[Illustration: FIG. 239]
Next in order of the compound chucks stands the eccentric, the use
of which is not entirely confined to mere ornamentation, as it is
often very convenient to the turner to have the power of shifting the
centre of his work. Thus, a _solitaire_ board may be drilled with
the necessary cup-shaped holes, or any work of a similar character
completed by the help of this chuck without the necessity for
constant re-centering. The _general_ work of the chuck in question
is nevertheless ornamentation, for which it is peculiarly adapted
either alone or in combination with other compound chucks, or overhead
apparatus. The sliding plate of this chuck works between chamfered
steel bars, the same as in the oval chuck. There is, however, no guide
ring on the lathe head to regulate the movement of the slide, and
therefore also no necessity for the projecting arms at the back. The
slide, in fact, is moved by a screw with a graduated head, similar
to those already described. Fig. 239 represents the common form of
this chuck, in which the wheel which forms a dividing plate is moved
by a tangent screw. The sliding plate is shown slightly drawn out by
its screw, the degree to which it is moved being that of its required
eccentricity. When the plate is drawn back to correspond with the
base plate, the centre will be in a line with that of the mandrel,
and any work turned upon the chuck in this position of the slide will
be cylindrical. The central screw of all these compound chucks being
alike and of the pitch of that on the mandrel, any of the ordinary cup
chucks can be used with them to hold the work; or the eccentric chuck
can be screwed to the elliptic, cycloidal, or any other in the set, by
which means an endless variety of curves can be described. The effect
produced by the simple eccentric chuck now described is as follows,
the slide rest being used with it as a matter of course. Let a piece
of box or other wood be fixed by means of a cup or other chuck upon
the screw of the eccentric chuck, and the slide rest with a single
point tool be brought in front of it. By means of this the work must
be carefully faced, and made uniformly level. A ring A, Fig. 240, may
now be cut, which will be concentric with the mandrel. The slide of
the chuck being now drawn down by a few turns of the leading screw
(the tool and rest being kept in its original position), the centre
of the work will thereby be shifted, and the tool being advanced to
touch the same, the circle B will be formed of the same size as the
first, but necessarily cutting it at two points. Another turn of the
screw will enable C, and similarly D, or any number of circles to be
successively formed. The centres of these circles will be in a line
across the face of the work. The ratchet wheel is added to enable
the turner to arrange his circles round a common centre, instead of
being thus obliged to keep them in a right line, and it will presently
be seen what a beautiful variety of interlaced circles can thus be
accomplished. The dividing wheel is, as previously explained, divided
on its edge into an equal number of teeth, or racked for a tangent
screw and divided on the face and edge. We shall suppose the number of
divisions to be 120. Face the work afresh, and, drawing back the slide
until the centre is concentric with the mandrel, as at first, cut a
boundary circle, A, Fig. 241. Move the slide of the chuck a few turns,
as before, and cut an eccentric circle. Now move the dividing wheel
thirty teeth, and cut a second, and, advancing by thirty each time,
cut a third and fourth, and Fig. 241 will be the result; the centres
of the eccentric circles falling upon four points of the inner dotted
circle, which is itself concentric with that first made.
[Illustration: FIG. 240.]
[Illustration: FIG. 241.]
[Illustration: FIG. 242.]
[Illustration: FIG. 243.]
If the same process is followed, but the number of the circles
increased, a very neat snake-like ring will be formed, constituting
a border, in the inside of which other combinations may be made. In
Fig. 242, twelve interlacing circles are shown; in Fig. 243, twelve
circles, described upon centres, which lie upon the circumference of
a central circle of equal size. This last pattern, when more finely
executed, by doubling or trebling the number of eccentric circles,
forms the device generally cut upon watch cases, under the name of
engine-turned. The best way to _try_ patterns, is to cover the face
of a piece of boxwood with paper, using a pencil in the tool-holder
of a slide rest instead of a cutting tool. If a softer disc is used
instead of box, round pieces of paper or thin card can be fixed
upon it with ordinary drawing pins; and if the first pattern is
unsatisfactory, a second, and any successive number of pieces, can
be mounted, and fresh patterns traced by the same means. It would be
mere waste of time to multiply specimens of the patterns that may be
executed by the aid of the chuck just described; and, indeed, this
could only be done by cutting in the lathe itself the blocks from
which such specimens must be printed. For the present, at any rate,
the _principles_ only by which such devices may be executed will
be given (as above,) and the designs will be left to exercise the
ingenuity and taste of the reader.
It happens, moreover, that few as are the works devoted to the
general principles and practice of plain turning, more than one has
been published on ornamentation by the eccentric and other compound
chucks, in which a variety of executed patterns appear, of more or
less beauty; and in the _English Mechanic_ has lately been printed a
selection of exquisite designs by Mr. G. Plant, whose chuck, indeed
(to be presently noticed), bids fair to supplant the most simple one
now described. The chief recommendation, perhaps, in the latter, is
its great simplicity, as it may be made by any amateur sufficiently
practised in the use of tools; whereas the geometric chuck is too
complicated to permit this. It will be observed, on inspecting the
drawing, Fig. 239, that the divisions on the face of the wheel are
continued on the side above the part that is racked; this permits them
to be seen when the piece of work overlaps the circle of the wheel.
The steel point shown at B, answers as an index, either to the surface
marks, or to those on the side. The tangent screw is now generally
fitted in a small frame, which is itself pinned at one end to the top
plate, and kept up to the dividing wheel by an eccentric cam. This is
not shown in the drawing; the plan is nevertheless good, as the screw
is instantaneously released from gear at pleasure, when the wheel
may be turned by hand to any desired position; after which a slight
movement of the cam brings up the screw, and all is made ready for
work. The eccentric chuck becomes available for such work as shown
in Fig. 244, representing the bottom of a candlestick, ringstand,
or similar article. In this case the centres of the eccentric work
(now cut quite through) are on the circumference of a circle larger
than, and outside, the work itself. Instead of cutting through the
whole thickness of the stuff the outer circle may remain such, and
the blackened part may represent an inner raised surface, when the
contrast formed by the sharp edges round the pattern with the smooth
circular part will be very agreeable to the eye. To improve still more
this design, the outer part may be ebony nicely moulded and edged with
ivory, and the raised part ivory; or the same may be alternations of
ebony and holly, which will form a contrast almost equally agreeable.
A small chisel-ended tool must be made for this work if the whole is
in one block, as it will be necessary to leave a level surface upon
the face of the lower part. There are an infinite number of designs
of similar nature, which will occur to the reader when the principles
of the chuck have been mastered, some of which would at first sight
appear to have been worked by other means. Fig. 245, for instance,
which is but a modification of the last, scarcely looks like lathe
work, but can be cut more rapidly this way than any other--of course
the fret saw will do similar work, but it would first have to be
marked out, and afterwards the marks of the saw teeth removed, whereas
the above is cut and polished at once. It may here be observed that
the eccentric chuck itself is used to fix the _position_ of the
various circles to be cut, whereas the _size_ of these circles is
determined by the slide rest. Thus in Fig. 246, while the centre of
the chuck is concentric with the mandrel, bring up the tool in the
rest and cut the circle F, G, H, of which B is the centre; draw down
the slide of the chuck until its centre is at C, leaving the slide
rest as it is, and the circle F, E, D, will be formed of _equal size
with the first_. Now move the screw of the slide rest so as to draw
in the tool towards the centre of the lathe bed without altering the
chuck, and the small circle will be the result, whose centre (being
dependent on the chuck alone) is the same as that of the larger
circle. Bearing in mind this principle, that the chuck determines the
various centres only, and the slide rest the radii, little difficulty
will be experienced in devising and executing designs. Such is the
simple eccentric chuck, of which the use is tolerably extensive; but
there are, nevertheless, certain positions in which the eccentric
designs are required, which cannot readily be obtained by its means.
Fig. 247 is one of these, in which a moment's inspection will show
the necessity of two distinct movements of the slide at right angles
to each other. Hence a second slide is attached to the first at right
angles, much the same in effect as a second chuck screwed upon the
first but standing across it. This is the compound eccentric chuck
to be subsequently described in detail. There is one drawback to the
use of these chucks, namely--their excessive weight, which causes
a great deal of vibration in the lathe itself, especially when the
eccentricity of the slide or slides is great. An accidental blow
moreover from the chuck under the above condition would be very
severe. Hence the various cutters eccentric and others, worked by
the overhead apparatus already in part described are infinitely more
pleasant to use and even more effective and more easily managed.
The eccentric chuck can be used in combination with these, and the
capabilities of the two will thus be vastly extended, but in this
case the chuck is kept stationary while motion is given to the tool,
and the defect just alluded to no longer exists. In cutting patterns
upon hard wood and ivory a common defect is shallowness of work, the
cuts should not be so light as to give merely an effect of a design
_scratched_ upon the surface. The cut should be deep and clean, and
the tool not only sharpened but polished so as to leave the device
boldly executed, the small triangular and other shaped pieces left
between the cuts standing up clear and solid. Some patterns, as the
shell, which will be presently spoken of, require to be deep at one
part and shallow at another. Some devices look best when cut with a
point tool with double and others with single bevel to the edge, and
the same design worked with different tools will appear almost like
two distinct patterns.
[Illustration: FIG. 244.]
[Illustration: FIG. 245.]
[Illustration: FIG. 246.]
[Illustration: FIG. 247.]
[Illustration: FIG. 248.]
The double eccentric is represented in Fig. 248. The part A is the
foundation plate, with a projection at the back, tapped to fit the
mandrel. B, B, the lower guide bars; K, K, the lower sliding plate.
All the above parts are precisely similar to those of the simple
eccentric chuck. Upon the face of this lower slide are attached two
chamfered guides, C, C, at right angles to the first. They are kept
in place by screws passing through oval holes on their faces, and
tightened when required by screws, tapped into four little square
blocks, D, D. Between these guides slides the upper plate, which
carries the screw for chucks, and the dividing wheel as before worked
by a tangent screw, G; to either end of which a key is fitted. The
leading screws, E and F, which move the two slides, have squared
ends projecting both ways, so that the plates can be made to work
eccentrically in either direction, which is sometimes an advantage.
The chucks do not screw down upon the face of the division plate,
on account of their projecting parts at the back; and very commonly
a round plate, O, somewhat smaller than the wheel and about 1/4 in.
thick is attached to the face of the latter to raise the work still
higher, so that the dividing plate can be readily seen. The more
compactly, however, the parts of this chuck are made, and the less
the work projects from its face the better; as there will be the less
strain upon the central pin, and upon the plates and their guide bars
when the tools are applied to the work.
To be able thus to place in the centre of rotation any given point in
a piece of work, whatever may be the form of its boundary lines, is
of immeasurable advantage, even though the capabilities of this chuck
are confined to objects of plane superficies, it being impossible
to reach by its means the side of a cylinder, or the surface of a
sphere or spheroid. It is evident that any line upon the face of a
box, for instance, whether the latter be square, round, octagonal, or
of any other form, may be followed with two movements of the slides,
combined with the rotatory movement of the dividing wheel. Thus, a
border of interlacing circles may be carried round the edge of such
a box, Fig. 248; or, a series of such circles forming constantly
diminishing octagons, hexagons, squares, &c., may be thus readily
executed. Nevertheless, what was said of the simple eccentric chuck,
applies with even greater force to the compound eccentric. It is a
heavy piece of apparatus, requiring a lathe with substantial poppets
and bed; the whole well braced to the floor and wall, to withstand the
excessive vibration caused by the revolution of the apparatus. It was,
indeed, in view of this and similar appliances that we insisted in our
initiatory paper upon the great importance to the workman, of adequate
strength and solidity in the various parts of the lathe itself.
In Fig. 249, we give a simple specimen of work to be executed by the
compound eccentric chuck.
[Illustration: FIG. 249.]
[Illustration: FIG. 250.]
The compound geometric chuck of Ibbetson, manufactured by Holtzapffel
and Co., is a double eccentric considerably improved and of very
extensive application. A full description of it is published in a
book written by the inventor, in which an immense number of patterns
executed by its means is given with detailed directions for their
execution. As these patterns are almost essential to a description of
the apparatus as exemplifying the working of its several parts, the
reader is referred to the book in question, or to a translation of it
into French in the supplement to Bergeron's work. To enable the turner
to execute patterns on the side of cylindrical pieces a chuck is used
called a dome chuck, similar to Fig. 250. A rectangular frame of
brass, A, carries a sliding plate C, at right angles to it, the latter
having a tailpiece which fits accurately between the frame, and is
tapped to receive the finely cut leading screw with divided head, B. A
nut at the back of the frame clamps the slide in any desired position.
Upon the upper face of the latter is a wheel racked on the edge so as
to be moved by the tangent screw, E. This wheel, like that of the
oval and eccentric chucks, turns on a strong conical central pin, and
has a screw attached of the same pitch as that on the mandrel. The
chuck is screwed to the mandrel by the projecting flange, F. The work
is thus mounted at right angles to its ordinary position.
By this arrangement any point in the side of a cylinder can be brought
in contact with a tool fixed in the slide rest, and by means of the
graduated screw heads of the latter and of the chuck various devices
can be accurately made. This chuck may be used alone or in combination
with the eccentric, and the quick revolution of such cumbrous pieces
that would be a great drawback to their use is less frequently
required, now that the following apparatus has been added to the
lathe, and eccentric revolving cutters, with drills and other tools,
have taken the place of heavier and more inconvenient apparatus. It is
indeed much more convenient in the majority of cases to keep the work
itself fixed, and to operate upon it by tools put in rapid motion,
because the latter, from their excessive velocity compared with that
which can be conveniently given to the material, make better work, and
at the same time from their lightness impart no tremor to the lathe
while in motion. The cuts thus made are in consequence very clean
and smooth, and free from those slight undulations apparent when any
vibration takes place in the lathe itself. The different varieties of
overhead apparatus have been already described and illustrated, and it
only remains to describe more in detail the revolving cutter frame,
drills, and other apparatus used therewith.
The following pieces fit into the top of the slide rest in what is
called the tool receptacle, and are advanced to the work by means
of a lever as already described. Fig. 251 is the revolving cutter
frame, the spindle of which is put in rapid motion by a cord from
the flywheel passing to the small pulley through the medium of the
overhead apparatus, as shown in a previous page. For the purpose of
cutting _small_ intersecting circles, a forked drill, Fig. 252, or
a crank formed drill, 253, will suffice, and if these are made to
cut deeply the result will be a succession of hemispherical knobs or
beads (these must not intersect). A drill like Fig. 254 will give a
knob raised in steps, and it is plain that by cutting the end of the
drill to a section of the required moulding the latter may be rapidly
executed. The flat inch long cutters used with the geometrical chucks
(when the work revolves instead of the tool) are, of course, made of
a variety of forms upon the same principle. Cases of these drills
and cutters beautifully finished are sold by all the leading dealers
in turning lathes and apparatus. It is essential that these tools be
kept very sharp, and that their cutting edges should be _polished_ if
first-class work is to be done. The difference in the appearance of
execution is very evident when the cutter is thus perfect, as every
cut bears a high polish, which cannot otherwise be imparted. Nothing
can be applied to finish eccentric work except friction with a hard
brush, and even this is much better avoided, as rubbing of any kind
tends to round edges which should be kept sharp and to obliterate
the finer and more delicate lines. It is likewise the best plan to
finish with any particular tool all the work to be done by it without
removing it from the tool holder for the purpose of sharpening. If,
however, this is necessary the following contrivance must be used to
insure the precise form which the cutter had at the commencement of
the work. This being likewise necessary with respect to the fixed
tools for ornamentation, the apparatus requisite in either case will
be introduced here, the drawings and description being extracted from
Holtzapffel's valuable work already alluded to.
[Illustration: FIG. 251.]
[Illustration: FIG. 252.]
[Illustration: FIG. 253.]
[Illustration: FIG. 254.]
Fig. 255 is arranged for flat tools of various angles, or drills with
single joints. A, is the stand of brass, with two turned and hardened
steel legs. To this is hinged at G, by a screw joint, the part K, the
upper part of which forms a semicircular arc, C. A second arc, B is
fixed at one end to the stand A, and passes stiffly through a mortise
at the top of K. The latter can be raised, therefore or lowered at
pleasure upon this second graduated arc, and clamped at any angle
by the screw H. To the lower part of K is pivotted the tool holder,
D, the upper part of which is pointed, and screws as an index upon
the arc C, showing the angle at which it is placed. This tool holder
is clamped by a nut at the back, which fits the end of a screw seen
near the point. The figure below shows a tool holder which fits into
the projecting parts of D, and serves to hold the small flat tools.
Below is a similar holder, used for round-shanked drills. F is one of
three flat slabs upon which the tools are to be ground, there being
one of iron, one of brass, and one of hard wood with a flat strip of
oilstone imbedded in it, flush with its upper surface. The tool and
its fittings are generally arranged in a box with three drawers; these
contain the slabs of oilstone and metal, with the powders necessary
for grinding and polishing. To use this instrument, the point of D
is adjusted to the required angle for one side of the point of the
tool. (It is shown at 40 deg. in the sketch.) The latter is then
placed in the holder, and made to project until, when the angle of the
chamfer is adjusted on the arc B, the part A is level, and therefore
parallel to the surface of the grinding plate. The whole thus forms
a tripod, the third leg of which is formed by the tool itself. The
latter is first rubbed on the oilstone with a little oil. It is then
finished more perfectly on the brass slab, dressed with oilstone
powder and oil. Previous to this the tool is moved one or two degrees
more upright by the arc B. A narrow facet is thus ground, having a
dull grey polish. The tool is now carefully wiped clean, and polished
with crocus and oil upon the slab of iron. If the point of the tool
is central, with a chamfer both ways, the point of the tool holder
is first adjusted on one limb of the arc and the tool ground, and
then the same adjustment made on the opposite limb, so that the other
side of the point can be operated upon. Thus tools of any angle and
any bevel may be sharpened to a nicety without fear of altering the
original form of the point, and this may be done, if necessary, during
the process of eccentric turning, although, as before stated, it is
better to fix the tools well sharpened at the commencement of the
work, and not remove them until at _least_ one complete set of circles
or other patterns have been cut.
[Illustration: FIG. 255.]
[Illustration: FIG. 246.]
[Illustration: FIG. 247.]
The instrument just described is evidently unsuited for the drills and
bead tools which present a concave edge like 246 A, B, C, enlarged
sketches of tools copied from Holtzapffel's work. For these the
latter directs to use large or small cones (247) of iron and brass,
to be dressed, the first (which is the polisher) with crocus, the
second with fine emery and oil, the flat side of the tool being held
towards the point of the cone, the bevel towards the thick end. Part
of the edge of C must be delicately sharpened by hand, as no guide
can be used for the step-like portion of the edge. The cones for
sharpening are either mounted in the usual manner, by one or both ends
in the mandrel of the lathe, or fitted into the spindle of a small
drilling lathe-head, the pulley of which is connected by a catgut
band with that of the mandrel of the small lathe-head, being fitted
with a tailpiece to fit the rest socket, or otherwise mounted on the
lathe-bed. The smaller cones especially require to be driven at a high
speed. When larger circles or mouldings are to be cut, these small
crank-form drills are no longer available, and are replaced by a very
simple, but most effective contrivance called the eccentric cutter,
by which any work that is within the scope of the eccentric chuck
and fixed tool may be executed with great precision and rapidity.
This is represented in Fig. 248[20]--a small oblong frame of brass,
about two or two-and-a-half inches in length, and half an inch or
so in breadth is traversed by a fine screw, prevented from moving
endwise by a collar, as in the slide rest (of which, indeed, this is
a miniature). A slide, C, with a little tool holder at the top of it,
is moved along the frame by the leading screw, the head of the latter
being graduated, and also the upper surface of one or both sides of
the frame. The projection A, fits into the end of the drill holder,
and is secured by a screw. Circles of a diameter equal to B, B" may
thus be cut, and their effect varied by placing tools of any form of
edge in the tool holder. Such a tool as A, will thus no longer cut a
minute circle forming a hemispherical raised knob, but will form a
circular moulding, such as that shown in part at Fig. 249, except when
the tool holder is on the middle of the frame and the tool concentric
with the mandrel. The single point tools, however, with single or
double bevel, are more commonly used, in this cutter, as mouldings
can be turned as efficiently with hand beading tools, with or without
the eccentric chuck, according to their required position. It may here
be mentioned that eccentric work should always be cut on wood of one
colour, or on ivory, as the veinings of the richer fancy woods, which
are so beautiful in other cases, only serve to confuse the tracery
made by the eccentric cutter. Of all woods for fancy work with the
eccentric chuck or cutter, nothing equals African black wood. It is,
however, costly, and only ranges to a diameter of five inches, as
great part is unsound. The rind is hard, thick, and white, similar to
boxwood. Next to this for such work stands, perhaps, cocus, or cocoa
wood, which is not the tree bearing the cocoa nut, the latter being a
palm, which is more like cane in texture. One of the most effective
patterns to be formed by the eccentric cutter is the shell, Fig. 250,
in which one side, or rather one portion of the circles composing it,
is very deeply cut, while the opposite part is shallow. This can be
simply effected by throwing the sole of the rest out of the level,
by placing a thin piece of wood or metal across the lathe bed, so as
to tilt up the rest and place it (with the cutter) in an inclined
position. The tool will thus begin to cut at one part before it
touches the surface elsewhere, and the desired effect will be readily
produced. In using the eccentric cutter great rapidity of motion
must be given to it, but the tool must be advanced very carefully,
or it will be broken. The lever handle is the best to use for the
purpose. Akin to the shell pattern are those in which part only of
the circles are cut, leaving an effect shown by the border round Fig.
250. This is produced in the same way as the last, being, in fact, a
ring of shells in their initiatory stages. This is a very effective
snake-like pattern, when fairly and cleanly cut. When the eccentric
cutter is used, it must be remembered that the principle of work is
not quite the same as with the eccentric chuck. With the latter it
was stated that the size of the circles depends on the slide rest and
the position of their centres on the chuck. In the present case the
eccentric cutter regulates the sizes, and the screw of the slide rest
itself the positions of the centres of the circles, since the part
A of the cutter will always be in the centres of the same, and this
part is attached to the rest. It will be understood that this remark
respecting position of centres only relates to circles lying on the
diameter of the work, such as Fig. 251, the distance between _a_ and
_b_ will be taken from the division plate on the pulley of the lathe.
The way to cut the above, for example, will be as follows:--Place
the slide rest so that when the cutter tool is in the centre of the
frame it shall be concentric with the mandrel. In this position it
will only make a dot in the centre of the work. Turn the screw of the
cutter frame until you have a radius sufficient for the centre circle.
Set the mandrel pulley with the index in No. 360, put in motion the
overhead apparatus and cut the circle, move the screw of the slide
rest a few turns (_thus fixing the centre of the second circle_),
until you find that the cutter will form the circle cutting the first,
and passing through its centre. (_Observe, this being the size of the
first, the screw of the cutter frame is not turned._) Cut the circle
in question, move the mandrel pulley a quarter round, so that the
index is in No. 90, and cut another; repeat the process twice more,
and 1, 2, 3, 4, will be cut. The _position of the centres_ of Nos. 5,
6, 7, 8, will now have to be determined as before, by working the main
screw of the slide rest; but, as their size is less than the preceding
set, the screw of the cutter frame must likewise be turned to diminish
them to the required degree. When by these combined movements their
position and size have been determined, they must be cut by the aid
of the division plate, in the same manner as the last, and so on,
till the whole have been cut. With respect to the ratio in which the
circles diminish, and the precise sizes of them, no rule can be given,
as this must depend on the taste of the operator. The sole object in
this place is to show the _principles_ whereby these patterns are to
be executed. A good deal of care is requisite in practice, and the
memory has to be often rather severely tasked. The best plan is always
to try a proposed pattern upon boxwood or paper, before risking it
upon more valuable material; and, where it can be done, it is well to
write down the numbers to be used on the various division plates. A
single false cut, it must be remembered, will spoil the whole work,
at a great waste of time, loss of material, and annoyance, only to
be appreciated by those to whom such an untoward accident may have
happened. The drilling apparatus, without the eccentric cutter, but
fitted with a round-headed drill, is used for the production of fluted
works, such as that shown in Fig. 252, A and B. The drill being
inserted in the end of the spindle, and its point or end (of any
desired form, either round, flat, or pointed) being brought opposite
one end of the flute, the lathe is to be put in motion as in ordinary
ornamental drilling, the mandrel being, of course, held fast by the
index and division plate. At the same time that the drill in rapid
motion is brought against the work by the lever handle, the screw
of the slide rest is slowly turned, and thus the groove or flute is
drilled out by the combination of longitudinal and vertical action.
The number of flutes in any given size of cylinder is determined,
first by a horizontal sectional plan on paper, and regulated
accordingly by help of the division plate and index. In making such
an article as Fig. 252, it will economise material, whether ivory or
blackwood, or a combination of the two, to form it of at least three
pieces, making the divisions at C, D. Care should be taken to leave
below the bowl, which should be as thin as paper if of ivory, the
part C on which the beads are to be drilled. The pedestal can then
be screwed into this, and will not penetrate the bottom of the bowl.
Ivory may be screwed in an ordinary set of stocks and dies if care is
taken not to screw up the latter too quickly. Lard may be used as a
lubricant in cutting this material, whether for sawing or drilling.
The part with raised mouldings between A and D is ornamented with
a vertical or universal cutter, and for greater ease and exactness
a template may be used in the slide rest by means of which all the
curves of the moulding may be accurately followed by drill or cutter.
The minute beads round the edges of the small mouldings are made with
two sizes of A, Fig. 246; a little knob is thus formed rising from a
hollow. The small knobs used as feet may be rapidly formed by a hand
beading tool of semicircular section, similar also to A, Fig. 246. A
pin may be left on each, or they may be drilled and attached by small
screws of brass wire made on purpose. The following cement will enable
the turner to make an ivory bowl for the above ornament so thin as to
be transparent; indeed it may be thus made so thin as to bend under
the fingers, although such extreme tenuity is not required in the
present case.
[20] A newer pattern appears on a later page.
[Illustration: FIG. 248.]
[Illustration: FIG. 249.]
[Illustration: FIG. 250.]
[Illustration: FIG. 251.]
[Illustration: FIG. 252.]
Take the finest sifted lampblack and make it into a paste with glue,
about as thick in consistency as paint. After turning the ivory
tolerably thin, paint this on the inside; let it dry, and repeat the
process till sufficient is laid on to form a kind of hollow core,
of strength sufficient to support the ivory against the action of
the tool. The material may now be thinned and ornamented from the
outside. When finished, soak a few minutes in warm water, and then
agitate in cold; it will become quite clean as before.
By altering the direction of the motion of the revolving cutter, the
several cuts made by it will assume a different character, and the
work will present a series of hollows scooped out, so to speak. The
cutter, 253, being fixed in the tool holder of the top slide, will
work vertically only, and produce patterns similar to Fig. 254, of
the nature of basket work. This is exceedingly effective, and, as it
may be cut so deeply as to penetrate the material of hollowed works,
the latter may be lined with red or other bright coloured silk or
velvet, and a variety of designs thus worked out. It is very necessary
in using the vertical cutters to move the tool holder forward very
gently, giving it at the same time great rapidity of revolution.
Without this it will at once stick fast in the work. The character
of the designs may, of course, be infinitely varied by using cutters
of different sections, as in the case of work done with fixed tools
with the aid of the eccentric chuck. The same cutters will, in fact,
serve both purposes. Fig. 255 represents a tool similar to the last,
but arranged to cut horizontally. With this, fluted work can be
done: but it is evident that the cord from the overhead apparatus
cannot here be directly applied, owing to the horizontal position
of the driving pulley. Additional guide pulleys, therefore, become
necessary, and, when these have to be arranged, the apparatus is
generally modified, and the universal cutter is used, of which one
form is shown in Fig. 256, and though it is not so good a pattern as
that which is described in a later page, it is nevertheless suited
for use with the old pattern of slide rest already delineated. With
this the direction of the cuts may be varied at pleasure--they may
be perpendicular, horizontal, or radial, and, when the templates
before mentioned are added to the slide rest, an infinite variety of
devices may be cut upon spherical and curved surfaces, so that the
cutter thus modified is fully entitled to its title of "universal."
The design, Fig. 258, is entirely the work of revolving cutters and
drills used with a template of the required section. It is intended
for a lady's workbox, opening with a hinge on the line, _a, b_, and
containing in separate compartments the various articles required.
It may be made entirely of ivory, lined with red or blue satin, and
the flutes round the body may be cut through to allow the lining to
appear. In the latter case, however, if the box is of ivory, black
velvet may be used to enhance the contrast, and, as the glossy pile
would be outwards, a second lining of any desired colour should be
added with the best side inwards. The rings for the handles, as for
all similar purposes, can be quickly made with the tool, Fig. 259. A
hollow piece of ivory being taken, and turned smooth inside and out,
one side of the tool is applied, as in the figure, so as to cut half
through the work. It is then removed, and the opposite edge applied
to the inside until the ring falls off completely finished. It is
then cut through with a thin saw or knife, and inserted in the tailed
ring or other projection intended to receive it. Handsome works in
ivory should always be kept under glass shades. The universal cutter
shown in Fig. 256 consists of a plate with chamfered edges to fit
the tool receptacle of the slide rest, having near each end small
poppets which support the round rod connecting the pulley bearing
piece, A, with the part, E, which carries the tool, F, the latter
being attached by a small slot and set screw to a cylinder revolving
in E, and having at its upper end the driving wheel, C. At G is a
circular piece or wheel racked on the edge, and turned by the tangent
screw, G. The hinder poppet is rectangular, and has divisions marked
upon it on each side of the angle numbered from the apex. The racked
wheel may with advantage be similarly graduated. When the part E is
vertical the cutter will be in a position to work horizontally, and
the pulley support will be vertical. By turning the tangent screw,
both the parts move together; but if desired the pulleys can move
independently by unscrewing D and L. The angular poppet may be made
semicircular if preferred, the degrees being numbered either way from
0" in the centre. When the tool holder is horizontal, or approaching
that position, the nut, D, must be loosened, and the pulleys placed
so that the cord will not slip off. They may be dispensed with if the
apparatus is to be used ONLY for vertical cuts (the _holder_,
E, will be horizontal); but if a radial pattern is to be cut, in
which the angle is to be constantly varied, the pulley piece must be
used and the pulleys re-arranged at D, as required from time to time.
There is a somewhat neat and serviceable little apparatus represented
in Fig. 259A, to take the place of the slide rest and its
revolving cutters, and although its powers are limited, much may be
done with it. The spindle A, works through brasses in the poppets, B,
B, and is put in motion by a cord from the overhead passing over the
pulley in the centre. This spindle, which holds the crank-formed and
other drills in a socket at one end, moves freely through the bearings
endwise, and is kept back from the work by a spiral spring working
against the end of the handle, C. This handle does not turn with the
spindle, but is mounted like the handle of a carpenter's brace, or
that of an Archimedean drill stock. The whole apparatus fits into the
socket of the ordinary rest. A screw should have been shown in the
drawing, passing through B towards the pulley, to regulate depth of
cut.
[Illustration: FIG. 253.]
[Illustration: FIG. 254.]
[Illustration: FIG. 255.]
[Illustration: FIG. 256.]
[Illustration: FIG. 258.]
[Illustration: FIG. 259.]
[Illustration: FIG. 259A.]
[Illustration: FIG. 260.]
Once fixed by the screw of the latter in its intended position the
tool is advanced to the work in a straight line by pressing the handle
C, and is released from the cut as soon as this pressure is withdrawn.
With different sizes of cranked, forked, or round ended drills, a good
deal of ornamentation may be done with this simple tool, which is also
useful for ordinary light drilling. By putting in the socket a round
ended drill, and using the radial movement (turning the whole round in
its socket in the arc of a circle), short flutes can be drilled out
deep in the middle, forming basket work similar to Fig. 260, which is
exceedingly pretty when carefully executed. There is little difficulty
in making drills and cutters, as steel of all sizes in round and
square bars may be had at the chief tool shops, especially at Fenn's,
in Newgate-street. In making the revolving cutters, however, it is
necessary to observe the position of the axial line, which must
pass through the cutting edge. After the drill is roughly finished,
therefore, it should be mounted in the tool holder with which it is
to be used, and carefully tested upon a piece of unimportant work.
If in revolving against the latter it leaves a part of the material
untouched, the edge is not truly in the centre of rotation. The flat
side of the drills are to be diametrical, and hence, as Holtzapffel
remarks, these drills can only be sharpened on the end. The latter
authority also says most of the drills embrace (in contour of edge)
only about one-fourth of the circle, as when the drills are sharpened
with one bevel they can only cut on the one side of the centre, and
if the drills were made to embrace the half circle the chamfer of the
edge on the second side would be in the wrong direction for cutting,
and consequently it could only rub against the work and impede the
action of the drill. All ornamental cutters and drills should be kept
in a box with small separate divisions to fit the shanks, which are
all of one size. The points can then be seen and the selection made of
any required pattern.