7x14 Chuck jaws are binding after mounting the chuck to the lathe.

Hi,

I have a 7x14 minilathe with a 4" 3 jaw chuck that came with the lathe.

The chuck is mounted to the spindle by 3 8mm studs. The chuck registers onto a 72mm boss on the spindle plate.

When I tighten up the 3 mounting studs, the chuck jaws bind and lockup so that I can't move the jaws with the chuck key. If I back off the nuts on the 3 mounting studs, the chuck key moves the jaws fine. It seem like when the mounting nuts are tightened, the chuck is being warped. That said I wouldn't have thought that was possible.



Has anyone experienced this problem before? And have a solution?

Cheers,

Peter

I have not seen that before and have used several spindles and heads from these lathes. The only issue I had with a replacement spindle was the backing plate was too large and needed turned down a bit. That was from LMS. I would not think this is the case, but are your mounting bolts too long? If not, then you may have some chips or embedded material in one or all the holes and when the screw is installed, it may pressure the worm gears. I would suggest checking the screw length and cleaning out the holes.

Thanks Lee.

I'm not sure I understand as the chuck has 3 studs in it that pass through the spindle mounting plate and are held on with nuts.

Cheers,

Peter

Ahh. It has been awhile since I actually messed with them. You are correct. Mine had studs, washers and nuts. These little chucks seem to have plenty of meat at the mounting flange. I would not think a small amount of misalignment would be detrimental. I would get out your gauges and start checking everything. Something should be apparent.

Hi Lee,

Will do. I was hoping someone was going to tell me what I was doing wrong. :)

Cheers,

Peter

Since all I have ever done with mine is basically what you are doing, I'd hazard a guess that you are not doing anything wrong. ;)

Lee,

I think I may have found the problem.

The 72mm boss on the spindle is 4.2mm high. The 72m recess in the chuck is 3.8mm. So when mounted the chuck is sitting on the boss and the 3 mounting studs putting all the pressure on the bottom of the recess.

I guess I'll need to reduce the height of the boss.

Cheers,

Peter

Hi Lee,

I trimmed a bit off the boss and all is good. :)

Thanks for your help.

Cheers,

Peter

Excellent.
Glad it was something fairly easy.