STV, Myplasm and Sheetcam oh my!

[broken]

Hi Guys, been using forums since the very beginning of the interwebs, it's where the real knowledge and information is.

We recently got an STV 5 x 5 table running the MyPlasm controller/software with a Hypertherm 45 torch.
While we've been able to get some usable stuff out of it there are some issues that no amount of turning the torch in the holder, speed, height, thc voltage, etc, will get rid of. Namely some of the holes are just trash both top and bottom, all we've been able to do is make them less bad so a bolt will drop through.

MyPlasm won't let you change the direction of the cut so it was suggested we try Sheetcam to reverse the cut direction and use it to generate the G-code.
After saving it as a .TAP file, which produces no errors, trying to load into MyPlasm (says it can do TAP files) results in 'file load error'.
I've tried TAP files from both the free and paid versions of Sheetcam with the same result.

Do I need a different post processor that is compatible with this controller/software? Is that a thing?
Do any of you agree/disagree that changing the cut direction can improve hole shape?

I'm not asking for perfect, just seems like my results are outside of what most of you would consider 'good'.
Thanks guys.

[djreiswig]

You need a post processor that formats the gcode correctly. There are a ton of them for SheetCam. I would guess there is one for myplasm, but I'm not sure.
If you're cutting the wrong direction that could definitely affect your quality.

[acourtjester]

Have you contacted Les with SheetCam about a custom post processor, he has done this in the past and with more people using Myplasm units.
I know there are members here that use that unit. Reversing the direction has its purpose and is used for different direction for inside and outside cuts, due to the plasma swirl pattern. Another thing does the Myplasm import .NC files these are another form of CNC files similar to .tap

[weldguy]

What direction are your interior circles being cut in? CW or CCW?

Can you post pics of your cut so we can see what your interior or small holes look like?

[broken]

Thanks for taking an interest fellas.
I have not contacted Les since I was using the trail version to test the direction theory, If it looks like it would help my problem I will certainly buy the license and ask for his help with the post processor.

The outside cut goes clockwise, the internal cut and holes go counter clockwise.
The one on the left is where we started, and the right is as clean as we can get with just speed, height etc. the metal is .120
and I've oriented them the same direction they were cut, the top is better than the bottom. Holes are .390 for .375 bolt

The next part I start to turn out will need to be tighter tolerance than these holes will seem to allow.
Am I asking too much or do you feel the direction will help here?

Thank you!

[acourtjester]

Ok you realize you can also plan how you cut a object, meaning you can cut on the line, inside the line and outside the line. This is controlled by the kerf diameter, inside the line for a circle shoud give you the correct inside diameter. And outside for the outer cut for parts. The one on the line can be used for metal scribing, drag knife, and some routing to exactly follow the line. Here is what a drag knife project look like.

[tcaudle]

While cut direction is important , cutting holes smaller than about3/8 needs special things. You first need to slow down the feedrate on those objects. In most cases you need to disable the THC . At the least you have to change the voltage setting because cutting slower causes the voltage to rise and will cause the torch to plunge . Typically you cut holes at about 1/2 the normal cut speed for the larger objects. I don't think you have any software control over the THC . Maybe there is a disable pin but I am not aware of it. If you use SheetCAM you have group the smaller holes using a separate layers and cut it with different parameters like feedrate. I don't think there are any other parameters like the preset volts, THC disable you can do out of G-code. The lead in type and feedrate should be settable along with the cut direction but you may find to get accurate holes you need more. The toolpath tracking built into the motion control software has a lot to do with how accurate the torch follows the cut path . Plasma in itself is not overly accurate and the kerf width changes with feedrates , air pressure, consumable wear and general motion capabilities (accuracy ) of the machine. general rule of thumb is about ..010 for most wire plasma. Fine cut on a Hypertherm will give you tighter tolerances but its not suggest on material thicker than 10ga. The myplasma is not a full 3 axis machine. Its basically an XY with a torch lifter you cannot control form a Z move in software. Thus the need for a special POST that has no Z moves . if all you want is to cut out shapes in plasma and tolerance is not important it does a pretty good job.

[Yotifab]

Did you ever find a solution to running sheetcam tap files with myplasm? I had contacted Les who said yes there was a post processor for sheetcam but I have been unable to find this processor as its not in the list in the program. Anyone have the post so I can import it?