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 Post subject: Re: Adjust Tru Chuck
PostPosted: Mon May 03, 2010 7:57 pm 
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Joined: Sun Nov 18, 2007 12:46 am
Posts: 411
Location: peekskill, ny
Smart money Harold is that this is a high mileage chuck with a fairly worn scroll. That would account for
the configuration of the jaws as seen in the picture.

But even if so badly worn, one should be able to take five thou of runout away with the
four adjustment screws.

There may be junk stuck in the scroll however.

Jim


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 Post subject: Re: Adjust Tru Chuck
PostPosted: Mon May 03, 2010 8:29 pm 
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Joined: Fri Jan 10, 2003 1:00 am
Posts: 1698
Location: Molalla, Oregon
Harold_V wrote:
It's clear to me that the majority of readers are not paying attention to the problem at hand, which is that the jaws are not closing as they should. That has nothing to do with how the chuck mounts, or how it is properly adjusted, and everything to do with the internal workings of the chuck. Assuming the jaws originally closed properly, it's possible the chuck experienced a crash, or has otherwise been damaged.

A true mystery, in my opinion.

Harold


I seen the picture and my first thought is one or more jaws are in the wrong slot, which could cause the problem shown in the picture. The other thought is that he has jaws from two different matched sets. The thing is you don't really know the problem until you have a chance to look at the chuck in person.

As far as the scroll being the problem the wear would be equal, so there wouldn't be the error shown in the picture. Unless the scroll was damage from crashing the chuck. If the scroll bearing was worn the jaws would still have the proper relationship to each other. Only the relationship to the chuck centerline would be affected. It still comes down to an inspection of each part.

Richard W.


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 Post subject: Re: Adjust Tru Chuck
PostPosted: Mon May 03, 2010 8:47 pm 
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Joined: Sun Nov 04, 2007 12:11 am
Posts: 1431
Location: Pleasanton, CA Land of perfect weather
I have another possible solution.

I believe that "set-tru" type chucks allow the user to precisely position the jaws by moving the scroll. It seems possible that the chuck backplate is very eccentric. Thus the chuck body is also eccentric. The scroll has been adjusted to make the part concentric. When the jaws (scroll) and chuck body are not concentric, the jaws hit on one side.

Just my guess.

Dave J.

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 Post subject: Re: Adjust Tru Chuck
PostPosted: Mon May 03, 2010 10:17 pm 
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Joined: Tue Jan 01, 2008 8:20 pm
Posts: 35
Location: Brooklyn, NY Paradise, PA
I took the chuck apart and found that the mounting plate had .003 run out
on it's face. Took a light cut and fixed that.
Everything else, the scroll, pinion, and jaws LOOK good but this is a
used chuck.
I've used these chucks before and I know exactly how they work and how to adjust them
Got it back together and the jaws still don't close correctly. (Yes they are in the right location)
Chucked in my good 3/4" ground shaft and was able to adjust to .0001
at 3" away from the chuck jaws, but there is absolutely no repeatability at all when rechucking.
You can see the run out.
I just located the new set of outside jaws that came with the chuck.
I'll put these in tomorrow and see if they close correctly
Angelo


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 Post subject: Re: Adjust Tru Chuck
PostPosted: Tue May 04, 2010 8:37 pm 
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Joined: Sat Dec 21, 2002 12:16 am
Posts: 1141
Location: Green Bay Wisconsin USA
I have the same chuck.
Bought it in 1977 and Mine has only a few hours on it.
When brand new, and the jaws tightened to full close, you can barely slide in a 7/64 (.1093) allen wrench into the jaw opening.
While Buck ground the jaws on a surface grinder with fixtures, I doubt anyone else can
match their setup exactly and so that method should not be used.
Looking at your pictures, there is no doubt that that jaws were ground IMHO

Try a Allen wrench and you will know how much material has been removed
Your jaws show flats , so I have to assume that the party that reground the jaws, also reground the inside surfaces and the angle approaches as well in order to get back to smaller stock sizes.
Most people do not realise that jaws on a 3 jaw or 4 jaw chuck can be ground , and still work fine, especially a 3 jaw adjust-true chuck.
6 Jaw chucks are a whole nother matter !!!
The only way to rework them (without a Buck Fixture) is to grind in place using axial pressure
on the jaws. Its easy to grip on a 3 jaw, even if one jaw is .040" short, the stock moves over, and we complain about a .040" error
On a 6 jaw, if one jaw is short, you have 5 grab the part, or 4, or 3. This is intolerable
The .003 error you found in the back plate tells me someone had a major crash with the chuck.
It was great for you to repair it

Now take some very hard rubber and place it between the jaws on the adjacent sides and tighten the heck out of it, and then grind the jaws. The rubber will exert the needed jaw deflection properly.
Then dis-assemble completely and wash in solvent to remove any grit.

It is a beautiful chuck and deserves the best of maintenace


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 Post subject: Re: Adjust Tru Chuck
PostPosted: Thu May 06, 2010 4:52 am 
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Joined: Tue Jan 01, 2008 8:20 pm
Posts: 35
Location: Brooklyn, NY Paradise, PA
Well,
The new outside jaws close a little better but you can never chuck in
the same piece twice and get the same results. You can tap the piece held in the chuck
to run true, but that's not right either.
I thought that the 1/4" opening in the jaws ( when fully closed) was normal,
so I guess the jaws were already reground.
I'm thinking that it's pretty well worn to try and repair.
Angelo


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 Post subject: Re: Adjust Tru Chuck
PostPosted: Thu May 06, 2010 3:08 pm 
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Joined: Fri Dec 20, 2002 11:02 pm
Posts: 13710
Location: Onalaska, WA USA
angelo49 wrote:
Well,
The new outside jaws close a little better but you can never chuck in
the same piece twice and get the same results. You can tap the piece held in the chuck
to run true, but that's not right either.
I thought that the 1/4" opening in the jaws ( when fully closed) was normal,
so I guess the jaws were already reground.
I'm thinking that it's pretty well worn to try and repair.
Angelo

If tapping the jaws alters the attitude of the piece being held, the scroll is shifting on its mount. A clear sign that the chuck is well worn. You may wish to investigate the idea of bushing the mount, which could serve to correct the problem, although if the chuck has that much wear, the slides may not be tight, either. Movement by any means is not conducive to acceptable performance.

Harold


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 Post subject: Re: Adjust Tru Chuck
PostPosted: Fri May 07, 2010 12:30 pm 
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Joined: Sun Nov 18, 2007 12:46 am
Posts: 411
Location: peekskill, ny
Yep chucks have to do more than just center up the workpiece.
They have to be able to hold it rigidly. I always wonder about the
folks that take a long time to painstakingly grind jaws on a worn
chuck.

Yes the part's centered. No it's not really held in place very well.

Jim


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