Automatic Pinion Cutter by an Unknown Maker - No. 49
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A automatic pinion cutter - probably European in origin - and dating from circa 1880 to 1920. It follows the typical form for such machines and - taking as an example the model produced by Sloan & Chace in the United States - would have been used to produce, one at a time, small gears up to an inch in diameter for use in pocket watches, clocks, typewriters and other mechanical devices.
After a suitable gear blank had been fixed in position it was automatically indexed through the required number of steps while a rotating cutter generated the tooth form. For light work, or where the quality needed was not so high, a single cutter was used to form the complete tooth profile but, if a lot of material had to be removed (or very precise gears manufactured) special versions of the machine could be ordered that mounted either two or three cutters on the spindle. Each cutter was ground so as to remove more metal than the one preceding it and each was automatically moved forwards into the position after the previous had finished its job. The mechanism was arranged so that each cutter could be individually adjusted to compensate for inevitable reduction in diameter that occurred as it wore in service, or after being reground to correct its tooth form. However, the makers of the Sloan and Chace model advised that, "In actual practice, a two-cutter machine (having one roughing cutter and one finishing cutter) has been found equal to the most exacting requirements." The Sloan and Chace example stands on a hollow cast-iron box that held the all-important coolant supply that was pumped over the cutter and workpiece before draining back, through filters, into the sump. The spindles and their bearings followed traditional watch-lathe design being conical in form and manufactured from the finest quality, hardened and ground steel. The work-holding and high-speed spindles were carried on dovetail slides that could be: "delicately adjusted by stop screws".
A special wall-mounted round-rope (gut-drive) countershaft was provided that ran at 700 rpm; this drove the cutter spindle at 1700 rpm and the worm shaft (by which means the automatic indexing and other movements were generated) at 1200 rpm.