CHUCKS.

No lathe can be considered well fitted until it is supplied with a

large number of chucks, by which strange term are signified the

various appliances for fixing to the mandrel the article to be

turned. When it is considered how varied are the forms which present

themselves to the turner, it may readily be conceived that much

ingenuity has to be exercised in contriving methods for mounting his

work in the lathe; and when in addition to variety of _form_, variety

of _size_ has to be taken into consideration, it is plain that a

large assortment of chucks is a necessary item in the workshop of the

turner. A vast number of these chucks are of necessity made of wood,

as required, and such wooden ones are altered from time to time to

suit different-sized work, till they eventually become so completely

used up as to be only fit for the fire. In addition, however, to

these, there are certain chucks of metal (chiefly brass or gun metal)

which should always be ordered with a lathe, or fitted to it before

any work (even the making of wooden chucks) can be satisfactorily

accomplished. The first of these, is represented in Fig. 20, the part

A, screws to the mandrel; while the work is attached to the taper

screw B. The use of this chuck is to hold short pieces or flat discs,

which allow of a hole in the centre and require to be turned on the

face. It is only used for wood-work. This is the chuck to be selected

when it is desired to make a wooden chuck. A piece of sound wood

being chosen of the requisite size, and roughly rounded by the axe or

chisel, a hole is made in one face by a gimlet rather smaller than

the tapering screw. The piece is then firmly screwed to the latter,

the opposite end dressed with gouge and chisel, and the rest being

placed across the end, a hand-drill for wood is brought to bear upon

the piece. The hole thus made in the centre is then enlarged by any

convenient tool until its diameter is only a little less than that of

the screw cut on the lathe mandrel. An inside screw tool is then made

use of to cut a thread of the same pitch as that of the mandrel, or a

tap of similar size and pitch screwed into it (the former is the best

but most difficult method to a novice), the piece detached from the

taper screw chuck, which is removed, and the wood attached to the nose

of the mandrel on which it may now be accurately fitted and finished

to the requisite form and hollowed out or otherwise, as may be

necessary. Numberless articles may be in a similar manner turned upon

the above chuck such as the bottoms of candlesticks, ring or other

stands, bread-platters, small wheels, and so forth; it may therefore

stand as number one of these adjuncts to the lathe.

[Illustration: FIG 20.]

Fig. 21 is the face plate, another most serviceable chuck of almost

universal application in such work as surface-turning and boring, and

where a hole in the centre is inadmissible. To this belong various

dogs or cramps, a few forms of which are shown at _a_, _b_, _c_, _d_.

These hold the work firmly down to the surface of the plate, being

tightened from behind by screw nuts. It will be seen that there are

four slots and numbers of holes in the face plate, some of the latter

being tapped for screws. These slots and holes may be increased in

number, and some of the latter may be square instead of round, and

the cramps may be of all shapes and sizes, because sometimes it may

be required to hold down a flat piece of brass the eighth of an inch

thick only, and the next job may be to hollow an irregular block of

wood of three or four inches in thickness, or it may be necessary to

bore out the boss of a wheel, or to turn the rim--all of which, and a

hundred others, are cases in which the aid of the face plate will be

in requisition.

[Illustration: FIG. 21.]

Fig. 22 is the chuck specially used for turning rods of metal. It

consists of two parts, the body A, which screws to the mandrel, and

the piece B, which passes through a slot and is clamped by a small

screw at one side _c_. To these must be added the carrier which is

of such forms as A1, B1, C1. Above is shown a rod of metal to be

turned with this chuck in position for use. Of this we shall have to

speak again when we arrive at the subject of metal-turning. There

should be several sizes of carriers kept in stock, from 1/4in. in the

largest part of the ring to 2in. or 3in., or even much larger for

heavy work. The amateur will, however, scarcely need these larger

ones. The usual method of making the wood-holding chuck for work that

is to be also supported by the back centre, is to have a socket cast

like Fig. 23, C, with a central hole to take the fork A, which is held

in place by a set screw. This socket is useful for other purposes as

it will hold short pieces of iron to be turned, but the fork is far

inferior for general work to the piece _b_; this is made of iron, and

the end of the cross (against which the wood to be turned comes) is

sharpened but must not be _too_ sharp. The end of the piece of wood

has then two saw-cuts made at right angles to each other into which

the sharpened edges of the cross fall, Fig. 23 D, and the whole will

turn together without any chance of slipping. It often happens, when

the ordinary fork is used, that if the tool chances to hitch in the

work, the latter is either thrown quite out of the lathe, or the

centre of the fork retains its place, while the other two points slip

and score the work. This can never happen with the form B, which is

the most reliable pattern that can be devised for work of this nature.

[Illustration: FIG. 22.]

[Illustration]

[Illustration: FIG. 23.]

Fig. 24 is to some extent self-centering. A piece of wood hollowed out

conically has three nails, or three-square saw-files so placed within

the cone as to present three sharp edges inwards. Any piece of wood,

if not too hard, will, if placed with one end in the chuck, while the

back centre is screwed against the other, centre itself in some part

of this cone, and, being at the same time held by the three sharp

edges, will necessarily revolve in the chuck. There are many cases in

which even in this rough form such a chuck will prove useful; but if

it were cast in metal and the three edges formed by slips of steel,

and the whole accurately turned, it would be a very efficient and

good self-centering chuck. In its more common form it is largely used

by the turners of mop and broom handles, who work rapidly and cannot

afford to waste time in chucking their work. With the above, the

lathe, if worked by steam or water power, is not even stopped,--the

screw of the back centre has a quick thread, so that a single turn

to or fro fixes or releases the work; and thus, one handle being

finished, another piece takes its place in the chuck, is fixed by a

half-turn of the back screw, and being set in rapid motion is turned

and completed by a practised hand in a couple of minutes or less.

[Illustration: FIG. 24.]

Fig. 25 represents another useful chuck, generally of boxwood, called

the barrel stave chuck. It is turned conical, the largest part being

towards the mandrel; it is then wholly or partially drilled through,

after which saw-cuts are made longitudinally, as in the drawing. These

allow a certain degree of expansion when a piece of work is fitted

into it, and it is tightened round the latter by driving on a ring of

iron or brass. This ring is sometimes cut with a coarse thread inside,

and a similar thread being chased on the outside of the chuck, it

is screwed upon the cone instead of requiring to be driven by blows

of a hammer. One important use of this chuck is to re-mount in the

lathe, for ornamentation by the eccentric cutter or other apparatus,

any finished work that could not be readily chucked in any other

manner, or to hold rings requiring (like curtain rings) to be turned

on the inside. Such articles will, from the nature of this chuck, be

truly centred at once; and their exterior parts will not be liable

to injury, as they would be by being driven into an ordinary chuck

hollowed out to receive them.

[Illustration: FIG. 25.]

Another useful chuck for turning short pieces of metal such as bolts

and binding screws, and which is in a great measure self centering

is made of cast iron, and is usually called the dog-nose chuck,

represented in Fig. 26. This is made with movable jaw hinged, as more

plainly seen in B. The screw clamps these jaws firmly together, and

any small piece of work is thus securely held. The centering, however,

is not accurate, though sufficiently so for many purposes. The die

chuck (Fig. 27) is accurately self-centering, and although somewhat

expensive, is a valuable addition to the lathe. This chuck consists,

first of all, of a socket for screw to fit the mandrel, and round

flat plate of brass cast in one piece, as in Fig. 28. This must be

carefully turned and faced in the lathe. Two pieces of iron or brass

are then screwed to the face, as B, B, 28A, leaving a space between,

the sides of which are to be truly parallel. These pieces may either

be chamfered to form V-pieces, or may be rectangular on their inner

edges; at C, C, a part of each is cut away, and the outer or back

plate is also filed down to receive the small plates D, D. E shows a

groove in which a screw lies, half of which has a right and half a

left handed thread; this is shown in Fig. 29. It will be evident that

if this screw is placed in the groove of the bottom plate, and its

ends pass through the pieces D, D, which are screwed to the plates,

it can revolve in its bearings, but will have no endwise motion;

the collar F resting in a recess under the top plate D. This screw

passes through a projection in the back of the pair of dies, which

projection also goes into the same slot in the back plate in which

the screw works when turned by the key (Fig. 27, B). The above being

nicely fitted, the dies moving evenly but stiffly in their places, the

plain top is screwed on, keeping all firmly together. This plate has

a long opening or slot (Fig. 27), through which the jaws of the dies

and part of the screw are visible. The ends of the screw should not

project, as any such projection is calculated to bring to grief the

knuckles of the turner--a consideration worth attention in every form

of chuck--the squared ends of the screw lie in a recess in the small

plates, as shown in the section of one of these plates (Fig. 28X).

Into this recess the key fits over the screw end; and by turning this

the dies are simultaneously moved asunder, or closer together so as to

grasp centrally as in the jaws of a vice, any small article, such as a

screw or short rod of metal placed between them, A similarly contrived

chuck is often used under the name of a universal chuck, for holding

pieces of large diameter, and is very useful for taking pieces of

ivory which have to be hollowed or otherwise worked, as will hereafter

be detailed. In this case the jaws may be semicircular in form, as

Fig. 30.

[Illustration: FIG. 26.]

[Illustration: FIG. 27.]

[Illustration: FIG. 28.]

[Illustration: FIG. 28A.]

[Illustration: FIG. 29.]

[Illustration: FIG. 30.]

It is however, evident that these two chucks have a rather limited

range. The first can only be used for small work, and the only case

in which the latter can take firm hold all round the work is when

the jaws are just so far apart as that they form portions of the

circumference of one and the same circle. Practically they will hold

the work tightly under an extended range of sizes, and they are thus

of great use to the turner. The following is however more perfect in

operation, from the fact that it has four jaws instead of two which

meet concentrically. This may be made either with two long screws at

right angles to each other, with right and left-handed threads to

each, as in the die chucks, or more simply and, in some respects more

satisfactorily, with four distinct screws, all of the same pitch, and

all with squared ends of equal size, to allow of the same key being

used to turn them. It is possible to use such a chuck as an eccentric

chuck if desired, which is certainly a recommendation in its favour

over those which work always concentrically. The face of this chuck is

shown in Fig. 31. The ends of the four screws have a bearing in the

small centre plate _b_, whilst the collars or flanges rest in a recess

under the several plates _c, c_. The face of this chuck is graduated

by each die, so that it is easy to set the jaws concentrically or to

place one or more eccentrically to take in work of other shape than

round or square. The jaws of this form of chuck are used for two

purposes, either to hold work inside them like a vice, or externally.

A ring, for instance, requiring to be chased on the outside is slipped

over the jaws, which are then caused to recede from the centre so as

to hold the work securely. If the latter does not run truly, one or

more of the screws can be slackened, and the opposite ones tightened,

or if the eccentricity appears to be in an intermediate part, two

adjacent screws will have to be thus slackened and the others

tightened. On the whole this is a most useful pattern of chuck.

[Illustration: FIG. 31.]

The following is a very excellent self-centering chuck now coming

into extensive use. It has been noticed in more than one periodical.

The description annexed is extracted from the pages of the _English

Mechanic_. "The chuck hereby illustrated seems to be a very convenient

form, easily adjusted and holding the drill securely. It is also

well adapted for holding wire to be threaded. Every piece of which

it is composed is of cast steel well hardened. It can be furnished

with a shank to fit the hole for the centre, screwed on the spindle,

or slipped on the centre. No wrench is necessary, the gripe of the

fingers being sufficient to secure the shank of any drill. The

inventor claims that he has used a one-inch drill, in tenacious

wrought iron in one of them, receiving a shank of only three-eighths

of an inch diameter without using a wrench."

Fig. 31A represents the shell of the chuck with milled bosses for the

fingers. The core, B, is threaded and receives a steel wire spring

which is inserted into the rear of each jaw, so that when relieved

from pressure, the jaws open automatically.

[Illustration: FIG. 31A.]

With this brief explanation, the operation of the chuck can be easily

comprehended. These chucks are made of two sizes, one with an opening

of three-eighths of an inch, and the other of three-sixteenths of an

inch, and they can be made of larger sizes. Patented by L. H. Olmsted,

Stamford, Connecticut, United States America.

Another chuck of self centering design, has likewise appeared in the

periodical above named, into which it appears to have been copied from

an American paper.

The accompanying engravings illustrate some improvements in the

arrangement of chucks which have been recently patented in this

country, the inventors being Messrs. Smith and Haight, both of New

York, U.S. The first part of the invention refers to an arrangement

of adjustable chuck, by means of which tools and other articles of

different diameters may be held firmly in the jaws of the chuck. Fig.

31B is a longitudinal view of the chuck, partly in section. The

spindle, _a_, is fitted so that it may be inserted tightly in the

mandrel of the lathe. On the front end of the spindle is a conical

screw on which is fitted the cap, _b_; this part is formed with an

opening at the front end, having three longitudinal slots in it. In

each of these slots an adjustable jaw, _c_, is fitted, the inner part

of which is threaded with a female screw, to fit the conical screw on

the spindle, _a_. An outer casing _d_, encloses the front part of the

chuck, and behind this is fitted a loose collar, which is screwed into

the casing _d_, so as to connect the parts firmly together. By turning

the cap, _b_, with the casing, _d_, and collar, in one direction, the

jaws, _c_, are moved forward and project out through the openings, and

they may thus be adjusted to grip a tool or other article of small

diameter. The opposite motion of the cap causes the jaws to recede,

and in this way they may be adjusted to grasp articles of different

diameters.

[Illustration: FIG. 31B.]

Another arrangement of the adjustable chuck is shown in Fig. 31C,

which is a front view, and Fig. 31D, a longitudinal section of the

same. A, is the body of the chuck, the front part of which is formed

with a rim or flange, in which are three radial recesses having

fitted therein the sliding jaws, B. In the rear of each jaw is a

bearing, in which is fitted a pin carrying a small lever, C, the

front end of which is rounded, as shown in the section, and enters a

slot made in the jaw, B; so that when the levers are moved outwards

they cause the jaws to contract or move towards the centre. The

back part of the body, A, of the chuck is threaded, and on this part

is fitted a collar, D, and in front of this is a sliding collar, E,

which is connected to the collar, D, by means of a pin which enters

a groove formed in the latter. The sliding collar is prevented from

turning round on the body, A, by means of a feather, which works in a

longitudinal groove formed in the inner circumference of the collar.

Three inclined planes, F, are formed on the periphery of the collar,

E, which extend to the backward ends of the levers, C, so that by

moving the collar to and fro, the jaws, B, are caused to contract or

expand, according to the size of the article to be grasped. A short

cylindrical block, G, made of a conical figure internally is fitted

loosely within the chuck, A, and serves to centre the end of a drill

or other short article, but may be removed when it is desired to pass

a rod or other article through the body of the chuck. To provide for

the easy turning of the collar, D, it is shown as fitted with a hand

wheel, H. With this arrangement of the several parts, the jaws of the

chuck readily adapt themselves to drill or bit shanks as well as to

articles of parallel form, or of a tapered or irregular figure.

[Illustration: FIG. 31C.]

[Illustration: FIG. 31D.]

The chucks last named belong to the class of compound or mechanical

tools; and though their usefulness is beyond question, they need

not be considered absolutely necessary, as the work which they are

designed to facilitate can be and often is done without their aid.

Indeed, success in the art of turning by no means depends absolutely

upon the possession of expensive apparatus, and the amateur or

mechanic will find the advantage of ransacking his own brain for the

devising of divers makeshifts and off-hand contrivances--especially

in this chuck-making department.

Among the simple expedients the following will be found well worthy of

adoption.

A, Fig. 32, is a simple flange or flat brass plate with a boss behind,

similar to a small face plate, and is to be turned up, drilled, and

tapped to fit the mandrel. If the latter has a diameter of 3/4 of an

inch, a few of these brass pieces should be cast from a set of wooden

patterns ranging from two to three or four inches across the diameter

of the plate, and, after having been fitted to the mandrel and turned,

four holes, countersunk for wood screws, should be made, as shown in

the sketch. These are intended to do away with the necessity of boring

out and tapping each individual wooden chuck. They can be readily

attached to any piece of wood by four screws, and a few minutes will

be sufficient to adapt the same to any required purpose. A flat piece

of board, for instance, itself too thin, or of too soft substance to

permit of its being attached to the mandrel in the ordinary way, can

thus be made into a temporary face plate, or a ring cut out of it, or

any desired operation performed upon it. Indeed, these socket pieces

will be found serviceable on many occasions, and will do away with the

necessity of a large set of cup chucks.

[Illustration: FIG. 32.]

A few of the latter, however, are very useful and will cost but

little. The castings are sold by weight, and the turner will

experience no difficulty in fitting and finishing them for himself.

Fig. 33 is the form of these, and needs no description. The substance

may be from 1/8 to 1/4 of an inch, and need not be more, as that

thickness will stand any reasonable shock caused by driving a piece

of wood into the chuck, and it is always well not to overweight the

mandrel with chucks of undue size or substance. The addition of

three to six screws to one or two sizes of the cup chuck extends its

usefulness. This form is represented in Fig. 34, A and B. In this

case, the casting may be rather more substantial (1/4 to “3/8 of an

inch in thickness). The screws _must be strictly radial_, pointing to

the centre of the circle, and their ends must be turned off or filed

flat. Their heads may be squared to enable a key or pair of pincers to

be applied, or round with a hole through them. It is better to make

this kind of chuck with six screws--three in one plane, and three

again _between_ these in another plane behind them. In fitting a piece

of work into the chuck, it will not at first be found an easy matter

to make it run truly. The best way is to centre it as nearly as can

be guessed, by means of the three screws nearest to the open end of

the chuck, and then, placing the latter on the mandrel, set the lathe

in slow motion and correct the eccentricity of the piece by means of

the three inner screws. Even after this it is probable that a little

alternate slackening and tightening of the different screws may be

necessary; but a little practice will quickly enable the turner to set

a piece of work in the true axial line of the mandrel without much

difficulty, and the work will then be held very securely. Any short

piece, such as the ring of an eccentric to be bored truly inside, may

be held by the outer set of screws alone; but if such a piece of work

as a small cylinder is to be bored, the six screws must be brought

into action. Here let the hint given when speaking of projecting

screws, be repeated, _Beware of the knuckles_, which are peculiarly

liable to be damaged in making use of these chucks. The shirt sleeve

or coat, moreover, does not always enjoy perfect immunity from similar

danger, and both should be kept out of harm's way, not for their own

sake only, but because the arm may be brought into violent contact

with the rest if the sleeve should get entangled (the momentum of the

flywheel being great, and therefore not to be checked entirely at any

given moment). A single rap of the above nature is not a _delightful_

even if _salutary_ lesson to the novice.

[Illustration: FIG. 33.]

[Illustration: FIG. 34.]

To hold rings and washers a tapering mandrel, Fig. 35, is used;

and of these it is necessary to keep a few different sizes to suit

different diameters. These may be made of iron or brass if for

permanent use, but box or other hard wood is a ready substitute, and

may be turned down for smaller work when the surface gets spoiled by

use. The expanding mandrel, "Hicks' patent," which will be treated of

hereafter, is a convenient substitute for the simple conical form here

spoken of; and in manufactories where large numbers of mandrels have

to be kept of various sizes, a great saving of time, money, and labour

is effected by their use. For amateurs and artisans in a smaller

way of business the simpler form is generally sufficient. A slight

modification is here appended, by which the common form may sometimes

be made more efficient in the holding a ring tightly while undergoing

the operation of turning, and this can be made applicable to metal

mandrels, though specially intended for wooden ones. Fig. 36.

[Illustration: FIG. 35.]

[Illustration: FIG. 36.]

The mandrel having been turned conical (N.B., the angle of the cone

must be small, so that the size will diminish very gradually from the

largest end), the wood is divided by a fine saw, just as the chuck

already described with the outside rings was sawn into segments, a

conical hole having been first made at the smallest end, as shown

in the section _b, b_. Into this a short cone of larger angle is to

be fitted, against the end of which the point of the back centre

will press, tending to drive it into the mandrel, which will thus be

made to expand. The ring to be turned will prevent the mandrel from

splitting by the wedge-like action of the plug, unless the said ring

is of light substance, in which case this form must not be used. The

work will, by the above method, be securely and centrally held and not

liable to slip towards the small end of the chuck.

In the Fig. 36, a groove, _c, c_, is shown at the bottom of the

saw-cuts. This should also be made round the boxwood spring chucks

with rings, as it gives more freedom of expansion to the segments.

With such a groove and the chuck itself completely hollowed out,

the pressure of a _strong_ india-rubber ring will be sufficient to

hold work whilst being polished: and this will, when the latter is

delicate, be even superior to the screwed rings, as the pressure

will be more gentle and equable. India-rubber rings for this purpose

must not be thin and flat, like those used for bundles of papers or

letters, but made of round material, the thickness of a quill or even

larger. They may be had of all sizes at an india-rubber warehouse

in Holborn, at the bottom of the hill on the left hand side going

eastward, and not far from Negretti and Zambra's shop. The writer is

not acquainted with the name of the proprietor.

Having had occasion to speak of tapping chucks of metal to fit the

mandrel, it will be as well to speak here of the requisite tools for

effecting this.

In the case of iron chucks it is not likely, as a general rule, that

the amateur or workman will obtain access to a screw-cutting lathe,

and to cut an internal thread by hand with the chasing tool is hardly

feasible, though readily accomplished in the case of brass chucks.

When, therefore, a lathe is purchased, a set of taps of the diameter

and pitch of the screw on the mandrel should be provided. Of these

there must be three--an entering taper tap, an intermediate one

rather less tapering, and a plug tap, which is cylindrical. And here

we must enter a caution. Do not let the tapering taps be too long.

For instance, let it be required to tap the boss of a face plate in

which the hole cannot be drilled through the plate. It is first bored

out to the size of the _bottom_ of the mandrel threads, or rather

less. Tap number one must then be screwed into it; but if this is too

long, so that it cannot enter to the end of the threads cut upon it,

the second tap will be too large and will not enter properly, but

will most likely start a new thread for itself and spoil the first.

Fig. 37, _a_, _b_, _c_, shows the form required; _d_, the form to be

avoided, except in cases where, as in the cup chucks, a hole can be

made quite through the article, so that the tapering tap can be worked

to the line _x, y_, or nearly so. The long tap, _gradually_ tapering

as it does from end to end, is of course the easiest to use, and for

nuts and such like is far the best; the conical tap of larger angle

requires more power, but in the case named it is a matter of necessity

to use it; and, if preferred, a set of four taps instead of three will

remedy any difficulty. The novice must take great care to place the

tap perpendicular to the face of the chuck, or the shoulder will not

fit close to that on the mandrel. If much difficulty is experienced,

such an arrangement as Fig. 38 may be of service. A represents the

standard of an upright drill-post, of which B is the bench, C the

screw by which to depress the drill and keep it to the cut. For the

latter, and brace by which it is worked, substitute the tap, and place

a spanner or wrench round the head of it. In the centre mark, which

is generally left from the turning, place screw point _c_. By means

of a plumb line or square, D, test the perpendicularity of the tap;

and as the latter penetrates, keep it to its work by the screw C; oil

the tap freely, and the chuck will be easily and accurately cut with

the required thread. Some kind of clamp will of course be required to

secure the chuck to B, while it is being tapped.

[Illustration: FIG. 37.]

[Illustration: FIG. 38.]

The upright drill should always have a place in the workshop. It is

much easier to drill with it than in the lathe, and the mandrel will

thus be saved considerably. The latter should never be used except

for light work. A variety of drilling apparatus will hereafter be

described in this series, so that we need not now write more upon this

part of our subject.

Somewhat akin to the chuck described as the cup chuck with six screws,

is a chuck mentioned in an old French work,[1] the purpose of which

is to turn up a cylinder, with a point at the end, so as to insure

the axial line being kept. In the ordinary course, the cylinder would

be turned up with the point and carrier, or driver, chuck already

described; the conical point would be then turned down as far as

possible, and the mark of the back centre afterwards turned off by

means of the boring collar. It is by help of a miniature lathe and

boring collar in one piece that the pivots of the balance of a watch

are finished. In both cases the work may be well done by the same

process. The chuck now to be described requires no boring collar,

but at the same time it does not seem to be well suited for any but

light work; in which latter case however it would be advantageous,

and must therefore have a place in our present paper. The body of

the chuck is shown in section, in Fig. 39. A is the socket with

screw to fit on the mandrel of the lathe. It will be seen that the

chuck itself is hollowed out cylindrically, and in this cylindrical

cavity slides a plug, _c_, bored conically, which can be fixed by a

thumb-screw, _h_, traversing a slot in the body of the chuck. This

cone is destined to receive one end of the cylinder to be pointed,

which will, according to its diameter, centre itself in some part of

the conical hole in the plug. The latter is made movable, so as to be

adapted to the length of the article to be turned. At the outer end

of the chuck is a groove dovetailed to receive a slide, shown clearly

in the cross section B. The slide must be of sufficient substance to

allow a clamping screw, _f_, to be tapped into it at one end, which

screw must be long enough to reach when fully advanced nearly to the

apex of the triangular opening seen in the slide. The action of the

whole contrivance is as follows:--The cylinder to be pointed is placed

in the conical cavity of the plug--the latter slid to or fro till

the point to be turned projects a short distance beyond the mouth of

the chuck through the triangular opening in the front slide; when it

is fixed by a turn of the screw, _f_, which forms the third point of

resistance, the sides of the triangular opening forming the other

two. As the point or apex of the triangle is always in the diameter

of the cylindrical chuck, it will only be necessary to move the slide

itself in order to bring the axis of the cylinder to be turned in a

line with that of the mandrel. As soon as this is accomplished so that

the piece runs truly, the screw, _g_, is turned, and the slide fixed

in position. A good deal of ingenuity is displayed by the inventor of

this chuck, a description of which was published twenty years ago, and

there are very many cases in which it will be called into requisition

by the mechanic. With a little care, moreover, the amateur might make

one for himself--the body of brass or gun metal, the plug and sliding

part of iron or steel.

[1] Manuel de Tourneur par H. Bergeron.

[Illustration: FIG. 39.]

Amongst the various devices connected with the lathe, many of which,

even as makeshifts, are valuable to the turner, is one not generally

known for keeping up the tension of the lathe cord in whatever groove

of the fly wheel or pulley it may be placed. The plan is not more

ingenious than practical, and the writer is acquainted with one

workman, a gasfitter by trade, who has had it in constant use for

many years. Directly over the mandrel pulley is another of larger

diameter, in which are two grooves of equal depth, fig. 40. This

upper pulley is suspended on a movable arm, D, which is pivoted at

E, and kept up by an india-rubber spring, F, or, as in the original

plan (before these rubber cumulators were known), by a cord passing

over a pulley, and having a heavy weight attached, as shown by the

dotted lines. In the fig. A represents the fly wheel, B the mandrel,

C the upper pulley. The lathe cord is very long, and passes upwards

from A, over the upper pulley in groove 1, down again and round the

mandrel, a second time over groove 2 of the upper pulley and down to

the fly wheel. The tension of the cord is thus always the same, and is

regulated by the spring or weight. If the cord is slipped to a smaller

part of the lathe pulley, the slack is instantaneously taken up by the

descent of the weight, and rising of the arm D, which in like manner

yields to allow the cord to be slipped to the larger groove of the

mandrel pulley.

[Illustration: FIG. 40.]

There are many other useful contrivances for chucking work in the

lathe, a few of which will be noticed on a future page. The main

thing to be attended to is the holding securely as well as centrally

the object to be turned. If this is attained, the precise form of

chuck is of little importance, and it matters not whether it be

made of metal or wood. The latter has indeed, in some respects, an

advantage resulting from its elasticity and the ease with which its

form is modified.