Re: [CAD_CAM_EDM_DRO] EMC and Rounded Corners

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.

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.rabun.net/~leswatts/shop.html

----- Original Message -----
From: "Toddy, Terry L CUBA" <tltoddy@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, April 08, 2002 10:18 AM
Subject: [CAD_CAM_EDM_DRO] EMC and Rounded Corners


> I have my CNC plasma cutter working. I cut the first pieces last night.
All
> went pretty well for a first try with a "live" torch.... but, I programmed
> sharp corners and EMC rounded them all with about a 3/8" radius. I am
> cutting at 200 IPM with 8in/sec^2 accel. Is the rounded corners due to
slow
> accel or is it a constant contouring feature? If it is a feature how do I
> disable it? I realize the torch will burn the corners off some, but there
is
> definitely a tool path issue here.
>
> TIA
> Terry