Broach
A tapering piece of steel used for enlarging holes and made with from two to eight cutting edges. Some broaches are made without cutting edges and are called polishing broaches. They are used for burnishing pivot holes. Care should be taken to see that the handles of your broaches are properly fitted so that they revolve truly. To test this, rest the points against the fingers of one hand and causing the handle to rotate by two fingers of the other hand and the broach itself should appear to remain true. Sealing wax answers the purpose as a handle for broaches very nicely, and the broach can be centered in it without much trouble. In the latter case hold the broach between two fingers with the handle downward, and rotate it while close to the flame of an alcohol lamp, so that the sealing wax forms a regular oblong handle. It is well to gently draw a piece of iron charged with rouge along the edges of pivot broaches in order to remove the thread of metal from them. Minute particles of this thread might otherwise remain in the holes, and occasion wear of the pivots.
To Broach a Hole Vertically. It is quite a serious thing for young watchmakers to broach a hole vertically, a hole in a plate, or that in a barrel, is seldom maintained at right angles to the surface, when they have occasion to employ a broach. They may be certain of success, however, by adopting the following method: Take a cork of a diameter rather less than that of the barrel or other object operated upon, and make a hole in the length of the cork through which the broach can be passed. When the cork has been turned quite true on its end and edge, the broach is passed through, and used to enlarge the hole; by pressing against the back of the cork, it is kept against the barrel, whereby the broach is maintained in a vertical position.