[How-To] Threading a chuck backplate

mmcmdl said:
Measure your spindle register , whatcha got ?
Click to expand...
My spindle register is 1.510.
Major on the spindle thread is 1.500.
I figured I would have to machine some things, even a new backplate.
The backplate on the new chuck will only go on maybe 1 thread then locks up.
That is why I think the thread is not finished.
This chuck shows hardly any wear, like it was never used, except for some grinding on the base jaws.
 
What is the backplate register diameter ? Exact diameter !
 
So , here is most likely your situation . You're trying to thread a bore with a 1.500 diameter over a thread with a 1.500 diameter which is the major diameter of your threads . You have no clearance . Any deviation in runout and you'll lock it up . Take .005 out of the backplate bore and try to thread it on . If it threads on , you know the threads are good . Once you know that , open up the backplate register to 1.512 ( .002 clearance for your spindle register ) , it should fit right on . Understand ?

If it does not thread on with the backplate diameter opened up , you have a thread problem and you'll have to open them up . And , you'll still need to bore the backplate register to size .
 
Yep, that is what I was thinking. Just wanted to make sure.
The thread was not finished for some reason, or the lathe it was on had a worn out spindle.
 
Jim F said:
Yep, that is what I was thinking. Just wanted to make sure.
The thread was not finished for some reason, or the lathe it was on had a worn out spindle.
Click to expand...
You don't know that yet . The threads are most likely good but the register is too small to go over the spindle threads .
Don't assume the threads are bad .
 
Put some prussian blue on your the backplate and screw it on . If it shows up on your spindle threads .......................
 
That will be a tomorrow thing, 5am was early today.
 
Ha ! I feel like I worked 16 hrs already and it's only 1.30 ! :rolleyes:
 
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