Re: EMC and Rounded Corners

Terry,

Have you already confirmed that your machine structure and mechanical
drive(s) is not creating/adding to this problem?

Hope this helps,

Ballendo

--- In CAD_CAM_EDM_DRO@y..., "Toddy, Terry L CUBA" <tltoddy@o...>
wrote:

> Les, Thanks for the quantitative analysis. The 3/8" rounding was a

wild

> guess, not an actual measured radius. It could well be more like

1". Here's

> the qualitative analysis: My parts look like marshmallows.
>
> It is a stepper system.
>
> Tonight I will try to find my max accel values. Yes, plasma and

routers need

> high accel values to run at high feedrates. Keeping the gantry mass

down

> helps with plasma but the routers need the rigidity.
>
> I think the G61(exact path mode) will eliminate the tool path

variation and

> maximizing acceleration will minimize the slow motion around the

corners.

> The EMC apparently defaults to G64(continuous mode)where tool path

accuracy

> is compromised to optimize velocity. That's probably a great

feature for a

> mill cutting a mold cavity at 10 or 20 IPM, and making slight

changes in

> direction, not so great for a plasma machine running 200 IPM trying

to cut

> square corners. Actually G64 may be useful with the plasma for

curves

> generated from small line segments as long as you go back to G61 to

make

> sharp corners.
>
> Terry
>
> >
> > Hmmm... is this stepper or servo?
> >
> > If you figure using the centripedal acceleration formula
> > a=v^2/r to relate acceleration to minimum cutting radius
> > that gives (solving for r)
> >
> > r=v^2/a= (3.33 in/s)^2/8 in/s^2= 1.39 in
> >
> > -much more rounded than you are getting.
> > If two coordinated axes were set to the same acceleration
> > and a corner was commanded it would have a parabolic
> > countour- just like a projectile path fired at 45 degrees.
> >
> > This brings up the fact that some of us need quite high
> > acceleration values in high speed routers and plasma.
> >
> > I think acceleration for a vertical mill might be more like 5
> > or so but that is not enough for us.
> >
> > I have been playing around with MAX_ACCELERATION
> > and DEFAULT_ACCELERATION in the .ini. I am running
> > about 20 for MAX... but I don't really know when one
> > or the other kicks in or whether they are numerically
> > accurate. Perhaps
> > someone could enlighten us.
> >
> > I think you need to play around with those as well. And feed.
> > That v^2 term would seem to give rapidly tighter corners as
> > you slow down.
> >
> > For example for your 8 in/s^2 accel,
> >
> > 200 ipm gives 1.39 " radius as mentioned
> >
> > 100 ipm gives 0.34"
> >
> > 50 ipm gives 0.083"
> >
> > The last thing to note... High accel like I am using requires
> > very careful pid tuning to avoid instability as the rapid starts
> > and stops excite system resonances. Before I did a careful
> > Zeigler-Nichols closed loop tuning analysis I could not run
> > with ACCEL more than about 10. This is for servos of course.
> >
> > It also puts a load on the bearings etc- but my machine is
> > designed for 0.5g
> > safely. That's a real sledgehammer blow
> > start and stop.
> >