GRBL Post processor for Sheetcam

Hey blokes,

I have been building a CNC plasma table for the last few months now, I had it running as a Router table first just to learn more about CNC machines first before I dived straight into Plasma. (I have had no CNC experience what so ever and I’m just an electrician so had to take baby steps to learn).

My machine is running an GRBL based Arduino platform based controller called a CNC Xpro V3 controller board which is basically just an arduino with everything packaged up neatly to use for a CNC machine.

So I have a relay off the spindle control circuit off that board which closes the switch on my plasma trigger.

I have got a few basic things cut out with it, using Fusion 360 and its inbuilt CAM software, but it only has basic plasma features no nesting or anything like that. So I downloaded sheetcam to see what its like and seems to have all the features that I need once I learn how to use it.

My question is, does any one know if there is a post processor for sheetcam that will support my GRBL based controller, or is it easier for me to convert my controller to mach3 so that I can also implement a THC?

Just a newby after some guidance please…


Nice build. :smiley:
I am at the same stage as you and thought I would add weight to your question in the hope that someone has already written a post processor for GRBL.

I have used a CNC shield on an arduino uno controlled from a headless Raspberry Pi which seems to work well.

Here are a couple of grbl posts I have. One uses a touch-off switch and the other not.

Awesome, thanks Les. Very much appreciated.

Trying to run the post without the touch and I get this error.

This post has thrown an error:
...home/chris/.SheetCamTNG-dev/posts/GRBL plasma.scpost:84: attempt to perform arithmetic on global 'firstPierce' (a nil value)
Do you want to edit the post?

Line 84 reads,

 if (pierceDelay + firstPierce > 0.001) then

I am not sure where the problem is.

Any help appreciated.

It looks like somehow you are missing a chunk of the post code. That should be line 204. Try downloading and installing it again.

Thanks for your response Les.

It is line 204 in the GRBL THC with scriber.scpost but it shows up as line 84 in the plain GRBL plasma.scpost

Using the same tool and operation I can post process the GRBL THC with scriber config but not the GRBL plasma config.

Oops, I didn’t realize that post had an extended first pierce. Look for:
function OnInit()
Afet that add this line:
firstPierce = firstPierceTime

That should fix it.

That did the trick, thank you Les.

Much appreciated. :smiley:

I am having the same trouble with my grbl plasma setup i tryed to down load the 2 post processors from this thread but it says i can’t anymore?? Can someone post a post processor that i can use with grbl please? I would make one but i have no idea what to do. Thanks

It looks like attachments were lost when I upgraded the forum. Here are fresh copies of the posts. Alternatively the development verison of Sheetcam comes with them.
GRBL THC with scriber.scpost (7.84 KB)
GRBL plasma.scpost (2.82 KB)

Thanks Les this is going save me alot of headaches. so the scriber one I can use a touch off with my “z” is this correct?

Yes, that is correct. If you go to Options->machine->post processor and click on the ‘Edit post’ button you will find a number of settings at the start of the file. These need to be configured to suit your machine. You can ignore the scriber stuff.

Ok easy enough one more question the switch for my floating head to find material do i just connect to the z limit or to some other input on the arduino? Like i think there is a probe input also

Connect the switch to the probe input.

Ok great thanks again Les now i can purchase the full ver knowing it will work.

Sorry for the reply on this “old” thread.

I found the GRBL THC with scriber.scpost very usefull for my cnc plasma. I’m using the openbuilds blackbox controller.
It reads the grbl code with no problem, but i find an error when cutting:

error 26: A G-code command implicitly or explicitly requires XYZ axis words in the block, but none were detected. [N0130 G02 10.0000 J-0.7500 F2500.0].

It seems like cutting smal holes is a problem, moving along straight lines is not…

Any suggestions?

Give this a try. To install this post, save the attachment to any convenient folder on your computer then run SheetCam and go to Options->machine->post processor. Click on the ‘Import post’ button. Using the box that appears, navigate to your post and open it. Go back to Options->machine->post processor and make sure your post is selected.
GRBL THC with scriber.scpost (7.73 KB)