Experiences with hydraulic 6 jaw chucks

Does anyone here have any experience using a hydraulic 6 jaw chuck? For the past 15 or so years we just used a standard hyd 3 jaw at the lowest pressures possible and even with pie jaws I get deformation. This is minimal but with tolerances getting ever tighter, and the boss pushing to get out of oil/gas sector and into aerospace, my bet is that I'm needing better work holding.

Machine is a Cincinnati TC250M with a fanuc control.

Material is mainly babbitt lined bronze in the 3/16 to 5/8 wall thickness. Sizes range from 2.0" to 9.5" These are finishing operations so feed rates are light and cutting forces small. Max rpm is 2k on smaller parts, 1200 on larger parts.

Ive got a quote on the smw at 25K and around 35K installed (the hydraulics have to be changed).

I have not received a reply from schunk, even after 4 attempts to get a quote. I've also tried talk to an apps engineer to ask them if this is their best chuck for this, and still nothing.

I'm also not sure that these chucks are the best possible way to hold my parts. If anyone has any suggestions, I'm all ears.

I'm also worried about the adaptability of these chucks for different parts. They seem to have less serrations than a typical 3 jaw. Currently i have about 60 part #'s and they all have their own set of jaws.

Chuck will be the 250MM size.


Clamping Technology


"SJL-C" on this page, looking at the serrated, not T&G.

Application Chucks - SMW-Autoblok US


Before i drop 35k on a chuck, i would like some input from anyone that has some insight.

I'd sharpen my pie jaw boring act, and maybe reduce the chucking pressure further (machine mod) or switch to a manual chuck ……..6 jaws will only give you 6 lobes.

With thin wall tube you always have to fight OD form errors and stress relief during cutting. If a truly round part is needed then sometimes you have to go back and forth from OD to ID to "work them round", and you might consider face holding (clamping along the Z axis) to get truly round ODs (well, as round as the spindle bearings allow).

I do like 6-jaw chucks for general work, but like anything, GIGO still rules...

What size do you have your pie jaws bored relative to the OD of the workpiece?

Limy Sami said:

I'd sharpen my pie jaw boring act, and maybe reduce the chucking pressure further (machine mod) or switch to a manual chuck ……..6 jaws will only give you 6 lobes.

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I do have a manual 6 jaw chuck that i install on that machine occasionally. Problem is, i can't trust my operators to get the same clamping force with it.

Too loose and they come out of the chuck. Too tight and they roundness goes to pot. Had to scrap that idea after the first run. Torque wrench would've helped, but we didnt have a good one at the time. also looking for the throughput that a hydraulic will provide.

Milland said:

With thin wall tube you always have to fight OD form errors and stress relief during cutting. If a truly round part is needed then sometimes you have to go back and forth from OD to ID to "work them round", and you might consider face holding (clamping along the Z axis) to get truly round ODs (well, as round as the spindle bearings allow).

I do like 6-jaw chucks for general work, but like anything, GIGO still rules...

Click to expand...

There are preliminary ops that true out the basic shape before hand. "working them round" is something ive tried and it works. just takes a lot more ops, and introduces more chucking errors. Face clamping is the way we do our steel bearings on the grinder. But it does introduce concentricity errors.

gbent said:

What size do you have your pie jaws bored relative to the OD of the workpiece?

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Depends on how beefy the jaws are.

I try to measure deflection of the jaws at the furthest point from jaw center line when clamping, then bore half the deflection amount under size.

MotoX said:

Face clamping is the way we do our steel bearings on the grinder. But it does introduce concentricity errors.

Click to expand...

Sure, what I do is rough, face clamp and turn OD, get concentric within a conventional chuck and finish bore.

Milland said:

Sure, what I do is rough, face clamp and turn OD, get concentric within a conventional chuck and finish bore.

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Agreed. Same thing we do here.

But in this case the parts are babbitt lined. In the process of multiple ops and different chuckings, the babbitt lining thickness can have concentricity errors.

Of course this secondary to the ID/OD relationship, I still need to keep the variance to a minimum.

MotoX said:

I do have a manual 6 jaw chuck that i install on that machine occasionally. Problem is, i can't trust my operators to get the same clamping force with it.

Too loose and they come out of the chuck. Too tight and they roundness goes to pot. Had to scrap that idea after the first run. Torque wrench would've helped, but we didnt have a good one at the time. also looking for the throughput that a hydraulic will provide.

Click to expand...

Exactly my experience but what else can you do ? I had an ongoing (50 at a time, not enough to spend $$$ on fixtures but too many to be convenient) job with parts about 8" diameter by maybe 3/8" wall. Bolted a 12" six jaw manual to the front of the 15" power chuck and yup, had the same too-tight, too-loose problems. Pies on that chuck were better so I don't think you will get away with normal jaws. Even three pies bored .005" over gave a measurable trilobe. Six got me a hex, at least

No way could a power chuck that size be delicate enough for those parts.

I would suggest an undersized manual chuck with overhanging jaws if possible ... the smaller they are, the better the feel.

If you couldn't afford a good torque wrench, why are you considering a $35,000 chuck ?

Another option would be to make or have made some sort of expanding collet. I can't remember the name now but there were places making hydraulic expanding arbors for holding parts on the bore - they even made splined ones. Pretty sure they had some big specials they had done in their catalog. If it's a long-running job, that wouldn't be too difficult to implement.

edit: Something like this

Inside Diameter Expand Mandrels & Expanding Collets

Expanding Mandrels | Kitagawa

Hydra-Lock is in Detroit but their website is so shitty I am not going to link to it. You may tell them that if you call.

Special Applications On Positrol Workholding

Or you could do your own, I don't think there's anything magic about these, and everybody involved seems really proud of their stuff.

W&S showed a job for IIRC Clevite.

They showed the shell bearings being finish turned in a W&S auto chucker.

I'll look thru my stuff to see if I could find it, I'm sure the work holding was detailed.

Thanks for the links. Positrol is a company I've not heard of before. They seem to have some good offerings.

For this operation, we clamp on less than 1/4" of stock and do most of the ID/OD work at the same time. I wonder if a diaphragm chuck is the way to go. Anyone use one of those?

This place had almost nothing as far as hand tools when i started. But much of that has changed in recent years.


I'm curious to see what that Clevite setup was like.

MotoX said:

Material is mainly babbitt lined bronze in the 3/16 to 5/8 wall thickness. Sizes range from 2.0" to 9.5" These are finishing operations so feed rates are light and cutting forces small. Max rpm is 2k on smaller parts, 1200 on larger parts.

Click to expand...

Have you considered potting the bearing shells into a thick walled steel cylinder using one of the low temperature (160deg F) metal alloys ? The metal alloy can be selected to expand slightly when it cools to insure a tight grip.

A good reference site for this is INDIUM.COM . Look for the section on "Chucks, jigs and fixture" applications. This is the method used for holding turbine blades when grinding the fir tree anchor at the base of the blade.
The part is removed from the potting metal by placing the fixture in a bath of hot water.

The potting method will be much less expensive than a hydraulic chuck and it will do exactly what you want.

The alloys are mixtures of bismuth, lead, tin, and cadmium. The metals are not a breathing hazard at the low alloy melting temperature.