On Sat, 08 Nov 2008 23:13:00 -0500, you wrote:

>Comments and suggestions are welcome, but if you want to make I/J/K
>optional in absolute mode, be prepared to define exactly what will
>happen in all cases, and come up with very good reasons to justify the
>additional complexity.

Hi John - when I was taught NC in the eighties, I was told it was "bad
practice" to mix absolute and incremental moves as it can, and does,
lead to confusion. I've always used abs arcs with abs files and vice
versa.

I know inc arcs seem to be more popular in the USA, that's simply down
to lazy machine install engineers leaving a Fanuc default setting in
place <G>. 

The way Mach implements them is incorrect IMO. Good practice to always
define XY position AND I and J or it "should" error. It makes life much
easier on anybody trying to understand or repair your code, and makes a
"run from here" easier to interpret. I and J should not be modal, or
accept a current position as a value.

All my post processors output the full parameters for maximum
compatibility and readability.

For instance a clockwise arc in XY plane reads

G2 X~ Y~ Z~ I~ J~

Steve Blackmore
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