Re: [CAD_CAM_EDM_DRO] Re: Adding friction to an axis? - or some other solution...

(Accumulated Error)
I believe it because of the long program that has many micro movements, an
accumulated errors can occur, even though cnc machines are very accurate,
they are not with out small amounts of error..... so the more moves it
makes, the more chance to accumulate errors.....

RC

----- Original Message -----
From: Peter <prenolds@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Thursday, May 30, 2002 7:20 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Adding friction to an axis? - or some
other solution...


> Jan, the machine in question is a BP clone with rockford ball screws on
> all axes and 1800 oz-in NEMA42 steppers direct coupled via helical
> couplings. The machine is in near new condition and all axes move
> freely. The problem I have is with long CAM generated files - I seem to
> experience a cumulative error somewhat in Y & mostly in Z it seems. If
> after running a 3D contour program for say 90 minutes if I return to
> machine zero, I could be .015" out in Z and say .005" out in Y and bang
> on in X. Accel rates etc have all been played with ad-nauseum. It
> seems to occur more as a function of run time, rather than speed. And
> while it would seem plausible that this could be a thermal problem or a
> lack of friction problem - I can't imagine what could be getting so warm
> as to cause a thermal problem.
>
> I'm running a Flashcut controller with '201 Geckos in full (10)
> microstep mode and even though I have been conservative with my
> accelerations, I guess it is still possible that I'm losing steps.
>
> For all 2.5D CNC work - even at higher step rates, everything works
> flawlessly.
>
> The mysteries never end...
>
> Cheers, Peter
>
>
> JanRwl@... wrote:
>
> > In a message dated 30-May-02 00:27:05 Central Daylight Time,
> > elson@... writes:
> >
> >
> >
> >>The current approach is to mount a hollow round
> >>cavity to the shaft, and have a heavy metal disc free floating in the
> >>cavity.
> >>The cavity is partially or completely filled with a viscous oil to give
the
> >>desired vibration absorption.
> >>
> >
> > I wonder if the machining and bearings of the axis in question have not
been
> > done so fine that there is simply insufficient FRICTION for steppers to
work?
> > Some DRAG can do magic things to a stepper-system, sometimes! Jan
> > Rowland, Troll who's BEEN there, done that!
> >
> >
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