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Adjusting a set-true type chuck info


Dec 4, 2010
McClure, PA 17059
I posted a request for help with a Buck set-true chuck (Set-true Buck Kalamazoo 7-1/2 chuck help) with no replies. However as mentioned I did mount a second chuck to the back plate. I think I know how to properly adjust the the set-true set screws and have done it on other set-true types with the 4 set screw adjusters. But I never had the instruction manual. So as not to assume how it's adjusted, can anyone tell me the proper as per manufacture's instructions the correct way to adjust the chuck? What I want to know is what torque should be used on installing the back plate, should the back plate screws be loosened slightly prior to adjusting the adjustment set screws.
Having the back plate screws very tight, oil was put on the surfaces before back plate mounted. Using ground pin I adjusted the chuck to almost no indicator movement but 1/2-20 adjustment set screws required quite a bit of torque to move them. Tested repeated chucking on other ground pins of the same diameter and they repeated within less than .0005". If at any time I need to readjust possibly due to jaws at different scroll location or part roundness I'm interested to know what is the "proper" method!
I have no instructions but, it seems fairly obvious that--yes--you're supposed to loosen the chuck mounting screws before you try to adjust the chuck. If you don't, you're temporarily or even permanently bending the chuck. The mounting screws should be lightly snug (finger tight), then do your alignment adjustments. The alignment screws should not be tight against one another either. Going to tighten one side? Loosen the opposite screw. When you're done, the set screws should end up being slightly snug and then tighten the mounting screws.
I was kinda hoping for the instruction manual directions. Some say to loosen the back plate mounting screws other say no! I have seen quite a bit of Joe Pie's videos, he has a 4 set screw set-true chuck. He states to loosen the 4 set screws then tighten as needed to adjust the run-out. I've never seen him loosen the mounting bolts nor say they should be loosened. Maybe there is a specific amount the mounting bolts are torqued. I really don't know but would like to determine the correct way.
I'm editing this post, I did search the web and after a few videos found a Buck Manual site! As per Buck the mounting bolts should be loosened. On mine it will be those 6 nearest the OD. However in one of the videos I seen the guy completely disassembles the chuck and cleans it well. The inner 6 bolts should be loosened. The difference I guess is in the size of the chuck. Mine being a 7-1/2" requires the outer set of 6 to be loosened!
Therefore you are correct DH
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As I mentioned in previous post directions found at Buck site in Chuck owners manual loosening the mounting bolts prior to making the adjustments via the 4 set screws. On the other hand videos made by someone like Joe Pie (Pieczynski), I don't see him loosen the mounting bolts. In other videos I seen state the bolts were not tighten when mounting the back plate. But bolts were tighten in one using what looked like a 3/8" ratchet and some pressure, certinly more than "finger tight". They made the adjustments after doing stupid things like putting the indicator on the chuck body, make adjustment then put a round shaft in the chuck jaws and adjusting again! In one video the indicator did change by .001" after tighten the mounting bolts so finial adjustment was made with the mounting bolts tight!
That seems to bring a question in my mind as the what is loose and tight! I never put a "cheater" on my chuck wrenches to tighten the jaws, none of the chuck wrenches have bent handles! Those I have acquired that were bent have been straightened!
My assumption for the set-true feature (regardless what the actual term is used by the manufacturer) is to adjust the chuck to as near zero run-out as possible on the item chucked. Doing it on something like a gauge pin means nothing.
I know the chuck is not intended to replace the 4 jaw independent chuck and to be used to adjust for slight chuck wear and shaft roundness. Adjustment of more that .015" should not be expected if that much!
Am I missing something?
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The set-tru chucks are not usually adjusted very far. Ten thou would be quite large for what I do, usually it is a matter of two or three thou.

With reasonably long mounting bolts, which are not "fitted" bolts, there should be more than enough ability to move the chuck that far without elaborate loosening and tightening of mounting bolts. I keep the bolts "snug", but not torqued tight, and find that there is no difficulty adjusting the chuck, but it does not move in use.

The adjustments center the work and chuck, the bolts keep it in contact with the backplate. "Snug" should be sufficient to hold it in contact. The bolts can elastically accommodate a few thou movement perpendicular to their length, since in most cases they are at least 1.5" long.

At 1.5" long, a chuck movement of 0.01" would stretch the bolt by 0.00003 inches, assuming "pinned ends". The slop in the mounting system is more than that.

If you have to move the chuck many many times per shift, then it is possible that there may be some issues with wear. Otherwise I see no problems.
The chuck I mounted with the L0 Back plate has the hole size thru the chuck body as 7/16" for 3/8" X 3-1/8" long socket head cap screws, head counter-bored in face of the chuck. Threads in back plate, I turned the screws 5/16" the entire length under the cap up to the back plate. See nothing wrong with that since 3/8" tap drill is near 5/16" plus about 1/2" of the bolt threads do not enter the back plate and remain in the hole in the chuck body! Now all the bolt in the 7/16" holes have been reduced to 5/16" including the 1/2" of threads. Should make it easier to adjust. As to number of times per shift, probably one! When other work is done my go-to chuck is non adjustable with 2 piece jaws that runs .002" true thru it's entire range. For extreme adjustment range for 3 jaw chuck I have one the has a scroll plus the jaws individually move like a 4 jaw chuck. However repeatability is not good! Have same in 4 jaw chuck but repeatability also is not good!
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Working in various shops nobody I've seen loosens the mounting bolts on smaller chucks. Regardless of what the manual says. On bigger ones, maybe 15" plus, seems you gotta loosen the bolts to get any movement.

I think the bolts are flexed sideways when the chuck is adjusted. How tight should the bolts be? Just tight enough I guess.
Nobody loosens and tightens those face bolts that I've ever seen. Just don't torque them ultra tight when you put the chuck and back plate together. Medium snug, heh. Anyway, the roundness or flex of the chuck body is not a problem if you use this method: when adjusting, first back off all adjusters. Then use one at a time to push the chuck to zero the part, and back off the adjuster just used after every push so there's no or very little tension on it. Once the part is zeroed, slowly bring the torque on each adjuster up in even increments until they're all tight. Double check runout and make a quick tweak if necessary. Sounds complicated and like it would take long, but that's not the case. Once you've done it, it's very quick and easy.

Also, I recently pulled a Set-Tru chuck apart to swap to a different backing plate so I could put the chuck on a smaller machine. I removed the face mounting bolts but forgot to back off the Set-Tru adjusters. I could not budge that bastard. Then I remembered to back off the adjusters and the chuck popped right off, easy as you please. I only add this in case you are worried about not tightening the face mounting bolts all the way. The Set-Tru adjusters actually do add a very non-negligible amount of clamping force.
Thanks guys! Most of those YouTube video are done by those that know very little! One I seen had one piece Jaws, guy spent 1/4 of the video explaining how to to put the jaws in, then mentions the jaws can be reversed. Maybe something was said by whomever was operating the camera so he corrected himself by saying some chucks need different set of jaws. There are No one piece jaws that can be reversed! Only piece on a 2 piece jaw set that can be reversed is the top jaw!
I reduce the shanks of 5/8" reamers for a customer (2 dozen). Was using PB set-true style but taper adjuster surface on back plate was worn so that with tapered adjuster turned completely in would not move the chuck body more than a thousandth or 2. To busy to fix it so I found these chucks on ebay. Now I have to figure out how come the jaws are hard to move when the back plate is tightened on one of the chucks.
I posted a request for help with a Buck set-true chuck (Set-true Buck Kalamazoo 7-1/2 chuck help) with no replies... <snip>

I just uploaded to VintageMachinery.org (link below), two instruction sheets for:

  • Mounting & Use of Buck Adjustru Chucks (1959)
  • Mounting & Use of Buck Adjustru Chucks, w/ maint items & parts breakdown (1979)
I'd give it a day or few for the website folks to review & publish the files. The files are now showing available for viewing or download.

The 1959 sheet is attached as a pdf hereon.



  • buck_adjustru_procedure 1959.pdf
    475.2 KB · Views: 7
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............................ There are No one piece jaws that can be reversed! Only piece on a 2 piece jaw set that can be reversed is the top jaw!
Actually, there are......

The "teeth" on the reversible ones are "football shaped" (US football), so that they can work either way. Usually those are not the best chucks, though.
We had set true collet chucks on some grinder work heads
We loosened and tightened the retainers to be even and just snug, the indicated adjuster all snug to about or less than 001, then made the retainers a little tighter /more snug and tightened the most-off adjuster and gave the chuck a knock with a brass knocker trying to get 50 millionths of so. Then brought up the other adjusters to make a snug and gave a light knock to get near zero. once very close and the retainers brought up to tight. They rarely went out but collets can be .0002 off, so collets would be tried in different positions to find the best position, if less than < 2-tenths was needed..

Sometimes the .0002 in the collet can offset the .0002 on the chuck.
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Thanks Morsetaper2 I'll check it out but did find owners manual for Buck adjustru chucks but more information is better!
My question before in the other topic (was why would the scroll be hard to turn after in the other topic (Help with Pratt Burnerd set-true chuck) the mounting bolts were tightened. Wrench will turn but with great force just about what is required to tighten the jaws on the work piece but nothing inserted!
One more thing to do mounting a adjuster true or set true chuck to a backplate for the first time.
Check the indicator runout on the face of the backplate before mounting. If it's more than a thousandth runout, pull the back plate and check for dings and burrs. Fix and remount the back plate and check again. IF you get the same runout or a tad less, take a skim cut to cleanup. This should help in getting your chuck running true. And when I say a skim cut, no more than 0.005" at the most.
If you intend to in place skim the backplate then:
If there is any way the face plate or chuck can be mounted /assembled differently be sure to mark it so it might be reassembled the same way if disassembled.
I would likely Ignore .0002, perhaps a little more.
Chuck though old seemed new (Buck Kalamazoo) no indication of wear or any use. Back plate was in same condition! Purchased separately from same seller. He had at least 5 or 6 same chucks but only 1 L0 back plate (I purchased 2 chucks and the only one L0 back plate). To be sure back plate ran true I did take a skim cut but only a few thousands were taken and face was perfect (didn't need it but was done to insure no run-out) Face did not extent to adjustment hub, factory undercut of maybe .010 deep about 3/4" wide that was not touched. Face of the adjustment projection was also skim cut so as to prevent any contact with inner surface of the chuck body.(checked with depth Mic. to insure no contact) Yes I have marked the back plate so if ever removed it can be replaced in the same location. Jaws are stamped on the end with the insertion sequence but the number is stamped on the face of the chuck body, I stamped the jaw numbers on the body OD and a #1 on the back plate OD in the same location as # 1 jaw.
As I mentioned the mounted chuck functions perfect and repeats! The other chuck I wrote about in the other topic is the one that the scroll will tighten when mounting bolts are tightened. The other chuck looks as good as the mounted one!
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