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Confused about G18, G19 Arcs

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JimDawson

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#1
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
.
.
 

Karl_T

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#2
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
 

JerryK

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#3
What are you cutting Jim ?
A sketch would help
 

magicniner

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#4
My CAM deals with all that, if it simulates right it cuts right and I only examine code where the simulation looks hinkey ;-)
 

JimDawson

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#5
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.
 

JerryK

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#6
Jim,

So if your in back of the machine, looks good ?
 

JimDawson

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#7
Yes, that is correct.
 

Karl_T

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#8
Are you saying the "right hand rule for G02" did not work?
 

JimDawson

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#9
Are you saying the "right hand rule for G02" did not work?
I think it does Karl, the problem is that my brain is not working. :faint: :grin:
 

JerryK

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#10
If you MDI a G18 G2 and it travels a G3
It’s probably the machine software.
 

JimDawson

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#11
The machine follows the predicted tool path. It's my feeble brain that is the problem. :)
 
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