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GRBL Error 33
Users of this postProcessor reported that occasionaly, it throws an Error 33 in GRBL. This error means that the start-point and end-point of an arc (G2, G3 with IJK words) do not have the same distance to the center of the arc... So GRBL doesn't know how to construct a circle-arc through these 3 points...
GRBL throws this error when : When the arc is projected on the selected plane, the distance from the current point to the center differs from the distance from the end point to the center by more than (.05 inch/.5 mm) OR ((.0005 inch/.005mm) AND .1% of radius).
I think the problem may be the right-hand side of the OR : for very small arcs (either a small radius, or a small angle) it is possible that with 'only' 3 decimal digits, a rounding error results in this condition to evaluate TRUE.
Why would you use those very small arcs ? I think it can happen in 'adaptive clearing' where Fusion calculates a toolpath to clear as much material as possible with minimum time and stress to the tool...
So how can we solve it ? There are 2 parts to a solution:
- Increase the number of digits, as more resolution will result in smaller rounding errors. I've decided to set to (maximum) 4 decimal digits for mteric/mm and 6 for imperial/inch. As Fusion will 'trim' these numbers, it will not add trailing zeroes, so in most cases it will not lead to more digits and bulky gCode.
- Increase the minimum size of arcs. Any arcs below a certain minimum size will be linearized, ie. replaced with a chain of linear segments. I increased these settings to around 0.5 mm, a value below any intentionally designed arc.