BUG: Probable rounding error in offset value arguments to G2/G3 G-code.

[tlum08619]

The I, J and K arguments to the G2/G3 commands represent an offset from the Start X, Y, and Z (respectively) to the arc center point, and must be an equal distance from the End X, Y, and Z points. There is an allowable tolerance of 0.05 inch OR (0.0005 inch AND 0.1% of radius).

For example:

N111 G2 X0.1563 Y0.246 I0.1562 J0

The origin is [-0.1563, 0.246, 0.1], so the following is the math:

Start           End                      Arc Center      Distance to Center			
X       Y       X       Y       Distance X       Y       Start   End     R-Error R-Error %
-0.1563  0.2460  0.1563  0.2460  0.3126  -0.0001  0.2460  0.1562  0.1564 -0.0002 -0.13%

This fails on the grbl controller with the controller specific message:

(error:33) Motion command target is invalid.

Changing the line to  "N111 G2 X0.1563 Y0.246 I0.1563 J0"  calculates like so:

Start           End                      Arc Center      Distance to Center			
X       Y       X       Y       Distance X       Y       Start   End     R-Error R-Error %
-0.1563  0.2460  0.1563  0.2460  0.3126   0.0000  0.2460  0.1563  0.1563  0.0000  0.00%

...and the file runs correctly. I can't say if this issue is with Fusion 360 core, or if it's related to one or more of the post modules, which in this case is grbl.cps v43881.

The problem lines are:

N111

N117

N123

This G-code is the Post from the 2D Contour in the Mill - Front setup, and is the finishing passes in that operation.