8" 4 Jaw Chuck Balance Issue

Charles scozzari said:
Thats interesting, I guess you only use the 4 jaw for shafting. The only way I could think this is possible is to disassemble the chuck and dynamically balance the outer shell and scroll, then static balance each of the jaws and related parts separate., The only thing I believe is once you lock the work in the chuck the balancing is gone. Do you have a three jaw to try. I know this is a silly question, but without a mounted chuck is there any vibration at the lathe spindle. If your working between centers is the tail stock dead on aligned. Hope that helps a little. Thanks.
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Yeah, it is me. the lathe is fine, only an issue when I mount the 4 jaw chuck, my 3 jaw and collet chuck are great and smooth sailing with just the spindle. The 4 jaw is a cast chuck which I got with my lathe from PM and it was okay until I was looking at the back and it had some really rough slag so without thinking I knocked the loose stuff out of it and it has been an issue ever since.
 
Dabbler said:
Some basic tests: have you indicated the chuck body?

Chuck up a piece of cold rolled or centre-less ground stock, at the centre of rotation, and than make an improvised balance stand. you can easily get a feel for how unbalanced the chuck casting is. Your 4 jaws won't be more than a couple of grams off from each other, so there wouldn't be any worries about them.

Of the dozens of 4J chucks I've used this is an anomaly. If you prove that the chuck is balanced this way, you can begin to look for other sources of vibration. I'm worried that your headstock is bent. Now that I have seen.
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I was worried about the head stock when this manifest itself although I could not think of anything I had done which woud have caused it to be bent, the lathe is a very new machine; but, when I removed the 4Jaw the vibration went with it, machine runs smooth and quiet.
 
Bummer, Well at least you know where the slag came from so You can just start adding weight back to that location until you are happy with it. Then glue in place.
 
mksj said:
I had that occur with the Chinese 4J that came with my first lathe, if one looked at the back of the chuck casting it was extremely uneven. Couldn't get the chuck past around 350RPM with the lathe shaking pretty bad. It is usually exacerbated using a VFD as you can hit the vibration nodes when changing speed. I relegated that chuck to my rotary table. It was replaced with a Taiwanese made 4J independent that was much better cast and also had balance weights on the inside of the chuck. It was smooth at all RPM's.
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Exactly...
 
You can grind some of the metal out of the back of the chuck, by balancing the chuck casting on a static balancing rig. You can get pretty close that way.

If you haven't done it before, you might try to find a local machinist that knows how to balance grinding wheels. the process is the same as drilling out a grinding wheel to balance it.
 
Cadillac said:
I had a similar problem with my 4jaw. I have a 14x40 lathe with a sheet metal base. The chuck is direct mount d1-4 with a open back. First time I mounted it and spun up the lathe everything was good until I adjusted the speed. I have a vfd. Between 500-575rpm the lathe wanted to rock or wobble. Go the 475 no problem go to 625 no problem pretty smooth but could feel a minor shake in the whole lathe.
My solution was I chucked up a piece of 3/4 precision ground rod about 12” long. Half stuck out the front and half out the rear of chuck. Centered the rod with a tenth indicator so it didn’t move. Then I have a balancer for my grinding wheels that I used. I placed magnets strategically to get the chuck balanced. Once balanced I weight each magnet and ground out the spot where it was the weight amount of magnets.
Doing so took up 80% of the shakes. I found that my lathe itself doesn’t like rpm’s between 500-600. Even with my 3jaw is has a minor shake at those rpm’s. I can’t say I have tried it with no chuck just the spindle to see.
. My lathe has a foot brake which the mechanism is under a pulley within the drive. My thought is the pulley itself is unbalanced and throwing the lathe off. Their is only the motor and pullley a belt and the pulley I speak of that drive my lathe. Motor decoupled spins smooth as glass. Belts on all other drive gears decoupled it has the shake at those specific rpm’s. Haven’t dug further into it. Sheet metal base is undesirable if reinforced as much as possible. I wish it was a cast.
Back to the chuck yes you can balance but you want to be absolutely sure of where and how much you take off. You can definitely make it worse. Once you have the magnets correct you could just epoxy in place instead of removing weight.
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Great information. I have a gear head lathe but now I am going to go back and run it through the gears to see if it has a noticeable shake at any particular speed, that is a good test because I haven't had this machine long. I think I will try the stick on weights.
 
Dabbler said:
You can grind some of the metal out of the back of the chuck, by balancing the chuck casting on a static balancing rig. You can get pretty close that way.

If you haven't done it before, you might try to find a local machinist that knows how to balance grinding wheels. the process is the same as drilling out a grinding wheel to balance it.
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I may do that, find a local machinist that is. The more I think about it damage already done, I am tempted to clean out the rest of the slag before starting so I do not get it balanced just to have the issue reappear. Thanks for your advice.
 
I’ve also reconstructed the sheet metal bases adding a lot of weight. Filling the cabinets with spare chucks and tooling to put weight low on the machine. It helped but not solved the problem.
 
verbotenwhisky said:
Yeah, it is me. the lathe is fine, only an issue when I mount the 4 jaw chuck, my 3 jaw and collet chuck are great and smooth sailing with just the spindle. The 4 jaw is a cast chuck which I got with my lathe from PM and it was okay until I was looking at the back and it had some really rough slag so without thinking I knocked the loose stuff out of it and it has been an issue ever since.
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So I would say the chuck was factory balanced with the jaws closed and when you removed the slag it went out of balance. Put the weights where the slag was.
 
I would not attach anything on the spindle to balance. If it gets loose, you could really hurt somebody. If you have to balance, grind material away.

If your chuck has a mounting plate, check if the chuck is mounted on center of this mounting plate and if the mounting plate is mounted on center with the lathe spindle.
 
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