Confused about G18, G19 Arcs

JimDawson

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I ran into something I don't understand.
The following code snippet is the lead in for a cut. The lead in is a G18 (XZ plane), with a G3 arc move. A G3 is a counterclockwise arc, but when standing at the front of the machine the toolpath scribes a clockwise arc. CamBam agrees with Fusion on the direction so I assume that the G code is correct and follows standard conventions. When standing in front of the machine the tool path is a reversed ''J'' with the tool starting at the top and following the ''J'' down which looks like a clockwise arc from the operator perspective.

In the XY plane arc direction is as expected when looking down on the part.

N4665 G17 (XY PLANE)
N4670 Z-0.175
N4675 G18 G3 X3.1825 Z-0.2 I-0.025 K0 (CHANGE TO XZ PLANE, AND SCRIBE A COUNTERCLOCKWISE ARC)
N4680 G1 X3.1575 F24
N4685 G17 G3 X3.1325 Y-1.0065 I0 J-0.025 (XY PLANE)


Here is an image of the tool path, Z is towards the top of the screen, X+ is to the right. The little yellow ''< '' is the start point.
1513964101670.png

Help me get my head around this. I guess the real question is: From the operator perspective is the direction backwards? Should I be looking at this from the machine perspective, in other words standing at the machine column? o_O
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point your thumb in the negative direction on the orthogonal axis. The fingers on your right hand are G02. fingers on your left are G03
 
My CAM deals with all that, if it simulates right it cuts right and I only examine code where the simulation looks hinkey ;-)
 
The machine cuts the part fine. The sketch above shows the tool path for the lead in. The problem is the operator :) I'm having trouble getting my head around the direction of the cut. To me it looks like it should be a G2 based on the direction rather than a G3.
 
Jim,

So if your in back of the machine, looks good ?
 
Yes, that is correct.
 
Are you saying the "right hand rule for G02" did not work?
 
If you MDI a G18 G2 and it travels a G3
It’s probably the machine software.
 
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