Use of G2/G3 not corresponding to expected

Jean-Baptiste

Hello everyone
I'm trying to get some circular interpolation trajectories with G2 and/or G3
I use the following code to for a part of my trajectory:
G3 X150 Y88.5 I150 J100
G3 X150 Y111.5 I150 J100
it should be a circle in counter clockwise but I've got lines (or it looks like lines and, worst of all, it goes in negative X and Y.
I'm a little fast to explain, if you need any other information, don't hesitate to ask.

alankilian

@Jean-Baptiste
THIS is a good GCODE previewer that I use for G2/G3

If I add a G0 X0 Y0 before your code I indeed get two partial arcs.

Can you describe where you think the centers of the circles should be and what the radius of the circles should be?

alankilian

Here are two examples:

; Make an anticlockwise circle centered on (0,0) with a radius of 10
; Move to a point on the circle's path
G0 X10 Y0
; Make the circle
G3 X10 Y0 i-10 j0

; Make an anticlockwise 90-degree arc centered on (0,0) with a radius of 5
; Move to a point on the circle's path
G0 X5 Y0
; Make the circle
G3 X00 Y5 i-5 j0

Jean-Baptiste

Thanks a lot @alankilian
Too used to CNC in which I & J are absolute position and not relative ones

Thanks for the Gcode previewer, it helps and will help a lot

dc42

@jean-baptiste said in Use of G2/G3 not corresponding to expected:

Too used to CNC in which I & J are absolute position and not relative ones

It's standard for I and J always to be relative to the starting position. https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=823374