4 Jaw Chuck Issues - Help!

[rwm]

I posted a while back about grinding my 4-jaw chuck. You can check it out here:

Replacement 3 jaw lathe chucks

Greetings folks, I am having to replace my Atlas 12 inch Pedestal Lathe mod 3996 3 jaw chuck.....The chuck will not keep the work piece tight in the jaws.....I am wondering where you folks have gone to buy tooling or would go to find a good (hobby style) chuck that will not brake the...

www.hobby-machinist.com

Ted

Thanks! Yes I have seen that method. Can I ask you where you got that grinding wheel and what type?
My current plan is to rough grind the jaw on my disc sander (cringe) to get it flat and then use a diamond wheel in my mill to finish grind. I would prefer the jaws flat rather than concave like your method yields. Your method may be my fall back move!
At this point the chuck is only good as an anchor for my fishing boat and not great for that either. I am now trying to figure the optimal way to grind it.

Bad:

 

[Nutfarmer]

Your picture of the two jaws on a flat surface clearly shows the problem. If you can grind them on the lathe in place , you should be able to correct the problem. Paying good money for a name brand chuck isn’t a sure thing. Quality control isn’t there even in some of the name brands.

 

[Winegrower]

South Bend is a brand owned by Grizzly now right? Not like the South Bend of old.

 

[Makintrax73]

I hate to even say what I did for this exact same problem on a cheap Chinese 4 jaw.....

Loaded the jaws 1 at a time and cut them in situ with a carbide boring bar until I was getting a clean surface from front to back. Carbide cut those jaws just fine BTW. It was worlds better afterwards. But I sure would've been hard pressed to try that if it wasn't the cheapest bottom of the barrel import junk.

Sure would be nice to have a surface grinder and set it up and make them flat at that exact angle, but I don't so I knocked the sharp edges down with a file and put that experience in the "you get what you pay for" file.

 

[atunguyd]

Bad:
View attachment 455287

Is this the correct way to test? I would think the bottom of the jaw that is resting on the surface plate is not the reference surface anyway. To me the reference surface is the rabbit cut into the tooth that the it slides along in the chuck . You need to ensure that the teeth are ground perpendicular to that. In my mind the only way to grind relative to that would be to grind the teeth in place on the lathe using a grinder mounted to the cross slide.


Sent from my SM-S908E using Tapatalk

 

[rwm]

The South Bend name is owned by Grizzly. They used it to make some pretty nice lathes for a couple of years but they did not sell well. I am very happy with the quality of my lathe. The 5" 3 jaw chuck that came with the lathe is awesome. Super high quality and very accurate scroll. The 4 jaw I am working with was not "cheap" but clearly has problems.
Using the bottom surface of the jaws is NOT a reliable method to test. The bottom surface is not a datum plane like the rabbets are. Nevertheless, I measured it with a mic and it is very close so it illustrates the problem. I think the most confirmatory test is the 1-2-3 block on the chuck face.
I am going to try to grind these jaws and I will post pics of how it goes.
I'm pretty sure if I can find a Pratt Burnerd that fits my machine I won't have this problem!

 

[talvare]

Thanks! Yes I have seen that method. Can I ask you where you got that grinding wheel and what type?
My current plan is to rough grind the jaw on my disc sander (cringe) to get it flat and then use a diamond wheel in my mill to finish grind. I would prefer the jaws flat rather than concave like your method yields. Your method may be my fall back move!
At this point the chuck is only good as an anchor for my fishing boat and not great for that either. I am now trying to figure the optimal way to grind it.

Bad:
View attachment 455287

This is what I used:

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Catalog #4522A246

Ted

 

[machPete99]

If you have a tool post grinder you could preload the jaws in the chuck and regrind them on the lathe. If you don't have the TPG you could possibly rig holder for a die grinder to do the same.

Getting them preloaded is the tricky part. You could make 3 spacers and put between the jaws so that they press against each other.

 

[RaisedByWolves]

Is this the correct way to test? I would think the bottom of the jaw that is resting on the surface plate is not the reference surface anyway. To me the reference surface is the rabbit cut into the tooth that the it slides along in the chuck . You need to ensure that the teeth are ground perpendicular to that. In my mind the only way to grind relative to that would be to grind the teeth in place on the lathe using a grinder mounted to the cross slide.


Sent from my SM-S908E using Tapatalk

Saved me the typing!

 

[Nutfarmer]

Pratt Burnerd is no guarantee to having a proper chuck any longer. A backing plate from them for my Hardinge was full of chatter on the taper mount. Looks like buyer beware no matter who the manufacturer is. Quality control just isn’t a priority anymore.