Advice on Heavy Chuck

Greetings!
I recently picked up a two jaw chuck for my 13" Sheldon and I have a bit of an issue with it. I bought the chuck because I make tobacco pipes and I wanted something self centering to grip square blocks and lone behold, the chuck is 80 lbs. Holy christ. I didn't think it would weigh this much and briarwood turns best at high speeds. I mounted the chuck to my lathe (L-00) spindle and ran the machine at roughly 1500 rpm. It was immediately apparent that the chuck is out balance and will need work. I took the shop made jaws off and I'm still getting some noticeable vibrations. I've turned parts in excess of 50 lbs and never had this issue. In an effort to balance the chuck, Id like to kill two birds with one stone here. Id like to drill out a lot of the dead space (its 5" deep by 9" wide) because it's completely solid. This seems absolutely absurd given the mounting plate that came on it. And I know it's a stock back because the Cushman marks and serial numbers match. Has anyone ever drilled out a chuck to make it lighter and can someone chime in on this? Is this a bad idea? Im only going to use it to turn wood. Thanks!!

Drew

Run the lathe spindle at said speed without a chuck, if it still vibrates it is not the chuck. If the machine has a Reeves type variable speed spindle drive look there first. If it is indeed the chuck you will have to balance it or have someone else do it for you.

Drew,

What model 13" Sheldon do you have? How about a picture or two of the lathe and the chuck.

Ken

It doesn't have the Reeves type speed adjustment, but I know it's not the lathe. My other three chucks all run fine at even higher speeds. I guess the bulk of my concern is drilling out the back of this chuck to lighten it up. Provided I can balance it, does anyone see any immediate red flags in doing this? I don't want to run such a heavy chuck in general because I want the bearings to stay as perfect as they are right now. For a 40 y/o machine, I indicate less than a tenth on the spindle nose. Ken, it's the UM-56-P. I can post a photo later tomorrow of the chuck.

You will not cause any bearing damage at the speeds that machine is capable of, balance becomes important at high speeds above 20,000 Rpm's or so. A simple home shop static balance is not terribly difficult to do but not suitable for high speeds.

Build a fixture as pictured below, the closer one gets to the center of balance the better the results. The low side is heavy so either remove weight there or add weight to the opposite side, this will get you reasonably close, if the jaws holding the test part are off center this will effect the outcome.

Most all chucks are dynamically balanced before they leave the factory. But, it doesn't mean they stay that way later in life. Try Wreck's method of static balancing shown above. That at least will tell you if the chuck has a balance problem.

Now, you mentioned that this chuck weighs 80 lbs. Thats a lot weight to be hanging off of the spindle of a Sheldon UM-56-P Lathe. AS you said you earlier, you have had this much weight in material turning on the lathe before, thereabouts. This lathe is belt drive between the headstock and the drive source using two B-Section belts. The center distance between the belts is probably close to 24". Having said all of this, I suspect the belts are "flapping" around just enough to cause the chuck to "bounce" from this uneven torque from the belts flapping. You may have the belts tight, initially, but they start stretching from pulling against the load of the chuck, thus casing this flapping. Just saying. You would think this would even out after a few minutes of running. Snug you belts down a bit more. Don't over do it and throw a bearing out in the gear box!

Edit: If interested, I have a 6" Bison two jaw chuck here I bought used and never used it. It is in new condition. If interested, drop me a PM and we'll talk.

Ken

Something like this might better suet your needs you could make an arbor for it.
https://www.pennstateind.com/store/CUG3418CCX.html

I actually bought a wood lathe chuck like the one you have above but a good hearty metal lathe chuck would serve me in turning wood and steel. Ken, I sent you a PM about the chuck. I might just steal the backplate off this chuck for a 4-jaw chuck I've been meaning to outfit. I have a dealer who will buy the backplate-less chuck for some moderate cash. It's just so much mass.