Here's the best explanation I've found of how far to feed in the compound for threading (and why).

Assuming the compound is set at 30 degrees, the compound travels along one leg of a triangle. The length of the side is the same as the crest to crest distance of one thread. Next, reduce that travel by 1/8th to allow for the root clearance and again by 1/8 for the crest. That's a total of 1/4 or 25%. The remainder comprises the 75% thread form.

Divide .750 by the TPI, and that's how far to advance the compound.

-Mike

Assuming the compound is set at 30 degrees, the compound travels along one leg of a triangle. The length of the side is the same as the crest to crest distance of one thread. Next, reduce that travel by 1/8th to allow for the root clearance and again by 1/8 for the crest. That's a total of 1/4 or 25%. The remainder comprises the 75% thread form.

Divide .750 by the TPI, and that's how far to advance the compound.

-Mike

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