Any ideas on how to go about such a balancing rig?
Aim: Dynamic balance a 4 pole shaded pole turntable motor for an old [1957] idler turntable restoration project.
Better to address the source of the noise before it gets to the platter and tone arm/cartridge.
This would all be easier if I could remove the stepped pulley from motor shaft and then have such a small rotor balanced by the guys who balance turbo impellers.
Pulley removal isn't going to happen without risk of bending the output shaft of motor [pressed on - no mounting screws].... and commercial balancing like this won't happen with the rotor installed in half the motor end case.
The more I look at this motor the more I think maybe better to buy a new 4 pole synchro motor that has sintered bush bearings, I modify trust bearing and have a new stepped pulley fabricated to fit the motor shaft..... and have the rotor fine balanced of course.
Commercial refrigeration unit condenser fan motors [8W or maybe even 20W max] are a fine choice if the balance issue can be addressed. More torque than original motor would be better too.
Anyhow, can't be too hard to use the motor [as assembled] to spin the shaft at 1,500rpm and by some means use a vibration sensor to detect imbalance vibration in the motor and then identify location on the rotor that requires removal of metal to achieve balance.
Dynamic balancing does not require high speed rotation as some people believe.
I've considered that a sensor could be cheap *** stereo phono pickup [less than $5 on eBay outa China]. With stylus correctly touching outer frame of the motor and cart statical mounted could identify maximum deflections from imbalance.... that would easily show on an oscilo scope no doubt. Cart can be wired for vertical displacement output rather than lateral.
A rotary encoder to determine angle location on rotor may not be necessary IF a strobe effect triggered by pickup could identify location instead?
Any ideas folks?
Aim: Dynamic balance a 4 pole shaded pole turntable motor for an old [1957] idler turntable restoration project.
Better to address the source of the noise before it gets to the platter and tone arm/cartridge.
This would all be easier if I could remove the stepped pulley from motor shaft and then have such a small rotor balanced by the guys who balance turbo impellers.
Pulley removal isn't going to happen without risk of bending the output shaft of motor [pressed on - no mounting screws].... and commercial balancing like this won't happen with the rotor installed in half the motor end case.
The more I look at this motor the more I think maybe better to buy a new 4 pole synchro motor that has sintered bush bearings, I modify trust bearing and have a new stepped pulley fabricated to fit the motor shaft..... and have the rotor fine balanced of course.
Commercial refrigeration unit condenser fan motors [8W or maybe even 20W max] are a fine choice if the balance issue can be addressed. More torque than original motor would be better too.
Anyhow, can't be too hard to use the motor [as assembled] to spin the shaft at 1,500rpm and by some means use a vibration sensor to detect imbalance vibration in the motor and then identify location on the rotor that requires removal of metal to achieve balance.
Dynamic balancing does not require high speed rotation as some people believe.
I've considered that a sensor could be cheap *** stereo phono pickup [less than $5 on eBay outa China]. With stylus correctly touching outer frame of the motor and cart statical mounted could identify maximum deflections from imbalance.... that would easily show on an oscilo scope no doubt. Cart can be wired for vertical displacement output rather than lateral.
A rotary encoder to determine angle location on rotor may not be necessary IF a strobe effect triggered by pickup could identify location instead?
Any ideas folks?
If I remember correctly kevinr in his thread restoration of Thorens td124 balanced his motor using small pieces of tape. It's probably worth checking this thread out especially if you're restoring an idler drive.
It's probably not the pulley that's out of balance so removing it and having it balanced probably wouldn't help. It's much more likely that it's the armature or winding of the motor itself that are causing any imbalance. Balancing the motor as a whole is the way to go.
Easier than your phono-cartridge measuring idea might be to compliantly mount the motor so it can move with the imbalance. Then use a marker pen and gradually move it up to the edge of the pulley until it just touches. The marker will mark the pulley towards the direction of the imbalance. Add a small weight opposite the mark (blutak) and repeat until perfect balance is achieved then replace the temporary weight with a permanent one of exactly the same mass and location. I've successfully used a similar method to balancing my platter and centre my arm bearings.
Hope this helps.
Niffy
It's probably not the pulley that's out of balance so removing it and having it balanced probably wouldn't help. It's much more likely that it's the armature or winding of the motor itself that are causing any imbalance. Balancing the motor as a whole is the way to go.
Easier than your phono-cartridge measuring idea might be to compliantly mount the motor so it can move with the imbalance. Then use a marker pen and gradually move it up to the edge of the pulley until it just touches. The marker will mark the pulley towards the direction of the imbalance. Add a small weight opposite the mark (blutak) and repeat until perfect balance is achieved then replace the temporary weight with a permanent one of exactly the same mass and location. I've successfully used a similar method to balancing my platter and centre my arm bearings.
Hope this helps.
Niffy
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It’s not a very simple job
See section 13.3.2
http://www.iitg.ernet.in/scifac/qip...i_rotor_bearing_system/rt_chapter13_part1.pdf
Only consider this :
George
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