"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....


As others have said all-thread is not accurate, but it is not quite that bad
over such a short distance. How is your stage made? It seems more likely
that there is some wobble in yaw or pitch that causes a difference in
position between where the nut is and where thee indicator measures. Also,
if the threaded rod is not straight, it will exert lateral and vertical
forces on the stage versus rotation angle that may cause such a wobble.