This question comes up a lot on hobby plasma tables, and the honest answer is not a single code. Firing a plasma torch is a machine-specific output, so the code that does it depends on how your controller is configured. Anyone who tells you “the” torch-fire code without knowing your machine is guessing.
Why there is no universal answer
The common motion G-codes are standardized, but many M-codes control machine-specific functions, and how a controller maps its outputs is up to its configuration. Firing a torch is exactly that kind of output:
- Hobby controllers running GRBL-style or Mach-style firmware often reuse a spindle-style code, so
M03fires the torch andM05turns it off, simply because the torch is wired to the spindle output. - Other systems use dedicated torch or output codes, sometimes
M07/M08-style or fully custom assignments. M20is not a standard universal code for this. If a machine uses it, that is a local assignment, not a general rule.
Where the code actually comes from
| Layer | What it defines |
|---|---|
| Controller manual | The documented torch-on / torch-off codes |
| Firmware config | Which output the torch is wired to |
| Post-processor | What code the CAM software emits |
| Machine wiring | The physical output being switched |
The torch-fire code is the output of those layers, which is why it varies and why you take it from your own machine rather than a generic chart.
What to do
Find the torch-on and torch-off codes in your controller’s manual and its configuration, and confirm with your post-processor. For the standard codes that are universal, like the common motion and spindle codes, recall practice helps: drill the common M-codes and common G-codes with beginner CNC code practice. A free tool like G-Code Sprint covers those; torch firing is machine-specific and is not something to guess at, especially given the safety stakes of a plasma arc.
Bottom line
There is no universal M-code to fire a plasma torch, and no standard M20 for it. Hobby setups often use M03/M05; others differ. Get the exact code from your controller’s manual and configuration. The other half of plasma’s code story, finding the plate and holding height, is covered in torch height control and G31 probing.
Sources
- GRBL wiki (firmware spindle/laser/output control)
- Wikipedia: G-code (M-codes are partly machine-specific)
- CNCCookbook: G-code and M-code cheat sheet
Frequently asked questions
What M-code fires a plasma torch?
It depends on the controller. Many hobby plasma setups map torch-on to a spindle-style code like M03 and torch-off to M05, because that is how the firmware is configured. Others use dedicated or custom codes. There is no single universal torch-fire M-code, so check your controller.
Is there a standard M20 for plasma torch fire?
No. M20 is not a standard universal code for firing a torch. If your machine uses it, that is a machine-specific assignment defined by its configuration, not a general standard. Confirm against your controller’s documentation.
How do I find the right torch-fire code for my plasma table?
Read your controller’s manual and post-processor or firmware configuration, which is where the torch-on and torch-off outputs are defined. A practice tool like G-Code Sprint helps with standard codes, but torch firing is machine-specific and not something to guess.
G-Code Sprint is a study and practice tool only. It is not a CNC simulator, machine controller, or safety authority. Always follow your instructor, employer, machine manual, and shop safety procedures.