On Sat, 17 Mar 2012 20:34:22 -0500, Ignoramus13020
wrote:

On 2012-03-18, Larry Jaques wrote:
On Sat, 17 Mar 2012 12:43:40 -0500, Ignoramus13020
wrote:

On 2012-03-17, Dennis wrote:
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....



I would look for problems elsewhere.

Ditto. Sounds like there might be some play in the leadscrew mounts.

Dennis, I have a spare (unmachined ends) RM1204 (12mm) x 300mm
leadscrew for sale fairly cheap, if you're interested. I also have 4
extra SBR12UU linear bearing blocks. (from a misunderstanding with a
Chinese supplier.)


I would first suspect the software, config and control system. Then
like you said, mounts etc.

If it was always off and always the same, I'd suspect the conversion
point he set in the software, but since it changes, I suspect loose
parts.

--
The greatest justice in life is that your
vision and looks tend to go simultaneously.
-- Kevin Bacon