Re: rough circle

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@y...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "afogassa" <afogassa@y...>

wrote:

> >
> > Hi all,
> > got a 3 axis servo driven gantry, rutex + deskcnc, it's working
> > ok,but when doing full or half circles using the cam generated

toolpath

> > the finish is not good at all, if I slow down the feedrate to

about

> > 1000mm/m it gets better but still not good enough.
> > I'm wondering if deskcnc does not have the necessary speed when

using

> > two axis the same time or it's the servodrive is not fast enough

to to

> > correct the possition.
> > It's not facets, it's more like the tool gouges in as if I was

using

> > a dull endmill.
> > It has a 2.5 lead leadscrew 500 ticks encoder, and x4

multiplier on

> > servo drive.
> > so, it's a 0.005mm per step with a max speed set at 3800mm/min.
> > that's = 200 steps per mm.
> >
> > Any sugestions.
>
>
> Do you get that great finish on straight cuts on both X and Y ?
> Do you also get a great finish on an angular cut, where both X and Y
> are moving ?
>
> I'm not familair with DeskNC, does it have look ahead programming ?
>
> Wjhat I suspect is that the machine has vibration so it cannot cut a
> smooth finish, or that the arc is being cut in segments and at the

end

> of each line, it pauses. at each pause, the cutter idles and cuts a
> little larger spot.
>
> Maybe if you made a semi-circle of only 16 points, you could see it
> each line end has athe same effect. then try 32 points and keep
> increaseing the number to see where it starts.
>
> Also, have you tried a G code to cut a circle ?
>
> Dave
>

I suspect that it has something to do with small line segments,
when doing large circles the finish is nice( longer line segments)but
when smal circles or arcs that have short line segments the finish
socks.
I think it has something to do with the look ahead, maybe it pauses
on short line segments enough to gouge the parts(movements gets rough)
Maybe I should make the acceleration curve longer, but than, it
slows down the milling speed.
I'm not shure but deskcnc can not do a real interpolation, (sends a
pulse out for x than y than z on each pin of the microprocessor)so
it sends like 100pulses on x axis waits it to finish, than 100 pulses
on y axis than on z axis, if so it would have to be alot faster than
it is.
Im wondering if turbocnc or any other dos software that uses the
parallel port can do real interpolation ( send pulses all at the same
time for xyz so it would move all the axis at the same time.