The accompanying description and illustration of a grinding and polishing machine made by the writer in about an hour's time and at practically no expense, may be of interest. The cheapness and ease with which it can be made are due to the utilization of certain parts of a bicycle (which is usually available or can be obtained for a small sum second hand) for the driving mechanism, and to the employment of a convenient workbench or strong table as a stand. The bicycle should have as high a gear as possible (it is not injured, and can be reassembled and used on the road again) and should have its front wheel, forks, handle bar, and back tire removed. In order to support the remaining parts, two boards about 1 1/4 x 4 inches, reaching from the floor to the top of the bench, should be provided, and these should each be drilled 16 inches from the bottom with a hole of a size to fit tightly on the nuts on the ends of the rear axle. These boards should be nailed to the floor on each side of the rear wheel, and nailed to a board at the top, so as to clamp the bicycle frame tightly between them, with the axle in the holes previously mentioned. This board should be firmly fastened to the top of the bench, and should be long enough to bring the grinding wheel in a convenient position, while its width should be sufficient to cover the tops of the axle supports. An upright board should support the head of the frame, so that the pedals will clear the floor by about 2 inches.

Fig. 28 - Dimensions of the grinder head.

The grinder head, used with this foot-power device, consists of a block of wood (see Fig. 28) about 3x3 inches fastened firmly on to the top board by nails or screws, and of sufficient height to bring the grinding spindle to the desired position, a brass bushing which is of about 1/2-inch iron pipe size tightly fitted in a hole in the top of the block, a grinding spindle, and a grooved wood pulley. The spindle is the only piece requiring lathe work, and even this may be eliminated by using a straight rod (the bushing tube being of a size selected to fit it) and very carefully threading it with a 3/2-inch 12 die for the collar and clamping nut. It is, however, much more satisfactory to have a turned spindle, as it can then be made a better fit in the bushing, and the inner collar and part carrying the wheel can be turned true with this bearing surface. The part of the spindle that goes into the inner collar should be made a drive fit in the collar, and the latter should be turned while in place on the spindle. A nut and large washer should be provided for clamping the grinding wheel on the spindle. The other end of the spindle is formed with a threaded taper for polishing and buffing wheels, although it would be cheaper to leave it blank. It could also be arranged to carry a second grinding wheel if desired. The pulley which goes on this spindle is cut (if possible turned) out of a piece of hard wood, and is bored so as to make a tight fit on spindle. If it should show any tendency to slip, a set screw can be run through it and against the spindle. This completes the machine with the exception of a 3/8-inch leather belt, a grinding wheel (3/4 x. 6 inches is a good size) and, if desired, a tool rest which can be rigged up around the wheel.

Pig. 29 - A simple foot-power grinder.