Backing plate fit??

restore49 · Apr 24, 2010

On my Whitcomb Blaisdell the 2 1/8 x 8 spindle has a .012 taper in 1 1/2 in. thread using the 3 wire system. Appears to be factory ?? the flat tips of the threads are proportional. Should I thread the new backing plate with a taper? Read the thread on Grizzly Backing plate and Garyphansen comment on loose class fit and was wondering if this is the path to take.
Bob

George Andreasen · Apr 24, 2010

It's my understanding that the taper is simply to make initial installation a little easier, and the backing plate is threaded straight. The critical fit is at the "register" on the spindle. The backing plate should spin on easily and only get "snug" during the last few turns as the register and backing plate mate up. Over time, the backing plate may wear slightly and the chuck won't run quite as true. My solution is to remove the chuck, stipple the backing plate edge, turn to truth and reinstall the chuck. This is admittedly a "quick fix", but is rarely needed anyway.

Lodsb · Apr 24, 2010

Cut your threads straight and the register square; fit doesn't seem to matter. Personally, I like to make them close and the neck of the register maybe a half-thou clear, even boring the plate and fitting a ring (loctite) in the belief that things won't stick, but that's probably more superstition than fact on my part.

Mike Powell · Apr 24, 2010

I agree with George. My 20" 1903 American Tool Works lathe has the same type of tapered threaded spindle. I, not knowing any better at the time had a friend cut me a tapered thread in my new chucks hub. It worked out OK but most likely was not necessary. Good luck!

Mike :cool:

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Backing plate fit??

restore49

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George Andreasen

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Lodsb

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Mike Powell

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