Power Chuck Runout, What is Normal?

NIDinc · May 18, 2015

Dialing in our used-but-new-to-us Mazak SQT-250MY. It has a 10" Kitagawa B-210 Power Chuck. Spent most of the day boring jaws and measuring runout and repeatability. The best we can get is about .0005 - .0015"

How normal is this? And what could we expect from a new chuck of the same type? I want tighter tolerances but I don't want to fork out $4K and end up with similar tolerances...

Thanks for the input!

iMillJoe · May 18, 2015

Thats about what you get.

If you use a boring ring while boring the jaws you MIGHT get a little closer, but don't count on it after you have changed top jaws. If you need better, you will still need to indicate every part by hand. I don't think a new 4k chuck will help. Add to that, you are using soft materials to hold your work, now you have issues with chips #ucking up the nice bore job you did.

kevin66 · May 18, 2015

Since it is a used lathe you have no idea the amount of cycles that the chuck has , or how often it was greased for that matter. We have a couple of Mazaks that we have had new since 1998 with B208 chucks on them and they can be counted on reliably to run within .0005 TIR or less. How do the T nuts look? They can get mushroomed out over time and cause runout problems, but usually on parallelism. If your are using some type of jaw backlash devise(boring rings, spider,or such) to bore your jaws i would be surprised if your TIR didn't improve. Its a pain in the butt but you might want to remove the chuck and see what kind of wear there is wheree the master jaws slide in the chuck body. It is possible that it just worn out or has a master jaw thats cracked.

NIDinc · May 19, 2015

Thanks for the helpful replies. I spoke to someone at Kitagawa and they confirmed that a new chuck may only improve things by .0002"
Sounds like there are other variables to check. As Kevin66 mentioned, mushroomed T nuts is one of them. Kitagawa swears by their Chuck-eez grease, claiming it can dramatically improve repeatability. They also claim that their factory top jaws make a difference. So, I have all new of the above shipping today. We also took the chuck off today, disassembled and checked it over. Master jaws and slots appear very good. We'll see how it goes with the new components and magic grease. It better be good at $385/case!

gregormarwick · May 20, 2015

iMillJoe said:
Thats about what you get.

If you use a boring ring while boring the jaws you MIGHT get a little closer, but don't count on it after you have changed top jaws. If you need better, you will still need to indicate every part by hand. I don't think a new 4k chuck will help. Add to that, you are using soft materials to hold your work, now you have issues with chips #ucking up the nice bore job you did.

A new 4k chuck can definitely help, just not if you go and buy another Kitigawa or similar.

I have a few Kitigawas in the shop that were bought new. There are far better chucks out there. I have a Berg that is pushing 30 years old with who knows how many cycles on it. With carefully bored soft jaws and good uniform parts it can repeat to 5 microns between parts no problem. The master jaws in the Kits have way too much clearance to hold that kind of repeatability.

The Berg chuck is so good they haven't changed the design - or even the part number - since. I'd expect others like Schunk and Autoblok to be considerably better than the common chucks as well.

Interestingly I have a Doosan with Samschully chucks that AFAIK are made under license from Kitigawa, but they seem to be a tighter fit between the master jaws and the body than the Kits.

Bluejeep · May 20, 2015

NIDinc said:
It better be good at $385/case!

Cncspecialtystore.com has 16oz. Chuck-ezz cartridges for about $20. ea.

Limy Sami · May 20, 2015

Have you stripped cleaned and inspected the chuck?

If not, you may be pleasantly surprised at the results, hard grease, chips, crap, damage and assorted nicks and burrs build up over the years.

Mtndew · May 20, 2015

NIDinc said:
We also took the chuck off today, disassembled and checked it over. Master jaws and slots appear very good.

It's always a good thing to remove the chuck and clean it out every once in a while. twice a month or so. Once you get the hang of it, the downtime is minimal.

dksoba · May 20, 2015

gregormarwick said:
A new 4k chuck can definitely help, just not if you go and buy another Kitigawa or similar.

I have a few Kitigawas in the shop that were bought new. There are far better chucks out there. I have a Berg that is pushing 30 years old with who knows how many cycles on it. With carefully bored soft jaws and good uniform parts it can repeat to 5 microns between parts no problem. The master jaws in the Kits have way too much clearance to hold that kind of repeatability.

The Berg chuck is so good they haven't changed the design - or even the part number - since. I'd expect others like Schunk and Autoblok to be considerably better than the common chucks as well.

Interestingly I have a Doosan with Samschully chucks that AFAIK are made under license from Kitigawa, but they seem to be a tighter fit between the master jaws and the body than the Kits.

And approximately how much would a Berg chuck cost?

Mtndew · May 20, 2015

dksoba said:
And approximately how much would a Berg chuck cost?

Back when I was pricing them, (late 90's early 2,000's) chucks were approximately $1,000 an inch.

Orange Vise · May 21, 2015

NIDinc said:
The best we can get is about .0005 - .0015"

How normal is this?

This is pretty normal. 0.0015 is a bit on the high side, but the chuck is used. Normally I'd say 0.0005-0.0010 is the best you'd expect on a new chuck - you'd get 0.0005 most of the time, but completely avoiding outliers around 0.0010" without indicating 100% of the parts would be unlikely.

There are "application chucks" out there that are much more accurate than a typical 3-jaw. The basic idea is somewhat similar to the comparison of a 16-degree ER collet vs an 8-degree slow-taper (SK) collet - you get less clamping range and application flexibility with the latter, but greater accuracy.

You may have seen the Northfield advertisements in MMS magazines (High Precision Diaphragm Chucks & Precision Air Chucks: Northfield). They make diaphragm chucks with guaranteed precision of 0.0002 radial TIR and 0.0001 axial TIR.

ManualEd · May 21, 2015

Orange Vise said:
They make diaphragm chucks with guaranteed precision of 0.0002 radial TIR and 0.0001 axial TIR.

You missed a zero there. It's .00002 and .00001...
How the hell is that possible?!?

gregormarwick · May 22, 2015

Orange Vise said:
...you get less clamping range and application flexibility with the latter, but greater accuracy.

Yes, that's true of my Berg. Probably has about half the jaw travel of an equivalent sized Kitigawa B-x.

It's still a wedge chuck though, not diaphragm.

NIDinc · May 22, 2015

success

Here's an update on my Kitagawa B-210 efforts...
As mentioned, I got new Tnuts, Kitagawa top jaws, and Chuck-Eez grease. We took apart our chuck and cleaned out all the old grease, used a stone lightly on the flat surfaces between the back plate and the chuck, carefully greased and torqued everything down evenly. Then we pumped more grease and opened and closed the chuck many times. Then we carefully bored with a nice carbide boring bar using about a 2" ring.

End result: we now have repeatable consistent .0005" TIR. Before it was jumping anywhere from .0005" - .003"
So, this is a big improvement and probably means we will keep this chuck for now. I was very close to going with an Autoblok and had looked into the Berg and was checking out the other resources and links mentioned above, which are all very helpful.
Thanks to all for the input.

321TJ · May 25, 2020

kevin66 said:
Since it is a used lathe you have no idea the amount of cycles that the chuck has , or how often it was greased for that matter. We have a couple of Mazaks that we have had new since 1998 with B208 chucks on them and they can be counted on reliably to run within .0005 TIR or less. How do the T nuts look? They can get mushroomed out over time and cause runout problems, but usually on parallelism. If your are using some type of jaw backlash devise(boring rings, spider,or such) to bore your jaws i would be surprised if your TIR didn't improve. Its a pain in the butt but you might want to remove the chuck and see what kind of wear there is wheree the master jaws slide in the chuck body. It is possible that it just worn out or has a master jaw thats cracked.

Kevin66, your T-nuts comment was a life saver! Should have been super obvious but one tends to overlook the simple things. Prior to swapping T-nut best i could get for runout after boring jaws was .002-.003. After swapping the last 3 borings have yielded .0001 or less!

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