Buck Adjust True chuck question

I have an 8 inch Adjust True Buck 3 jaw scroll chuck. Its in like new condition for being made in 79. I am having an issue getting that final adjustment. I removed the chuck from the lathe and took it apart, cleaned it all up, stoned a few rough spots, lightly lubed with high pressure grease on the back plate and re mounted it, same issue. What I am wondering is if the 12 screws that hold the front plate, scroll and back plate together are too tight that it prevents the 4 adjustment screws to move the back plate for the final few fine adjustments. . Does anyone know if there is a torque spec on those screws?

I have called Buck Chuck Company several times, left voice mails and sent emails without any response yet so I figured I would ask here.

I modified a generic 8" 6-jaw to have adjusting capability, and the main clamping screws do have to be set at a lower torque to enable the body to slide on the backing plate. A good finish on the mating surfaces and a little grease will help, but if you have a major roughing job to do you may want to adjust, tighten the mount screws, then do the cutting. Loosen when you want to adjust the chuck again.

As for actual values, well, whatever allows movement of the body. Just play with it to find out what works for you.

dwebster, I have the same chuck, same vintage that you have. I loosen the clamp screws to the 'barely snug' point, make my adjustment and tighten them up again. I never have any drift on the adjustment by doing it that way. It takes the same effort and time to dial in as a four--jaw.

I was taking to my Dad about it, the lathe and chuck was his. He said that its very possible that this could be the problem. Since I never had it apart and never tightened those bolts it never dawned on me that they may be too tight to begin with. This is the first time I ever really needed to be less than .0005" TIR, so I never messed with it before. I will play with the bolt tightness and see what I can come up with.

dwebster said:

I am having an issue getting that final adjustment.

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There is no "final adjustment". You adjust them all the time, whenever you change jaws or bore new soft jaws or whatever. They are sort of a cross between a four-jaw and a three-jaw. When grinding bores, I'd adjust the chuck for every part (gear teeth held over wires.)

edit: Simultaneous posts on the tightness issue

Yet another thread that would benefit greatly from a photo or two....

I'm not even sure what you are saying. On my Buck 8", it wouldn't make any difference how the two halves are bolted together. all the adjustment is on the back side where the chuck fits against the backing plate.

But either way, if you are using a 3 jaw scroll chuck of any sort and expecting to reliably hit under .0005" TIR you're probably a Kenny Roger level gambler...

If you are good until you try to get under .0005 you may have problems with your spindle bearings. Try a few good ground shafts with an indicator and see how they behave. Bad bearings will repeat on a multi-revolution basis, not a single revolution basis.

YES! you are correct- the backplate bolts can be so tight that the chuck body cannot slide on the backplate, making adjustment difficult or even impossible. Back off on the mounting bolt torque- they only need to be tight enough to keep the back plate and chuck body faces in contact with each other- once you have the chuck adjusted for runout its not going to move unless you are really hogging material or have a severe interrupted cut.

Dan from Oakland said:

. . .its not going to move unless you are really hogging material or have a severe interrupted cut.

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Unlikely even then since the four adjusting screws are in firm contact with the plate boss.

So true, but sometimes you back off the adjusting screw to get that last little adjustment or go too far and back one side off completely and then screw the other side in to get zero leaving the opposite totally loose.

Anyone adjusting anything knows you always approach from the tightening side.

GregSY said:

Anyone adjusting anything knows you always approach from the tightening side.

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Agreed. You introduce the equivalent of 'backlash' in your adjustment if you do anything else.

I have a Bison three jaw that I made my own true adjust back plate for. It has four fine thread set screws for the adjustment (10-32s). I used six rounded head cap screws to attach it to the chuck: rounded head to keep the overall dimension down so the back plate did not have to be too thick. Those six screws each have a spring washer under the head so I can loosen them a bit but the chuck stays in contact with the back plate.

I loosen the six screws. Then I adjust it as close as I need. I then partially tighten them and check the centering again. The fine thread adjusting screws make this easier. Then tighten the screws again. Usually two cycles of tighten and adjust are OK. Sometimes if I am making a small part or anticipate light cuts I will only partially tighten them and just go ahead and cut.

Those spring washers make the process easier as they hold the chuck and back plate in contact. And I can loosen the screws more and with less care to the exact degree of looseness while keeping this condition so that also makes it go faster. Finally, if I have some heavy work pieces or anticipate heavy cuts, I can torque the screws down until those washers are completely flat so things are just like having no washer there at all.

This works for me. And spring washers could be added to almost any true adjust style chuck.

That was the problem. Two opposing screws were overly tight and holding the back plate from moving. lossened everything up and then re tightened equally all the way around and it works great. Thanks.