Balance 4-jaw chuck for PM 1236

[Winegrower]

Somebody please explain how a 4 jaw chuck can be so unbalanced. There must be a huge manufacturing defect, no? Maybe if the jaws weren't adjusted equally, like say a newby might do, I could see that. Otherwise, send it back.

 

[Digger42]

Nice job. Do you have any videos in operation?

Fine tuned after video made so chuck stopped without any more movement. Chuck was over 3 oz out of balance at start. Used various sizes of strong earth magnets inside back of chuck as counterbalance. After final tune also superglued magnets. So far magnets have not shifted.

 

[verbotenwhisky]

I'm sorry, @Digger42, I should have tried to field your question a little more honestly before unpacking the sarcasm.

I think balancing chucks is a good idea in general, if the factory didn't do a good job initially first. I skipped that step with the last half dozen chucks I bought, because secondary balancing by the end-user is a disqualifier on my personal quality agenda. If it were a three jaw scroll chuck, I would have saluted and said good work, carry on. But because it was a 4-jaw independent, and independent chucks are fundamentally imbalanced, I made the comment to see if you would pick up on that fact. I made it obvious by asking if it would work under a non-symmetric part. I could have also suggested an off-center part, since the 4-jaw is how you accomplish an eccentric hole, for example. This alludes to the usage of independent chucks for deliberate off-centering or for gripping nonuniform parts. Both of these conditions are inherently out of balance and off-axis.

So what I'm saying is, I narcissistically posted to see if you catch on, and if not, I started popcorn. I apologize for using you for my own entertainment. I probably owe a lot of people around here the same spiel.

Actually, sarcasm aside, if I want a piece truly centered I use the 4 jaw. In all honesty if you run the jaws in equally the damned thing should be reasonably balanced and the one I have isn't, I thought it was a piece of slag I had knocked off the back but it wasn't. I would like to get mine balanced within reason so as not to add to the imbalance when I am handling an off center part or odd part.

 

[verbotenwhisky]

Fine tuned after video made so chuck stopped without any more movement. Chuck was over 3 oz out of balance at start. Used various sizes of strong earth magnets inside back of chuck as counterbalance. After final tune also superglued magnets. So far magnets have not shifted.

I believe I am going to use the lead weights like we use to use on mag wheels and aluminum wheels.

 

[Digger42]

Somebody please explain how a 4 jaw chuck can be so unbalanced. There must be a huge manufacturing defect, no? Maybe if the jaws weren't adjusted equally, like say a newby might do, I could see that. Otherwise, send it back.

PM indicated this is common with China chucks. Normally cleaning out back takes care of most of problems. Mine appeared to have had a casting mold void. Was easy to balance so went that route.

 

[verbotenwhisky]

Fine tuned after video made so chuck stopped without any more movement. Chuck was over 3 oz out of balance at start. Used various sizes of strong earth magnets inside back of chuck as counterbalance. After final tune also superglued magnets. So far magnets have not shifted.

I have the same lathe PM1236, likely the same chuck and a similar issue.

 

[pontiac428]

3 ounces is a whole lot! A big casting cavity would have to exist in order for that to occur. Now I understand why your lathe was hopping.

Usually, 4-jaws are only faster turning than surface plates in the lineup. That's second to last slowest RPM limit. The solution for them being a little out of balance by the work fixturing requirements is to just slow their roll. Initially, 800 RPM seemed hopeful for a 12" lathe with an independent chuck, but not impossible, which is why I was surprised by the amount of struggle you were having. Now that makes sense! I would have to try with a purpose to get that much imbalance on anything roundish I could chuck up. It's not the fact that you had vibes, but the magnitude that seemed wrong. Now it makes sense. Normally, a little bit of imbalance isn't an issue for a ton or more of iron to damp on quality bearings. Now methinks you might want to try another chuck.

 

[Ischgl99]

Fine tuned after video made so chuck stopped without any more movement. Chuck was over 3 oz out of balance at start. Used various sizes of strong earth magnets inside back of chuck as counterbalance. After final tune also superglued magnets. So far magnets have not shifted.

That’s a lot! I would check to make sure there are not any defects in the chuck, but glad you are able to get it balanced. A four jaw chuck of that size should be able to run at least 1,000 rpm without any objectionable vibration, so hopefully you have something usable now.

 

[MrWhoopee]

Speaking of Sharpies, I have one that is at least 45 years old and still working. It's a blue one that came from a scientific supply and is easily identifiable by its yellow body. I got it while working for Shell Development. I left that job in '78 to go learn to be a machinist .

 

[Just for fun]

Good job on the balancing!

I balanced my 4 jaw in a similar fashion. Mine was good to about 400 rpm then it would really start shaking the lathe. It's good to over a 1000 rpm now.