The saving of files, time, materials, and patience, by the employment
of such rotary cutters as may be profitably used in connection with a
foot lathe, can hardly be appreciated by one who has never attempted
to use this class of tools. It is astonishing how much very hard labor
may be saved by means of a small circular saw like that shown in Fig.
1. This tool, like many others described in this series of articles,
can, in most instances, be purchased cheaper than it can be made, and
the chances are in favor of its being a more perfect article. However,
it is not so difficult to make as one might suppose. A piece of sheet
steel may be chucked upon the face plate, or on a wooden block
attached to the face plate, where it may be bored to fit the saw
mandrel, and cut in circular form by means of a suitable hand tool. It
may then be placed upon the mandrel and turned true, and it is well
enough to make it a little thinner in the middle than at the
periphery.
[Illustration: Rotary Cutting Tools.]
There are several methods of forming the teeth on a circular saw. It
may be spaced and filed, or it may be knurled, as shown in Fig. 2, and
then filed, leaving every third or fourth tooth formed by the knurl,
or it may, for some purposes, be knurled and not filed at all. Another
way of forming the teeth is to employ a hub, something like that used
in making chasers, as shown in Fig. 3, the difference between this hub
and the other one referred to, is that the thread has one straight
side corresponding with the radial side of the tooth. The blank from
which the saw is made is placed on a stud projecting from a handle
made specially for the purpose, and having a rounded end which
supports the edge of the blank, as the teeth are formed by the cutters
on the hub.
The saw, after the teeth are formed, may be hardened and tempered by
heating it slowly until it attains a cherry red, and plunging it
straight down edgewise into cool, clean water. On removing it from the
water it should be dried, and cleaned with a piece of emery paper, and
its temper drawn to a purple, over a Bunsen gas flame, over the flame
of an alcohol lamp, or over a hot plate of iron. The small saw shown
in Fig. 4 is easily made from a rod of fine steel. It is very useful
for slotting sheet brass and tubes, slotting small shafts, nicking
screws, etc. Being quite small it has the advantage of having few
teeth to keep in order, and it may be made harder than those of larger
diameter. A series of them, varying in diameter from one eighth to
three eighths of an inch, and varying considerably in thickness, will
be found very convenient.
These cutters or saws, with the exception of the smaller one, may be
used to the best advantage in connection with a saw table, like that
shown in Fig. 8. This is a plane iron table having a longitudinal
groove in its face to receive the guiding rib of the carriage, shown
in Fig. 9, and a transverse groove running half way across, to receive
a slitting gauge, as shown in Fig. 8. The table is supported by a
standard or shank, which fits into the tool-rest socket. The saw
mandrel is supported between the centers of the lathe, and the saw
projects more or less through a slot formed in the table. The gauge
serves to guide the work to be slotted, and other kinds of work may be
placed on or against the carriage, shown in Fig. 9.
It is a very simple matter to arrange guiding pieces for cutting at
any angle, and the saw table may be used for either metal or wood. The
saws for wood differ from those used for metal; the latter are filed
straight, the former diagonally or fleaming. Among the many uses to
which metal saws may be applied we mention the slitting of sheet
metals, splitting wires and rods, slotting and grooving, nicking
screws, etc. Fig. 10 shows a holder for receiving screws to be nicked.
It is used in connection with the saw table, and is moved over the saw
against the gauge.
To facilitate the removal of the screws the holder may be split
longitudinally and hinged together. Another method of nicking screws
is illustrated by Fig. 11. A simple lever, fulcrumed on a bar held by
the tool post, is drilled and tapped in the end to receive the screw.
After adjusting the tool all that is required is to insert the screw
and press down the handle so as to bring the screw head into contact
with the saw.
Where a lathe is provided with an engine rest, the cutter shown in
Fig. 6, mounted on the mandrel shown in Fig. 5, is very useful; it is
used by clamping the work to the slide rest and moving it under the
cutter by working the slide rest screw.
To make a cutter of this kind is more difficult than to make a saw,
and to do it readily a milling machine would be required. It may be
done, however, on a plain foot lathe, by employing a V-shaped cutter
and using a holder (Fig. 7) having an angular groove for receiving the
cylinder on which the cutting edges are formed. The blank can be
spaced with sufficient accuracy, by means of a fine pair of dividers,
and after the first groove is cut there will be no difficulty in
getting the rest sufficiently accurate, as a nib inserted in the side
of the guide enters the first groove and all of the others in
succession and regulates the spacing.
One of the best applications of this tool is shown in the small
engraving. In this case a table similar to the saw table before
described is supported in a vertical position, and arranged at right
angles with the cutter mandrel. The mandrel is of the same diameter as
the cutter, and serves as a guide to the pattern which carries the
work to be operated upon. The principal use of this contrivance is to
shape the edges of curved or irregular metal work. The casting to be
finished is fastened--by cement if small, and by clamps if large--to a
pattern having exactly the shape required in the finished work.
[Illustration: METAL SHAPING.]
By moving the pattern in contact with the table and the mandrel, while
the latter revolves, the edges of the work will be shaped and finished
at the same time. By substituting a conical cutter for a cylindrical
one, the work may be beveled; by using both, the edge may be made
smooth and square, while the corner is beveled.
The tool shown in Fig. 12 might properly be called a barrel saw. It is
made by drilling in the end of a steel rod and forming the teeth with
a file. To avoid cracking in tempering a small hole should be drilled
through the side near the bottom of the larger hole. To insure the
free working of the tool it should be turned so that its cutting edge
will be rather thicker than the position behind it. This tool should
be made in various sizes.
Tools for gear cutting and also cutters for wood have not been
mentioned in this paper; as they are proper subjects for separate
treatment.