CENTERS.
An indispensable article on a foot lathe, where any fancy work is to be
done, is the centers—of which I have before spoken—shown in Fig. 46.
These consist of a common set of heads, with spindles fitted to them.
One spindle has an index plate and spring, and the other has a common
center. These heads set on a slide that is moved back and forth over a
rest, screwed to the lathe bed as usual. It is easy to see that, with
this, we can do some very fine cabinet work. Suppose we have a round
vase turned up handsomely, and wish to flute the base or make it a
series of curves all round; to do this, we have only to put it in the
centers, set the index so as to come out even, as before explained, and
go ahead.
[Illustration: Fig. 46.]
The kind of cutter to be used is a sort of gouge, set in a cast-iron
head, something as a plane iron is set in its stock. That is, fitted
tight to a groove and held by a set screw. Two of these cutters should
be used, at equal distances apart, and the cutter head should be keyed
on a short shaft, set between the main centers of the lathe. The whole
should be accurately balanced, or else the work will be full of
chatters or ridges. Since centrifugal force increases as the square of
the velocity, any thing that runs a little out of truth, will be very
much exaggerated as the speed increases. By using cutters of different
shapes, beautiful effects can be produced; as, for instance, suppose we
take a common round-nose cutter, set the index so as to divide the
circle of the job we are to work on in twenty-four parts, and execute
that part of the design, then take a tool forming an ogee, and work out
the spaces intervening, we shall find that the article, when completed,
will have a beautiful appearance, and that, instead of being round, the
bottom will be octagonal, which will present a pleasing contrast to the
rest.
[Illustration: Fig. 47.]
The centers can be set at any angle with the cutter shaft and a
pineapple pattern can be made on straight surfaces, by executing one
part at one angle, then reversing the rest that carries the centers,
and finish the remainder, one part of the pattern crossing the other.
I present here views of a novel ornament which exhibits great
mechanical ingenuity and manual dexterity, but is otherwise of no
value. It consists, in one form, of a globe with a series of rings or
globes inside, and a six-armed spur projecting through holes—all cut
out of one solid piece. Fig. 47.
[Illustration: Fig. 48.]
Fig. 48 shows how the points are turned. After the internal rings are
cut out with a quadrant tool like Fig. 49, and the spur also severed,
by cutting in the ends of the holes (not boring them out solid), the
globe is put in a shell chuck, with three set screws in it, as shown.
The set screws go through the holes in the globe, and the cross pieces,
in between the spurs, serve to steady the job. Any number of points may
be turned in the globe. Fig. 50 shows a polygon with many spurs turned
inside. At first sight it would appear that the tool, severing the
rings, would cut off the points also, but it will be seen that this is
not the case, for the holes being bored so as to leave a core standing
(which afterward serves to make the points of the spur), the severing
tool falls into the holes and goes no further, and each division serves
as a guide for the tool in the next hole, so that the globe is made the
same size, without jags. The quadrant tool, shown before, must be
followed round the shell in the act of cutting it out, so that it will
make the same round, and the globe must be shifted in the chuck, to
reach all the holes. It is no easy task to make this little affair, for
all it looks so simple.
[Illustration: Fig. 49.]
[Illustration: Fig. 50.]