Do not let the file obliterate the lines at the rough[p. 53] cutting, but leave enough material so you can make a good finish at the line.
Cutting a Key-way.—Another job you may have frequent occasion to perform, is to cut a way for a key in a shaft and in a wheel hub. Naturally, this will be first roughed out with a cold chisel narrower than the 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[p. 54] 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.
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| Fig. 50. | Fig. 51.[ToList] |
| Filing Metal Round | |
