Slide thread pitches, handwheel graduations?

[bugbear6502Participant @bugbear6502]

I was looking at the topslide on my Simat. Having watched (too many!) videos on youtube where lathe work is done by using the engravings on the hand wheel, I noted that (unlike some cheap/early/small lathes) the plastic wheels on the Simat are engraved (actually, they''re injection moulded).

At first glance, they're marked 0/3, 1/3, 2/3 on the conical section, with normal "ticks" closer in. Counting the ticks, there are 7 (SEVEN!!!) in each third, for a total of 21 divisions.

"Slightly" confused I measured the thread, which turns out to be 24 TPI.

Each tick is thus 1/21 of 1/24 of an inch, which is 1/504. 2 thou within 1% tolerance. Oh, very clever.

But the whole 7ths/3rds thing will make my brain explode for any movement other than small depth-of-cut increments.

I suppose I'd better see what weirdness awaits on the lead screw + wheel

BugBear

[bugbear6502Participant @bugbear6502]

[bugbear6502Participant @bugbear6502]

Lead screw measured with a thread gauge at 14 TPI; the handwheel has 5 divisions labelled 0, 20, 40, 60, 80, and each division has 5 ticks.

Each tick is 1/14/25 = 1/350, or 2.857 thou.

I understood the cross slide better!

BugBear

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