Buck Chuck-Out of Balance???

Hello Everyone.

I need some help concerning lathe chucks. I have a 8 1/4" Buck, Adjust True, three jaw chuck with a D1-5 mount on a Nardini 1440E lathe. The faster I turn it, the more it shakes. My other chucks run smooth. At one thousand RPM, it is had a strong vibration. The chuck is repeatable to .0005" and TIR on the outside of the the chuck body is .0015" The Model number on the chuck is 4831.

Are chucks used on indexers or super spacers different than chucks used on a lathe? The above referenced chuck has two sets of smooth jaws.

What do I do next?

Thanks,

Grits

Hey Grits

You could have the chuck balanced either statically on knife edges or take it to a shop that does dynamic balancing. You would need to make a mandrel to mount it on to adapt the chuck to the balancing machine. I think you should be able to take the jaws out for this without effecting the balance. This could get expensive as balancing tooling needs to be very accurate as far as runout is concerned. Runout is a major factor in unbalance. When I make a balance mandrel, all finish turning is done between centers in order to minimize runout. You may want to first of all try to eliminate your .0015" of chuck runout by remounting the chuck to it's backing plate. Make sure there is no axial runout on the face of the chuck as well. Check for balance holes drilled into said plate. Make sure there is no debris in the holes as well as in the chuck body/scroll plate assembly. If you know anyone that does vibration analysis, they may be able to balance your chuck on the machine without you having to build tooling to do the balance job on a balancing machine.
You stated that your other chucks run smoothly on this machine, so I don't think it's a machine problem so much as in the chuck itself. Try taking out the jaws and spinning up the chuck to see if the jaws are mismatched in mass. Are the bolts holding the interchangable jaws mismatched? Symmetry is key to keeping things balanced. LOok for a broken jaw tooth section in one jaw perhaps. Take the chuck apart and look inside for anything unusual. Hope this helps.
Rick

Grits, You may check on having someone come to your shop that has a portable balance unit. That way they could balance the chuck on your lathe. Portable balancing is common. Some motor shops offer this as a service. Not sure of the cost involved.

Richard

Guys

The chuck is an adjust true type. The chuck moves on the back plate to center the jaws to the axis of the lathe. I can take the runout of the chuck body with the adjustment screws which gives me an idea. The part of the back plate the adjustment screws ride could be out of round. It would be a simple task to true it up and a thou or two would not make any difference. I will check the chuck and the back every which way there is to check it and I will report on what I figure out.

Checking the screws is a good idea. I have some very precise laboratory quality scales I use in handloading. I will weight every like screw and work my way up through the jaws.

Even though I recently cleaned the chuck, I am going to take it apart and check everything. I am going to run the backplate on the lathe and see if I get any vibration. I will work forward from there. If need be, I can send it to a shop that specializes in chucks. It is a high quality chuck in good shape and I feel it is worth spending some money on. The replacement would be pretty strong. A Bison is between six and seven hundred dollars. I feel the older Buck is a better chuck. I hope it is something simple.

If it were a cheap chuck, nothing would surprise me. Every Buck chuck I have used has been nothing but good.

Thanks

Grits

As manicmachinist suggest I'd give it a good inspection and clean up with the backplate off check the TIR on the backplate step and the measurement of the recess on the chuck to the outer body. .0015 runout does'nt seem like enough to shake a Nardini that bad. Since your Buck chucks things up so well you could chuck up a shaft center drilled on both ends and hang it between live centers with no preload and I'll bet the heavy side shows up in a hurry unless it's really bad dynamic imbalance.

Shimitup

I will do just that.

Something else that occurred to me, the spindle bearings may need adjusting although I dono think so. I may be setting up a harmonic vibration. A few insignificant things get together in just the wrong way and cause things to really shake.

Twenty years ago I had an SVO Mustang that ran like a scalded dog. When you took the car up to around ninety, it felt like it was going to shake itself apart. There was so much shake in the steering collum, the wheel was hard to hold and it would unlatch my watch. The runout on the tires was perfect (the old Goodyear V rated Gatorbacks), the drive shaft and rear axles were in spec; however when it all got together, it was hell to pay. Ford replaced the rear axles and drive shaft and the problem was gone.

I am a farmer and it is raining, hard, outside now. I will have a few hours to play in my shop. That will be my first project and delay cleaning up my mess.

Grits

Grits, my dad had the same trouble with his chuck.

http://www.practicalmachinist.com/cgi-bin/ubbcgi/ultimatebb.cgi/topic/1/19628.html?#000001

He ended up turning the OD down. The vibration is gone now. This was probably not the most elagant of approaches, but it did make a differance.

I think think counter weighting would do a much better job. Dads technique only accounted for the outside material, not the offset of the internal workings or the offset center hole.

Luke

Lately I purchased a cast iron backplate for a chuck, which I had to bore out quite a bit larger and thread the ID. There were rather large voids in the casting as I got farther in. This could easily be the cause of an imbalance.

You might be able to improve the balance yourself. Chuck a straight, smooth shaft in it, the shaft being long enough to project out both sides of the chuck. Check the chuck body for runout with the shaft resting in V-blocks first of all. If you cannot get it running true, then there may not be much point in proceeding.

Set the rig up on a pair of levelled knife edges or parallels. The heavy side will roll down.

Mark the backplate so that it will be fitted always the same way to the chuck. Then, drill some shallow holes inside the backplate (where it will not show) to remove weight. Take care with what radius you remove weight at, near the outer radius of the backplate has a more pronounced effect than near the center.

Another method would be to drill and tap a regular bolt pattern of some sort in the backplate, and install setscrews for counterbalance weights. Through trial and error, you may luck out on finding a good combination.

you can get a portable balancing machine to help with locating where to put your set screws to obtain the correct counterbalance. we use this portable balancing machine to do similar operations throughout the shop. its called a best balance 1000. you can hook the machine up and it would read the vibration and display the unbalanced part and the compensation of unbalance, etc. its works good for what we need it for.

good luck

Could be a fun project. After clean and checking runout and all that, take a rod say 1"dia x 8"long and bend an ear (maybe 1 or 2")90 degrees on one end using a torch. Then use this to search out the heavy spot in the chuck. With soapstone mark a starting spot on chuck and work your way around with ear until vibration is gone or improves. When vibration is greatly improved opposite the ear should be heavy on the chuck.

My Bison 6-jaw almost always stops with the 0 jaw mark at or near top dead center. I've assumed that this is because the opposite side is heaver, but I suppose it could be spindle bearings or something. Does your Buck tend to stop in the same position as the lathe winds down when shut off?

This is just a thanks to everyone who posted here. I have a new Bison chuck with the same problem, and was just about to post something to ask what to do. I get one the forum, and find ten answers to a question I hadn't even asked yet.

the chuck is stopping like you said standish because it sounds like it is automatically statically balancing it self. you are exactly correct that the heaviest part is at the bottom. the question is, how much do you have to compensate at the top to balance it? ou can stick it on an arbor or run it like sarg is talking about. i dont know how accurate it would be. you could also get one of those portables that tyyler mentioned. there are may ways to do it, some less accurate then others of course

It could also stop at 12:00 because you've parked it there and the belts have taken a set. I think the chuck would have to be hugely out of balance, to the point of wanting to flip the lathe over at speed, for it to overcome the drag of the bearings, belts, gears, etc., and stop there by virtue of imbalance alone.

Of course, if it's some sort of diamond turning machine with air bearings and a direct drive spindle ...

I think I would check to see if the machine is still level and the legs are properly adjusted. Buck chucks are normally fairly well balanced.
Also if the adapter face doesn't run perfectly true ,take a skin-cut if it is soft steel

Grits
I had a similar problem with my newer Nardini when it was new with a Pratt Berard 8 1/4.
Machine ran smooth with anything but the chuck, including the face plate to 1250.
I ended up hiring a guy with a portable laser balancing system to get it corrected. ($600!) We ended up taking an amount equal to two 3/8 diameter holes about 1 inch deep from the back of the body about 1/2 inch apart.
I would suggest removing one of the face screws and running the spindle, selecting the next one around the periphery till you find a smoother point of operation. ONLY run it with one screw out at a time. This should give you a good indication of the heavy spot. You can also add weight to one of the outer threaded holes of the master jaws to accomplish the same thing.

I know you are smithing with this lathe. I've owned Nardinis since 91. Please feel free to call if you have questions.

Alan Warner
Warner Tool Co