ATM - Fractional HP Motors for Grinding machines

[Adam Perkins <scopeguru@yahoo.com>]

Hi Everyone,

Perhaps some of you can help me with choosing a motor
for my proposed mirror grinder (yes, still not even
begun...).  
I'm searching for a 1/4 hp or better motor for my
machine, and came across the following ad on Ebay:


-----New motor. A.O. Smith 322P726. HP 1/4, V120, Type
FLL, RPM 825/ 2 Spd, thermally protected type C.
Weighs approx 12 pounds-----


I have no idea how a "2 speed" AC motor achieves its
lower speed, but assume this one to have a "high"
speed of 825 rpm (developing 1/4 HP at this speed).
  
Is there a standard ratio of speeds for a 2-speed
motor? Is there a loss of power if switched to the
lower rpm setting?

At first glance, this particular motor seems well
suited to my scheme, I'm all ears.

On a related note, I've seen some mention of running
large DC motors with a rectifier (and sometimes an AC
dimmer switch).  I have no idea what a rectifier
capable of powering a fractional HP motor costs, would
it balloon up my expense?

And finally, some thoughts on an alternate scheme I'm
considering.

I have a large floor-mounted drill press and am
considering using it as my power source for my
machine.  The grinding machine chassis would be bolted
to the base plate of the press, and would have a
drive-spindle protruding from the top to be chucked
into the drill press.  The belt system in the drill
press would provide all of my speed changes,
eliminating a stage or two of reduction to be built
into the grinder.  I'm thinking of only two available
ratios for overarm/mirror table rpm's, but plenty of
speeds. 

My reservations about this scheme are:

     -will a too-long drive spindle (floor mounted
machine and a +/- 50" chuck height) twist into a
pretzel if I use a size convenient to chuck in the
press and fit in a 1/2" or so ball-bearing at the
bottom?

     -Are two ratios enough for mirror table/eccentric
speeds in an elgin type machine used for figuring,
polishing, and grinding?

     -Is there a possibility of damaging my drill
press?  I do realize that side to side loads on a
drill press quill are not good, and will capture the
end of the drive spindle between two bearings to
eliminate this load from the pulleys. 

Thanks for your input.

Adam Perkins
Covington, Louisiana
USA














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