Atlas 3995 Chattering

[Charles scozzari]

You need a tool with a small radius at the tip to give a smooth finish

When I am cutting common hot rolled If the work is not too long ( because it is slower ) I have been successful running at 50 r.p.m. using a round insert and getting a decent finish that can be dressed easier.

 

[Jake M]

You need a tool with a small radius at the tip to give a smooth finish

I havn't been following this post, but just reading it now, This is my thought. I've never used one of those 'knife tools", but looking at it, and the fused on aluminum some posts back... I'm not convinced it's cutting freely. I'd bet that tool has a place, but I'd want to see a more conventional tool bit fail as well before I blamed the lathe entirely.
As somebody said somewhere back, with troubles like this, there is very often (more often than not), more than one issue at play.

 

[gedkins]

One more point on the cutters. I now have over 15 different new and used turning bits of all types, HSS, carbide, carbide insert. None of them produce a smooth surface, and the surface produced by all is very much the same, plain poor. I have a bullnose cutter and it does not produce a smooth surface. This is true for all materials tried. I am no machining expert, but to me the law of averages tells me the cutters are not the problem. It is drive train or lack of rigidity or both. The spindle bearings and races are smooth and appear unworn to me as I inspected them again on 3rd tear down of head done today.

 

[Backyardmachineshop]

What gears are set up in the gear train going to the quick change gearbox. I wonder if the PO set the gears up for metric threading or special threading, and it's messing up your feed chart readout. Also make sure the slide gear is in the correct position. Another option is this lathe has saddle outer gib strips that run along the sides of the bed to take up for wear in the bed, make sure those are tight. An easy way to check that is an indicator mounted to the bed, measure the front of your tool post and pull / push on the tool post, it should be VERY LITTLE movement with the cross slide screw play taken up. I HIGHLY doubt there's anything actually wrong with your lathe, beyond something not being set right. Mines mounted to a POS MDF door. It's the definition of lathe holding the bench straight and not the other way around, and I get great surface finish with $2 asian dcmt 21.51 inserts using the stock gear ratio.

Something funny, these are great hobby lathes and are pretty simple design, and are fairly Ridgid for there profile. There can only be a couple things wrong here that we haven't explored yet, and im thinking it's carriage rocking under load. Which would be the side gibs or something funky being loose. Also check the bolts that hold the headstock in and make sure they are tight.

 

[Backyardmachineshop]

Also make sure your quick change is set to E-9. Im Sure it is... But the photo from your restoration has is set on e1 which is a really course feed

 

[Backyardmachineshop]

Actually.... If you are in e9, looking at the photo of the aluminum cut. It looks like your slide gear is in the IN Position. Do me a favor. Set the quick change gearbox to e-9. Zero your z indicator to the carriage, engage the half nuts and rotate the chuck 1 turn. And tell me what that idicstor reads. If it isn't close to .0048 it's a gear issue

 

[gedkins]

Actually.... If you are in e9, looking at the photo of the aluminum cut. It looks like your slide gear is in the IN Position. Do me a favor. Set the quick change gearbox to e-9. Zero your z indicator to the carriage, engage the half nuts and rotate the chuck 1 turn. And tell me what that idicstor reads. If it isn't close to .0048 it's a gear issue

All of my cuts have been by hand to date. The feed has remained in Neutral all along. Trying to keep a minimum number of variables.

 

[ShagDog]

Just a thought. I have a 1928 South Bend Junior lathe with Bronze spindle bearings. I was having a chatter issue. It took me a while to figure it out. I know your lathe has Timken bearings, a completely different set up from my South Bend Junior. However, on my South Bend the bronze bearing were in fine shape. The problem was in the way the bearing were seated in the headstock cradle. I had movement when I would move the spindle back and forth in Y axis which I think is front the operator side of the lathe to the back side of the lathe. I put some brass shim stock (.001" thick) between the cradle and the bronze bearings. No more movement and no more chatter. I cannot explain why the fit was improper. Lathe runs great now.

Again, I know I am comparing apples to oranges here and maybe grasping at straws here; but while you have the bearings out, have you considered checking the fit of the races to the headstock?

 

[gedkins]

Just a thought. I have a 1928 South Bend Junior lathe with Bronze spindle bearings. I was having a chatter issue. It took me a while to figure it out. I know your lathe has Timken bearings, a completely different set up from my South Bend Junior. However, on my South Bend the bronze bearing were in fine shape. The problem was in the way the bearing were seated in the headstock cradle. I had movement when I would move the spindle back and forth in Y axis which I think is front the operator side of the lathe to the back side of the lathe. I put some brass shim stock (.001" thick) between the cradle and the bronze bearings. No more movement and no more chatter. I cannot explain why the fit was improper. Lathe runs great now.

Again, I know I am comparing apples to oranges here and maybe grasping at straws here; but while you have the bearings out, have you considered checking the fit of the races to the headstock?

I had thought of this. I rechecked the pressed in races and they are seated perfectly in the casting.

 

[Backyardmachineshop]

All of my cuts have been by hand to date. The feed has remained in Neutral all along. Trying to keep a minimum number of variables.

So that cut between centers on the aluminum was by hand? That cut wasn't bad if not just inconsistent. It's an engine lathe use that power feed. See if that makes a difference with that particular cutter, feeding by hand didn't even enter the realm of thought for me.