Single Phase Induction Motor Rotor Balancing

[Meldonmech]

Hi Guys
             During the repacement of  the bearings of a single phase Bench Grinder, the rotor accidentally rolled off the bench and bent one or more vanes on the fan. When re assembled the motor ran well but would vibrate and start to slowly walk across the bench. The rotor obviously needs to be re balanced by gently tapping the aluminium vanes to re balance. Practical methods of this procedure would be welcome. I thought of placing it across the bed shears of a lathe, and observing the roll. But am not sure of the correct method.
                                          Cheers David

[John Stevenson]

Probably too much rolling resistance on the bed shears, you could do with knife edges.

Straighten everything up before you start so you know where you are. Are there any pillars in the alloy end as well as vanes ? They often cast pillars in so you can slip a washer on the pillar for balancing.

If you don't and you only have vanes then don't try bending them, it will be an exercise in futility knowing which way to bend them and you will probably end up snapping one off.

Instead find the heavy spot at the bottom and snip a bit off the corner of a vane with wire cutters, just a tad and then try again. Sound crude but this is how they are done in the rewind shops.

Careful you don't snip anything else off     

[awemawson]

Years ago, an accelerometer and amplifier flitted by on eBay for not a lot, and I got it intending to try a bit of vibrational analysis by holding the accelerometer against the circumference of an object and 'taking it round the clock'. Output is a varying DC value showing displacement that can be displayed on a multimeter.

Initial tests were very promising, but other things got in the way and it still sits in a drawer in the workshop 

[Meldonmech]

Hi John
               Thanks for your interesting, and practical information. I will look through my stock of "come in handy" items and materials, I am sure I can find something to provide a low rolling resistance for the rotor. There are no pillars on the rotor just vanes, and surprisingly one vane has been drilled and a nut and bolt fastened to it. I like the idea of snipping the vanes to balance, I would not have thought of that.

 Don't need to worry about snipping anything else, already been done!

                                                 Cheers David

[Meldonmech]

Hi Andrew

                       You are not the only one to purchase items for future porjects, then realise that they lay untouched for some time. In fact I am often quite pleased and surprised to find things that I had aquired sometimes years ago.

                                        Cheers David

[DavidA]

David,

Just wondered if you have tried running the motor without the fan. Maybe you bent more than the fan blades.

Dave.

[Meldonmech]

Hi Dave

               Thanks for your suggestion, the fan is actually apart of the aluminium rotor body casting, so cannot be removed.

                                                 Cheers David