11" O Feed per rev.

JohnEvans · May 27, 2018

Will someone enlighten me on how to figure feed per rev from the threads per inch. Plate on QC box says for feeds multiply 2.502 X the number of threads per inch ??? I don't get and answers that way that mean anything. I'm sure my old brain is missing something but be dammed if I can see it.
TIA ,John

Red James · May 28, 2018

First convert 'threads per inch' into inches per revolution, i.e. 1/tpi. Now multiply by the 2.502 to get a number that is in inches per revolution, or what you expect 'feed' to be expressed in. The 2.502 comes from the gear ratio between 'thread' lever and 'feed' lever, and will likely be different depending on your particular lathe.

johnoder · May 28, 2018

Left over from turns per inch - an old way to express feed

(my 1917 Lodge & Shipley has a finest feed of "88" )

2.502 times say 10 tpi is 25.02 turns per inch

Take the reciprocal of that - .039968 - and that is the modern way to express feed in inches per revolution

Thumbnail illustrates a QC with a finest thread of 112 tpi. The one shown says 2 1/4 times that for feed

Ergo, finest FEED on one shown is 2 1/4 X 112 = 252, the reciprocal of which is a finest feed of .003968

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11" O Feed per rev.

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