Fig. 1102.
[Fig. 1102] represents a single-tooth adjustable reamer, in which the body a is ground to the standard diameter, and the wear of the cutter c is taken up by placing paper beneath the cutter. In this case the reamer cannot, by reason of the wear of the cutting edge, ream too small, because the body a forms a gauge of the smallest diameter to which the reamer will cut. The cutter may, however, be set up to the limit allowed for wear of cutting edge, which for work to fit should not be more than 1⁄5000 inch.
Fig. 1103.
An adjustable reamer designed and used by the author for holes not less than 11⁄2 inches in diameter, is shown in [Fig. 1103], in which a represents the body of the reamer containing dovetail grooves tapered in depth with the least depth at the entering end. The grooves receive cutters b, having gib heads. c is a ring or washer interposed between the gib heads of the cutter and the face or shoulder of a, the cutters being locked against that face by a nut and a washer e. By varying the thickness of c, the cutters are locked in a different position in the length of the grooves, whose taper depth therefore causes the cutters to vary in diameter. Suppose, for example, that with a given thickness of washer c, the cutters are adjusted in diameter so as to produce a hole a tight working fit to a plug turned to a 2-inch standard gauge: a slightly thinner washer may be used, setting the cutters so as to bore a hole an easy working fit to the plug; or a slightly thicker washer may be employed so as to produce a hole a driving fit to the same plug. Three or more washers may thus be used for every standard size, their thickness varying to suit the nature of the fit required.
It will be noted that it is mentioned that three or more washers may be used, and this occurs because a diameter of fit that would be a driving fit for a hole of one length would be too tight for a driving fit of a much longer hole, the friction of course increasing with the length of hole, because of the increase of bearing area.
For large sizes, a reamer of this description is an excellent tool, because if it be required to guide the reamer by means of a plain cylindrical shank, a washer, or sleeve, having a bore to fit the shank at the termination of the thread, may be used, but such a reamer is not suitable for small diameters, because of the reduction of shank necessary to provide for the nut and thread.