I don't really know any thing about this, but I'd say that is the expected
behavior based on the description of G64 Path Blending:

"On G2/G3 moves in the G17 (XY) plane when the maximum deviation of an arc
from a straight line is less than the G64 P- tolerance the arc is broken
into two lines (from start of arc to midpoint, and from midpoint to end).
those lines are then subject to the naive cam algorithm for lines.[1]"

It sounds like your Q value is larger than the radius of your compensation
lead out, so the arc is broken up into two line segments. Since these line
segments are within Q of a linear move they are collapsed into one linear
move, and since this linear move is within Q of the original linear move
the whole path is collapsed in to a single linear move which is treated
essentially becomes a long compensation lead out move.

Just thinking out loud here, again, I am a complete noob so take this with
half a grain of salt.

[1] http://linuxcnc.org/docs/html/gcode/g-code.html#gcode:g61-g61.1

Kurt

On Thu, Feb 16, 2017 at 1:32 PM, Todd Zuercher <[email protected]>
wrote:

> I was playing arround with G41 and G42 in a simulation and I think I might
> have found a bug with the Naive CAM Detection.
> The shape I was simulating was a semi circle with the start/end point on
> the flat side and a single G2 arc move connecting the end points.
> The simulation behaves strangely. With a tool radius of .125" and .25" and
> staight G64 the tool path precisely followed the path (white and red lines
> over lapped). With G64P0.001, the same. The expected behavior is cutting a
> straight line parallel to the programed line offset the tool radius, cut an
> arc around that end point to connect to the offset path of the commanded
> arc cut. all good right.
> With G64P0.001Q0.2 there is odd behavior. It moves in a straight line from
> the beginning of the compensated straight line cut to the begining of the
> compensated arc cut completely ignoring the compensated end point of the
> straight cut. I know having such a large Q setting is a little odd. I also
> see simular behavior with G64P0.2 (no Q specified, same as Q0.2) only with
> more rounded corners.
> I seem to see the odd behavior when ever Q is about 2/3 or more than the
> tool diameter.
>
> --
>
> ========================================
>
> Todd Zuercher
> mailto:[email protected]
>
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