Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: ajclay on September 24, 2009, 08:07:22 PM
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Hello, I've got a plasma cut quality problem and just can't get to the next step with it. Progress in all areas except for this. See attached photos. I've got some hesitation in arcs. No problem in circles, squares, triangles, or lines. Just at the end of one arc and the start of another arc, like in the 4in fleur-di-lis. Maybe a 15 - 20ms hesitation, just enough to see when the machine is running at 50 to 60in per minute. The faster The machine runs, the more outstanding the marks become.
I've got good repeatability to about .0005 - .001 and have good accuracy. I've worked on the motor tuning / velocity, and speeds till I'm at my wits end.
I'm using autocad 8 to make the drawing, save as a .dxf, import into sheet cam to post. I don't believe it's mechanical because of the time I've spent. I believe it's in something I've got wrong in Mach or it's the way I'm making the G-code.
Any suggestions would be greatly appreciated. I've been hammering on this problem along with other things for about a month.
Thank You! Aj
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I should of added the .dxf file just in case.
Aj
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Hi ajclay
looks like you're in exact stop mode. Add this: N0025 G64 (CV On)
Cheers
Ian
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Sterling,
I don't believe that turning CV on will help his problem. I suspect that already is using CV. I am having the same kind of problem with my Router CNC machine cutting solid surface material. I have not determined how to fix it. I think it is a signal problem. I have ruled out the computer. In my case the pattern is closer together and not random. His pattern is not random. I bet if he cuts a diagonal pattern like a diamond on its point or at a 45 degree. He will see the pattern also.
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Hi SailFl - I don't do "beliefs" or "suspicions" - I give it the best shot I can with the evidence available.... I also don't gamble - sorry. ;D
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General config screenshot shows CV is on and code doesnt have either G61 or G64 so unless some previous code put it in Exact Stop then it should be in CV. It is however best to always have G64 at the start of your code as this always makes sure that things will be done in CV (if that is what you need of course)
The clue may be in the faster you go the worse it gets, Its hard to tell from the pic and I know you said its not mechanical but are these gouges lining up with the axis? If so check for backlash.
Hood
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Mach, is in CV mode.
I'm going to give adding G-64 a try today.
I don't really have any backlash. I had another problem in the past when I just got the machine up and running (two months ago) and spent a good while checking backlash. The backlash has to be less than .001.
The machine has good repeatability and accuracy..
I don't want to be quick to say everything is perfect like so many, because I do have a cutting problem.
The notches don't show up on any other shape, even 45deg cuts. They only seem to serface on the 3 point arcs or ellips and line up with the nodes in the drawings. The hessitation can be seen with the eye at the end of the arcs. The arcs don't show a big change in direction. I could understand a sharp turn because of deceleration, but this is basicly going the same direction.
There's no doubt - The job is in the details!
Thanks for the suggestions, Aj
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Just looked at the code in Mach and there are very short arc moves which coincide with 4 out of the 6 points you are having issues with. Afraid I have no software here to view a DXF so cant see whats in that but kind of looks like that may be an issue.
Hood
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AJ - Don't work with plasma so I could be off base here. I opened your dxf file in AutoCad and noticed the center of your arcs in your fleur-de-lis (caught my attention because it is the symbol for my city) corresponded apparently exactly with the marks on your symbol.
I walked through your code and saw pauses within the arcs at their centers. Looked at your code and saw several lines in those areas that called for an a very slight straight line movement (G1) within the arc that should not have been there. I have edited most (maybe all) those lines out of the attached code.
My first thought is your cad software is adding a line at the center of the arcs
No guarantees that my observations or suggestions works.
Bob@BobsShop
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As it turned out I finally hit the nail on the head. The guy from CandCNC - (Tom) pointed me in the right direction.
He told me to turn off all selections in "General Config" "CV Control" and make sure that "Motion Mode" was set to "constant velocity".
I did that without and change in cut quality.
Here's the trick..... I had to use the "1024" screen, which I didn't have a clue about, go to the "settings tab" and turn off "CV Feedrate" . CV Distance, on or off didn't seem to make a difference with any of my problems, so the question remains on whether this should be on/off and what value it should have.
I instantly saw the improvment in machine motion.
No exaggeration - my machine will run 4 times faster on that little 4in part and without any vibration or shaking... 200in/min
Now I'm in business......
That CV Feedrate setting should be on the "plasma screen" if it's that important.
Thank you guys, I'll talk to you later.
Aj
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Great to hear you got it sorted, will have to try and remember that in case anyone else using a plasma has that issue.
Thanks for posting the fix :)
Hood
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Glad you got it sorted aj. I've been re-looking at your problem again today and just kept coming up with - CV is either turned off or it's not working - I just couldn't come up with anything else.
I took a look at your solution and I'm a tad surprised you're the first (plasma) user to raise this issue.
If it helps - I took a look and here's what actually seems (as far as I can tell anyway) to be going on. For some unknown reason and as you rightly say, the plasma screen doesn't have the screen controls for CVDistance and CVFeerate. BUT and here's the big BUT - it has the CV distance (invisibly) turned on and set to 0 - effectively turning CV off.
By loading in the 1024 set (the Mill set) which does have these CV screen controls, you were able to turn CV distance off and hence turn CV on.
I'm sure someone will tweak the plasma screenset and sort this one out in no time...
cheers
Ian
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Thanks for trying to explain things a little more. It's been a steep learning curve to say the least. I'm new to Mach3, New to Plasma cutting, and this is my fist machine to build. Servos, controllers, power supplys, electronics.... my brain is almost shorted out. I've been on this project for a little over 2 years and just now started cutting parts.
Take Care, Aj