On 01/15/2019 01:02 PM, John Figie wrote:
I Also want to add that John Elson seems to be saying the opposite of the
LinuxCNC gcode reference. Was that a mistake? Am I missing something?
http://linuxcnc.org/docs/html/gcode/g-code.html#gcode:g2-g3
"It is not good practice to program radius format arcs that are nearly full
circles or nearly semicircles because a small change in the location of the
end point will produce a much larger change in the location of the center
of the circle (and, hence, the middle of the arc). The magnification effect
is large enough that rounding error in a number can produce
out-of-tolerance cuts. For instance, a 1% displacement ....."
Well, I've been using EMC, EMC2, and LinuxCNC since 1998.
And, I never program more than 90 degree arcs, so have not
run into this issue. It is absolutely true that full
circles CANNOT be specified with the R form. I have no idea
how any particular post processor deals with this problem,
but it seems likely (since this is NOT a LinuxCNC-specific
problem, but due to the way the G-code language is
specified) that a good post would limit R word arcs to 90
degrees.
I use a bunch of C programs I have written over the years to
write G-code for specific operations (round holes, slots,
etc.) and these all use R word arcs in quadrants.
Now that the arc tolerance has been made easily adjustable
without recompiling source, it is a lot less of an issue.
Jon
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