5c collet chuck

[COMachinist]

Hi All
I have a mod “3910-5” 5c chuck made in Polland”did a search and it came back to a Bison with out the yellow medallion with the buff on it. I thought these were really good chucks? It is mounted on a D1-4 back plate that has less than .0002 run out on the face. It was machined on my PM-12x36t that has 0 spindle run out and only has about 10 hr use. Got it last June 2018. I can see the nose on the chuck with out collet wobbling. I measured it with my .0005 Sterrett DTI and it has .025+ tir inside the tapper. It almost looks like the back surface is not perfectly perpendicular to the bore of chuck. Any ideas how to get it running true. I thought about clamping a 1” ground drill rod in my set true 3 jaw with less than .0002 run out on a 1” mill. Then turn the mating surface on the back of the chuck, but not real sure about the collet, it is Shars pression collet. I was woundering if it can be sent back and referbished? It is an older used chuck. Perhapes it would be better to just scap it and look for a newer chuck. I realy hate to toss a Bison 400.00 chuck.
CH
PS There is no burs or dings on the surfaces that are critical. Or on the back plate fresh machined and has not been off the spindle

 

[Cadillac]

I wouldn’t blame the chuck till you can verify your problems.

 

[COMachinist]

I wouldn’t blame the chuck till you can verify your problems.

Well Im not sure what you mean by this statement? The back plate mounted on the lathe that machined it with no run out. Mount the chuck to it and the nose of the chuck is .025+ tir. It is so bad you cand see it wobble with out a DTI. No chips, no burs are at fault. Not the lathe other chucks run true, not the d1-4 back plate. Am I missing some thing, please feel free to explain.
CH

 

[wrmiller]

I recently acquired a 5" set-tru collet chuck from PM, along with a collet set. Mine says 'made in Poland' and according to Matt, it is made in the Bison factory but doesn't have the roll-marks nor label.

Anyway, mine runs very true fortunately. Your idea has merit IMO and that would be the next thing I would try. My only concern would be the 5c collet's ability to hold the chuck true to the TGP bar?

 

[JimDawson]

I guess I would do what you suggest and clamp it on a 1 inch ground bar. You need to find out exactly where the problem is at. It could be that the register surface is not concentric to the bore but 0.025 is a lot, and I would be surprised if that was the problem. My best guess is the back plate register is not fitting correctly in the chuck.

 

[COMachinist]

Well clamping it to a 1” end mill in my zero set 3 jaw and checking the back with the indicator sounds to easy. The collet is an unknown and my feeling is I don’t want to make things worse, If you know what I mean. I have had this chuck for a couple years, and never used it so don’t know much about it. When I got my PM12x36t last summer. It didn’t have a D1-4 back plate so I bought one. Mounted it up and did the skim cuts, and cut the boss to fit the chuck. Tried to get it to trued up which turned out impossiable. So I spun it up at about 200 rpms, and the nose wobble is so bad you can see it. I put a 1” end mill in a Collet and it wobles with the nose. The inside taper has the same TIR as the mill and nose. i didn’t see much runout at the chuck back plate junction. None of my other plainback chucks has over .0015-.002 TIR, with the set true chuck at less tha .001 repeatable from mount to mount up.
CH

 

[JimDawson]

I suppose it is possible that the chuck is out as much as you are seeing, but I really can't imagine anything that bad would make it through Bison QA. In any case, you are going to have to trust something to have a starting point to get some measurements from. The collet can't be that far off. Worst case you could turn a ''5C collet'' as a stub arbor and then you know you have a concentric surface to start with.

With 0.025 runout it should be pretty easy to find the surface that is off.

 

[Cadillac]

What I mean by that statement is don’t assume your work is right and the bison chuck is the culprit and go cutting the chuck to match your backplate and then be out that much more.
If the chuck is a bison I cannot see it being out .025. Maybe .002 but .025. I don’t think I’ve heard of a lousy 3 jaw having that much.
Did you check figment of backplate to spindle prior to machining?
Did you mark a pin to locate where you made your cuts from?
Have you mounted just the backplate and taken readings from every surface.
Do you have a flat surface to put chuck on and take some measurements?
You want to verify where this amount is off before cutting anything.
Can you take a picture of back of bison chuck. Does it have factory grind marks?

 

[Superburban]

It almost looks like the back surface is not perfectly perpendicular to the bore of chuck.

Find a way to mount the chuck backwards, with the bore perfect, then you can measure the runout from the bore, on the back of the chuck.

You could take the largest collet you have and turn a bar to fit it, and hang out 4 or 5 inches, then mount the bar in the collet, and then in a regular chuck. Or better yet, if you can purchase, or borrow a ground rod about 1" diameter, and about 6" long.

Or get the biggest mandrel that matches a collet you have, and mount it into the chuck, and then between centers on your lathe.

Do not take any cuts on anything, until you have verified where the runout is, and you can take the assembly apart, and remount the chuck, and get the same runout in the same place. If possible, also with different collets.

 

[Bob Korves]

Make quite sure you do not have an issue with the back plate fitting the spindle properly. The spindle has a male taper, the back plate has a female taper. The design is so that the two tapers fit together snugly while the flat spindle end of the back plate also mates perfectly with the flat spindle face. There should be no light showing through a gap between the backing plate and the spindle face with the back plate mounted in place, checking around the entire circumference of the assembly. There should be complete contact all around the circumference of the flat faces. Use a bright flashlight from the back side looking for light and check carefully, this is a common problem, and it will cause the back plate to lean one way or another, causing the chuck to wallow around. If you find that problem, get back to me and I will tell you how to fix it. Do not try to figure it out alone, or you can make big mistakes while removing a small amount of metal.