Problems with machining chuck back plate

T

Tuba Dave

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I purchased an ER32 collet chuck and threaded back plate from a reputable company. I followed the instructions on how to fit the plate to my lathe, but when I installed the chuck there is almost .007 runout. The chuck fits well to the plate, I can't wiggle it when they are mated. I did need to enlarge one of the mounting holes on the plate because they did not match well enough with the chuck (the holes on the chuck are threaded, the holes on the plate are just counterbored clearance holes). The x axis runout is excellent (simple facing) but an indicator on the collet taper shows the mentioned runout, as well as visible "wobble" on all the untouched (by me) surfaces. This bothers me because before I turned the mounting surface of the plate, I installed it backwards and faced the backside surfaces to eliminate this wobble (purely cosmetic, but I did not want to see it). Then I removed it from the spindle, turned it around and proceeded to machine the mounting surface. It was at this point I noticed the previously machined surfaces on the back are not concentric and indeed wobble. (??) Though I don't think this should affect the front surface after it is faced

Is it possible that the spindle threads and the chuck mounting holes on the plate are not concentric to each other? Does the runout come from the chuck mounting bolt holes or the spindle threads? If the spindle threads are somehow out of alignment with the surfaces of the plate, I assumed a back and front facing would true it all to my lathe.

My next step would be to remove the bolts, rotate the chuck and drill new mounting holes, but I am not sure how to do that in a concentric manner (compound slide drill and tailstock center?) Before I try this, I wanted to see if I missed something, or if it is possible the plate (or the chuck?) is defective.

FYI this is on a Maximat 7 in very good condition, so I know the runout is not coming from my spindle or its threads.
 
Did you contact the reputable company you bought it from. It probably was bad from the get go.
 
I'm familiar with the style of chuck but don't own one myself. Do the plate and the chuck mate together with a shoulder or do they rely on the mounting
bolts for alignment? If it's the former then the chuck is probably machined wrong and will have to be returned.
A mistake like that would be difficult to correct on your Maximat without some additional tooling and a bunch of time and fiddling
-M
If the shoulder mating surfaces are wrong and you are willing to void the warranty there is another option: Turn off the shoulder completely then drill the mounting bolts slightly oversize. Then with the bolts hand-tight, use an indicator and tap the chuck into alignment then give a final tighten.
There may be a slight angular error but hopefully too small to worry about
 
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If it was brand new then there might be a defect in the plate. Plus they want you to succeed not have issues with their product. I would have called them first.
 
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