South Bend Lathe has Chatter

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rogerl

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My dad purchased a used 11" South Bend Lathe in 1978. The lathe has the 1 5/8-8 spindle thread and the 7/8 thru hole in the spindle. I was in a school for many years of its life. He completely refurbished it and used it for years. 3 years ago my dad passed away and last year I brought the lathe to my shop. I have been noticing lately that when I use the parting tool or if I take heavier cuts I will get chatter. I have an Aloris BXA tool post on the lathe.
I am thinking I need to tighten up the spindle bearings. I think I remember from helping him rebuild the lather that there is a shim pack under the bearing caps and I can remove or replace a shim to tighten the bearings.
I have never done this before and I am seeking advice from people who have done this before. I do not want to make the bearings too tight and cause them to gall. How do I adjust the bearings or test the bearing set up I currently have. The chatter might be coming from somewhere else. The compound is set very tight and I rarely use it.
Any information would be greatly appreciated.

Roger L
 
Joe Py may help with your set-up.
Everyone struggles with parting at some time or another. My 13" South Bend would always suggest, "use the horizontal saw".
Rigidity is key.
 
What do you mean by "chatter"? What is the model number of your lathe?

Here's the spindle bearing adjustment proceedure for year 1940 and younger lathes. I don't know if your 11" would adjust the same.
 

Attachments

  • SBL_Headstock_Bearing_Adjustment.pdf
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Did you add the QCTP? Make sure that there is an air gap between the top of the t-nut and the bottom of the QCTP. If not, it will not be properly clamped to the compound rest, even if the bolt is tight. This is important with all t-nut setups, and I have seen the problem often on milling machines. It is easily fixed by milling down the top of the narrow part of the t-nut enough so it sits below the clamping surface when tightened. Look for it when tightening down a t-nut anywhere.
 
Bob, just checking, but you did mean to make sure there is NO air gap between the T-nut and the tool post, right?
 
Thank you for all of the good information. I will take a bar and see if there is the proper looseness in the spindle.
I will also verify that the T nut is not too high and is not clamping properly.
When I say chatter I mean that I get vibration when I am taking a heavy cut, or using the parting tool. It seems to be worse with my larger 3 jaw chuck on the lathe. The part is out farther from the end of the spindle.
I will try to check this tonight and reply back.

Thanks Again
Roger L
 
Might want to check the chuck jaws -- I have one 3-jaw that's a bit bell-mouthed by now and it can get the shakes going at times. It's not a solve, but I find that using a thin shim on the jaw noses (like a thin strip of copper or something) helps. Just one more thing to check, especially if you find the chatter happening more with one chuck than another.

-frank
 
Another thing to check is that the gibs on the cross feed and compound aren't loose. For parting off, you could snug the
compound gib up to eliminate all movement, and make sure the cross feed is only loose enough to feed the tool.
 
Update on the chatter problem.
I measured the looseness in the spindle. It was less than .001". from the data in the attachments it is a little tight. The bearing caps do not get hot while running. I am going to let that go.
I went to measure the gap of the T-nut to the bottom of the tool post and I could not get a .004" feeler gauge under it. I took the tool post off and machined .020" off the top of the T-Nut. Now I can get the feeler gauge between the nut and the tool post.
I put the piece of stock back in the same chuck and with the same spindle speed parted off a thin piece from the end. NO CHATTER. I put a smaller 4 jaw scroll chuck on the lathe and made the same cut and NO CHATTER. I then tightened up the gib screws a little locked down the carriage and took the same cut and it cut very smooth. I think I found cause the chatter problem the tool post was not clamped tight against the top of the compound. Thank you Bob for suggesting checking the gap under the T-Nut.

Thanks Again
Roger L
 
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