The gear's bore was 6mm (I think). So it needed boring to fit the shaft. Additionally, my plan was a slip clutch made of Delrin with a set screw that would allow slip but not too much. So a .625" OD piece of Delrin with a .500" ID bore.
Problem 1: I cannot bore a .625" hole in the available space.
Solution: drill two holes through the face of the worm gear to attach a .500" ID x .5" wide Delrin ring. I can tap a hole in the Delrin for the set screw to lightly hold the Delrin and therefore lightly hold the worm gear.
"usa made" and carbide drill bit
Problem 2: Drilling two holes in the worm gear with repeatable precision for the Delrin ring requires finding the center of the gear. The usual center finder for holes will not work with a .500" ID hole.
Solution 2: Find worm gear center by finding center between vise jaws. (I am assuming it is symmetrical.) Zero Y. Once you have that, go inside the hole and find inner edge. Zero X. Find inner edge of other edge on opposite side of circle. Verify this matches the caliper measure of hole. Calculate real center. Move finder to that spot and zero the X axis.
Now I can position the two holes.
Caliper says .573" diameter. Edge finder shows same diameter. Center is therefore (.265, 0).
I am currently planning to tap the worm gear and use through holes on the Delrin piece.
UPDATE: There is not quite enough room in this worm gear to drill and tap 6-32 on the bottom portion. I have never used smaller screws except for pistol grip screws, but I looked to see long enough 4-40 or 3-48 stainless steel screws were available. No. But there is an outer portion of the worm gear that is wide enough for a 6-32 hole. Not with any margin for error. Another solution. Turn the Delrin part to slide on to the exposed hub and tighten a set screw to it and then a set screw from Delrin to shaft.
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