[Driftwood]

Just wanted to confirm my thinking here, would appreciate any comments...

We have a 93 Hitachi Seiki HT20-SII turning centre that we recently bought used and brought online... Its got an 8" 3 jaw Kitagawa power chuck...

We were having some problems with parts being out of centre and it looks like this seems to happen whenever any kind of heavier cut is taken...

For example, current parts: 3/4" 316SS round bar, 0.1" OD turning depth of cut, 0.012ipr, 2500rpm, bar is sticking out about 3" from the chuck... at the end, we would notice between 0.01"-0.02" off center...

We have two of these machines, the other one with a new chuck... when looking how the jaws deflect when clamping, the old chuck looks to deflect noticeably more... also, we've measured that one of the jaws deflects less that the other 2, which makes sense, as we repeatable get the off centre drift to be away from this jaw...

So looks like its time to replace the chuck? Or just certain parts? (the master jaws?) Anything other thoughts or comments?

I'm thinking the whole chuck needs to be replaced...

Follow up question: how can i determine the mounting system? I believe A2-6 is standard for 8" chucks, so thats probably what I have... but I'm not really sure what A2-6 looks like, how can i confirm this? (Before I take off the chuck...)

Thanks...

[Geof]

It sounds like you are using the regular hard jaws. A work-around for excessive and uneven jaw deflection is to machine custom jaws using a boring ring so that the jaws are loaded and deflected the same way they will be in use.

This could give you the time to accumulate the funds for a whole new chuck.

[Driftwood]

Hey Geof,

Thanks for the input... while its true that I'm using hard jaws, I don't think the boring ring and soft jaws will help with this problem...

The off centre problem is cutting operations relative to each other in one clamping... ie: roughing is off centre with finishing, drilling, etc... so don't see how that would help...

With the current parts, I've doubled the number of roughing passes, reduced the feed... has made a big difference, I'm getting good parts now... but that's not a long term solution...

[underthetire]

Chucks do wear out. Then they become projectile throwing devices. Deflection could be the master jaws, however it seems to usually be the chuck body. This happens a lot quicker if the chucks dont get regular greasing, and taken apart for periodic cleaning. If you can get away with it, throw a collet chuck on it, and run the larger diameter stuff on the other lathe.

[txcncman]

Have you disassembled, cleaned, and inspected the chuck for worn parts and damage? Is the run out consistent with the same point on the chuck each time?

I have seen situations where a chuck is not serviced properly causing this type of problem.

[fizzissist]

I have the B210 version, and even with the master jaws getting sloppy, it's perfectly fine using soft jaws clamped and bored in place. Repeatability has also been good.

Have you disassembled and thoroughly cleaned yours? With mine the repeatability got somewhat better after it was cleaned and re-lubed. If your jaws are shifting under load that'd be the first thing I'd do, to optimize the master jaws seating properly when clamped.

Btw, I get good prices on soft jaws from CHUCK JAWS - SOFT CHUCK JAWS, ROUND JAWS, HARD JAWS
Not a plug, just bein' helpful.

[underthetire]

IMO, no one changes chucks often enough. Seen first hand (or head) what happens when chucks wear out to the point of projectile throwers. People will buy new mill vises every 5-10 years, but will run a lathe chuck for 20 years with little or no maintenance or inspection.

[fizzissist]

IMO, no one changes chucks often enough. Seen first hand (or head) what happens when chucks wear out to the point of projectile throwers. People will buy new mill vises every 5-10 years, but will run a lathe chuck for 20 years with little or no maintenance or inspection.

Once you've had a projectile into the window make you change your shorts there's little religion... Been there, done that.

Another point to make, not directly a wear issue, but with potentially the same results, is the failure to make sure the jaws are clamping within the range! There's a reason for those little lines on the jaws and chuck.