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What does this backplate fit?

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682bear

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#1
When I bought my South Bend 14 1/2 lathe, I acquired 3 chucks with it, a 9 inch 3 jaw Union chuck, a 10 inch 3 jaw Rohm chuck, and a 12 inch 4 jaw...

The spindle thread on the lathe is a 2 3/8 x 6 tpi... the Union chuck had a backplate mounted to it that is threaded 2 3/8 x 5 tpi.

So... it won't fit my spindle. I ordered a new backplate from Penn Tool for the Union chuck so I can use it if I need to.

Does anybody have any idea what this backplate might fit?

Also... if anyone needs this backplate, let me know... I'll make you a deal that you can't refuse... after all, I can't use it...

-Bear
 

RandyM

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#2
Are you sure that is 5TPI? 6TPI is standard UN for 2.375. What are the chances that you have a metric thread? 2.375 is really close to 60mm. Or that backplate was just made wrong.
 

4gsr

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#3
I do recall one lathe manufacture back in time that used 5-pitch thread for their spindle nose thread. 4-pitch thread is more common for spindle nose threads instead of 5-pitch. Generally the the threads are larger in diameter.
Randy, I agree with you, for 2.375 thread, 6-pitch would be more common.
 

682bear

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#4
Are you sure that is 5TPI? 6TPI is standard UN for 2.375. What are the chances that you have a metric thread? 2.375 is really close to 60mm. Or that backplate was just made wrong.
It may be metric... I don't know... the best I can measure, it is right at .200 from the peak of one thread to the next... it could be an m60x5.0?

-Bear
 
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