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VPI motor - upgrade to 300 rpm?

I hsve a HW-19 mk 4 plus or something, with the Black knight platter and inverted bearing, along with the SDS, The SAMA is the Hurst 600 rpm. This has run, now, for five years. Recently I have had problems with pitch variation, not easy to locate. The problems have been somewhat solved by glueing the pulley to the shaft and by oiling the motor, helping a lot, but perhaps not fully. Should I order a 300 rpm motor and new pulley? Advice is appreaciated, especially, experiences going from the 600 to the 300 rpm motor.
o_holter
ptmconsulting
1,000 posts
 
You can easily pick up a new Hurst motor on the web. You don't even have to go through VPI to get it.

On another note, I believe there was some discusison about which motor was actually better. Something to do with the cogging effect, since the number of poles differ on each motor. Maybe someone else who has more knowledge of this will chime in.
markd51
741 posts
 
What your problem may be, is the Drive Belt? When was the last time it was changed?

The SAMA Motor shouldn't be changing, or fluctuating speed, and the SDS should be providing stable voltage-frequency to the Motor.

But, if your SAMA is using the newer, "stepped drive pulley", that one can adjust speed at the pulley in very small increments by which little groove the Belt is placed on, it is possible that an old, or worn belt is wandering on the Pulley?

Those ridges on the pulley are very small. I'd try this forst before resorting to Motor swap-outs. Mark
markd51
741 posts
 
Not sure yet if my first response will be posted, but besides the possible issue with the Belt changing places on the Pulley, another cause could be the possibility of your SAMA not remaining stationary?

I'm finding that out myself with a recent SAMA installation, that the stock rubber SAMA feet seem to be inadequate. My SAMA I note is beginning to pull towards the Platter, that I'm noting inconsistency of Belt Tension due to this "pull", I'm seeing the Rubber feet bend-lean under this pressure, and am in the process of retro-fitting my SAMA with a set of Herbies Tenderfeet.

They are a few mm taller, but a wider foot, at 1.1" x 1.1".

Other devices out there could be used. I think the important thing, will be providing a rock solid anchoring of the SAMA to whatever Shelf-Rack you use. Mark
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