Atlas 3995 Chattering

gedkins said:
All, It is 2:30 AM and I am 99% sure I have figured the problem out and the clues were there all along, even before I started rebuilding it. I will know within 24 hours, Here is my hypothesis. When I took the lathe apart I noticed, but quickly dismissed that the two spindle v-belts were in tough shape, but in a way I had not seen before. They had shards of rubber sort of peeling off from the sides and at the top of the belt. Who am I to say why, I figured they were REALLY old. Fast forward. I installed Power Twist belts from Fenner to replace them. I know this will cause many to say "see, those things are terrible", but hear me out, they may be terrible and I will soon know. I noticed about a week ago that the belts were rubbing up against the base of the headstock as they exit to the lower cabinet countershaft. The light goes on! Add up what I have witnessed (some of which I did not bring up here prior as I saw them as not connected).

1. Old belts oddly worn.
2. Bad surface finish on workpiece.
3. Under higher speed settings motor gets quite hot.
4. At highest speed setting, chuck takes a LONG time to get up to speed
5. Spindle speed slows and many times does not recover if cut is heavier.
6. Surface finish is generally slightly better at higher speeds, but still really poor.

Here is my thinking on this. At higher speeds the centrifugal force is higher on the belts. They press harder on the casting. Which impedes its ability to spin back up. At higher speed the Twist belt links are passing the casting at a higher frequency and thus the slightly better surface finish. More power is needed to turn the restricted belts, thus the motor works harder and gets hotter. The old rubber v belts wore themselves out and eventually were barely rubbing. Since they were smooth backed, unlike the Power Twist, they did not impart a beat frequency like the Power Twist does into the headstock.

As I sit here and type this I certain this is the issue. I am hoping someone here can tell me the A number for the belts I need. The first thing I am going to do is yank the head stock and grind a relief for the belts in that casting. Reassemble and try the Power Twist for clearance, but since they sit high in the pulleys I may have to abandon them. Anyone have a belt number for these beyond 1/2 inch by 44 (I think that's what the manual lists)?

Pretty sure I found the problem, does anyone concur?View attachment 516373
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Not going to grind after all. The belts were rubbing clear down the inside walls of the bed on both front and back. Going to look for a lower profile v belt if I can.
 
Unfortunately the belts were not the problem. The issue persists. I now believe something in the drivetrain is out of balance and is simply vibrating the machine and causing the issue. This is not a rigid machine so a vibration that propagates does not cause the entire machine to vibrate in sync. I am going to look at a South Bend tomorrow. Thanks all, but its time to move on.
 
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gedkins said:
Unfortunately the belts were not the problem. The issue persists. I now believe something in the drivetrain is out of balance and is simply vibrating the machine and causing the issue. This is not a rigid machine so a vibration that propagates does not cause the entire machine to vibrate in sync. I am going to look at a South Bend tomorrow. Thanks all, but its to move on.
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Make sure you verify operation before purchasing, maybe even take one of your toolbits with you and see if it works better than on your machine.

It's awfully hard for us to see you give up on this one though. What will you tell prospective purchasers, couldn't figure it out so will sell it cheap?

Sorry if this offends, I only jumped in near the end because I also struggled with surface finish on my first lathe. Pretty sure if you can take it apart and put it back together you can figure out this problem, but do what you will....

John
 
@gedkins I'm going to encourage you to fix it as well. Any buyer will want to know what the issue is. Could you take some video of you cutting it? You got this! Don't let a mere machine win! lol!
 
I did not pay anything for the machine. I am going to sell it for the cost of the QCTP and the holders. I will show the buyer of the issue.
 
gedkins said:
I did not pay anything for the machine. I am going to sell it for the cost of the QCTP and the holders. I will show the buyer of the issue.
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You will have a line around the block at that price. Please make sure it goes to someone worthy, not just the guy who will flip it without even caring how it functions.

John
 
matthewsx said:
You will have a line around the block at that price. Please make sure it goes to someone worthy, not just the guy who will flip it without even caring how it functions.

John
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Looking at the way the cut was started it looks to me that you plunged into the work. I was wondering if MAYBE you chipped the insert and that caused the finish you got.
 
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