Re: Ace Hardware grinder Sync conversion? Slot depth opinions

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 7/20/05 11:15:00 AM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:

Jim,

Yes, make two flats, 180 degrees apart.  It doesn't matter
where you start as long as the faces are parallel (opposite)
as you said.  Your small diameter armature and low
cap value leads me to believe that you have a cap run motor.

There are various opinions about the best depth for the
flats.  For 3600 rpm units they can range from a 1/2" width
to a 1.2" width.  Something like that.  I just happens that
I've modified a lot more 1800 rpm motors than 3600 rpm
motors, so I have more experience with the 1800 rpm ones.
In one case I modified a small 3600 motor that had a 1.75" dia
armature or so, and I made the flats about 7/8" wide I think.
This worked very well.  In other 3600 rpm cases I made the flats
narrower, but the motors seemed weaker.  But these were all
different motors so it's hard to judge.  Some folks talk
about a dead pole method.  I believe that this applies best
to larger motors of 2HP or larger.  Four electrodes on a
rotor will give you 240 bps running at 3600 rpm.  By
simply shifting the phase, you can make it run at 120 bps,
still with teh four electrodes in place.

Since the armature is small in diameter, the balance will
be less critical than if it was larger.

John


> I dismantled the grinder a few minutes ago and it
> has a 6.0 uf in the base which seems to go to a
> separate(s) windings for Startup?. All in all I
> think it is the right ticket. Just as Terry's
> pictures show. I am thinking of putting 4 gaps on
> the 12" disk for better balance. These would be
> at 90 degrees each. I have not done any math on
> that yet nor have I calculated the instantaneous
> value of E in a long time:-). I'll just figure on
> the timing based on the rotor speed and the
> length of a 60 cycle sine wave time. It would be
> nice to run 240 BPS. All the electrodes (12) are
> 30 degrees apart. I'll remove the 8 for now. I
> have a slew of new CD caps and a well voltage and current controlled pig.
>
> Ok so I think I need 2 slots cut 180 degrees
> opposing for 3600 right? How deep should they be
> machined to get max torque but suitable sync. The
> armature is smallish 1 5/8" wide including the
> aluminum ends and Mics to 2.041 - 2.042 in
> diameter. Does it matter where the cuts are made
> in the armature as long as they face each other?
> Multiple opinions welcome. I think I will take
> this to a machinist friend of mine.
>
> Thanks much for the info. This should blow my
> static blown 15/120 away! I'm jazzed.
>
> Jim Mora