Re: Mini-Lathe CNC conversion question

Hi Tad,

I agree with John, I have Vexta PK268-02A's 187 OzIn on both Z and X
with 2:1 reduction driven at 2A and 35V, and 4mm pitch (Z) and 3mm
pitch (X) leadscrews, and this is plenty of power, if you first
address the bed thickness.

As supplied it seems the thickness of the bed ways on the 7x mini
lthes is not constant, so you need to address this if you want to use
these smaller motors for Z.

Rick Kruger did an excellent (as always) write up here:
http://warhammer.mcc.virginia.edu/ty/7x10/vault/Lathes/7x10-7x12-
Projects/TaperedSaddleGibs/Bedways.html

I didn't address this thickness issue so my Rapids are limited to
about 30 ipm due to the torque required to avoid binding near the
tailstock end. In the looser part of the bed by the headstock I can
get nearly double this speed.

Looking again at your motors specs, you will have a substantially
slower motors than Johns and mine in practice. Although they have
nearly the same holding toque, they are higher inductance and will
have a steeper torque curve (lower power). At cutting speeds (I tend
to use around 30-100 mm/min during cutting, down to 5-10 mm/min for
parting) your motors will be providing about the same power as mine.

What are you going to do for leadscrews? If you stick with the
standard ones, then you already have a much higher gear ratio, and
direct drive might work fine. With these high inductance motors, you
really want to try and reduce friction on Z by running the leadscrew
in bearing instead of the bushing blocks, or better still getting a
ball screw for it.

Regards,
Mark
www.wrathall
http://www.wrathall.com/Interests/interests_index.htm