# Machsupport Forum

## Mach Discussion => General Mach Discussion => Topic started by: flick on April 22, 2010, 02:34:24 AM

Title: g02/g03 reversed with g18?
Post by: flick on April 22, 2010, 02:34:24 AM
Title pretty much says it.  As an example, I would expect this code:

G91 G18
G02 X-2 I-1

to begin movement in the -Z direction, bottom out at Z-1, X-1, and then start moving in the +Z direction finishing at Z0, X-2. In other words, clockwise circular interpolation. To get that behaviour I have to instead use G03.  ??? In G17 mode this isn't a problem - G02 is clockwise, G03 is counter-clockwise, as expected.

I'm using Version R3.042.029 (the current Tormach distro)

It's not really a big deal to work around, but I rather dislike having to be cognizant of it all the time - I'm using it a lot right now for the work I'm doing.
Title: Re: g02/g03 reversed with g18?
Post by: ger21 on April 22, 2010, 05:51:11 PM
Make a fist with your left hand and your thumb sticking out. In G17, point your thumb Z+, and your fingers are pointing clockwise.

For G18, point your left thumb in the Y+ direction. Your fingers are pointing in the clockwise direction. Opposite of what you're expecting. And correct. :)
Title: Re: g02/g03 reversed with g18?
Post by: flick on April 22, 2010, 06:30:43 PM
Got it.  When I'm standing where the operator normally stands, I'm looking at the XZ plane from the negative end of the Y axis, unlike the XY plane, which I look down upon from the positive end of the Z axis.  Likewise, if I arbitrarily stepped around to the left end of the table (X-) to look at the YZ plane (G19) it would also seem counter-intuitive, but if I were to step around the right side of the table (X+), it would behave more like I expect.

Good lesson.  Thanks.