Lathe - Barber Shop Pole Pattern, Loose Carraige?

dti on the motor shaft and motor pulley? ditto on the drive shaft? just to rule out a bent shaft or wobbly pulley. sounds like you're getting close. any chance you can borrow a motor off someone to test the large with?
 
I have to agree with Jim, motor rotor out of balance. Or as Matt said, bent shaft...
With the belts off of the motor sheave, rotate the motor shaft by hand and feel it's smoothness. Is it rough or is it smooth. Then rotate it fast, does it roar or no noise at all. Could be bad bearings in the motor???
 
dave2176 said:
Coolidge,
I have the same lathe. The last picture is interesting how the light repeats the pattern so exact. I see you are turning on B2 or B3 for your two rpms. What about A1 or C1? Get off the "B" gear for a test. What diameter is your piece? I'll see if I can try it tomorrow on mine with your speeds. What is the gearbox set at?
Dave
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I have not tested A or C turning but may do that this morning. That's brass stock 1.25 inch in diameter, turned down now to about 1 inch. Another test I'm going to run today is turning with the lathe cold, then run a 20 minute warm up procedure and re-test. The harmonic seemed to get closer together as the lathe warmed up, started about 3 seconds a cycle and was about 2 seconds a cycle when I finished testing. The spiraling seemed to lessen as it warmed up as well.

I have the gearbox set at C-8.
 
JimDawson said:
Is it practical to send the motor/drive shaft assembly out for balancing? That is exactly the type of sound you get in a twin engine aircraft or boat when the engines are running just a few RPM difference.
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Honestly I don't think the motor is of the quality to bother with, I'd like to replace it with a Baldor but they don't seem to make one with this frame. Leeson makes one that's reasonably priced, those or manufacture in China now but they are an upgrade from this and inverter rated. I have a 3hp Leeson on the mill and its pretty nice.
 
[QUOTE= I don't know exactly what the problem was with a bearing but the rotation of a bearing will bring any given ball or roller around to the same spot on 2 revolutions.


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now i tried to get my head around that one but couldnt grasp it
i would think the diameters of the inner ring, the outer ring and of the roller would define when the roller will pass the same point on either rings
 
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to me its a bearing issue
probably not in the spindle but in the driveshaft, as tensioning the belt makes a difference
there are 27 lines and they are not straight, but radial in an angle
the culprit will be the bearing that has a ratio where 27 rollers/balls pass the same point in either the inner or outer race for every time the spindle makes one full turn, and that has a ratio to the spindle equal to the angle by which the pattern advances/retards
 
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