Balancing pullies

**morrisman** · 25th August 2015, 08:51 PM

I have a lathe, somebody has done a bodge and tried to fit a 3 position pulley system on the motor / countershaft .

Problem is it is all out of balance . Removing the belt and running the motor alone, reveals vibrations from the pulley on the motor . The motor pulley is actually 3 separate pulleys joined together , somebody has machined them to fit against each other . Should I junk it and just buy a 2 step aluminuim pulley ? Or would it be worthwhile trying to balance it ?

The large 3 step counter pulley has a badly machined bore and it wobbles on its shaft .

I was reading of a guy who dynamic balances pulleys and wheels by resting a DTI tip on the shaft housing and watching the indicator needle wobble , he applies clay to the pulley and adjust it til its running smooth .

**RayG** · 25th August 2015, 09:15 PM

Is the pulley cluster bored to the correct size for the shaft, if it's been bored oversize and wobbling you should rebore the pulley cluster concentric and make a sleeve for the motor shaft.

You've lost me completely with the clay thing?

**morrisman** · 25th August 2015, 09:30 PM

Originally Posted by RayG

Is the pulley cluster bored to the correct size for the shaft, if it's been bored oversize and wobbling you should rebore the pulley cluster concentric and make a sleeve for the motor shaft.

You've lost me completely with the clay thing?

The modelling clay is adding weight to the circumference of the pulley/wheel, you move it around and adjust the amount of clay , the vibrations are reduced or increased , find the sweet spot and you know how much weight is needed . Somewhat like the weights on car rims . Or do they still use them these days ?

Yes the bore of the large pulley will need to be sleeved . The bore is concentric and slightly oversize and the finish is horrible , it has deep scouring

**morrisman** · 26th August 2015, 08:18 PM

I had a play with balancing . It worked out rather well, with about 90% of the vibrations removed from this bodged up pulley . It needs a final tune and it should be OK . Instead of the modelling clay , I used magnets . In this case , It works best with the weight under the keyway for some reason .

The DTI gives a sensitive indication of whats going on

**jhovel** · 26th August 2015, 10:14 PM

Once you know the weight required to balance the pulley, you can remove that weight on the exactly opposite side by drilling out material of that weight. I suspect the magnet version might be just as reliable if they are prevented from slipping around under accelearation or a sudden stop. with a smear of epoxy glue.

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