Adjust Tru Chuck

[angelo49]

Hi
I have this Buck Adjust Tru 6" 6Jaw universal chuck.
I can't be "adjusted" enough to remove about .005" wobble / run out on a round stock
at 1" away from the jaws.
You can see that the jaws do not meet each other correctly.
Can anything be done to fix this?
Thanks
Angelo

[GlennW]

Can anything be done to fix this?

Sell it on eBay

[Harold_V]

Have you explored the chuck when it is opened slightly? It may line up properly in that case.

Because the angled portion of the jaws may not have been ground, they make contact unevenly when you tighten the chuck, as you have. It's possible that when you use the chuck within it's rated capacity, they never make contact, and don't influence the way the jaws come together.

Is it safe to assume the chuck is well used, and has some slop in the slides?

Harold

[GlennW]

You don't mention the type of spindle mount.

Here is a generic answer that is applicable to most chucks and mounting types...

If it uses an adapter plate, I would seperate the chuck from the adapter, install the adapter on the lathe and indicate it to see if it runs true to start with. If not, I would inspect the mouting surface interface with the lathe spindle for imbeded debris or dings and blue it to see that it has proper contact. If that is good I would remove and install it a few times indicating it each time and see if the error repeats. If it repeats I would make a light clean up cut on the surface that the chuck mates to. Then inspect the mating surface on the chuck for dings or imbedded debris. Bolt the chuck to the adapter and see what happens with a ground test bar of about 1" dia. (Thompson Shaf) in the jaws then. If still not good, I would remove the top jaws and make sure they are all properly installed on their respective masters as well as disassembling/cleaning/lubing the scroll.

If it is a direct mount chuck, inspect the mounting surfaces, jaws for proper pairing, and clean the scroll as described above.

There are lots of places for error to hide...

[spro]

It might be a good time for A tutorial about "Adjust Through" and "Adjust True" and what that means.

[Richard_W]

I see that the jaws are 1 piece.

1. My first question is are they in the right slot? There should be a number in the slot and on the jaw.

2. Has the chuck been torn apart and cleaned?

3. Are the jaws worn bell mouth and in need of regrinding? Most likely this is the problem if questions 1 and 2 were answered "YES".

Since all adjust true chucks have an adapter plate they are mounted on I assume that has been cleaned and checked for dings, if question 2 was answered "yes."

Richard W.

[spro]

I could be wrong but consider that the backing plate origionally had three adjust screws or Allens, that would shift the chuck by a minor amount from the axis. Then chuck retightened and checked till it was perfect. Then consider that plate was retained or modified and another one without those adjustments but "fit" was substituted.

[angelo49]

The photo shows the chuck closed enough, (not tightened) so you can see that the jaws are not meeting correctly.
The run out is there with a 1/2" dia or a 2" dia piece.
I indicated a 3/4" ground known good shaft with the same results.
I got the chuck with a machine I bought and it does look well used but there is
no slop in the slides.
It has a 1 1/2" 8tpi threaded spindle mount.
I mounted this chuck on another machine and has the same run out.
I'll take it completely apart and give it a good cleaning and check the mounting plate.
Angelo

[Bill_Cook]

Your description leads me to believe that the part chucked doesn't have as much runout at the jaws as it has out an inch. This could mean a few things.

The chuck isn't mounted and running true. This can be easily checked with a dial indicator on the outer edge of the face. Keep the indicator back so it doesn't drop too far into the jaw ways. Or with the amount the stock wobbles, runout on the chuck face can be seen with the naked eye if something mounted on the compound is parked near enough. Or a soft pencil mounted in the tool holder and brought up to the chuck while the lathe is running.

Bell mouthed jaws, (A misnomer). The jaws are much harder than the chuck body. Any significant wear would be in the ways. Since chucks don't get used evenly at all diameters, regrinding the jaws will only (if at all) solve the problem in the position they are reground at.

If the runout is nearly the same at the jaws as out an inch:

It could be the scroll bearing is worn. This, like Bellmouthing, would give inconsistant rechucking - off in different directions when loosened and retightened - particularly when it is tightened with the chuck key in a different pinion. Easy to check.

I assume that you were turning the chuck by hand while measuring. A loose spindle bearing (not most likely) could be the cause. Pulling on the top of the chuck body to turn it would pull it to the side.

One or more of the jaws may be from another chuck. If so, with a little good fortune it could be used as a 3-jaw.

In the unlikely event that the mounting holes were not drilled and tapped concentric and/or evenly spaced, the clearance holes in the chuck can be enlarged. 1/64th larger would give about .015" more adjustment in any direction and won't affect the chuck's utility.

BC

[Richard_W]

Bell mouthed jaws, (A misnomer). The jaws are much harder than the chuck body. Any significant wear would be in the ways. Since chucks don't get used evenly at all diameters, regrinding the jaws will only (if at all) solve the problem in the position they are reground at.

I agree to part of this. Chuck jaws get worn bell mouth because the parts being chucked do not always cover the whole jaw length. It's the many different length short parts that wear the outside of the jaws first. I have seen new 3 jaw chucks that need to be reground at about 3 years of use. The slide fit is perfectly good yet due to the longer contact length of the wear surface, it’s the wear from many short parts that wear out the jaws. Even though chuck jaws are hard, the contact area is small and can wear quickly. Depending on the condition of the material being chucked. (Ground finish, cold roll, hot roll or casting) Regrinding chuck jaws is just a part of regular maintenance. Some shops just buy new jaws and other shops regrind the ones they have.

You are right on that regrinding a chuck will only make it purfect at the ground diameter. But it will improve the accuracy at all other diameters because the part is now held in true center line of the chuck. Not tilted at an angle by worn jaws.

In the unlikely event that the mounting holes were not drilled and tapped concentric and/or evenly spaced, the clearance holes in the chuck can be enlarged. 1/64th larger would give about .015" more adjustment in any direction and won't affect the chuck's utility.

BC

Bill I had thought of this later after I had posted. If the chuck was drilled for inch screws and metric were required for a different backing plate. This could be the trouble. Say the hole was drilled for a 3/8" (.375 dia.) bolt in the chuck, but the backing plate was tapped for 10 MM bolts ( about .393 dia.). Then the amount for the chuck adjustment is reduced and if the holes were tapped off location the adjustment could be even less.

The point about the scroll bearing is a good one, which in my opinion most people don't even think of. If you chuck a part and can tap it to center by tapping lightly on the jaws, then the scroll bearding is worn and needs to be repaired. Most people just buy a new chuck at this point.

Richard W.

[jim rozen]

How have you been trying to adjust the chuck?

Have you used one like this before, do you understand the function of the
four screws on the periphery of the chuck, which bear on the boss on the
backplate, and how to slack the mounting bolts between backplate and
chuck when you do that adjustment?

Five thou of shift should be trivally achieved using the adjust-true feature.

Possibly you are omitting something from the procedure, give us the
rundown on exactly how you performed this.

Does not hurt one bit to remove the jaws, clean the scroll, and inspect.
As mentioned the jaws are numbered but from the photo you already
have them in the correct slots.

Do NOT grind the jaws on this chuck right away.

Jim

[Harold_V]

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.

In order for the jaws to close properly without making contact on the angular portion first, grinding relief on the places that contact now may solve the riddle----but I would do that only when I had assured myself that there isn't a problem with the scroll and threads on the backs of each jaw. Grinding the relief may not allow the jaw to contact as it should.

A true mystery, in my opinion.

Harold