Cone pulley runout causing vibration?

[bentwrench]

I have been trying to figure out why my heavy 10 vibrates at higher speeds, it is a slow oscillation that cases the headstock to sway back and forth. It only happed at higher rpm, but seems to happen in every gear. My machine is on a VFD.

I thought perhaps that unevenness in the belt was causing it, but I put a dial indicator on the cone pulley and found .010 runout. It is worse on the large pulley but still .006 on the small diameter. Has anyone seen this before? Is this normal for flat belt pullies.

I an going to investigate the underdrive next, but I was surprised to see that much runout on the spindle cone pully. I did pull the bull gear pin and rotate the spindle while holding the cone pulley still, and had zero runout so it is the cone pulley and not the spindle itself.

 

[johansen]

Sounds like the two cones with their runout have a constructive and destructive interference changing the belt tension. Is your driving pulley rigidly mounted or is the whole system rocking back and forth?

 

[texasgeartrain]

I'd check the shaft and bearings on lower cone pulley in under drive. Maybe grab the vee belt pulley that drives it at 6 oclock and lift or try to push it toward 12 oclock. That'll check any abnormal wear or play there.

The run out on spindle cone pulley could be the bushing inside that upper cone pulley. Release belt tension and unpin gear. Use a pry bar under the upper cone pulley to see if you can move it up and down a little. Same here, I'd try to pry at 6 oclock.

Be it upper or lower cone pulley, replacing bearings or bushings is doable. The bushing in upper cone would have to be made and pressed in.

 

[bentwrench]

The upper cone pulley has a very nice fit to the shaft, it has either worn on the outside or was manufactured with the runout it has. I will check out the underdrive, but when i moved this lathe last year, I had to re-assemble everything and the bearings were fine on the countershaft.

 

[rons]

Does the belt have a "set" in it?

 

[Dobermann]

Which bench does your lathe sit on? Could by any chance be the bench made out of bent tubing? I have that bench and it has a couple of resonant frequencies which will cause the whole late to shake at a couple of speeds. I just avoid running at them.

 

[jim rozen]

Does the belt track in a stable position, and is it tracking to the center of both the upper and lower sheaves?

 

[BritWithSB's]

Sounds like the two cones with their runout have a constructive and destructive interference changing the belt tension. Is your driving pulley rigidly mounted or is the whole system rocking back and forth?

The upper cone pulley has a very nice fit to the shaft, it has either worn on the outside or was manufactured with the runout it has. I will check out the underdrive, but when i moved this lathe last year, I had to re-assemble everything and the bearings were fine on the countershaft.

I'd check the shaft and bearings on lower cone pulley in under drive. Maybe grab the vee belt pulley that drives it at 6 oclock and lift or try to push it toward 12 oclock. That'll check any abnormal wear or play there.

The run out on spindle cone pulley could be the bushing inside that upper cone pulley. Release belt tension and unpin gear. Use a pry bar under the upper cone pulley to see if you can move it up and down a little. Same here, I'd try to pry at 6 oclock.

Be it upper or lower cone pulley, replacing bearings or bushings is doable. The bushing in upper cone would have to be made and pressed in.

I had a similar problem on my Heavy10. There was so much movement between the lower cone pulley & shaft that as they rotated the belt tension caused the pulley to rock on the shaft, giving terrible vibrations & loosening the grub screws. I rolled a piece of shim steel & slid it between pulley & shaft, leaving a gap for the screws. It now holds solid, there is a small amount of eccentricity with slight vibration, probably due to the gap in the shim. It can live with it for now, until I have the time for a proper fix.