SCRAPERS, ETC.
To suit different kinds of work, as previously stated, various tools
are needed, but the reader must not expect to see them all illustrated
in this book. The workman will learn what tools he needs, and make them
for himself, which will be of more advantage to him than engravings
could be. The tools here shown, will be found very useful in different
places.
[Illustration: Fig. 9.]
Fig. 9 is the end of a thin-edged, flat scraper, and is chiefly to be
used on brass work. It may be of any length and size, but for small
lathes, and light work, it is cheaper and handier to make it of thin
sheet steel, one eighth or one tenth of an inch thick, and to form the
reverse end into a round nose, or half-circle scraper.
[Illustration: Fig. 10.]
It often happens that fillets or hollows occur, as in finishing
ornamental brass work, in connection with flat surfaces. By having such
a tool as this, the necessity of laying one tool down and picking up
another, is obviated, for the two are combined in one. For iron work,
it is customary to use a heavier and thicker tool for finishing. As in
Fig. 10, the front edge is slightly raised or concave, to make it sharp
and hold a cut well. All turning tools for finishing iron are made
thicker than those for brass, and should have lips, or curved cutting
edges. Such tools cannot be used for brass, as they are too sharp; the
edges jump into the metal and spoil the work.
A tool for scraping brass work of some kinds is made as shown in Figs.
11 and 12.
[Illustration: Fig. 11.]
[Illustration: Fig. 12.]
There is no occasion to make the ends at different angles, except the
convenience, before stated, of having four cutting edges on one piece,
for any angle can be easily given by the position of the hand or the
direction of the rest. These tools, here alluded to, are only to be
used when the job has been all turned true and the scale removed; they
_scrape_, merely, they do not cut.
Such tools sometimes save a few steps at a critical period; that is,
when the tool is well set and in place, so that the work is done better
and more expeditiously. Apart from this consideration, there is the
chance of cutting or injuring the hands, by the proximity of sharp
edges. Under the control of an expert, however, there is little danger
from this cause, as inspection will show. Skilful men that have worked
a lifetime at their trade, have few marks or scars on their hands, as a
general thing.
When these scrapers are used on cast iron, or, indeed, on brass of a
peculiar composition, they sometimes “chatter,” as it is called, and
leave the work full of deep, unsightly marks, like those on the edge of
coins. The cause of chattering is the rapid vibration of the tool, so
that it springs away from, and against the work, with great rapidity,
leaving traces of its edge on the work. Chattering may be prevented, by
putting a piece of sole leather on the rest, between it and the tool.
The tools with long handles are chiefly intended for heavy work, or
that which requires both hands to the cut, but there are smaller tools
than these, used by amateurs, wherein the common file handle, or one
like it, only a little longer, is employed instead.
CHASING AND SCREW CUTTING.
In an engine, or power lathe, all screws are cut by trains of gears, as
mechanics well know, but in the hand lathe, which was the first
machine, screws, both male and female, must be made by chasers or hubs,
both inside and outside. The chaser itself must be made first, however,
and that is done by a simple tool called “a hub.”
[Illustration: Fig. 13.]
[Illustration: Fig. 14.]
[Illustration: Fig. 15.]
The chaser is first forged in blank, for an outside chaser, as in Fig.
14, and as in Fig. 15 for an inside tool. It is then filed up, and held
against a hub, shown in Fig. 13, running in the lathe. This rapidly
cuts away the chaser blank, and forms the teeth in it perfectly. The
lines across it are spiral grooves, cut completely round from one side
to the other, so that the hub cuts the blank like any other tool. Fig.
16 represents the chaser.
[Illustration: Fig. 16.]