Re: Look Ahead

[William Scalione <scalione-at-home.com>]

>
>
> > I also noticed that when I was
> > milling the
> > table (made from mdf not metal) to be true with the cutting tool, it would not
> > go all
> > the way to the end of the x axis if I had a high feedrate. see example code
> > below.
> >
> > X0Y0
> > Z-.05
> > X20
> > Y.25
> > X0
> > Y.5
> > X20
> > Y.75
> > X0
> >
> > At a low feedrate x would go all the way to 20 but at a high feedrate X would
> > only go
> > to 19.75
>
> That's a quarter of an INCH?!?  Yikes!  But, it is not really that surprising.
> Increasing the acceleration parameter will reduce this effect, but you need more
> powerful motors to handle the more rapid accel/decel profiles.
>
> When you expect this sort of problem to crop up, you can put a dwell
> command there (G04) or use the exact stop mode, (G61).  This will slow
> things down, as it requires a full stop on most moves, but it will make the
> machine go all the way to the end of a move before starting the next move.
> I use this when drilling PC boards with tiny drills, to make sure the XY
> position has settled completely before starting to plunge the drill in, and that
> the drill is fully retracted before moving X & Y to the next hole.
>
> Jon

Sorry, the 1/4 inch error was when I was doing this, not what I wrote before.
making 180 degree changes, not 90.

 X0Y0
 Z-.05
 X20
 X0
 Y.25
 X20
 X0
 Y.5
 X20
 X0

I will try to avoid things like that in the future, did not really need to do it
that time
anyway. I'll also try to increase the acceleration. If that doesn't help on the 90
degree
turns I'll try G61. Is this a modal command or is it required on each line. If
it's  modal
what is used to turn it off?

Bill