3 Jaw chuck, soft jaw problems

[Myth446]

I'm re-machining a set of steel soft jaws. I have the ring installed and run the program. The stroke is about half and everything machines fine. I check the runout before un-clamping and it's 0.0005" ish. When I unclamp I retest the runout and see two of the jaws are 0.0005" to eachother but the third jaw is out 0.003"-0.004". When I load a part it sits 5" away and the runout is over 0.010"
Any idea what is going on, or how to fix it?

 

[david n]

How old is the chuck? She could be just plain tired...........................or here's a dumb question..............are the cap screws tight on that third jaw?

 

[Myth446]

Screws are tight, I have no idea on the age or abuse as I'm less then one year in this shop.

 

[guythatbrews]

One jaw may not be getting grease. A guy in my shop ruined one because one zerk was stopped up and he didn't tell anybody. Just greased the other two. Into the scrap bin the chuck went and had to buy a new one.

 

[Garwood]

One jaw may not be getting grease. A guy in my shop ruined one because one zerk was stopped up and he didn't tell anybody. Just greased the other two. Into the scrap bin the chuck went and had to buy a new one.

I've also seen them where one of the checkballs is missing from a zerk so the grease that goes in it gets flung right back out.

 

[Mr.Chipeater]

Sounds like bad/lack of grease to me

I'd pump each jaw full till it start oozing out to try to flush any contaminants, cycle them open/close a few times then see if it is improved. One downside to this is that the next time you turn the spindle on, you're going to be painting the inside of the lathe with all that excess grease.

 

[Booze Daily]

Are you OD clamping on the ring or ID clamping?

 

[Mtndew]

When's the last time you pulled the chuck apart and cleaned it out?