"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....



OK - THANKS for all the replies, there's a lot to think about!

I got stuck doing other things so I've not had a chance to "play" with the
machine again.

From reading all your replies I think the approach I'll take is:

1) Recheck all lead screw bearings / lead-nut mounts for tightness & play.
2) Check lead nuts for play (these are fairly tight)
3) Use dial gauge & check translation at 1mm increments over 10mm or so.