I dunno the context of the comment that compressor-rated motors aren't
reversible, but that comment isn't accurate.
Compressor-rated motors, as well as any other specific type of motor
may be reversible.

I can understand that an air compressor manufacturer might specify a
single direction of rotation, because a reversible motor wouldn't be
required for their particular application, and the motors would cost
less than a reversible version of the same model of motor (fewer power
leads and/or terminals, lower cost).
This would result in the availability of non-reversible
compressor-rated motors, but there are many of the same which are
reversible.
Generally, any type of motor that wasn't produced for a specific
appliance/machine application, will be available as a reversible model.


I think the application you're contemplating is a motor located between
two separate shafts/arbors, and each shaft intended for a different
use.
In the assumed application, the nuts securing the grinding and buffing
wheels may loosen when the motor is started, if there is no
consideration given to preventing that.

On a typical single shaft arbor, the mounting/securing nuts are
separately left and right hand threaded, since the arbor is always run
in one direction only.
Placing your wheels on opposite ends of a single shaft would probably
be easier to implement (most certainly safer). Then there would be no
need to reverse the motor direction.

Compressor-duty motors are built/intended for high starting and running
torque, but aren't absolutely required for grinding or buffing
applications. Another type of motor would be adequately sufficient,
although a c-r motor would also provide very good performance.

Switching reversible motors to run in either direction isn't extremely
complicated if the motor is a reversible model. There was an in-depth
discussion within the last week concerning this same topic, here in
RCM.

Motor efficiency is related to running hours, to be of any major
significance. For cost-effectiveness, one might consider 3-phase power
as less costly, as 3-phase motors are generally cheaper to purchase.

WB
...............

Bernard Arnest wrote:
Hi,
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the proper
rotation I would have to reverse the rotation of the motors.

Assuming a conventional, reversible motor (I'm not on the question
of compressor motor or not here), does this involve rewiring the motor
each time? Even if just 10 minutes of work, it would be a nuisance;
since it would not just be a one-time rewiring, but every time I want
to switch between machines. Could I build a simple device that would
rewire it by flipping a switch, if this is the case?


btw, how much more efficient is 3 phase over 2? It seems a
converter is affordable off of ebay, and it looks like it would make
every subsequent motor cheaper, and/or more efficient and
smoother-running?

thanks!
-Bernard Arnest