"Kudzu" wrote in message
...
I am looking for a little input in case I have missed something. I found an
old J-line bowl lathe and bought it. I am have been looking for a motor to
power it. I have looked at a bunch of motors, controllers, AC, DC, 3-phase,
single phase etc. I think I have settled on a DC motor largely because of
cost. After some searching and a lot of scrap paper math I think I have
made my choice. I have found a 1 HP totally enclosed motor, 1725 RPM,
sealed unit and rated for continuous duty. It costs more than some of the
other DC motors but it seems the better choice in a dusty environment like
a lathe. It

Having no experience with DC motors I have some concerns about the loss of
low speed torque. My plan is to run a variable speed control and since my
lathe came with a 3 step pulley on it and I I have decided to use pulleys
with a 3", 4" and 5" diameter and a second one with a 1 5/16", 2 9/16" and
3 3/8" dia. That way If I need to I can run the motor at a higher speed
and keep the spindle speed down and torque up.

On the lowest setting my max. spindle speed would be 455 RPM and I have
close to a 4 to 1 multiplication factor in my favor, so even at very slow
speeds I should still have plenty of torque. The next step provides for
1120 RPM and a 2 to 3 ratio. The highest setting is almost 1 to 1 and
would be way faster than I think I would ever need.

While I hope to just set it and not have to change the belt location at
least if I find that at slow speeds on larger items that I am lacking
torque I have the option to gear it down and speed up the motor. Or have I
missed something here?

I think you should be OK to the extent that it is worth a try. You might
find you do want more than 1725 rpm sometimes for small diameter stuff. I
wonder if the 1-5/16" dia pulley is going to get enough grip on the belt to
start rotating a big blank - I have a small pulley on my bandsaw and it can
be a problem slipping.

Are you using a commercial DC motor controller? They should have a better
torque/constant speed characteristic than just varying the DC voltage
open-loop.

Good luck,
Billh