help please, plasma table ghost

My problem is that my machine cuts holes and arcs in the wrong spot sometimes. I have been having the issue for a while. And its always with holes or curves, never with straight lines or say a hexagon instead of a circle. During a cut say it cuts eight mounting holes, some will be a 1/4 inch off from where they are drawn to be. The problem is random in that i don't know when it will happen, but it is repeatable. You can move or rotate the part in sheet cam and regenerate the g code or just put a new piece of metal down and the problem will be exactly the same. Sometimes redrawing it in cad will fix the issue even if i draw it exactly the same was as the first time. I get no error codes or warnings from sheet cam.

My machine and setup: linuxcnc, sheetcam, progecad, pmdx breakout, keiling digital drives, timing belt reduction and drive, miller plasma,everything else homemade, square tube frame, extruded alum gantry, pieced together computer and control cabinet, etc etc..

Things i've tried: At first i thought my machine had the issue. checked calibration, zeros are always on the money, not losing steps, no backlash issues,
reasons to back up my mechanical reasoning, it cuts straight lines perfect no matter how many direction changes or start stops there are.

Second i thought it was when i mirrored an image in cad because in one instance all the originals cut fine but the mirrored pieces had issues. but i've since found that even without mirroring, i still have the issue at random

I've tried several post processors, ive saved my cad files in different formats, measured from a reference point on cad and sheet cam and they are the same, the live plot seems to be the same as in the image looks like it should but cuts it wrong.

I'm at a loss here and would love any help or suggestions even if they are wrong because maybe it will lead to an idea that is right. Thanks in advance. I will load pictures of the some cuts if it helps.

If you can get the problem to happen with a very simple small gcode file, someone here can test it to see if we have the same problem.
Sounds like a cam problem to me though. Is your sheetcam up to date (maybe it was a bug).
Also, is there any feature like making vectors invisible or something like that, which could throw you off?

ok , lets take it one step at a time, you say the problem is repeatable ? , by that do you mean it is at the same point where the problem arises if you run the code more than once .

which version of sheetcam are you using ?
if you can post your cad dxf file , the gcode which has the problem , and your sheetcam post processor and i'll take a look and see
and any notes on the point where it goes wrong .. gcode line number etc would help

Guys, thank you very much for your help.

Alan, that's a really good idea. I'll try to get it to mess up on a short run. Most of my files now are kinda long and its hard to tell where it happens because it doesn't cut in order to help reduce heating.

My sheet cam was v4.0.19 and I just updated to 20 but haven't tried it again.

Cncbasher, You're exactly right, if i run the same code more than once the problems are exactly the same. The shapes are all right, like the size of a circle will be correct, just in the wrong position. And if its off 1/4 inch it will be off 1/4 every time. Ill do like Alan suggested and try to get it to mess up on a shorter gcode. The ones i have now are kinda long. I really appreciate you taking a look at the files though. That's awesome.

Ill run a some shorter codes and try for errors and make note of them as i get home tonight and report back. And again, thanks guys.

ok , by what you say it could be sheetcam , although i doubt it , i use it everyday and not had that symptom , but these things can happen

check your PM and i'll give you my email add

Dave