Is this bad?

Bamban

Bamban

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H-M Supporter Gold Member
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Jul 13, 2014
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I was in the process of dialing my 6J 8 inch Bison, a used one I picked up on eBay. When I started tightening the front screws after dialing the 4 adjusters, I noticed that the any time I tightened any of the 3 front screws I could see the 0.0005 indictor moves. Ignoring the movement I finished tightening the screw, then curiosity got the best of me, so I tugged on the 1 inch ground test bar. The indicator moved back and forth close to 0.0025 in any directions for a total close to .005, but will spring back to the same position?

I changed to a tool post mounted 0.001 indicator and repeated the test. I pushed the rod and pull back, same results, about 0.0025 movement in both directions.

Normal?

If not normal, what's the potential problem?
 
How far from the chuck are you measuring the deflection? If it's right at the jaws, then it could be the mounting on the spindle, or the spindle bearings. If it's a ways out from the jaws, and you have quite a bit of leverage, then it could just be the bar deflecting.
 
JimDawson said:
How far from the chuck are you measuring the deflection? If it's right at the jaws, then it could be the mounting on the spindle, or the spindle bearings. If it's a ways out from the jaws, and you have quite a bit of leverage, then it could just be the bar deflecting.
Click to expand...


I have a 12 drill rod and I have about 8 inches inside the chuck, indicating about 3 inches out. The end is unsupported.
 
Push on the chuck and see if you get about the same deflection, if you do, then set the indicator on the spindle and see if the deflection is starting there. This will tell you if it is the spindle or the chuck mount.
 
Thank you for the responses.

I indicated on the chuck and pushed and pull on the rod, there is movement, about .001 in either direction. Have not indicated the spindle yet. The 6J set thru chuck is not new, bought it used on eBay. I was just following the instructions on how to properly adjust them.
 
Yea but it's new to the lathe. If you had no problem before and now do, I would look at the chuck it's self
 
Does it thread on the spindle? could need a new, better matched backplate.
 
When you say the “front screws”. Do you mean the cap screws that go all the way through the chuck into the back plate? I leave those cap screws alone and always adjusted to very snug. When I need to true the chuck, I only play with the 4 ajust-tru. And when done, make sure all 4 are firm, so everything is locked…Good Luck, Dave.
 
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