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Sudden Onset Chatter Issues - riding the struggle bus and need some HELP, please.

MyLilMule

Hot Rolled
Joined
Jan 5, 2021
Location
Ohio, USA
About a week or so ago, my 13" South Bend started chattering like crazy. It's REALLY bad. And I am at a loss as to why. I've owned this lathe for 3 years and never had any serious issues with it.

I attached a video of the bearing clearance checks as well as some video of cutting a piece of mild steel - a piece I have machined on in the past with no issues. I've tried several pieces of stock and can't seem to figure this out.

What I have checked:
  • Spindle bearing clearances. Within tolerance (.0007" to .0010"). If any more shim is removed, the spindle binds up.
  • No detectable fore and aft spindle play.
  • The spindle is being lubricated. The reservoirs are full.
  • Swapped the 3-jaw for a 4-jaw with the same issues (No spindle collet setup for this lathe)
  • Checked the headstock bolts and they are tight
  • Checked screws holding the apron to the saddle and all were tight.
  • Checked the cross slide gib. It was tight. It has some wear so a shim was added just in case.
  • Compound gib is fine. Tightened it to the point it's difficult to move. Problem persists.
  • There's backlash in the cross slide and compound lead screws, but not that much that it's concerning. No change since it's been in this shop.
  • Swapped QCTP's with my other lathe.
  • Swapped compounds with the other lathe. No luck.
  • Checked the saddle gib and it's tight as it can be.
  • Tried varying spindle speeds and turning speeds with no significant change in surface finish.
  • Tried three different insert geometries that have been perfect for me in the past.
What am I missing? What is left to check?

Help me Obi-wan Kenobi, you're my only hope! ;)

 
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I see that you have already tried to rule out the most likely culprits. Regarding the chucks, I would make sure of two things: first, that the back plate contacts firmly the shoulder on the spindle (sometimes, chips in the threads could prevent that). Second, if the jaws are a little worn, they might bell out and hold the piece only on the back side. By compressing strips of paper towel between the jaws and the bar, you might attenuate the problem.
Another test I would do to determine if the chatter is caused mainly from the headstock or from the carriage, is to support the bar with a well lubed dead center in the tailstock: if the chatter is significantly reduced, the issue is with the headstock. If not, it might be caused by wear in the saddle.
The saddle tends to wear more at the ends and it would start rocking on the middle. You can test that by mounting the indicator base in turn on each of the four tips of the saddle, with the indicator resting on the ways. Then apply downward pressure at each of the tips and observe the movement of the indicator.

Paolo
 
If I use tail support, it does get better.

The thing that is baffling to me is this lathe was working perfectly a week or so ago and this came up all of a sudden. No crashes, outside of a broken cutoff tool, to speak of.
 
Check and see if you have a loose leveling screw on the tail end of the bed at the floor.
Could be that Chinese tool post your using! :o I'm kidding I hope.
 
Here's a video using a live center in the tail stock. It's "better" but not at the larger diameters. I was taking off a good chunk there for a bit.

The last two cuts were at .050 DOC and .025 DOC and you can see the crappy surface finish. The smaller diameter looked fine.

 
More a combination of a harmonic and a built up edge ,due to running at too slow surface speed for carbide .Try some fre cutting steel ,or brass.
I've been using this lathe for 3 years with zero problems like this, like I said in the original post. I've cut this exact piece of material for a different project. This exact piece.
 
I'd definitely look at the insert with magnification. Was there a weather change recently? One time I had a problem like that show up out of the blue and realized I had turned on the radiant heating system, so the floor must have moved. I snugged up the leveling pads, leveled the lathe and things were back to normal immediately.
 
I'd check the bearings for lower cone pulley, what drives the spindle via flat belt.

If you have a vent cover on left end of base, remove it. Laying flat on your back, reach up and try to push the large vee pulley that motor drives. Or maybe a pry bar to try and move or lift that lower cone pulley assembly.

Depending on age of lathe, there are two different styles of bearings. Newer style used ball or roller bearings. Old style used gits cups for lube, and was basically a bushing on each end that shaft rides in.

With either style wore out, that lower cone pully will shake and bang around at speed with flat belt engaged and taking some tension up.
 
Have you recently removed a bunch of stuff and/or weight from your lathe stand? A bunch of weight can add a lot of dampening.
 
Greg, check the jaws on your chuck to see if they are gripping evenly, and not heavy on the rear or a particular jaw, that might cause you stock to move. With the cold weather as in my shop effects how much heat I can load into the chip with the machine or stock cold. Your chips appear too cold also, increase the feed rate to get closer to 600 degrees (at least straw to blue (blue is better) colored in you chip formation. Start with your cutting speed about 200 FPM and lower or raise it to get the chip color also. When the forming temperature is correct, the cutting force decreases and can help with chatter also.
 
Same results different chucks different tooling. Hmmm..
Screw on chucks? Make a thin circular paper 'gasket' to bump between the chuck and the register on the spindle. Think of it as a temporary shock absorber. Give it a go with the gasket and see. Then you can blame the mating surface if the chatter stops. *This should have changed between the two chucks though.

D1 style chuck mount? Then forget about the paper gasket test

Long shot:
Is the machine laying flat on the floor? If so perhaps it's vibrating a bit. Make a steel wedge that tapers to zero and pound it under one corner of the machine for a test.
 
I'm going to replace the two thrust bearings on the spindle. They're cheap enough. The front bearing has some galling, but no more than it had when I got it and refurbished it the first time. I'm also going to replace all of the laminated shims and go through the procedure to strip off layers until I get the correct clearances.

If that doesn't solve it, I will look further at the motor and the lower cone pulley, although I know how much of a PITA that is going to be to remove and inspect. I do have a possibility to either confirm or eliminate that as the source. I have a 1960 13" lathe that is currently being disassembled. I have just removed the motor and lower cone pulley and will be replacing bearings in all of that very soon. I COULD, pull all the junk out from the 1942, and if it fits, put the 1960 guts up inside? I would really hate to go through that exercise, though. Maybe as a last resort.

The lower cone pulley bearings I believe are poured babbitt? I could be wrong about that, but they are not ball bearings. They have an oil trough on top that I keep filled from time to time.

It's not sitting on the floor. Has been on leveling feet since day one. There's no additional weight added or removed.

I've tried both chucks (they are threaded on the spindle) with the same result. It's not that.

My shop is heated. I keep it at 62 degrees most of the time. It's not related to temperature.

I can't reiterate enough, that it is NOT the cutting tool. I have tried MANY different inserts, insert geometries, carbide, HSS tools, freshly ground and honed. I went through the process of trying a dozen or so different speeds and feeds with no difference.

I will keep on trucking and update this thread when I get new bearings and shims installed. They are all on the way.
 
Check your leveling feet. Things don't stay level forever! Lathe beds move and shift around over time from many things. South Bend lathes are notorious for this, too.
 
I'll be the first to admit how little I know, however isn't this the reason for the Silent Drive on type O's? Single phase caused vibration broken up by the chain drive?
Bob L
 








 
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