High speed spindle vibration

Take the belt off and run the motor.

Bad noise still there? It's the motor Bad noise gone? Motor's OK

GWE

Without the belt, I can feel vibration in the motor. It seems that with the belt on and a disk in place, the vibration is amplified. The motor is mounted on some 1/2" x 2 rails hanging off the machine top. It's kinda like a tuning fork. I want to say it's like a sympathetic or harmonic amplified vibration. Does that make sense? I have a new motor coming tomorow and the pulley is mounted in the lathe as straight as I can get it. +/- .002" on the OD. I'll resurface the face and edges and bore and bush the arbor so I know it's square. If that don't do it, I'm screwed...high speed spindles are tricky and expensive.

"Tom Gardner" wrote in news:Y%DXg.12485$ snipped-for-privacy@newssvr29.news.prodigy.net:

The motor will cause vibration to be amplified at the spindle. The belt can act as an amplifier. The motor may not be as much of the problem as the pulleys.

Yes, I wanted to say that. You can easily get resonances at these speeds. Get a good V-belt. Remove the cut-off disk. Do you have vibrations then? You might need to change / add some damping or change the mass to the motor mounting / belt tensioning. If that doesn't work, continue with the pulleys. They are cast, so turn them down a bit on all sides to get an equal shape. 10000 RPM isn't just a bit! If that fails, the motor needs some looking after.

HTH, Nick

Kinda' what I thought but I needed someone to blame if it's wrong...thanks! I'l find out today or so.

Well, I can't redesign the spindle for V-belts very easily so, I'll redo the pulley and install a new motor today...we'll see!

Anything cast rotating at that speed is suspect. Why not take everything to a good electric motor shop and have it precision balanced?

Randy

No, sorry. Keep with the belt design you've got. Just replace it. And get the pulleys balanced. At least kind of by turning off the cast part.

Oh, how does the design of the bearing look like? Are they pre-loaded propperly?

Nick

You can't use V belts at 10,000 RPM. They will flip over and self destruct. Obviously this setup was made with flat belts. With a flat belt, the belt is less likely to be the problem, but it is still possible. Any runout in the pulleys will cause insane problems at these speeds. The changing radius of the pulley causes the motor to try to alternately speed up and slow down the spindle every revolution of the bad pulley! It doesn't take much runout at all to cause this with a 10,000 RPM spindle.

Jon

*Any* rotating shaft will have at least one resonant frequency and possibly more. Adding mass and rigidity should help. Adding pulleys, a belt and another shaft will create other resonant frequencies and complicate the issue.

That said, what happens as the speed ramps up and down? If the vibration simply scales with the speed, I'd guess you have relatively simple balance problem. If the vibration peaks and dips with motor speed, you've got a resonance issue.

I wrote "V-belt" without thinking. Vlat-belt. :-)

Nick

A Flat belt on a 7" pulley @ 3450 rpm ??? the belt's a flappin in the breeze--go to a small V belt & try that.

[snip] Do I misunderstand, or is that flat belt running direct on the 1" spindle? If so, you have a 7:1 speed-up from the motor. Given the motor at 3450rpm, that puts your spindle at 24,150 rpm. That's seriously fast...

Actually..a good flat belt or a wide PolyV are probably the best for high speeds. Tension it up good.

Gunner

Rule #35 "That which does not kill you, has made a huge tactical error"

Oh, no...it's about a 3" barrel shaped on the spindle.

Vlat-belt! I like it!