Today I cut the pinions for the clock motion work. These were made from 5/16" and 1/4" leaded brass rod. The rod did not have to be resized, since the arithmetic worked out exactly. A 15-leaf 48-DP gear is 15/48 or 5/16" and a 12-leaf 48 DP pinion is 12/48 or 1/4". Technically, these should be a bit larger to allow for a tooth "addendum" but it works out fine to ignore this slight addition.
The pinions were cut from lengths of rod which were first thinned to about 1/8" on one end. This to allow the cutter to clear the rod when it is indexed. On the same end, a center tool was used to make a center on the end of the rod which will fit the center on the rotary table tailstock. This is to support the rod at the outer end when the gears are being milled.
I cut a long length of pinion, making a stick from which several pinions can be sawed to be used in later clocks.
As usual, the pinion blanks were coated with layout fluid, so that the cutter could be set into the blanks at the proper depth. I usually increase the cutting depth a trial 0.005" at a time, making two cuts to cut one tooth until there is only a slight blue land left on the end of the new tooth. Then the rest of the teeth are cut.
I always use a calculator to keep track of the number of degrees which must be dialed on the index for each cut. Some calculators will repeat the last addition operation, adding to a cumlative total, with each press of the "=" key. This makes keeping track a lot easier. Otherwise, indexing errors are sure to happen.
Today's links: