On a threaded spindle, what are the critical features to capture?

[WobblyHand]

Need to make a copy of my spindle to use for fitting a backplate that I intend to make. Where are the critical features? Is it the back face that the backplate hits, or the cylindrical feature that is perpendicular to the back face? I have the piece roughed, and need to know what to really watch out for. Any tips would be greatly appreciated.

 

[mmcmdl]

Both ! Back face and diameter behind the threads is what locates and seats the plate . The threads themselves should be slightly undersized on the spindle ( as to thread specs ) so just copy what yours measures .

 

[WobblyHand]

Both ! Back face and diameter behind the threads . The threads themselves should be slightly undersized .

I'm assuming the undercut of the diameter is important as well? To make sure the backplate seats square?

 

[mmcmdl]

As long as you're below the root diameter of the thread , it wouldn't bind .

 

[mickri]

Another option is to remove the chuck with the back plate still in the chuck and then test the fit of the back plate on the spindle. That's what I do.

 

[WobblyHand]

As long as you're below the root diameter of the thread , it wouldn't bind .

Confused. I wasn't talking about the thread relief, but at the junction of the back face and the cylinder.

 

[mmcmdl]

Oh ! That's just an undercut for a possible sharp edge on your plate . Just chamfer your plate .

 

[WobblyHand]

Another option is to remove the chuck with the back plate still in the chuck and then test the fit of the back plate on the spindle. That's what I do.

I could do that if I could fit the backplate in my smaller chuck. My larger chuck is a bit too heavy (for me) to do that with something in it.

 

[WobblyHand]

Oh ! That's just an undercut for a possible sharp edge on your plate . Just chamfer your plate .

Chamfering the backplate would be a lot easier!
How is that undercut done? With some sort of knife edge tool?

 

[mmcmdl]

You don't need it on your model if you chamfer your backplate , but that undercut is just put in with an angle tool .