"Dennis" wrote in message
. au...
I've just test run a little CNC router / mill I've put together.

At the moment I'm using M10 x 1.5mm pitch allthread for the lead screws
and PVC blocks for the nuts.


I've calibrated the axes (Mach3) using the 1.5mm leadscrew pitch and the
known motor steps/rev.


With a dial gauge on an axis, when I do a 1mm move sometimes I see 0.90mm
or 0.95, sometimes 1.0. It seems repeatable, ie if I reverse the steps I
see the same values.

What do people think? I guess this is typical for cheap bit of allthread
from the local hardware store?


ACME leadscrews are on the drawing board when finances are willing....

Precision Acme screws will be better, but there is an old feature in Mach
that says you can map your lead screws. I have not tried it yet, and there
does not seem to be much documentation on it. Also, you can calibrate steps
to your leads if they are off or unknown pitch. I have done that. Its
pretty easy with a dial indicator.