Vibration with toothed pulley

jroddds · Jan 19, 2022

Hey all,
I changed my mill from a poly-V belt to a timed pulley - HTD5. The poly belt was slipping during tapping cycles on larger taps. The timing belt is working great except for one thing:
I am getting a noticible amount of vibration in one specific speed range. Outside of this range, everything is pretty smooth.
The spindle motor is 1750RPM Vector Duty with full HP at 2x speed.
The spindle is geared up 2.2x, giving a speed range of 200-7700RPM.
The vibration ONLY happens between 1700-2100 RPM.

I was wondering if this is a "harmonics" issue with the mill. At that speed it just finds a rhythm.
I have several hours on the machine since changing the pulleys. Hoping the belt would run-in and this was a temporary issue. But not much relief so far.
If you guys have any suggestions, I would welcome them.
Jared

Milland · Jan 19, 2022

Could be an acoustic or vibrational resonance. Acoustic due to the right speed allowing the air to squirt out of the closing volume of belt to tooth area in some resonant period, or vibrational as the "free" side of the belt starts to vibrate.

A recording of the sound might help with diagnostics.

Richard King · Jan 19, 2022

What brand and model machine? How are you holding the tap? Using tapping fluid? What size tap? We don't have a crystal ball...

atomarc · Jan 19, 2022

To my knowledge, HTD profile belts/pulleys use a recommended tension that one would not think appropriate..they run loose. Is there a chance you have over tightened the drive, and that could be your problem.

Worth looking into.

Stuart

jroddds · Jan 19, 2022

atomarc said:
To my knowledge, HTD profile belts/pulleys use a recommended tension that one would not think appropriate..they run loose. Is there a chance you have over tightened the drive, and that could be your problem.

Worth looking into.

Stuart

Seems like an easy thing to check. I will get back with any updates.

dgfoster · Jan 20, 2022

atomarc said:
To my knowledge, HTD profile belts/pulleys use a recommended tension that one would not think appropriate..they run loose. Is there a chance you have over tightened the drive, and that could be your problem.

Worth looking into.

Stuart

Interesting idea. I could see how over-tensioning might cause poor seating of the teeth in the pulley grooves with teeth hanging a bit on the opposite sides of the grooves on the “upstream” and “downstream” sides of of the pulley. It could be interesting to spray a little paint on the grooves of the pulley and run it tight and spray and run it again at proper tension comparing the observed wear patterns, especially if Stuart’s suggestion is the answer.

You did not say so, but I guess most of us assume the toothed pulley eliminated the slippage?

Denis

DDoug · Jan 20, 2022

Are your (2) pulleys even numbered ?

BoxcarPete · Jan 20, 2022

Without intending to insult your intelligence, double-check your set screws. A set screw standing slightly proud will slap the belt each time it goes around, and could be another possible driver for the "harmonic" frequency you see. Ask me how I know

Easy to take a look, anyway.

Mtndew · Jan 21, 2022

My guess is belt tension also.

jroddds · Jan 21, 2022

Sorry to leave you all hanging. I adjusted the tension on the belt by loosening it. It did help, somewhat. but vibration remains. Took the belt off and confirmed that running the motor/pulley without a belt produces zero vibrations. I continued adjusting tension tighter and looser and got the vibrations down, but the belt was far looser than I would expect.
To answer other questions:
The pulleys are 108 teeth on the motor and 50 on the spindle.
There are no set screws on the teeth. The motor has a set screw on the hub, the spindle does not have one.
Timing pulley did fix the slippage issue (for sure).

I may try the painting idea to see where it goes. Otherwise, I just got a new pulley in the mail. Will see if swapping for a new pulley provides any results.

dian · Jan 22, 2022

how about an idler?

CarbideBob · Jan 22, 2022

I'd be tempted to put a DTI on the backside of the belt at the max contact area (back of the pulley) and look for runout.
One can not just indicate the pulley as the peaks do not matter.
You can mount a very cheap USB camera/microscope and watch the profile pass for runout but if the tooth spacing messed up the vibration will still be there as the belt climbs and drops.
Have you considered that maybe the belt tooth spacing is bad at one spot? Not an often problem on good quality ones but it does happen.
Tried more than one belt?
Bob

HappyWyo · Jan 22, 2022

It would be nearly impossible to eliminate all vibration when using a toothed belt. Take a toothed belt in your hand, bend it and slowly roll it. Notice the tooth portion is ridged and the void portion bends easily. Now imagine that happening at high speed.

jroddds · Feb 9, 2022

Just to provide some resolution: I changed the pulley out for a new one with a taper bushing (instead of a set screw) and it runs much smoother now. Must have been have been a bad pulley on the motor.
Thanks for all the insight.

gustafson · Feb 9, 2022

jroddds said:
Just to provide some resolution: I changed the pulley out for a new one with a taper bushing (instead of a set screw) and it runs much smoother now. Must have been have been a bad pulley on the motor.
Thanks for all the insight.

Thanks for getting back, it really helps future readers

Search

Largest Manufacturing Technology Community on the Web

Search

Vibration with toothed pulley

jroddds

Plastic

Milland

Diamond

Richard King

Diamond

atomarc

Diamond

jroddds

Plastic

dgfoster

Diamond

DDoug

Diamond

BoxcarPete

Stainless

Mtndew

Diamond

jroddds

Plastic

dian

Titanium

CarbideBob

Diamond

HappyWyo

Aluminum

jroddds

Plastic

gustafson

Diamond

Similar threads