New Project. Chuck Back Plate.

What are the 3 holes you already have drilled? I think the holes in the chuck could be through holes if you take the chuck apart? Would that be easier and more precise? I'm gonna assume you don't have a rotary table? Another idea if you know (or can measure) the bolt hole circle diameter is to machine a very shallow groove in the back plate that you have measured out from center on the lathe. Center punch your holes in that groove. Then you know that the radius is dead on.
I personally would take the chuck apart and use the housing with transfer punches to mark the holes. You could even use the chuck as a drill guide but be careful not to mess it up.
Here's one way I did it using an old back plate as a drill guide for a new one.

26725325706_ee1f2069fe_h.jpg
Robert
 
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Could use just a set screw sharpened to a point.
What I will likely do is make a short drill hole punch. I will likely make one. Punch a hole, drill it out, put the bolt in and do the opposite side etc. I will oversize them appropriately to build in some run-out adjustability for the chuck later on. This is all home made, I'm sure it's not perfect. However, I put the dial indicator on the face while it's screwed onto the spindle and its within .001". Not bad...
 
rwm said:
What are the 3 holes you already have drilled? I think the holes in the chuck could be through holes if you take the chuck apart? Would that be easier and more precise? I'm gonna assume you don't have a rotary table? Another idea if you know (or can measure) the bolt hole circle diameter is to machine a very shallow groove in the back plate that you have measured out from center on the lathe. Center punch your holes in that groove. Then you know that the radius is dead on.
I personally would take the chuck apart and use the housing with transfer punches to mark the holes. You could even use the chuck as a drill guide but be careful not to mess it up.
Here's one way I did it using an old back plate as a drill guide for a new one.

26725325706_ee1f2069fe_h.jpg
Robert
Click to expand...
No, no rotary table. No, the chuck does not come apart. The holes you see line up with my 5" chuck. I mounted this plate to it to get the initial shape hogged out. All those are now are nuisance holes.
I was likely going to measure it all out, but I was sure someone had a better, less room for error, method.
 
Presto!
All done and mounted. The side body of the chuck near the back plate run-out is .001". I can get a 3/4" end mill to run at .0005" run-out. Hoowweeeveer... on the face of the chuck I have a .007 run-out. I will have to go back through everything and find that. It causes a mild vibration. Gotta find and eliminate it. I assume it might be a chip or a burr somewhere in my backplate bolt holes. Because when I metered out the back plate after the last pass it's run-out was negligible.

Having never used a 4 jaw chuck before it appears there is definitely an art to centering a piece in 4 independent jaws. Took me a few mins to remember whether I need to screw in or out specific jaws to obtain a reading I desire.

IMAG0798.jpg
 
Shawn, good work. Thanks for bringing us along with you.
 
Heimann transfer screws!!!

Brino, thought I'd help you out a little.
 
Can I junk phone in and ask a related question?

I have a 3 jaw Chuck coming ups in the morning.
I have a 7.25" used backplate that was a failed attempt to fix very old chucks runout issue.

I would like to use this for the little 6 inch chuck that is coming as it is still new, unmarked and.. .80 thick over all.

My problem is that the old mounting holes will indicate up being right at the edge of the new chuck. Just barely!
Csn I turn this backplate down 100 thou smaller then the new chuck? I looked at all of my chucks and it seems like every one of them is a little larger than thier mated back plate...

Is this the way it is done typically?

I really don't want to wait to get another new blank BP and trash this one simple because there is a 16th inch over lap with the old mounting holes.


Anyone?

Sent from my SM-T800 using Tapatalk
 
If you don't mind how it looks you could just turn it down intersecting the extra holes. Most back plates match the diameter of the chuck but this is not mandatory. The back plate can be a little smaller or even theoretically larger. The registration boss is the critical diameter. Just plan out where the new mounting holes will fall. You don't want a counterbore extending through the O.D. of the back plate. If you look at my pic above you will see how close the counterbore is to the edge. Counterbore is not mandatory but it is safer to have the screw heads recessed.
Robert
 
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