e key is to be, and also slightly shallower than the dimensions
of the key.

A flat file should be used for the purpose, first a heavy rough one, for
the first cutting. The better way is to have the key so it can be
frequently tried while the filing process is going on, so that to fit
the key in this way is a comparatively easy task.

KEY-WAY DIFFICULTIES.--But the trouble commences when the groove is
filed for the depth. Invariably, the mistake will be made of filing the
width first, so the key will fit in. As a result, in deepening the
groove the file will contact with the walls, and you have a key-way too
wide for the key.

To avoid this, file the depth, or nearly so, and then with a fine file
cut in the corners in the direction indicated by the dart, Fig. 48.

A proper key is square in cross section. In such a case the depth of the
key-way, at each side wall, is just half the width of the key-way.

An excellent key-seat rule can be made by filing out two right-angled
pieces, as shown in Fig. 49, which can be attached to the ordinary
six-inch metal rule, and this will enable you to scribe the line
accurately for the key-way on the shaft.

[Illustration: _Fig. 49. Key-seat Rule_]

[Illustration: _Fig. 50. Fig. 51. Filing Metal Round_]

FILING METAL ROUND.--It is sometimes necessary to file a piece of metal
round. This is a hard job, particularly where it is impossible to scribe
the end of the piece. Suppose it is necessary to file up a bearing
surface, or surfaces, intermediate the ends of a square bar.

You have in that case four sides to start from, the opposite sides
being parallel with each other, so that you will have two dimensions,
and four equal sides, as shown in Fig. 50.

The first step will be to file off accurately the four corners 1, 2, 3,
4, so as to form eight equal sides or faces, as shown in Fig. 51. If you
will now proceed to file down carefully the eight corners, so as to make
sixteen sides, as in Fig. 52, the fourth set of corners filed down will
make the filed part look like the illustration Fig. 53 with thirty-two
faces.

[Illustration: _Fig. 52. Fig. 53. Making a Bar Round_]

This may be further filed down into sixty-four faces, and a few cuts of
the finishing file will take off the little ridges which still remain.
By using emery cloth, and wrapping it around the bearing portion, and
changing it continually, while drawing it back and forth, will enable
you to make a bearing which,