up on a short

arbor between the centers of the lathe; then pass the file backwards

and forwards across the edge until the cuts are formed, slowly

advancing the file in the meanwhile, so as to form the cuts around the

circumference without once raising the file. The cutter must then, of

course, be hardened.

[Illustration: _Fig. 209._]

=424.= =Forming Cutters with a Milling Tool.= The roughing of a

round-edged, or even of a square cutter, can also be effected with

the aid of a milling or “nurling” tool, proceeding in the same manner

as when milling the heads of screws, etc. The tool must be in good

condition, well provided with oil, and applied with considerable

pressure against very soft steel.

If necessary, the workman can make the mill for himself; it is shown at

M, Fig. 210. F shows the method of applying it to the cutter, and by

partly turning the mill (of course carried in a strong holder) around

its point of contact with the cutter, as indicated by the dotted lines,

the rim of F will be evenly roughed all around.

[Illustration: _Fig. 210._]

With good steel fairly satisfactory results are obtained in this

manner, but it is needless to observe that such cutters never bite as

well as those made in the usual manner.

=425.= =General Observations.= When cutters are used with steel they

must be driven at a less velocity than when cutting brass, and, as M.

A. Phillippe has observed, it is best to make the cutters for steel

of small diameter (about half an inch). They are more easily made and

are less distorted in the hardening. The velocity should diminish as

the diameter increases; for too great a velocity, especially when the

diameter is great, will dull the cutter and soften it, owing to the

heat produced.

Cutters must be turned very true: it is advisable to give them a last

stroke with the graver after they are fitted to the cutter-arbor that

will subsequently carry them.

When operating on steel it is best that the cutter frame of the

wheel-cutting engine be advanced by a screw so as to give it a slow

and easy motion; the results obtained are more satisfactory than when

it is advanced by hand or with a lever.

The following practice is not uncommon in factories when it is

desired to reproduce the exact form of a cutter. A notch is made

with the cutter in the edge of a piece of steel, X, Fig. 211, or a

series of notches _o o′_, etc., can be made by several cutters in the

circumference of a disc Z (same figure). After being hardened and

sharpened at the cutting edge, this disc is fixed at the center of

the division-plate of a wheel-cutting engine, and can then be used to

complete the grooving of any cutter that is set in position on the

cutter-arbor before hardening. The positions opposite to which the

notches were cut should be marked on the chuck, so that they may always

be set-square to the cutter.

[Illustration: _Fig. 211._]

=426.= Besides the forms of cutter above described for operating on

steel, we may mention that circular cutters may be used in which

all the notches around the circumference have been polished, thus

removing the burr, and preventing them from acting in the manner of a

file. But while, with the former kind, a somewhat rapid rotation is

necessary (although not so rapid as when cutting brass), with this

latter class the movement must be comparatively slow, and produced by

means of a hand-wheel; otherwise they will not cut, since the action

depends rather on the application of pressure, and resembles that of

a slide-rest cutter. The distance apart and width of the teeth of the

cutter, as well as their inclination, are of importance; if too far

apart they occasion a waste of time; if too large the machine will act

in a jerky manner, and when too narrow, an excessive pressure will be

needed in order to make the cutter bite the steel, which, it is to be

observed, must always be thoroughly annealed. The edge must be well

supplied with oil or soapy water when in action.

It is generally found best to advance the cutter against the edge of

the steel rather than across it.

TOOL FOR MAKING CUTTERS.

[Illustration: _Fig. 212._]

=427.= The instruments usually employed for making cutters for the

teeth of wheels and pinions are complicated and expensive, but the

author has designed one for his own use that is comparatively simple,

and can be made by any watchmaker. When the reader has grasped the

principle on which it acts he will be able, without difficulty, to

modify it so as to suit his requirements.

[Illustration: _Fig. 213._]

The frame B B _b_, Figs. 212 and 213, consists of the body of the tool,

B B, and a bar _b b_, which is attached to it by screws. Between the

two the division-plate P rotates on an axis E R. The end E of this axis

is formed as a chuck to receive the cutter _f_, which is clamped by a

screw _t_.

The support S _s_ J is held with friction in the lower part of this

frame, to carry the cutter-holder A L M. This cutter-holder is hinged

at _n_, so that it can receive a double motion, revolving about a

horizontal axis J, and about an inclined axis _n_.

The portion A L of the cutter-holder carries a perforated arbor _a c_,

with a ferrule _c_ that receives the tail of the small rose-cutter,

which will presently be described.

The end M rests against a guide G, held by a vane _o z_, which is

pivoted on a pillar _z_, and can be clamped in either of the directions

_z y_, _z x_, or by one of the screws _o_, _o_.

=428.= We will now consider the mode of action of the machine. Having

set the little arbor _c a_ in rotation, rest the end M of the arm

against the guide, and gradually advance the rose-cutter towards _f_;

the edge of _d_ will form the first notch in the grooved rim of the

cutter, and then will be raised from contact with it, owing to the

influence of the guide G. After moving the tool-holder back to its

initial position, advance the wheel P by a tooth, repeat the operation,

and so on.

=429.= If the cutter _f_ has to be notched on both sides, it must

be reversed on the chuck; turn the guide so as to point in the

direction _z x_, corresponding exactly to _z y_; then having set the

cutter-holder in the line _z h_, recommence operations. The two grooves

of the cutter will then necessarily be of similar form.

Teeth can be cut on the rim of _f_ by using a cutter of the form F,

Fig. 214, and holding M against a straight vertical guide.

With a given divided wheel, P, the teeth can be brought nearer together

by reducing the diameter of the cutter, and _vice versa_. It is well to

have some change wheels, but a better plan is to advance the division

plate by the aid of a tangent screw.

[Illustration: _Fig. 214._]

=430.= =To Make the Several Accessories.= _Form of the rose or

star-cutter._ The rose-cutter is formed of a mushroom-headed piece of

steel. Such a conical cutter is shown at C and R, Fig. 215, and at F,

Fig. 214. F and C are cut in the same way that conical cutters are

always made, and R is a small triangular prism that only cuts by its

three corners, _a_, _a_, _a_. As it is necessarily very small when

employed in making the cutters for watch pinions, it must, in such a

case, be supported at the neck by a little fork. Moreover, it must be

brought gradually against the steel to be operated upon, so as only to

engage a very little at a time. With a view to this, it is advisable

that the cutter-holder be advanced by a screw.

[Illustration: _Fig. 215._]

The star-cutter, shown at E, Fig. 216, is at times substituted for the

rose-cutter. It cuts with the corners _e_, _e_, etc., whether it be

going to the right or left indifferently. Or a triangular cutter like

T, Fig. 216, can be used in its place; but its angles are fewer and

less acute, so that they become dull more rapidly.

A few trials will be needed in order to determine the most convenient

rate of movement of the several parts; and the edge of the cutter _f_

must always be liberally supplied with oil. A little can may be so

arranged as to allow oil to fall drop by drop on to the cutter _d_,

Fig. 213.

[Illustration: _Fig. 216._]

=431.= _To make the guide._ Having mounted a plate, G, on the vane _o

z_, trace out the approximate form of the cutter with the point of

M; then cut off the superfluous metal, leaving a slight margin. This

excess is necessary because the curvature of the guide is not the same

as that of the cutter, for the indentations as they spread out from

the center (_t_) become gradually deeper. The guide should be tested

from time to time by operating on a blank brass disc fixed in place of

the cutter _f_ and the guide must be modified as experience shows to

be requisite. Its edge must be saddle-shaped so that the middle may

correspond exactly with the two dotted lines _z x_, _z y_, Fig. 213.

The position of the disc on the chuck _t_ must be brought to correspond

with the guide by carefully turned washers placed behind it.

=432.= _Driving attachment._ Fig. 217 shows one system that may be

adopted for connecting the ferrule C with a driving wheel. All that is

required is that the instrument be set in such a position that this

ferrule is placed as indicated in the figure with reference to the

distributor.

[Illustration: _Fig. 217._]

=433.= _Cutters of uneven thickness at the circumference._ It is

well-known that the edges of the cutters of rounding-up tools (=435=)

are made to taper off around the periphery. In order to indent such

a cutter, the guide must be mounted on a slide, so that it may be

gradually displaced while the operation is in progress, by an amount

previously determined upon.

The desired result can be obtained with sufficient accuracy by moving

the guide backwards by successive stages with a screw. The end _k_ of

the arm M, Fig. 213, is slightly tapered, so that a gradual depression

of M occurs, and each cut is deeper than that which preceded it.

[Illustration: _Fig. 218._]

=434.= _Modification in the construction._ This instrument may be

modified as follows: The disc to be operated upon is fitted to the

chuck of the division-plate D, Fig. 218, which is vertical, and the

entire system is capable of a movement of rotation round the axis of

the base P. Having set the disc in the plane _a b_, as shown in the

figure, clamp P; then, by traversing the cutter-holder, the teeth on

the side of the cutter towards _a b_ are made. This cutter frame having

now been removed, the base P is turned until the cutter is in the plane

_c n_, such that it is equally inclined on the opposite side of the

axis of the cutter frame; the teeth on that side may then be made, the

star-cutter being rotated in an opposite direction.

It is unnecessary to prolong our explanations of the instrument, as the

details already given will suffice for any intelligent workman.

TOOLS FOR CORRECTING THE FORM OF TEETH.

=435.= =Rounding-up Tools.= In Europe it is the practice, in making

watch wheels, to first notch the circumference by means of a flat

circular cutter in a wheel cutting engine, thus forming a number of

square teeth. They are subsequently rounded off to the usual form,

after the wheels are riveted to their pinions, in a special tool.

The apparatus employed for this purpose is termed a rounding up tool,

and its principal feature is a mill cutter F, Fig. 219, the portion

_a b_ of whose circumference is cut away and replaced by a guide _g

f_ made of steel spring, and so fixed as to coincide with the edge of

the cutter at _f_, and incline at _g_ in order to compel the cutter

to pass, at each rotation, into consecutive spaces of the wheel. Two

screws are provided, the one _f_ for setting the guide opposite the

edge of the cutter, and _g_ for placing the free end of the guide

opposite to a space.

This tool acts with great rapidity, a fact which has led to its being

very extensively used in the factories of France and Switzerland,

although the ordinary system of wheel cutting is preferred in England

for all the better class of work. For it should be noted that the

rounding up tool does not correct any errors that are due to bad

dividing; for example, if a wheel is found to have some of its teeth

larger than others, the tool can not be relied upon to correct them; on

the other hand, if a wheel is exactly divided it is improbable that the

employment of this tool will occasion irregularity.

[Illustration: _Fig. 219._]

The instrument we are discussing is, however, not much used by watch

repairers, although they are frequently called upon to touch up the

teeth of wheels, or to slightly reduce the diameters of their pitch

circles, operations which cannot be done by hand with much chance of

success. The limited use to which rounding-up tools have been put is

owing, in great part, to their high price, but cheaper tools on this

principle are now coming into use.

=436.= One of these is shown in Fig. 220. The wheel to be operated upon

is held against a small table at D between two vertical runners with

guard-pivot centers, and a cutter of the form shown at Fig. 219, is

fixed at C to a suitable chuck of a small lathe-head B; this is caused

to revolve by the hand-wheel A, a supplementary pulley K taking all

strain off the axis. The three milled-headed nuts seen at E, F, and G

are for adjusting the instrument; E for moving the lathe-head, so that

the cutter is in the same plane as the axis of the runners, a position

which is determined by the pointer I; F for advancing the wheel against

this cutter; and G for setting the plane of the wheel to pass through

the axis of the lathe-head as indicated by the index H. The instrument

is accompanied by a number of cutters to suit the various sizes of

teeth ordinarily met with, as well as of tables to support wheels of

different dimensions.

[Illustration: _Fig. 220._]

=437.= =Ingold Fraise or Cutter.= =Rounding-up Cones.= Either the

cutters devised by M. Ingold, or the rounding-up cones of M. Berlioz,

may be used for correcting the form of wheel teeth.

The Ingold fraise is a small steel cylinder perforated through the axis

so as to be mounted on an arbor, and having a number of longitudinal

notches on its circumference which makes it resemble a pinion, the

points of whose leaves have been ground off. The spaces of the fraise

are of the exact form required to be given to the teeth of the wheel,

and their surfaces are covered with fine file cuts so as to enable them

to remove metal from the wheel operated on.

Having mounted the arbor that carries it between two centers of a

depthing tool (made especially strong for the purpose), the wheel

is supported by its axis between the second pair of centers (with

guard-pivot points). If now the fraise be advanced by the screw until

its teeth engage with those of the wheel, and either be caused to

rotate, it will drive the other, and the fraise will thus shape the

teeth to a pre-determined form, the faces of each notch acting the part

of a minute file introduced between the teeth.

It will be observed that such an instrument is preferable to the

ordinary rounding-up tool, in that it may be relied upon to bring all

the teeth to the same shape, but, on the other hand, the latter tool

has an advantage in being available for slightly reducing the diameter

of a wheel when a depth is found to be too strong.

=438.= An objection has been urged against the Ingold fraises on the

ground of expense, as each dimension of tooth evidently requires a

cylinder specially adapted to it. This fact has led to the introduction

of “rounding-up cones” the invention of M. Berlioz, which act on

precisely the same principle, but are conical instead of cylindrical,

so that each fraise evidently takes the place of a number of Ingold

fraises. The total number being proportionately reduced. But great

dexterity is required in their use, so that they cannot be successfully

employed until after numerous trials.

=439.= =Exact Rounding-up Tool.= The author has devised an instrument

for giving to the teeth of wheels the exact form determined upon by

theory, but as it is of too elaborate a nature to come into general

use, we shall not do more than here refer to it. It is rather of

a nature to be used for scientific work, but might be found of

considerable value for accurately forming the blades of cutters that

are used in grooving the circular cutters employed for cutting the

teeth of wheels.

=440.= =To Round Up Teeth By Hand.= We have seen a country watchmaker

proceed somewhat as follows: His method was only effective, however,

for ensuring the verticality of the file, and did not maintain it

straight, nor could the curvature of all the teeth be relied upon to

be the same; these two conditions are satisfied by the system here

explained.

Formerly watchmakers possessed very considerable skill in this kind

of work, as the teeth were always formed by hand; but at the present

day, for want of practice, there is not one to be found in a hundred

competent to round up a wheel properly by hand alone. Recourse may be

had to the following expedient in an emergency; it necessitates the

construction of a small special tool, but this is so simple that it can

be made in a few hours by an apprentice.

=441.= Take a bar of metal or hard wood, made smooth on its faces and

square at the corners (R, Fig. 221), and adapt to it a slide, _c c_,

through the center of which a slot is cut to receive a clamping screw;

it slides between the four pins indicated in the figure. An arbor _a_

is supported by _c c_, parallel to R, having a plate at its end on

which a wheel to be operated on can be fixed by three screws and a

loose plate. It is centered by the circumference before clamping these

screws, rotating _a_ with a bow, and it may be well to place a piece of

tissue paper under and over the wheel in order to avoid scratches. V

is a tongue that can be introduced into the space between two teeth in

order to prevent the wheel from moving.

[Illustration: _Fig. 221._]

Two arms, _p p_, screwed to the bar R R, support the handle of the

rounding-up file _l_, which consists of a large cylinder _t_, _t_, that

slides in the arms _p_, _p_. The cylinder T must be exactly parallel

to the arbor _a_, and the longer it is the better. The file-holder

_s_, also shown detached at Y, Fig. 222, is merely driven onto the rod

_t_. The distance between the center of the axis _t_ and the face of

the file (_b b′_, Fig. 222) is equal to the radius of the circle that

embraces the external curves of two or more teeth, as will be explained.

[Illustration: _Fig. 222._]

The several parts being arranged as shown in Fig. 221, and the bar

clamped in a vise at E, it will be obvious that, if the wheel is

held in two fingers of the left-hand so as to prevent it from being

displaced, while the rod T is moved up and down, at the same time

rotating it with the right-hand, the curves of two teeth will be

adjusted to correspond with the arc _o o o_ (Z, Fig. 223), and, by

transferring the tongue V to the next succeeding space, the curve _i i i_

can be struck.

[Illustration: _Fig. 223._]

=442.= _Observations._ The curvature of the point of a tooth coincides

very closely with a circular arc described from a certain definite

center, and comprising either two or three teeth. In order to realize

these conditions in practice, the slide _c c_ is so adjusted that the

axis of T passes just within the circle that passes through _o_, _o_,

_o_, etc. (Z, Fig. 223), at which the points of the teeth commence; by

making trials with two or three file-holders that differ in regard to

the distance _b b′_ (Y, Fig. 223), it will be easy to select the most

suitable for producing the required curve. After operating on all the

teeth in succession, advance the wheel by means of the screw D, and

again work around the circumference, and so on. The progress of the

work should be frequently examined with the glass.

It is possible to dispense with the tongue V, and to merely steady the

wheel by hand; the work is thus done more rapidly, but must be examined

with very great care.

We would insist that the lengths of the two axes are an element of

success. In operating on watch wheels T should not be less than six

inches long.

By suppressing the tongue the motion of the two axes may be

co-ordinated so as to form any theoretical curve; This is the case

in the exact rounding-up tool already referred to, but it of course

renders the instrument more complicated.

=443.= =To Ease a Train of Wheels.= In very many of the cheaper watches

and timepieces now met with in commerce the teeth are rough and badly

cut, and the pinions but little polished, so that watchmakers are

constantly complaining of the difficulty of securing even a moderately

good depth. In such cases they have a simple method to adopt in

addition to those already referred to, namely, to polish the teeth with

a piece of charcoal.

A piece of smooth, even charcoal, with regular fibre, is moistened with

oil or water, and passed across the teeth individually; first with the

fibres lying in the direction of motion, and afterwards with them at

right angles to that direction.

If the charcoal is carefully selected and lightly applied for a

sufficient length of time and no more, the ogives will be found to be

nicely smoothed, and the depth will run far more easily than it did

previously. It is dangerous to use quick-cutting charcoal, as it is apt

to deform the teeth.

Smoothing with a brush charged with charcoal powder cannot be regarded

as anything more than cleaning; if the action is too much prolonged the

form of the teeth will be spoilt.

TO TEST THE ACCURACY OF CERTAIN TOOLS.

=444.= =Drilling Tool.= First center the runner in the lathe, and

ascertain that it is straight, cylindrical, and exactly centered; then

fit a ring to it so as to slide with friction to (temporarily) limit

the descent of this runner in the vertical stock of the tool.

After placing it in position, adapt to its lower end a collar, provided

with a long index of soft brass, which is bent so as almost to touch

the plate at its circumference. Rotate the runner and it will be shown

to be perpendicular to the plate if the point of the index remains at

the same distance from the plate.

As a confirmatory test the runner may be drawn up in the stock, and

the trial repeated after bending the index nearly to touch the plate.

=445.= =Uprighting Tool.= If the two stocks or tubes that receive the

runners are exactly in line, a runner should move easily through the

two at once.

Setting the points in contact in various positions in a vertical line,

observe whether they coincide, both when at rest and when rotated

together or independently.

First ascertain that the table is at right angles to the axis in the

manner already explained for the drilling tool, making the necessary

tests with the two runners independently. Then support between their

points a short arbor carrying a soft brass index. The position of the

lower runner being maintained constant by means of a collar as above

explained, rotate the upper one by hand; its friction will carry the

index and arbor around, the point of this latter being set close to the

plate. Repeat the operation by raising the pair of runners and bending

the index down to the same amount.

If in these various positions the point remains at the same distance

from the table, it affords evidence that the tool is accurate.

An uprighting tool consists of two parts: the table carrying the lower

stock, and the bridge that forms the upper stock. The base of this

latter is a ring turned flat and co-axial with the stock, and is fitted

accurately into a square groove surrounding the table, where it is

fixed by screws.

Any watchmaker understanding this mode of construction will easily

perceive when he has tested the tool in the manner above indicated,

both what are its faults and how far he can correct them.

=446.= The English uprighting and drilling tools, and some of foreign

construction, are combined on the same stand, and a good arrangement,

made by Boley, is shown in Fig. 224. It will be seen that the drill

can be set in motion by a hand or foot-wheel; the table is fixed in a

vise and provided with two dogs for clamping the object. The drilling

spindle is perforated throughout its length so that the drill can be

held by an American split chuck.

[Illustration: _Fig. 224._]

=447.= =Depthing Tool.= As the value of a depth depends essentially

on the overlapping of the teeth being the exact amount required by

theory, it is specially important that the tool used for determining

the distance between the centers of the wheels and pinions should be

of the utmost attainable accuracy.

First ascertain that the spindle which serves as an axis for the two

halves of the tool does not change position when they have been several

times separated and brought together. For, if this were to happen, and

a runner were uneven or the hinge not smoothed within, the parallelism

of the two pairs of runners would be impaired.

The runners must be of equal thickness throughout, and should pass with

ease from one head to that opposite. Their points and center holes

must be seen to be in good condition, and, on placing them in their

turns, they must be found to be both true and cylindrical. Having

restored them to their places with the points together, move the

pair lengthwise from one head to the other, examining the points in

successive positions to ascertain that they coincide accurately, both

when the runners are loose and when clamped. When the adjustment has

been carelessly done the runners will be found to bend under pressure,

causing the points to be displaced.

Having set two runners side by side and level, describe with them

circular arcs on a smooth piece of brass from centers previously

marked, first with the points just projecting from the heads and then

projecting more and more. These tests may be made both within and

without the tool; so that there will be four sets of tests in all.

It is very important in making the last-named trials, that the tool be

maintained at right angles to the plate on which the circular arcs are

traced; this condition can easily be satisfied by a special device,

or by merely causing the compass to slide along a set-square. It may

be added that the series of arcs should be drawn end to end, in order

that it may be easier to observe their agreement or difference when

examining with the glass.

=448.= When this series of tests has been gone through, and the points

have been examined so as to make sure that there is no burr which bends

over while tracing the arcs, it is possible to determine the value of

the tool; we know whether it is perfect or not, and what corrections

are required. As a rule there are two points mainly at fault; the

holes in the heads are not exactly continuations the one of the other,

so that they need to be broached out afresh and new runners have

to be made. A careful and intelligent workman who is provided with

suitable tools will be able, from the information given in this work,

to correct, or at least improve, a defective depthing tool; but, as a

rule, it will be better done by the maker.