Is there a decent small format 3 phase motor that develops its best torque
and HP in the 30-120hz range? Typically small tools needing a compact motor
use a universal brush motor. For example your typical mini lathe. My
little 7x10 (now 7x16) has a universal brush motor. I've been tinkering on
and off over the last couple years with converting it to CNC. I finished
the Z motor and lead hardware a long time ago, and I finally figured out how
I want to do the X. I've got a few little trinket parts on order, and I'll
machine the saddle and brand new t-slot table (for gang tooling) to fit
shortly when they arrive.

One of the things I want to do is improve the spindle motor setup when I get
to that point. The universal brush motor with its Chinese speed control
works ok, but its not wonderful. For manual turning if it bogs down I just
reach over and turn the pot. An AC servo is a little more than I want to
put on the machine for a spindle motor. At about half the cost I can put on
a small VFD, a 3 phase motor, and a cooling fan. I think I know that there
are inherent reasons why AC induction motors tend to be much larger than
universal brush motors for similar gross power ratings, but I can't believe
a 1/3 to 1/2 hp 3 phase motor can't be made a lot smaller than say a 1 or 2
hp motor. I intend to make a mounting plate for the motor anyway, so I
could certainly use a physically larger motor, but it just feels so
"sledgehammer inelegant" to me.

Its a really light weight machine still so a spindle motor with any more
power (and I have a few laying around) might allow me to program code that
would allow the machine to tear itself apart. Its still just a light
weight, but I have a few parts I could make and sell for a small profit if I
could just semi-automate them and walk away. Besides, I am having fun
converting this little toy lathe over to CNC operation.

Have you considered DC? Wide variety of sizes available cheaply.
Smaller size than AC for the same power. Servo controllers readily
available for reasonable money. Used with feedback, versatility is good.

"Bob Engelhardt" wrote in message news
Have you considered DC? Wide variety of sizes available cheaply.
Smaller size than AC for the same power. Servo controllers readily
available for reasonable money. Used with feedback, versatility is good.

************

Well, DC servo is an easy option, but I could (in theory) just use the
existing universal brush motor as a DC servo by slapping an encoder on the
spindle. I'm actually trying to get away from having a brush motor in an
out of the way difficult to service location behind the lathe (among other
things). I went ahead and ordered the AC Servo motor and control. The
motor body is only 60MM and supposed is a little higher power than the stock
UB motor. Priced at under $300 complete or a little more with straight plug
in extension cables its not much different than a DC brush servo by the time
you figure, motor, controller, cables, encoders, back emf supressor, etc.
Heck I could as easily have thrown on a closed loop stepper. LOL.