Re: Ace Hardware grinder Sync conversion? Slot depth opinions

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Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>


Hi Jim,

Comments interspersed.


Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

""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. ""

I dont think a 4 electrode rotor is any easier to balance than a 2 
electrode rotor.  If you have 4 electrodes on your rotor, you will 
have 240 BPS given a two pole motor at 3600 rpm. To convert to 120 
BPS just remove two opposing electrodes

""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.""

Two flats for a two pole motor, each at 180 degress to the 
other.  The depth of the flat is determined by the stator coil.  Find 
the width between bundles of wires in the stator and this will 
determine the size of the flat. The flat needs to be of a depth so 
the width of the flat spot on the rotor matches the spacing between 
wire bundles (main wire bundle not the starter coil bundle).  Make 
this measurement first and post the results before grinding the flat 
in case I haven't described the stator coil correctly. Grinding the 
flat is fairly easy and doesn't require a machinist.  You can use a 
right angle grinder for the flats.  A mill may grab the laminants and 
tear the armature up.  Terry showed me how to make the modification 
last year and put a template on the armature to identify the width 
and position of the flat and then inked in the flat boundry.  Going 
to shallow on the depth means locking torque is too small and it may 
hunt.  Going to deep makes the motor run too hot.  Where the flats 
are made on the armature is not important as long as the two flats 
are opposing each other (like at 180 degrees apart)

Gerry R.