Re: [CAD_CAM_EDM_DRO] Re: backlash

OK- I give up. Will go for ball screws.
Alex

----- Original Message -----
From: Tony Jeffree <tony@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, January 05, 2003 2:55 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: backlash


> At 23:47 04/01/2003 -0600, you wrote:
>
>
> >Tony Jeffree wrote:
> >
> > >Tim -
> > >
> > >That is only because the crude approximations to backlash compensation
> > >start with the assumptions that:
> > >
> > >(a) a given program will not do both climb milling and "normal"
milling, and
> > >
> >No, the problem with climb milling is that the rotating cutting tool can
> >pull the work into the
> >cutter, causing a broken cutter, wrecked workpiece, damaged machine, etc.
> >
> > >(b) the backlash is constant over the travel of a given leadscrew, and
> > >(c) the backlash value is accurately known.
> > >
> > >
> >No, it still doesn't work. The problem is that when an axis reverses
> >while the cutter is making a
> >cut, the machine cannot get from one side of the backlash to the other
> >side instantaneously, so it
> >allows the table to be unconstrained by the motors for a moment. This
> >is a situation whenever
> >you are milling a circular hole or pocket, a wonderful thing to be able
> >to do with a CNC machine.
> >
> > >It would be possible to provide sufficient information to the control
> > >software to allow it to do a significantly better job of backlash
> > >compensation than most controls manage currently; however, the real
> > >question is whether it is a worthwhile thing to do, given the
alternative
> > >of building a better machine to start with.
> > >
> > >
> >The problem stated above just can't be fixed with software, no matter
> >how hard you try.
>
> It could be made to work as long as the control software has a complete
> picture of the backlash at all positions on each axis (not just the
average
> or max value), and as long as it is programmed to interrupt a cut (in
order
> to change the direction of pre-load) before the direction of cut changes.
>
>
> Regards,
> Tony
>
>
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