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dceg said:How to measure TPI on lathe spindle. IF measured the same way as acme thread I have a 7-1.5" Do I count the half thread? Thanks
If the spindle in question is on a Logan-South Bend-Atlas or similar and a 1.5 diameter 99% it is 8 thread as that size is very common on those machines. Get a decent thread gauge solve the whole issue.
I'm hoping this is a nominal size 1.5" spindle thread aka 1.5" x 8 TPI. Never know for sure until I buy a back plate.
Don't buy anything until you KNOW. Plenty of lathes out there working still that the last time you could BUY something that would fit was too far back to remember
That is when those machinist folks step in and MAKE something to fit. I think we have some of those that frequent this forum.
Thumbnail is a simple cheap way to KNOW FOR CERTAIN about pitch (another you can't "buy" for - 3 1/2 - 4 on very old Leblond Heavy Duty)
7 TPI 1.5" is the TPI 1.5" is the diameter. I'm looking for a chuck backing plate. My search found acme threads to start measuring at the top 1/2 thread and measure to top of 1/2 thread within 1". Another words you count full threads in between and two half threads count as one. an acme thread of 8 TPI has 7 FULL threads and 2 HALF threads. IF this is the same way to measure spindle threads then I have a 7 thread count. ODD yes.
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