# Problem Rebuilding Jacobs Chuck - Suggestions?



## Nogoingback (May 10, 2017)

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?


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## EmilioG (May 10, 2017)

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


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## Nogoingback (May 11, 2017)

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.


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## whitmore (May 11, 2017)

Nogoingback said:


> [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.


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## EmilioG (May 11, 2017)

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.


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## 4GSR (May 11, 2017)

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!


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## Nogoingback (May 12, 2017)

whitmore said:


> 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...
> ...



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.


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## Nogoingback (May 12, 2017)

EmilioG said:


> 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.


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## Nogoingback (May 12, 2017)

4gsr said:


> 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.


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## RandyM (May 12, 2017)

Nogoingback said:


> 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.


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## Nogoingback (May 12, 2017)

Thanks Randy.  I think I'm going to send an email to Jacobs and see what they say.


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## bfd (May 12, 2017)

did you try sliding the 2 good jaws into the bad hole or slide the bad jaw into the other 2 holes this will confirm that the larger jaw is in fact bad and not the hole. otherwise I would try to polish the slightly larger down till it fits if we are talking about chuck run out do you know how much run out was initially with this chuck. I don't think you will put the chuck out of normal range. of course this all depends on how much slightly over it is. slightly over is not really a machinist term. maybe less than .001" bill


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## Nogoingback (May 12, 2017)

The #1 and #3 jaws slide into all three bores, while the #2 sticks in any of the bores, though one of the bores seems slightly smaller.  (Haven't measured them).  I don't have the numbers in front of me, but the #1 and #3 jaws measure
the same diamer, while the #2 jaw measures .0005 larger.  This suggests to me that the problem is the jaw, not the chuck body.
Naturally, I have no idea how Jacobs toleranced these parts, so I don't know if that puts the #2 jaw out of range.

As for run out, I have no idea what it was before: I bought this chuck on eBay for a lathe I'm refurbishing, so I've never used it.


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## bfd (May 12, 2017)

so at .oo05" I would polish the bad jaw until it just fits might only take .00025 to get it to fit and at that number runout will be minimal at best. at least you will have a chuck to use with no additional cost. you might have got a hole at the very least of its tolerance and a jaw at the very most of its could happen. I repeat polish it until it just fits bill


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## woodchucker (May 12, 2017)

My wife bought me a small drill press 25 years ago, a Delta 8". Useless because of size. But more useless because the Jacobs chuck had one jaw that was no true. So bits wobbled. I may send that back so I can sell the damn thing.   I find it odd when everyone says how good we used to build things in the US. Certainly we COULD build some really good stuff, but we also lost that ability and were still making it here, and it was no better than China.


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## Nogoingback (May 13, 2017)

bfd said:


> so at .oo05" I would polish the bad jaw until it just fits might only take .00025 to get it to fit and at that number runout will be minimal at best. at least you will have a chuck to use with no additional cost. you might have got a hole at the very least of its tolerance and a jaw at the very most of its could happen. I repeat polish it until it just fits bill



You have a good point: it'll cost me nothing to try, and the worst case is that I' ll have to buy another kit.  I'll probably give that a try.


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## 4GSR (May 13, 2017)

]Sometimes, the jaw will go in if turned 90 degrees from normal and go in.  If you can get it to do just that, twist the jaw several times to get a dull spot in the ID of the chuck body.  This would indicate positive metal that needs to be removed.  Now it the jaw will not go at all turned 90 degree, then it could be the jaw.  I have polished the jaws too to get them to go in.


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## bfd (May 14, 2017)

as far as I know there is not a numbered hole just the jaws and thread part so fit the biggest jaw into the largest hole and set the jaw sequence from there but I may be wrong about this been a long time since I rebuilt one of these. bill


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## Nogoingback (May 14, 2017)

4gsr said:


> ]Sometimes, the jaw will go in if turned 90 degrees from normal and go in.  If you can get it to do just that, twist the jaw several times to get a dull spot in the ID of the chuck body.  This would indicate positive metal that needs to be removed.  Now it the jaw will not go at all turned 90 degree, then it could be the jaw.  I have polished the jaws too to get them to go in.



Now that I think of it, I can turn the jaw 90 degrees into the bore.  I'm out of town, but when I get home I'll have another look with that in mind.


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## Nogoingback (May 14, 2017)

bfd said:


> as far as I know there is not a numbered hole just the jaws and thread part so fit the biggest jaw into the largest hole and set the jaw sequence from there but I may be wrong about this been a long time since I rebuilt one of these. bill



The holes are not numbered, but the jaws have a sequence that has to be observed.  So, I can start anywhere as long as they are in sequence.  If I can get the one jaw sorted, I can figure  out the optimum position to start from.


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## Nogoingback (May 15, 2017)

DONE:



bfd said:


> so at .oo05" I would polish the bad jaw until it just fits might only take .00025 to get it to fit and at that number runout will be minimal at best. at least you will have a chuck to use with no additional cost. you might have got a hole at the very least of its tolerance and a jaw at the very most of its could happen. I repeat polish it until it just fits bill





4gsr said:


> ]Sometimes, the jaw will go in if turned 90 degrees from normal and go in.  If you can get it to do just that, twist the jaw several times to get a dull spot in the ID of the chuck body.  This would indicate positive metal that needs to be removed.  Now it the jaw will not go at all turned 90 degree, then it could be the jaw.  I have polished the jaws too to get them to go in.



I decided to take the advice on polishing.  Taking my time, I slid the jaw into the bore and looked for the worn spots when it was pulled out.  I started with 400 grit emery paper and finished with 1500,
which gave a better surface finish than the parts had when received.  I just kept working at it a little at a time, until the jaw slid in normally.  I really didn't take much material off: the jaws are pretty
hard, and when I measured it had barely changed from measurement taken last week.  Assembled it with some chuck grease,  it works just fine.

I did go back and measure the parts that came out when I took it apart.   They measured up exactly the same as the #1 and #3 jaws.  I think that #2 jaw was a bit out of tolerance from Jacobs,
but it's all good now. 

Thanks to everyone for your suggestions.


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## EmilioG (May 16, 2017)

That's great. At least you have a working Chuck.  Let us know how it drills and if you check TIR using a 1/2" dowel pin/Indicator,
please let us know how much run out the chuck has.


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## Nogoingback (May 16, 2017)

I measured the run out at .004 - .005".   Not great, but I have a 4 jaw chuck if I need better.


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## EmilioG (May 16, 2017)

.004-.005" TIR is actually not that bad considering the jaw problem. The spec for that Jacobs is around .005" TIR.
So you did ok. The Jacobs super chuck spec is .004" TIR,  You got Jacobs Super Ball Bearing chuck TIR with a plain bearing chuck!


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## dlane (May 17, 2017)

I'm having a problem rebuilding my 16n superchuck, Jacobs wants $285 for the kit
20n $598 for the kit. It's just a few parts.


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## EmilioG (May 17, 2017)

Rebuild kits for 16n and 20n come up on Ebay, sometimes.  Do you have a Hartford, CT USA 16n or the new?
I bought a 14n rebuild kit on Ebay, NOS for $30, complete with bearing balls. I would follow search on Ebay and get email updates.
I've never seen the new Import kits on Ebay.
Msc has the 16n kit for $130. All of these new rebuild kits are for the new Import Jacobs.
https://www.mscdirect.com/product/details/08595167


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## 4GSR (May 17, 2017)

dlane said:


> I'm having a problem rebuilding my 16n superchuck, Jacobs wants $285 for the kit
> 20n $598 for the kit. It's just a few parts.


Dlane,

I may have an extra 20N jaw kit that I'll sell you if you're interested.  I promise not to charge over $498 for it.  
PM me if your interested.

Ken


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## EmilioG (May 17, 2017)

First you need to know if his Jacobs are service kit models, new import or USA Hartford CT. chucks.
Jacobs changed the race design for the newer chucks. They are not inter-changeable.


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## 4GSR (May 17, 2017)

EmilioG said:


> First you need to know if his Jacobs are service kit models, new import or USA Hartford CT. chucks.
> Jacobs changed the race design for the newer chucks. They are not inter-changeable.


The kits I have are for the older chucks.  The difference is like you said is the nut and bearings used.  Now, you can use the same jaws from the old to the new, at least, the 16N will let you do it.   I've done so  on one of the rebuilds in the past.  Ken


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## 4GSR (May 17, 2017)

For  those that have not encountered a newer Jacobs ball bearing chuck.  The older ones have loose steel balls that have to be loaded one at a time. And you generally loose one or two in the process of assembly.  Don't worry, if you loose a few, its not the end of the World, it will work fine with the missing steel balls.
The newer chucks has a plastic retainer that the steel balls are loaded into at the factory, that keeps you from loosing them.  Also, the steel balls are a little smaller in diameter.  And there are some other differences in the chuck body and sleeve.  But appears the jaws themselves did not change, at least in the 16N chuck.  Ken


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## dlane (May 17, 2017)

Ied like to find a NOS kit for the 16n super ball bearing chuck , mine doesn't tighten properly
Could it just need dissembling and cleaning ? , I've never had one apart yet
Thanks ken , I have a 16n and 18n USA super chucks the 18 seems good it's for the mill.


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## 4GSR (May 17, 2017)

dlane said:


> Ied like to find a NOS kit for the 16n super ball bearing chuck , mine doesn't tighten properly
> Could it just need dissembling and cleaning ? , I've never had one apart yet
> Thanks ken , I have a 16n and 18n USA super chucks the 18 seems good it's for the mill.


dlane,

I have a 16N kit too if interested.  It's for the old style chuck.


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