Atlas 3995 Chattering

[gedkins]

I recently restored an Atlas 3995 lathe. Spindle bearings were absolutely unworn and not replaced. TIR of spindle ID is .0011. The Cushman 3 jaw chuck OD indicates .0043. I cannot get a decent surface finish on virtually any material with any cutter type. Speeds and feeds all within spec. The chattering when parting off is just about unbearable. The cuts appear as if the cutters are literally moving in and out against the workpiece. I could get a better finish with a drill press and a file. I have close to one hundred lbs. of steel shot bags sitting on the lower cabinet shelf to add mass. I do have the lathe on adjustable machinery feet vs. sitting directly on floor. The bed is very level (twist). Even close to the chuck the finish is typically awful. I have used HHS, carbide inserts, and standard carbide on free machining steel, mild steel, brass with more or less the same result. I have checked and rechecked the gibs for all slides, the preloading on the spindle bearings. It has an Aloris tool post.

I am beginning to believe the lathe may never make a decent surface on a consistent basis. Looking for help on what to attempt next.

Thanks.

 

[4WHLDRFTN]

Is the HS tight ?

 

[Pevehouse]

I recently restored an Atlas 3995 lathe. Spindle bearings were absolutelyunworn and not replaced. TIR of spindle ID is .0011. The Cushman 3 jaw chuck OD indicates .0043. I cannot get a decent surface finish on virtually any material with any cutter type. Speeds and feeds all within spec. The chattering when parting off is just about unbearable. The cuts appear as if the cutters are literally moving in and out against the workpiece. I could get a better finish with a drill press and a file. I have close to one hundred lbs. of steel shot bags sitting on the lower cabinet shelf to add mass. I do have the lathe on adjustable machinery feet vs. sitting directly on floor. The bed is very level (twist). Even close to the chuck the finish is typically awful. I have used HHS, carbide inserts, and standard carbide on free machining steel, mild steel, brass with more or less the same result. I have checked and rechecked the gibs for all slides, the preloading on the spindle bearings. It has an Aloris tool post.

I am beginning to believe the lathe may never make a decent surface on a consistent basis. Looking for help on what to attempt next.

Thanks.

I can’t really be of much help I don’t believe but I’m sure someone will come along and chime in to help. May want to post a few pictures of your setup and a few of what the machine is actually doing if you can.

 

[gedkins]

Is the HS tight ?

Yes. Thanks.

 

[Rickinlexky]

It sounds like something is flexing. How thick is your workpiece stock, and can you get any movement at all out of the compound rest when it's locked down tight? and I assume the cutter is on the centerline of the workpiece...

 

[4WHLDRFTN]

Yes. Thanks.

Just freshened a SF1896 and had the same problem. The belt was slipping and changing the spindle speed.

 

[pontiac428]

Parting is tough on the Atlas, but it can be done. Bearing preload is a big one. Bellmouthed chuck will give you grief too. Then the usual stuff, tool edge and position, parting as close to the chuck as possible, keeping all moment arms as short as you can, oil everywhere. A pic or a video clip might help, otherwise this is the kind of spitball shooting answers you will get.

 

[ARC-170]

My suggestions:

Check the cutters:
-Is the cutter on center?
-Is the cutter geometry correct?

Check the motor:
-Is it running smoothly?
-Does it spin freely without any load? Take the belts off/disengage any gears and see if it'll spin.
-Run it without any load and see if it feels and sounds normal.

I'm curious to know what you find. I had an issue with bad finish on my lathe when using the power feed and I've traced it to the lead screw being bent.

 

[markba633csi]

The 1.1 spindle taper runout sounds high- I would expect less than half that- but I don't think that's the issue
Can you post a photo of one of your setups so we can take a look? I suspect cutting tools may be part of the problem
Mild steel as a rule will "tear" somewhat when cut and give a rough finish
How does it do on aluminum? Are the chuck jaws worn perhaps?
This is an underdrive machine- is the dual drive pulley loose on the spindle and knocking around? There are bushings in it that wear

 

[Nutfarmer]

It is hard on an Atlas to part off anything. Not chattering near impossible. Anyone who can manage that my hat is off to you. I gave up part off on my atlas. The cut off saw just does a better job with no broken cut off blade parts flying at you.