New chuck doesn't fit new spindle

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Zoltan

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I'm fitting a new spindle to my mini lathe so I can upgrade to a 4" chuck without an adapter plate. However, the register on the spindle is 72.02mm while the register on the new chuck is only 71.9mm. I can see the spindle register being a little oversized to allow it to be turned down once installed. However, I have a hard time believing the chuck is supposed to be 0.1mm undersized.

Did I just get a defective chuck? Can someone help me figure out what's going on?
 
Two ways to look at it. It is only 0.0039" smaller than nominal, so it might be in tolerance? Is your measuring instrument correct? Either way you may be forced to modify the spindle or return the chuck.
Pierre
 
If you have the means, bore the chuck rather than alter the spindle. A phone call would be in order first though.
 
Zoltan said:
I'm fitting a new spindle to my mini lathe so I can upgrade to a 4" chuck without an adapter plate. However, the register on the spindle is 72.02mm while the register on the new chuck is only 71.9mm. I can see the spindle register being a little oversized to allow it to be turned down once installed. However, I have a hard time believing the chuck is supposed to be 0.1mm undersized.

Did I just get a defective chuck? Can someone help me figure out what's going on?
Click to expand...

I read it the same way, the new spindle might need to be turned once installed to get least run out. Is the new spindle installed and have you put a DTI to the spindle to check run out?
 
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It can quite possibly be that the spindle diameter is on the high tolerance for machining and the chuck is on the low tolerance. I have seen this happen many times when tolerances are not done right on prints. When putting together special machinery I ran into this often when trying to assemble stations. Sometimes 2 different people are doing the drawings and something gets missed.
 
If you would mention the brand and model of lathe, maybe some of us with the same spindle could provide our measurements for comparison.
 
Most spindles are made to a standard and are intended to take a chuck that fits that standard. The reason being that the register on the spindle is what determines the accuracy of the chuck. I agree with Tony that it is better to make the chuck fit the spindle dimensions and a phone call might help to sort out what the spindle standard is.
 
using soft jaws (pieces of copper or alum chuck up the chuck on the spindle backwards and indicate the face and register bore in. if you can get it perfect then machine the bore to whatever fit you want. if you cant get it perfect then polish and stone it to size then you have a great fitting chuck. bill
 
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