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New Power Chuck has a run out, what could be wrong?

1NoobMachinist1

Plastic
Joined
Oct 18, 2023
Firstly hello everyone, I'm pretty new to cnc machining and in dire need of advice as I am currently stumped with what to do any further, as the company I bought a 10" chuck from is insisting that my hard jaws are a problem.
Long story short, I bought a CNC machine roughly a year ago everything was going great until a horrible accident happened where I forgot to set one tool's offsets correctly up, in doing so once putting in a new stock piece for machining my turret ran unto my chuck at practically full speed, the result of this is that one of the master jaws had broken, forcing me to purchase a new chuck. What could cause this I checked the chuck itself while spinning and it only has +-0.01 mm runout, I also clamped a chrome chuck to show the runout experienced, its almost like there is a wobble even though all the hard jaws are correctly set (as shown in the photo, albeit attempting to place the hard jaws all level with the master jaw there is some slight discrepancy, 1 feels flush with the master jaw, the other 2 are either slightly protruding over the master jaw and the other slightly under the master jaw), I've uploaded some videos to this link (the website directs you to the temporary videos I've uploaded to WeTransfer), I also noticed that, the build quality of the master jaws don't look of high quality, I've counted the total gaps between the master jaw teeth and 2 of the master jaws had 50 "slots" and one had 49 I raised this and was told this has no matter, also as you can see in one of the photos one of the hard jaws one of the serrations are damaged which I ground out, but they insist that the runout is caused by that which I find to be impossible because of one serration being damaged? I am at a cross roads with this as the only way I could prove now that I do indeed suspect I've been sold a faulty chuck is by purchasing brand new hard jaws (which cost about $315), hence why I made this post to find out what else could be causing so much run out, any suggestions?

 

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Well, that looks like a Chinese chuck to me, but, with that said, if there is only a .0003TIR on the body then I'd say even Japanese makers would be more than acceptable of the result.

OTOH
If you're looking for a better ( or even remotely similar ) runout on hard jaws ...

My take: If your hard jaws run out less than .02TIR then you're more than all set and don't complain!
 
Well, that looks like a Chinese chuck to me, but, with that said, if there is only a .0003TIR on the body then I'd say even Japanese makers would be more than acceptable of the result.

OTOH
If you're looking for a better ( or even remotely similar ) runout on hard jaws ...

My take: If your hard jaws run out less than .02TIR then you're more than all set and don't complain!
What has me confused though is that with my previous chuck I never had this issue I had virtually no run out when clamping a chrome shaft with the same hard jaws which in this case it does not give the same result it imposes a problem in regard that I can not set the center height of my tools either (fyi: I had to replace my turret as well)
 
If you want to share videos put them on youtube.

Repeatability is the only thing that counts on a power chuck. Master jaws and hard jaws are all mass produced and are not fitted to each other, so you can expect some runout, and this is going to be significantly worse on cheap chucks compared to better quality name brand ones.

If the runout matters to you, mount the jaws and recut them in-situ, just as you would a set of soft jaws.

Don't overthink it. That said, I disagree with Seymour's post that you should be happy with .020" on hard jaws. I will tolerate a couple of thou, maybe, before I will recut them.
 
If you crashed that lathe as bad as you described and your only problem is runout with some hard jaws?
You should feel lucky, I have seen some crashes but none cracked the hard jaws.
 
What I am getting from your jaw positioning procedure, it appears that you are placing the hard jaws as close a possible to the same position on the master jaws. You may have better results positioning the hard jaws so the material gripping surfaces are all as close as possible to the same radius.

Dave
 
If you want to share videos put them on youtube.

Repeatability is the only thing that counts on a power chuck. Master jaws and hard jaws are all mass produced and are not fitted to each other, so you can expect some runout, and this is going to be significantly worse on cheap chucks compared to better quality name brand ones.

If the runout matters to you, mount the jaws and recut them in-situ, just as you would a set of soft jaws.

Don't overthink it. That said, I disagree with Seymour's post that you should be happy with .020" on hard jaws. I will tolerate a couple of thou, maybe, before I will recut them.
Hi thank you for the input for perspective this was a a gear shaft I did a while back with the old chuck, material EN19T which was pre-machined on a manual lathe and then to the CNC, I had virtually no run out or at least it was not visible to the naked eye while turning, with the current chuck I can forget doing such a job with my hard jaws as when I machine one side and turn it around and clamp on the other side I'd experience the same amount of run out. I wouldn't mind if I had a runout of about max 0.03mm as i'd make that up in the cuts but 0.2mm is tough as some of the free issue material is usually almost to size e.g (raw being 250mm dia and final cut being 249.5mm).

I'm currently uploading a video to youtube but it's taking long demonstrating a job I did with the hard jaws (16mm stainless steel rod) with the hard jaws on with my old chuck where as now if I attempt to do that same job with this chuck I'd never be able to even drill at the center point.

Also I had reason why I had not remachined the hard jaws is because I was told that you dont machine hard jaws but I'll take this into consideration if I can not have this chuck replaced. I'll also attempt to remove the cover plate tomorrow and use the finger dial to see if all the master jaws would give me the same reading.

The image: showing only the master jaws ( Blue: remove that cover plate, Orange: Measure the hard jaws from the while clamped...).
 

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The difference in position of the master jaws from the center of rotation is not nearly as important as the position of the hard jaw gripping surfaces from the center of rotation. You may need to clock the hard jaws to different master jaw stations to achieve equal (or at least closer) distances of the gripping surfaces to the center of rotation.

Dave
 
If you crashed that lathe as bad as you described and your only problem is runout with some hard jaws?
You should feel lucky, I have seen some crashes but none cracked the hard jaws.
Oh no doubt very very lucky! Here is a photo of the chuck, in hindsight I shouldnt have had my jaws stuck out so much, learned the hard way.
 
What I am getting from your jaw positioning procedure, it appears that you are placing the hard jaws as close a possible to the same position on the master jaws. You may have better results positioning the hard jaws so the material gripping surfaces are all as close as possible to the same radius.

Dave
Hi Dave how would one achieve this? I've always just used my caliper measured the depth on one of the jaws and set up the rest according to that depth that same method does not work here as with one of the jaws it seems like I'd have to move one teeth lower than the measured depth with the caliper.
 
The difference in position of the master jaws from the center of rotation is not nearly as important as the position of the hard jaw gripping surfaces from the center of rotation. You may need to clock the hard jaws to different master jaw stations to achieve equal (or at least closer) distances of the gripping surfaces to the center of rotation.

Dave
I will attempt this and see what happens tomorrow. From what I understand you are saying that I should use a dial gauge to set up all my jaws and that should have it clamping much more accurately?
 
From what I understand you are saying that I should use a dial gauge to set up all my jaws and that should have it clamping much more accurately?

Index your turret to a tool that is already set in X.
MDI that tool to the diameter of the part you want to hold on to.
Handwheel the turret over to the hard jaws about 1/8" away or closer.
Visually line up the gripping part of the jaw to the X diameter that the tool is set to.
Tighten jaw.
Repeat for all 3 jaws.

It's easily done with a boring bar. A turning tool can be used as well.
I've done it this way for over 30 years.
 
Set up as Mtndew posted above.

With the1.5mm serration pitch you should easily be able to gage by eye equal jaw positions against the positioned boring bar
 
Index your turret to a tool that is already set in X.
MDI that tool to the diameter of the part you want to hold on to.
Handwheel the turret over to the hard jaws about 1/8" away or closer.
Visually line up the gripping part of the jaw to the X diameter that the tool is set to.
Tighten jaw.
Repeat for all 3 jaws.

It's easily done with a boring bar. A turning tool can be used as well.
I've done it this way for over 30 years.
I'll attempt to do so today, and see if this yields better results.Thank you for the input I'll get back to let you know if it helped resolve the problem.
 
I've exaggerated of course, but the point was that expecting no runout with hard jaws on a hydraulic chuck is nuts.
I've noticed people are kind of bonky about chucks here but I'd get better than twenty for sure ... put the jaws in the best place and drag out the toolpost grinder, touch 'em up and bob's yer uncle. This crap with "take the part out and turn it around", where did they learn machining ?
 








 
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