Problem Rebuilding Jacobs Chuck - Suggestions?

[Nogoingback]

I recently bought a Jacobs U36 chuck repair kit off eBay for my 59B headstock chuck. Pressed it apart,
cleaned everything up and tried to re-assemble. What I've found is that one of the new jaws won't slide
back into the chuck without binding. The jaw looks fine: no nicks or burrs or any other damage that I can
see.
I looked over the body of the chuck and cleaned up some burrs, but it still won't slide in all the way. The only thing I found
is that it measures slightly larger than the other two jaws: about 5 tenths larger OD. The other two
measure up the same. The kit is an quite old NOS Jacobs kit, so I don't know if they would warranty it or not.
Anyone run into this kind of problem before?

 

[EmilioG]

These sets are sold as matched. I've done quite a few Jacobs rebuilds and have only seen your problem when, A. the jaws/split nut were mis matched or B. the body of the chuck has been damaged. I think it could be A. One jaw could be from a different rebuild kit/Jacobs model.
or C. you're not matching the jaw with the right bore. The jaws have little grooves designating their order number to each bore. Take a look at the Ebay link, it shows instructions,

There really isn't a fix for this. Any grinding will lead to a very inaccurate chuck at best. Sellers don't realize that you can't mix and match jaws/nut kits. They're all ground together to fit. These rebuild kits come up on Ebay from time to time. Check the jaw holes on the chuck body again. Does the over size jaw fit in any hole? Don't force it, just make sure the bores are clean.

There is no warranty on these kits or the chuck. They are no longer made for older vintage Jacobs. look, another kit on Ebay. You can return the set you have now if they are not as described.

See: http://www.ebay.com/itm/Jacobs-Chuc...681830?hash=item41c21ef0a6:g:VU0AAOSwpkFY7SKH

 

[Nogoingback]

The set appears to be fine: there is no evidence that it was put together from a mismatched set. The parts appear new, and the split nut halves fit perfectly together. I'm also aware of the procedure
for assembling the parts in the proper order: the parts came with a diagram of the jaw sequence, and I also looked up the procedure on the Jacobs website. The problem is obvious without
assembling the chuck with the nuts in place. If I take each jaw and try and insert them individually into the chuck body, two of them slide in and jaw #2 sticks as I try to push it in. I also cleaned
the body of the chuck carefully, and did clean up some burrs on the edges of the holes. It is an old chuck which has obviously been used, but there's no evidence of damage. Like I said, the only
discrepancy I can find (if it is one) is that the #2 jaw is slightly larger than the other two. What I don't know, of course, is if half a thou is significant or not.

 

[whitmore]

[about rebuilding a Jacobs chuck]
The set appears to be fine: there is no evidence that it was put together from a mismatched set. ... If I take each jaw and try and insert them individually into the chuck body, two of them slide in and jaw #2 sticks as I try to push it in. I also cleaned
the body of the chuck carefully, and did clean up some burrs on the edges of the holes.

I had a sticky chuck, and the problem was it had taken a bit of a dent so one
jaw was sliding in an off-cylindrical bore. The fix, was to get a drill bit that
fit into the jaw's bore, and (hand-held) slide it until I felt the
irregularity in the sidewall. It's easier than it sounds...

Then, just draw the sharp edges of the flutes of the drill against the
irregularity, scraping gently at the non-cylinder. When it feels right,
try the jaw again. I finished up with cleaning and applied light grease.
It worked REALLY well.

If that was the original problem, the original jaws and split ring are maybe
still good.

 

[EmilioG]

A mis matched set would look normal. It's impossible to tell if one jaw is not part of that set.
They were made within a certain spec, but ground so they all matched. It could even be a bad set from the factory.
The body of Jacobs chucks are soft, so the slightest damage, can ruin those chucks and throw the bore out of spec.

 

[4GSR]

I have never had a bad set of new jaws give me trouble installing them. Now I have mic jaw set before and sometimes get a 1/4 or 1/2 thousandth variation from set to set, but that's about it.
I have fought with many abused, damaged chuck bodies to get a set of jaws installed. I have discarded a few really bad chuck bodies I was never able to get fixed and run reasonably true again. The biggest problem is, the chuck body gets mushroomed metal from over tightening the chuck from many years of use. This positive metal is what keeps the jaws from installing and moving freely without binding. I generally use a straight rat tail file, like the one's used for sharpening chainsaw chains with. A drill the right size works good, too. To go in and try to remove the positive metal with. Lots of trial and error getting it right.

Be careful of some of the eBay sellers selling used worn jaw sets. They are junk!

 

[Nogoingback]

I had a sticky chuck, and the problem was it had taken a bit of a dent so one
jaw was sliding in an off-cylindrical bore. The fix, was to get a drill bit that
fit into the jaw's bore, and (hand-held) slide it until I felt the
irregularity in the sidewall. It's easier than it sounds...

Then, just draw the sharp edges of the flutes of the drill against the
irregularity, scraping gently at the non-cylinder. When it feels right,
try the jaw again. I finished up with cleaning and applied light grease.
It worked REALLY well.

If that was the original problem, the original jaws and split ring are maybe
still good.

I'll have a look with this in mind. Because this is a headstock chuck, it's much larger and heavier than the usual jacobs chuck, so it would take a pretty good hit to deform it. Of course that doesn't mean it didn't happen. If I had a
bore guage I could measure it, which is probably the best thing to do, so I might try to run one down and try that first.

 

[Nogoingback]

A mis matched set would look normal. It's impossible to tell if one jaw is not part of that set.
They were made within a certain spec, but ground so they all matched. It could even be a bad set from the factory.
The body of Jacobs chucks are soft, so the slightest damage, can ruin those chucks and throw the bore out of spec.

If it isn't a problem with the chuck itself, I'm thinking it's a bad jaw. If I press the jaw into place and assemble it, all
the threads line up properly and the nut rotates as it should: it just binds up during a portion of the travel.

 

[Nogoingback]

I have never had a bad set of new jaws give me trouble installing them. Now I have mic jaw set before and sometimes get a 1/4 or 1/2 thousandth variation from set to set, but that's about it.
I have fought with many abused, damaged chuck bodies to get a set of jaws installed. I have discarded a few really bad chuck bodies I was never able to get fixed and run reasonably true again. The biggest problem is, the chuck body gets mushroomed metal from over tightening the chuck from many years of use. This positive metal is what keeps the jaws from installing and moving freely without binding. I generally use a straight rat tail file, like the one's used for sharpening chainsaw chains with. A drill the right size works good, too. To go in and try to remove the positive metal with. Lots of trial and error getting it right.

Be careful of some of the eBay sellers selling used worn jaw sets. They are junk!

The more I think about it the more I want to measure the bores on the chuck first. But, the fact is the other two jaws slide in without a problem, and the "bad" jaw doesn't, and it measures a bit larger than the other two, (which measure exactly
the same). I might also send an email to Jacob's technical help folks and run the dimensions past them. This set was sold as a new set, and while you never know, they certainly look new.

 

[RandyM]

The more I think about the more I want to measure the bores on the chuck first. But, the fact is the other two jaws slide in without a problem, and the "bad" jaw doesn't, and it measures a bit larger than the other two, (which measure exactly
the same). I might also send an email to Jacob's technical help folks and run the dimensions past them. This set was sold as a new set, and while you never know, they certainly look new.

I had a Jacobs chuck that I bought years ago, brand new. It always gave me trouble from day one, with a very loose fitting key. I contacted them just a year ago as it seem to be getting worse and I was tired of messing with it. They had me send it in for evaluation and discovered that it was broken and the no longer made the repair parts. In the end they sent me a brand new chuck. I was even prepared to just buy a new if this all did not pan out. I say you have go nothing to loose. Good luck.