HARD-WOOD TURNING.
We now discard almost entirely the gouge and chisel used for soft woods,
and fall back upon an entirely different set of tools, similar to those
used for metal, but ground to rather more acute angles. These tools are
held horizontally upon the rest, because depressing the handles causes
the bevel below the edge to rub upon the work; and in addition, the grain
of hard foreign woods is such that it cannot well be cut by placing
the tool at a more acute angle, as would theoretically be required.
Hence we can only regard these as scraping tools; but as such they will
do excellent work in skilful hands. I have said that we discard the
gouge, but there are some woods that will bear this tool, to take off
the roughest parts of the work, before the application of others. The
roughing-tool, however, may now be considered to be the point-tool, and
the round-end tool, or “round” as it is often called; a narrow one makes
a good tool for this purpose.
Hard wood is easier on the whole to work than soft, because we have for
the purpose a large stock of tools of all shapes, suitable to the various
mouldings required. Hollows, round-beading tools, compound and simple
moulding tools of various sizes, to say nothing of those which are made
for use with ornamental apparatus, such as are required for fluting,
beading, and eccentric work, spirals, and so forth. It is indeed in hard
wood that most amateurs are accustomed to work; ebony and ivory, singly
or in combination, being more extensively used than any other.
To turn a cylinder, or any work requiring to be held at both ends,
you will invariably find the cross-chuck the best to use,—the fork or
prong not taking hold in the hard material. Rough down to shape as
before, using the gouge if it will work, but keeping the rest as close
as possible, and only taking a light cut. Then finish roughing with
a round-tool, and proceed generally as in soft wood turning, except
inasmuch as you have to scrape instead of cutting the work into form.
In addition to the tools already described, you will have to obtain a few
beading-tools, if you want to do very good work, for these give far more
beautiful mouldings than you can cut in any other manner. Fig. 53, A to
C, represent these. The bevel is on the under side, and it is better to
interfere with it as little as possible, by always sharpening the flat
face only. If it should be _necessary_, however, to touch the bevel, it
must be rubbed by a slip of oilstone, rounded on the edge, as used for
sharpening gouges. Conical grinders, revolving in the lathe, are also
used, especially for small beading-tools, to be fixed in the slide-rest.
In the same figure, D and E represent another useful hard-wood and
ivory tool. It is called the side-parting tool; and it is usual to have
several of these, the hooks increasing in length. The edge is only on the
extreme end of the hook. These tools are used for economy’s sake to cut
solid blocks of ivory and hard-wood from the inside of boxes, instead of
cutting the material into a heap of useless shavings. Similar tools, G,
H, curved instead of rectangular, serve to cut out a solid piece from
the inside of a bowl. In ivory work it is essential to use these tools,
because such material is very costly; $2.50 a lb., and upwards, being a
common price.
[Illustration: Fig. 53.]
K is given to show what are meant by beadings. If these are exactly
semicircular in section, they are far more beautiful in appearance than
if of such curves as can be roughly cut by a chisel. The bead-tools are
beautifully formed for this very purpose. To use the same side-parting
tool, you must proceed as follows, which you will understand by the fig.
L:—A common straight parting-tool or narrow chisel is first applied to
the face of the work to cut a deep circular groove or channel, as shown
by the white space at N, and in section at L. This allows the narrowest
of the hooked tools to be applied to _under-cut_ the solid core _x_. This
being withdrawn, a rather longer hook is applied, the hook being held
downwards as at O, until it reaches the spot where it is to work, when it
is gradually turned up (bevel below). Eventually, it is plain that the
solid core or centre block _x_ will fall out entire, which may be used
for other purposes. M shows how a similar but curved block can be removed
from the inside of a cup or bowl, the curved tool not requiring an entry
to be made for it, as it cuts its own way entirely from first to last.
P and Q show a ring-tool and the method of using it. A recess is turned
in the face of a piece of wood as if it was intended to hollow out a box.
The ring-tool is then applied bevel downwards, and with the left cutting
edge a bead is cut half-through from the inside. The right edge is then
applied to the outside, and when the cuts meet the ring neatly finished,
will fall off. With this tool you can turn them very rapidly, and they
will require only a rub of sand-paper to finish them.
R, S, T are three more tools for hard wood. The first two cut on the
outside of the curved part all round. These would be used to hollow out
humming-tops and all similar articles, and to finish the insides of
bowls, for which T is also designed. Indeed, I might go on to describe
all possible shapes of curved tools, each intended for some special work;
but you will not do better than to go to Fenn, Buck, or any tool-maker in
London, or elsewhere, and pick out at 7s., or so, per dozen, all shapes
and sizes, or if you live at a distance and write to either of the above,
they will select you the most useful; and you can trust these tradesmen
and all first-class ones to send you no tools which are not of the best
quality.
In finishing best work in hard wood, be very careful of all sharp edges
of mouldings. Sand and glass paper round off these, and spoil the beauty
of the work. If you are _obliged_ to use such substances, touch off again
the edges with very keen tools, which ought to leave brighter and more
beautiful surfaces than any sand-paper can produce. Indeed, the secret
of _finished_ work in hard wood is to have tools whose edges and bevels
are _polished_. In ornamental eccentric and rose-engine turning, where to
use sand-paper would be to ruin the appearance of it, the little drills
and cutters pass through three stages of sharpening, being ground on the
oilstone, finished on a slab of brass, fed with oil and oilstone powder,
and polished on a slab of iron with oil alone or oil and rouge. After
this every cut that is made with them reflects the light; and as the
surface is otherwise purposely grailed or dulled by cutting a series of
fine light rings with a point tool, the pattern itself shows out clearly
and lustrously.
TURNING BRASS AND OTHER METALS.
I shall now teach you how to turn iron and brass, which, though harder
than wood, are not very difficult to cut, if you go to work in a proper
manner and understand how to use your tools. What these are like I have
already told you, and also how to mount a bar in the lathe by using the
driver or point-chuck with a carrier. If the piece to be turned is _not_
a bar, you will have to drive it into a chuck of wood, or clamp it upon a
face-plate, or in a self-centring chuck if you have one.
I shall suppose, first of all, a mere straight bar of iron, centred at
the ends, as I have shown you. Take off the lathe-cord that you use for
wood, and fit one to go upon the largest part of the mandrel pulley, and
the smallest upon the fly-wheel. When you now put your foot upon the
treadle to work at your usual speed, you will find the mandrel turn quite
slowly; but I may at once tell you, that what you lose in speed you gain
in power. Set your rest for iron (which is not that used for wood, but
one with a broad, flat top) so that it stands a little below the central
line of the lathe mandrel and work, which will bring the edge of the tool
exactly _upon_ that line. This is always the position of the tool for
metal-turning, at any rate for iron.
Begin by trimming the end of the bar next to the back centre. Use a
graver, held as I directed you; that is, with the bevel flat upon the
_face_ of the iron, which is in this case the _end_ of it. Only let the
point cut, and a very little of the edge beyond it, and do not expect to
take a _deep_ cut so as to bring off a thick shaving. In metal work you
will always have to proceed slowly, but nothing is more pleasant when
once you can do it well.
You will at first have to experimentalise a little as to the exact
angle at which to hold the tool, but you will soon find out this; and
the advantage of hand-tools is, that you can always _feel_ as well as
_see_ how they are working, and can ease them here and there to suit
the material. It is rather difficult at first to hold the tool still in
metal-working, but, like all else, it becomes easy by practice; so much
so, that to hold the tool steadily in one hand is not only possible, but
is the mode always followed by watchmakers. While you are about it, you
should turn the graver over and try it in other positions; for although
the two sides of the bevel nearest to the point are the only ones to
be used, these may be applied in either direction, because they are
both sharpened to angles of 60°, and so long as you present them at the
correct angle (the smallest possible in respect of the work), it matters
not which face of the tool lies uppermost. After squaring off one end,
the approved plan is to remove the carrier, reverse the bar, and do the
same to the other end. Then begin to turn from the right hand. Place the
graver as before, with the point overlapping the end very slightly (so as
only to use the extremity of the cutting edge close to the point), and
take off a light shaving along the bar for a distance of about half an
inch, or even a quarter, keeping the edge of the graver which is on the
rest in one position, and moving the tool, not by sliding it along the
rest, but by using the point upon which it lies as a pivot. It is very
difficult to describe this exactly, but Fig. 52, O, will help to explain
it. The tool is to rest upon one spot, and the point to move in short
curves like the dotted lines, being shifted to a new position as you feel
it get _out of cut_. The left hand should grasp the blade and hold it
tightly down upon the rest, while the right moves the handle to and fro
as required. The curved dotted lines are necessarily exaggerated, but the
_principle_ of the work is this, whether you use a graver or a heel-tool.
You should turn about half an inch quite round, and then go on to the
next, by which you will always have a little _shoulder_ upon the work for
the tool to start upon, and this will be nice, clean, bright metal, and
will not blunt the tool. But if you go to work differently, so that the
edge of the tool comes continually in contact with the rough outside of
the iron caused by the heat of the fire, and which is exceedingly hard,
the point of the tool will be quickly ground down, while the iron will
not be cut into at all.
I need tell you no more about turning a _bar_ of iron in the lathe,
because the above directions apply in all cases; but if you have to
turn the _face_ of a piece of metal that is carried in a chuck of some
kind, you should always work _from_ the middle towards the edge, and
if the graver is used, its bevelled face will lie towards you during
the process. Take care to chuck the metal very firmly, for it is most
annoying to have it suddenly leave the chuck or shift its position after
you have been at the trouble of turning part of it truly. In such case it
is very difficult to replace it exactly as it was before, and all your
work has in consequence to be gone over again. When taking the final cut,
or before, if you like, dip the end of the tool into water, or soap and
water, and see the effect. The surface turned in this way will be highly
polished at once, and the tool will cut with much greater ease, so that
a large, clean shaving will come off. When using a slide-rest, you will
find it always better to keep water just dripping upon the work and point
of the tool; but there is a drawback, nevertheless, to this plan, for, as
might be expected, it makes a mess and rusts the lathe, and sometimes the
work as well, so the water must be constantly wiped off it.
THE SLIDE-REST.
I shall now pass on to describe a mechanical arrangement called a
slide-rest, of which there are two separate and distinct forms, one
for metal and one for ornamental turning in ivory and hard wood. The
ornamental work that can be done I shall pass by for the present,
because few boys are provided with the costly apparatus required, and
I am rather addressing those young mechanics whose tastes incline them
to model machinery and to practise the various operations of mechanical
engineering on a small scale. To such a slide-rest is an _almost_
necessary addition to the lathe, for there is a great deal of work which,
I may say, cannot be done without it; for instance, boring the cylinders
of engines (except small ones of brass), turning the piston-rods and
various pieces which require to be accurately cylindrical and of
equal size, perhaps for the length of a foot or more. Hand-work has
accomplished _something_ in this way in olden days, but the inability
of workmen to advance beyond a certain standard of perfection with
hand-tools alone, became such a hindrance to the manufacture of the
steam-engine, as improved by Watt and others, that had not Maudsley,
Naysmith, and others developed the principle of the slide-rest and
planing machine, we should not yet have lived to see those gigantic
engines which tear along like demon horses with breath of fire, at the
rate of sixty miles or more in as many minutes. So likewise would various
other machines, which now appear absolutely necessary to supply our
various wants, have stood in their primitive and imperfectly developed
forms; for it is necessary, before constructing a machine, to have the
means of turning cylindrical parts truly, and producing perfectly level
plates where required.
The object of a slide-rest is to provide means for holding a tool firmly,
and giving it a power to traverse to and fro and from side to side, so
that by the first we may be able to cause such tool to approach or recede
from the work, and by the second we may cause it to move in a perfectly
straight line along its surface from end to end. This is accomplished
in the following manner:—The drawing being a representation of one of
the first machines constructed for the purpose. A rectangular frame,
A, of iron is carried by a pair of strong uprights, B B, fixed to the
sole-plate, C, by which it is attached by a bolt to the bed of the lathe.
Lengthwise of this frame runs a screw, prevented by collars from moving
endwise, but which can be turned round by the winch-handle, D. Thus a
nut through which this screw passes, and which only has endwise motion,
will, when the latter is turned by its handle, traverse it from end to
end in either direction, according as the screw may be turned from right
to left or the contrary. This nut is attached to the under part of a
sliding-plate, E, which has a part projecting between the sides of the
frame, and also two others on its outside, by which it grasps the same
with great accuracy, and is prevented from any shake or play as the
whole with the nut is made to traverse to and fro along the frame.
Lengthwise of this sliding-plate, that is, in a direction the opposite to
that of its own traverse, are two bars bevelled underneath, fixed exactly
parallel to each other, which are so arranged to guide the cross traverse
of another plate with chamfered edges to fit the bevels of the guide
bars. This second plate has on its upper surface two clamps which secure
the tool. It is plain, then, that by this arrangement the two required
movements are attained, the lower plate sliding along in one direction
parallel with the lathe-bed, and the other across it. In the original
rests, this upper plate with the tool was moved by hand, and in the
modern rest for ornamental turning (which this was also constructed for)
the same is done, but a hand-lever is added for the purpose.
But although a similar arrangement is needed for metal, it is plain
that the top plate should have a more easily regulated motion, and
that we should be able to advance the tool as near the work as may be
desired, and then to retain it securely at that distance while giving the
necessary movement in the direction of the length of the object to be
turned. The method of effecting this is at once suggested by the screw
and nut of the lower part, and by merely adding to the top a similar
arrangement, the desired end is at once attained.
[Illustration: Fig. 54.]
The actual construction of such rest varies somewhat, but Fig. 54, H,
shows it in its most ordinary form. The lower part is, of course, to be
clamped down securely to the lathe-bed, there being a projection below
which is made to fit accurately between the bearers similar to that
beneath the poppits. This projection secures the correct position of
the rest, of which one frame or plate will travel lengthwise of the
bed, while the other will move exactly at right angles to it. But in
the _compound_ slide-rest, which is very general, there is also a third
circular motion, by which the upper part can be set at any angle with
the lower, instead of being permanently fixed at right angles to it. By
this the tool can be made to approach the work more and more as it passes
along it; and it will therefore cut deeper at one end of its traverse
than at the other. The result will be that what is thus turned will not
be a true cylinder, but a cone, _i.e._, it will be larger at one end than
the other, although otherwise smooth and even.
We are thus provided with the most valuable addition to the lathe ever
devised by mechanics, and it is no longer a question of the strength and
skill of the workman whether we can produce a perfect piece of work, but
simply of the accuracy with which the lathe and rest are constructed, and
of the form and condition of the tools to be used. The latter are not
exactly like those ordinarily used, although the principle of the cutting
angles already laid down needs to be adhered to even with more unfailing
attention than that required for the correct formation of hand-tools.
Moreover, it is plain that—here we shall no longer feel whether the tool
is working as it ought to do—we shall be unconscious of the precise
amount of _strain_ that is being brought to bear against its edge, and if
it is by chance working in a bad position, at a wrong angle, we cannot
re-adjust it in a moment as we could a hand-tool by a slight movement of
the fingers or wrist.
Hence you will see at once how very important it is that tools for the
slide-rest should be shaped with the _most rigid adherence_ to correct
principles; and, further, that they should be so fixed in the slide-rest
as to meet the work at the precise angle, and at the height exactly
suited to the material of which it is composed. As regards the latter
point, it may be taken as an almost invariable rule that the work should
be attacked on its axial line (that is, a line that would run from end
to end of it dividing it lengthwise into equal parts, or, as it would
commonly be named, its _middle_ line). If the tool meets it above this,
it is most likely that it will rub against it, and the point will be out
of cut. If it meets it below, there will be a tendency for the point to
catch in, and the work to roll up upon the face of the tool, which, in
fact, it very often does with careless workmen, and then there comes a
smash of some kind—lathe centres snapped off, the tool broken, the bar
bent beyond remedy, and possibly the operator’s toes made unpleasantly
tender.
The most common slide-rest tool for outside work is that given at H².
It is made straight, as shown, or bent sideways to right or left to
cut shoulders on the work, or enter hollows, or creep sneakingly round
corners, or any other of those crooked ways in which man delights; but
whether straight or not, these tools have all most commonly the cranked
form shown here. This gives the tools a _slight_ degree of elasticity—not
very much, because that would only injure the perfection of the work;
therefore they are not very considerably cranked. The angles are ground
as directed in the table of tool-angles, and if the point is too low,
slips of iron are placed below the shank upon the tool-plate of the
slide-rest; if too high, the grindstone must be resorted to; and the
advantage of these cranked tools is, that they can be ground down several
times without being brought too low to be packed up with iron slips to
the right level. Thus a cranked tool is by far more advantageous for the
slide-rest than one made straight like those used for hand-turning. For
inside work, however, or “holing,” the crank form is not possible, unless
the hole is of large size, and so, for this purpose, straight side-tools
are used, like K.
If the tool is well placed, as well as correctly made, nothing can be
more easy and delightful than slide-rest work. You merely advance the
tool to take the required cut (beginning generally at the right-hand end
of the bar), and then gently turning the other handle, you will see it
traverse along, as if work was a pleasure to it, as it ought to be to all
young mechanics. Not infrequently, however, instead of this even, steady
work, the tool jumps and catches, or rubs and shrieks: it is out of
temper, I suppose; at any rate, in some one or more particulars it needs
correction.
Although with the slide-rest you can generally venture upon taking a
deeper cut than you could with hand-tools, it is by no means well to
hurry the work. At first, especially before it has become cylindrical,
the tool will only cut partly round its surface, and the work is done in
an uncomfortable, jerking, dissatisfied sort of way, and the deeper you
drive the tool the worse it is; but as soon as the outer skin is off, and
the work has become cylindrical, a long, clear, bright shaving curls off
pleasantly from end to end, and the surface ought, if the tool is wetted,
to become at once of a finished appearance.
You should always, with a slide-rest, take the whole run of the piece
from end to end to a certain depth, and then, commencing again at the
end, repeat the same process, and so on until the required size is almost
attained. When it is, take out the tool with the pointed end which has
been in use, and insert one freshly sharpened with a broad point, getting
it so placed as to cut the shaving both from the surface below, and from
the shoulder to which it is attached at the side, as I explained to you
in the chapter on grinding and setting tools, and which must be well
understood before you can hope to make good work with tools rigidly fixed
in a slide-rest. With this tool, kept wet with soap and water (or soda
water, which is better for this than for your stomach), take a _very_
light shaving from end to end, taking especial care to turn the handle
which gives the traverse slowly and _evenly_. If you stop, or almost
stop, the tool will be sure to draw a little deeper into cut, which will
make a scratch upon the work, or, it may be, plough a groove, and so far
spoil the appearance of it.
Whenever you finish turning any bar that has been centred at each end,
be careful to leave the centre marks just as they were when the work was
in the lathe. The ends will have been otherwise trimmed off at the very
commencement, and it may happen that at some future day it may be desired
to re-mount the piece for repair, when, if these marks are gone, and new
centres have to be drilled, the whole will run so much out of truth that
it will have to be entirely re-turned from the commencement. Do not,
therefore, fancy that these centre marks are unsightly, and forthwith
file them out, but be content to leave them.
Slide-rest tools, made in the ordinary way, are so far troublesome in use
that if they get broken you must have them re-forged, and few country
smiths know anything about such matters. I have a tool now lying by me
made by a smith (true, it was a Welsh smith), and although I stood by
and explained how it should be done, and cut one out of a piece of wood,
it never arrived at a proper shape, and was never even placed upon the
rest. I keep it as old Izaak Walton kept the Londoner’s artificial fly,
viz., “to laugh at,” and as a caution to all concerned, never to go to a
country blacksmith for slide-rest tools. The following plan answers very
well for many kinds of outside work, and is on the whole a plan that may
be satisfactorily followed by the young mechanic.
Instead of having the tools constructed from a large bar of steel half
an inch or so in the square, they are made of short pieces about an inch
long, fitted into a peculiar holder.
The advantage of this arrangement consists in the ease with which you can
make your own tools out of broken round, triangular, or square pillar
files, small chisels and such like. These can be shaped by the grindstone
alone, and the blacksmith will not have to be called into requisition. I
shall give you two forms of tool-holders, more or less simple, because I
may suppose my young mechanic to be fast growing into an old hand, and
able to appreciate differences in these arrangements.
Fig. 55, A, B, represents two of such holders, one for round, the other
for flat steel cutters. You can see at once that when these are upon
the bed of the rest, they form a tool with cranked end, as previously
described, and can therefore be used in precisely the same manner. I
shall give no directions for _making_ these tool-holders, which are,
nevertheless, very simple affairs, and can be readily understood from the
drawings here given.
[Illustration: Fig. 55.]
Another form is shown at C. The part _d e_ is a clamp, which is
separately drawn at _f_. This, like the last, enables one to use all
sorts of odds and ends for tools. There are several other patterns
of tool-holders, arranged either to use the little pieces of square,
round, or triangular steel bars, so that one side, at least, of these
may remain without grinding, and others in which two entirely new faces
must be given to the tool by the grindstone. The latter are, perhaps,
generally the best, because you can then, with the aid of the table of
tool-angles, shape your cutters very accurately to the work required of
them.
Although such tool-holders and cutters are generally used for metals,
there are others intended for wood; and constructed to hold miniature
gouges and chisels, which perform their work admirably. A capital tool
for outside work, Fig. 55, E, which was used extensively at Portsmouth
dockyard for brass turning, is made simply by filing off at an angle of
about 45° a round short bar of steel. This angle, however, is unusually
small for brass and gun-metal, 80° being better. For iron it will answer
better, because though filed, or rather ground at 45°, the cutting edge,
a little way from what may be called the point of the tool, is nearer 60°.
Similar to these last are the tube gouges, short bits of steel tube
ground off and sharpened. These fixed in a holder answer beautifully for
soft wood, and do not “catch in.” If the holder is bent so as to bring
the tool into proper position, inside work can be rapidly effected by
these, such as hollowing out large bowls and similar heavy work. All this
can, of course, be done rapidly with the slide-rest, so far as regards
the removal of the greater part of the wood. But in the case of a bowl,
in which a curve predominates over a straight line, hand-tools must be
used to finish it (generally the inside hook-tool). This last is, in
fact, almost identical with the tube gouge; for the slide-rest, and that
which makes it so difficult a tool to use, is that, being a hand-tool,
and subject to slight unintentional changes of position upon the part of
the workman, it catches in, and is either wrenched out of the hand, or a
piece is chopped off the wood. Rigidly held in the slide-rest, the exact
angle, once found, is of course maintained.