Pivot Polisher
The pivot polisher is used for grinding and polishing conical and straight pivots and shoulders. It is also useful for drilling, polishing or snailing steel wheels, milling out odd places in plate or bridge, where only part of a circle is to be removed, etc. The base being graduated to degrees, it can be set at any angle. The spindle has a taper hole for drill chucks, which makes the fixture very useful for drilling either in the center or eccentric, and by using the graduations on the pulley of the head-stock an accurately spaced circle of holes may be drilled. Fig. 251 is the American Watch Tool Company's polisher; Fig. 252, the Mosely, and Fig. 253, the Rivett pattern.
The polisher is used as follows: After the pivot is turned to proper shape, put on your polisher (spindle parallel with lathe bed), with lap back of pivot. Use cast iron lap first. (Square corners for square shoulders, and round corners for conical.) Lap for conical shoulder can be readily cornered with a fine file, and cross-grind with fine oil-stone to remove any lines made by graver. Lines on end can be removed same way, or in fingers rubbed on piece of ground glass which has on it a paste of oil-stone and oil well mixed. This will rapidly bring them up to a sharp corner nicer than by the graver. On the iron laps use No. 1 crocus or very fine oilstone powder, well ground down in oil to a paste. When roughed out to your liking, wipe off the crocus, and with a little oil touch the pivot gently; repeat the second time. Then change lap for one of box-wood, and use crocus No. 4, very fine and ground down to paste. Proceed as with first lap, being careful at all times to keep the lap properly oiled and not pressed too hard against the work, particularly in the last operation. Also be sparing of your grinding or polishing material. About three specks of polish with point of small knife is sufficient. Bring the lap up carefully against the work until spread all the way around, then proceed, bearing in mind that grinding is not polishing, and that to polish nicely the work and lap must be very nearly the right shape. To thoroughly clean the laps, dip in benzine.
Fig. 254 illustrates the Johanson polisher, which is one of the latest on the market. Fig. 255 shows a front view of the same machine. It consists of a shaft mounted in nicely fitted boxes, adapted to give a lateral motion, which is controlled by set collars on the shaft as shown. The front end of the shaft is bored to receive the tapers of the cutting tools, and also with an outside taper to hold the laps, the laps and cutters being shown at Fig. 256, while the other end has a knob to enable the fingers to control the lateral motion of the shaft as desired. Pulleys of rubber are fixed upon the shaft and two idlers are mounted on a vertical stud at the rear. The boxes which carry the shaft are swiveled upon two screws in the base plate and are controlled by a lever, as shown in Fig. 255, or they may be held rigidly in position by a set screw shown under the lever. This constitutes the tool proper. When it is to be used in the hand rest, a stud, shown in Fig. 255, is screwed into the base plate and supports the tool in the hand rest, so as to be readily adjustable in any direction. When used in the slide rest, this stud is removed and the plate clamped between two hollow cylindrical supports by a stud which is slipped into the groove of the slide rest and fastened by a nut at the top, the whole forming a turret-like mount of great strength, as shown in Fig. 254, and upon which the machine can be readily swiveled in any direction. Other cutters and laps may, of course, be used with the machine, so that it is capable of a wide range of work.
Fig. 257 illustrates the Hardinge pattern, which is a hand polisher. It is attached to the lathe bed the same as the T or hand rest, Grinding and polishing slips are furnished with this machine, which is very simple and inexpensive.