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Constant Velocity solution for some
« on: January 18, 2013, 09:57:44 PM »
After banging my head against a wall for the past few days trying to figure out how to solve my CV problems (having no cv at all, very slow or just not working like I wanted) I came across a solution that works for me and maybe some others so I thought I'd share it, since after reading all the posts on this forum about cv problems and none of the offered solutions working for me, this is one method I didn't see suggested.

Note this is only with mach 3 and cambam, so if your using another CAM package there may be a similar option for you.

First the problem, the machine i'm using is my very first home built one so of course its a little rough and doesn't have high velocity or acceleration and everything was stuck together using a spirit level :P but it works. Because of the low speeds/acc I assumed this was why CV was not working as desired for me, it was basically just the same as running in exact stop mode. No matter how much I played with lookahead, cv dist tol, cv feed rate or cv angles I could not get it to run smooth. CV angles didn't even seem to respond to anything, I had to have it set to 180 or off completely just to have it run. In the end I opted to use plasma mode and this helped a lot but still not as good as I want. I noticed it always stopped/slowed down heaps just as it got to a G2 line...

The solution, in the cambam mach 3 post processor you are using, go down to "options" and you will see "Arc output". Change this from normal to "convert to lines". This gets rid of all the G2 commands and replaces them with a lot of G1. So your curves become made up of a lot of little straight lines. Under the next settings, "arc output tolerance" i think its called, the lower the number the more little "lines" your curves will become. This will balloon your file size the smoother you want your curves/arcs but does that even matter? and now my machine speeds around and cv dist tol and cv angle does exactly what its supposed to do.

My settings;

lookahead: 20 (any more seems to do nothing for me, less makes corners sharper but slower)
cv dist tol: 10 (I use millimeters and 3000 feed rate usually, 10 is my sweet spot, less than this makes it jerky/exact stop and more makes the corners become too rounded)
cv angle: 90
cv feedrate: off

My motor tuning is only like 3000 velocity and minimum accel (which is like 12.5 or something).

Everything works fine as it should. With my next machine I'll beef the vel/acc up and then arc ouput should be fine as normal but until then this works great.

Offline ger21

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Re: Constant Velocity solution for some
« Reply #1 on: January 18, 2013, 10:32:03 PM »
Try these settings.
CV: On
CV Feedrate: Off
CV Distance: Off
CV Angle: 181
Plasma: Off
G100 Adaptive: Off

These settings should give you smooth motionwith arcs in your code, which is preferable to the workaround you're using.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Constant Velocity solution for some
« Reply #2 on: January 19, 2013, 01:53:00 AM »
Cheers but already tried it, and every other method in the 50-somewhat cv threads.

I believe my own problem is lack of vel & acc, which will be fixed in the next machine i build.

Thanks anyway.
Re: Constant Velocity solution for some
« Reply #3 on: March 11, 2018, 01:15:04 PM »
ger21 I use your 2010 screenset, by the way I love it works great. These CV setting you mention are they set in the general config section or in the settings section of your screenset, or both? I ask because I get rounded or cut off corners on square corners, especially on text. Thank you
Safe machining everyone

Offline ger21

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Re: Constant Velocity solution for some
« Reply #4 on: March 11, 2018, 01:47:19 PM »
ger21 I use your 2010 screenset, by the way I love it works great. These CV setting you mention are they set in the general config section or in the settings section of your screenset, or both? I ask because I get rounded or cut off corners on square corners, especially on text. Thank you

Both. You basically want to turn off all CV settings, except Stop CV on Angles in general Config. Start with an angle of 89, but you may need to play with it if you still see rounding.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html