Re: 3D Contouring - Loss of Accuracy

Hi Peter,
I've wondered if somehow a software provision/mechanism for
periodically re-home-ing during long duration programs could be
done. This is sort of a bandaid fix, but would reset the
accumulating error. Also, I've been (just) thinking of how one might
make a super accurate home position switch.
Just ideas,
-Lee

> make sense when you look at the G-code - it has absolute XYZ
> coordinates. The error occurs relative to a fixed datum such as a
> switch closure or a nail head pointer.
>
> Cheers, Peter
>
>
>
> Egroupscdh (E-mail) wrote:
>
> >Ok, I'm no expert here but I'll stick my neck out ...
> >
> >As I understand it you're using the parallel port in all cases.

Could it be

> >that the error is occurring during direction reversals only one

step at a

> >time?
> >
> >Possibly the edge of the 'direction' line is not correctly

oriented with

> >respect to the 'step' line.
> >
> >While watching the step and direction lines with your scope (dual

trace I

> >hope) you might try configuring a test case such as:
> >
> > -----
> > |
> > A |
> > X ----- |
> > I | | |
> > S | | |
> > ----- | -----
> > A | | |
> > | | |
> > | -----
> > |
> > |
> >
> > AXIS B
> >
> >using different combinations of axis with and without motion in

the third

> >axis to see if the error shows up.
> >
> >You might also try purchasing a parallel port card and trying

that.

> >
> >Cheers,
> >
> >Chuck Hackett
> >"Good judgment comes from experience, experience comes from bad

judgment"

> >7.5" gauge Union Pacific Northern (4-8-4) 844
> >Railroad: Camp Creek Railroaders, Waverly, Nebraska, USA (3000',

7.5")

> >Home: Elkhorn, Nebraska (just west of Omaha)
> >
> >
> >>From: Peter [mailto:prenolds@s...]
> >>
> >>Hi all,
> >>
> >>I'm stumped! ....
> >>I find is that running a large 3D file I gradually accumulate a

small

> >>error typically in one of the most active axes which often

exceeds 0.3mm

> >>or .012" after half an hour to an hour of running time. It is

usually

> >>in the same direction, but not always.
> >>....
> >>
> >>Cheers, Peter
> >>
> >
> >
> >
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