This is an educational explanation of why beginners see crashes on a G00 line. It is not operating instructions or safety advice for your specific machine. Always work under your instructor or employer and follow the machine manual.
A G00 is a rapid: it moves to a coordinate as fast as the machine can. It does not cut, which is exactly why beginners are surprised when it crashes. The code did nothing wrong; it went fast to the wrong place.
The usual causes
Most G00 crashes trace back to a mismatch between what the program assumes and what the machine actually knows:
- Wrong work offset. If
G54(or whichever work offset is active) is set wrong, the machine’s part zero is in the wrong spot, so every rapid is shifted. - Wrong or missing tool length offset. The Z rapid assumes a tool length. If that offset is off, the tool rapids too low.
- Rapid into the stock or a fixture. A rapid planned for clear air becomes a collision if the stock, vise, or clamps are taller or positioned differently than assumed.
- Absolute vs incremental mix-up. With
G91(incremental) left active when the program expectedG90(absolute), a rapid lands somewhere completely different. See G90 vs G91 crash prevention. - A non-straight rapid path. On many controls a
G00does not move in a straight diagonal, so a path you assumed was clear can clip something.
At a glance
| Cause | What is actually wrong | The concept to learn |
|---|---|---|
| Wrong work offset | Part zero is in the wrong place | G54-G59 work offsets |
| Wrong tool length | Z assumes the wrong tool height | Tool length compensation (G43) |
| Rapid into stock/fixture | Path not actually clear | Clearance planning |
| Absolute/incremental mix-up | Mode not what the program expects | G90 vs G91 (modal state) |
| Dogleg rapid path | Path is not a straight diagonal | How G00 actually moves |
Why this is a recall problem too
Notice every cause is a code or concept you can know cold: what G00 does, how G90/G91 change it, what G54 sets. Beginners who can read G00 vs G01 and the common G-codes without hesitating are far less likely to misread a setup. Recall does not replace careful checking on the machine, but it removes the confusion that causes many beginner mistakes. Building that recall is what beginner CNC code practice is for. A closely related failure mode worth understanding is the Z-axis plunge crash.
Bottom line
A G00 crash is almost always a wrong number reaching a fast move: an offset, a tool length, a mode, or a path that was not really clear. Learn the setup codes cold, verify offsets, and use your machine’s safe-checking features under supervision.
Sources
- LinuxCNC G-code reference (G0, coordinate systems)
- Wikipedia: G-code
- CNCCookbook: G-code and M-code cheat sheet
Frequently asked questions
Does G00 cause crashes because it is a cutting move?
No. G00 does not cut. It crashes things because it moves at the machine’s maximum rapid rate, so a wrong coordinate, offset, or mode sends the tool somewhere fast, with no time to react.
What is the most common G00 crash cause for beginners?
A wrong or missing offset: the wrong work offset (G54 to G59) or a tool length offset that does not match the tool. The program is fine, but the machine’s idea of zero is wrong, so the rapid goes to the wrong place.
How can I avoid G00 crashes while learning?
Learn what each setup code does, verify offsets, and use your machine’s safe checking features under supervision. A practice tool like G-Code Sprint helps you recall what codes like G00, G90, and G54 mean, but it is not a controller or a safety system. Always follow your instructor and machine manual.
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.