Re: G02 / G02 I and J arguments

Hi Larry,

Think of the I and J as offsets BACK TO the center! I think Ballendo
posted some good descriptions of G02/G03 some time ago. I use Vector
CAD/CAM to generate Gcode, and as a tool to learn EXACTLY how these arcs
work. You can eval Vector (and BobCad), and learn a LOT that way!

This command draws an arc clockwise from 67.5 deg. to 315 deg. First we
move to the start of the arc (G00), then we cut TO the X,Y of the G02
command. In the arc command, I denotes the X offset to the CENTER of
the arc, and J denotes the Y offset.

N1000 (#3 CW 67.5 -> 315)
N1005 G00 X 0.1913 Y 0.4619
N1010 G02 X 0.3536 Y -0.3536 I -0.1913 J -0.4619

I'm told that most newer controllers CAN handle full circles.

N1100 (#1 CCW 360 circle @ 67.5)
N1110 G00 X 0.191 Y 0.462
N1120 G03 X 0.191 Y 0.462 I -0.191 J -0.462

Notice that the G03 X,Y destination is the SAME as the place the arc
started!

Sounds like you're writing an HPGL to Gcode program! Could be useful!
The early CAD programs I was getting HPGL output from only used the
minimal commands. ARC's were drawn by a set of cords.

I don't care much for the 'R' variation of the command. It can't do
large arcs!

Hope this helps a little. I'd like to hear more about your program.
Contact me off line if you wish.

Alan KM6VV


Larry Edington wrote:

>
> Could someone explain to me how the I and J values are used on the circular interpolation commands?
>
> I understand the G02 and G03 commands when using the R "Radius" argument but haven't found a good example of the I and J calculations necessary for arcs. I understand if you need to do a 360 degree circle, in G code you have to split it up into a G02 and then a G03 command.
>
> I'm trying to convert an HPGL AA ( arc absolute ) command to it's G code equivilent. AA gives you X and Y center along with the arc's angle in degrees.
>
> thanks,
> Larry E.