Referring to the second, the spacing of the teeth must be determined to a great extent by the size of the reamer, and the facility afforded by that size to grind the cutting edges to sharpen them.
Fig. 1088.
Fig. 1089.
The method employed to grind a reamer is shown in [Fig. 1088], in which is shown a rapidly-revolving emery-wheel, above the reamer, and also a gauge against which the front face of each tooth is held while its top or circumferential face is being sharpened. The reamer is held true to its axis and is pushed end-ways beneath the revolving emery-wheel. In order that the wheel may leave the right-hand or cutting edge the highest (as it must be to enable it to cut), the axis of the emery-wheel must be on the left hand of that of the reamer, and the spacing of the teeth must be such that the periphery of the emery-wheel will escape tooth b, for otherwise it would grind away its cutting edge. It is obvious, however, that the less the diameter of the emery-wheel the closer the teeth may be spaced; but there is an objection to this, inasmuch as that the top of the tooth is naturally ground to the curvature of the wheel, as is shown in [Fig. 1089], in which two different-sized emery-wheels are represented operating on the same diameter of reamer. The cutting edge of a has the most clearance, and is therefore the weakest and least durable; hence it is desirable to employ as large a wheel as the spacing of the teeth will allow, there being at least four teeth, and preferably six, on small reamers, and their number increasing with the diameter of the reamer.
