Test bar for new 6 in 3 jaw Buck chuck

O

ome

Forum Guest
Register Today
Buck co. Suggest chucking up a test bar and indicating the bar.

If not close enough, then take a small amount from the lathe , which i am not totally clear on it.
Anyway i do not want to make my own so where to look, i looked at ebay, all i found were mt2 or mt3 ..
i was thinking 1 " round and just long enogh to stick out of the chuck enough to indicate.

Need help
thanks to all
jon
 
All you're looking for is something that is accurately sized, and very straight. It must also be rigid. Some people prefer hollow, ground OD mechanical tubing for it's weight to strength ratio. That's a good theory, and true, but harder to come by unless you can make it yourself. For more practical purposes, a ground, straight test bar can be had with plain ends. Often, drill blanks, which are also hardened can be used on the smaller machines, as they aren't all that long, but sufficient. For your 6", I would not want anything shorter than about a foot, to allow enough to fully engage the chuck jaws and still hang out far enough to be meaningful, yet not so long as to droop or sag.

The purpose of this is to test the TIR (Total Indicated Runout, or Total Indicator Reading, depending on who you ask). If this is a Set-Tru chuck, simply chuck the bar, indicate it in near the jaws, then move the indicator further out and see if it is still running true. This will tell you the parallelism of the jaws. If it is not a Set-Tru style, it will tell you the runout you will see chucking material or parts for machining. Often, I think too much is made of this issue, as many parts can be made virtually complete in a single chucking, or soft jaws can be machined to finish any second operations with ner zero runout. But to each his own. There should be some specifications accompanying the chuck which you can compare readings to, and complain if they are not met with your chuck. Buck is usually pretty good to work with, because they have a reputation to keep up.
 
ome said:
Buck co. Suggest chucking up a test bar and indicating the bar.

If not close enough, then take a small amount from the lathe , which i am not totally clear on it.
Anyway i do not want to make my own so where to look, i looked at ebay, all i found were mt2 or mt3 ..
i was thinking 1 " round and just long enogh to stick out of the chuck enough to indicate.

Need help
thanks to all
jon
Click to expand...

If you are using a three jaw chuck expect .002 to .003 run-out. I read that on another manufacture's website. Might consider using a .500 harden dowel pin as a test bar.
 
a test bar is something worth making yourself to indicate your headstock/tailstock alignment (turned between centers).
 
I just want to present a different approach. I read a lot about 3 jaw chuck problems. They are real. Seems like most of what folks are doing is just one of a kind. one part. A 3 jaw has its limitations, even top drawer. A story. Years ago I started in the toolroom of a large jack mfging co. First thing I did, based on what the production foreman told me was take that ( dammed ) 4 jaw off and put the 3 jaw on. I did and it was ragged. oh well. Next day the Chief Engineer strolled into the tool room. Looked at the lathe and said take that ( dammed ) 3 jaw off and put the 4 jaw on. And so I did. He was my boss. That 4 jaw stayed on that lathe for 5 years. I got so good at indicating a piece of stock in that chuck , you can't imagine. There is no trick to it. Every once in a while the production foreman would come in the toolroom dragging a hank of round steel and want to do it himself. Every machine he supervised , production lathes, had oviously 3 jaw chucks. Sorta his mindset. I rarely made two of anything, only if I scrapped it. Crap happens. Don't writeoff the little 4 jaw. Try it, you might like it. For what its worth. Believe me chuck run out will never be a problem.
 
lrsglory said:
I just want to present a different approach. I read a lot about 3 jaw chuck problems. They are real. Seems like most of what folks are doing is just one of a kind. one part. A 3 jaw has its limitations, even top drawer. A story. Years ago I started in the toolroom of a large jack mfging co. First thing I did, based on what the production foreman told me was take that ( dammed ) 4 jaw off and put the 3 jaw on. I did and it was ragged. oh well. Next day the Chief Engineer strolled into the tool room. Looked at the lathe and said take that ( dammed ) 3 jaw off and put the 4 jaw on. And so I did. He was my boss. That 4 jaw stayed on that lathe for 5 years. I got so good at indicating a piece of stock in that chuck , you can't imagine. There is no trick to it. Every once in a while the production foreman would come in the toolroom dragging a hank of round steel and want to do it himself. Every machine he supervised , production lathes, had oviously 3 jaw chucks. Sorta his mindset. I rarely made two of anything, only if I scrapped it. Crap happens. Don't writeoff the little 4 jaw. Try it, you might like it. For what its worth. Believe me chuck run out will never be a problem.
Click to expand...
thanks, i fully intend to buy a 4 jaw buck 8" in a short while.
I just want to properly set up this 3 jaw
thanks
jon

- - - Updated - - -

Tony Wells said:
All you're looking for is something that is accurately sized, and very straight. It must also be rigid. Some people prefer hollow, ground OD mechanical tubing for it's weight to strength ratio. That's a good theory, and true, but harder to come by unless you can make it yourself. For more practical purposes, a ground, straight test bar can be had with plain ends. Often, drill blanks, which are also hardened can be used on the smaller machines, as they aren't all that long, but sufficient. For your 6", I would not want anything shorter than about a foot, to allow enough to fully engage the chuck jaws and still hang out far enough to be meaningful, yet not so long as to droop or sag.

The purpose of this is to test the TIR (Total Indicated Runout, or Total Indicator Reading, depending on who you ask). If this is a Set-Tru chuck, simply chuck the bar, indicate it in near the jaws, then move the indicator further out and see if it is still running true. This will tell you the parallelism of the jaws. If it is not a Set-Tru style, it will tell you the runout you will see chucking material or parts for machining. Often, I think too much is made of this issue, as many parts can be made virtually complete in a single chucking, or soft jaws can be machined to finish any second operations with ner zero runout. But to each his own. There should be some specifications accompanying the chuck which you can compare readings to, and complain if they are not met with your chuck. Buck is usually pretty good to work with, because they have a reputation to keep up.
Click to expand...
Thanks Tony,
it is a set tru with 4 adjustment screws with about 20 thousands of adjusment when bolts are loosened, holding it to plate.
Where can i find a 12" long and 1 " round precision drill blank, cause the dpins are not that long.
Thanks,
jon
 
Will somebody please explain how these "Tru-Set" chucks work?

Ray
 
Theres a special backing plate that tweaks the exact position of the chuck body through the use of 4 set screws.

Basically you adjust the similar to how you would a 4 jaw, just without having to loosen the opposing jaw first.
 
Another option for an "out of the box" test bar is a piece of TGP (turned, ground and polished) shafting. In lengths up to about 12 inches it is very straight. McMaster Carr is one source for it.
Terry S.
 
twstoerzinger said:
Another option for an "out of the box" test bar is a piece of TGP (turned, ground and polished) shafting. In lengths up to about 12 inches it is very straight. McMaster Carr is one source for it.
Terry S.
Click to expand...
Thank you very much.
Regards,
jon
 
You must log in or register to reply here.
Back
Top