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G-Code, CAD, and CAM discussions / G2 or G3 moves in the XZ plane

« on: October 09, 2009, 03:25:39 PM »

I am trying to do a circular tool path in the XZ plane but I think I may have a bug in my MacH3   I have version 1.84.001.   I know it is old but it has been working fine for me up to this point.   I have a vertical mill that I use in a pinch as a vertical lathe.   I want to cut a spherical radius on the end of a shaft.   Lets say the shaft is 1" dia and the stationary cutting tool moves in the x axis.  Positive X direction of the tool will move it into shaft.   When Y = 0 the cutting edge of the tool is on the center line of the shaft.   When X =0 the tool is just touching the outside diameter and when Z= 0 the tool is at the bottom end of the shaft.   

So lets say I have the following  g-code:

G0 X0 Y0 Z0
G18 ( TO SET THE XZ PLANE)
G0 X-.1  (FOR CLEARANCE)
G0 Z-.5  (MOVE SHAFT DOWN TO START OF CUT POSITION)
G1 X0 F5    (BRING CUTTER IN CONTACT WITH SHAFT)
G3 X.5 Z0 R.5  (THIS SHOULD GO THROUGH 1/4 OF AN ARC AND CUT A SPHERICAL RADIUS ON END OF THE SHAFT.)

However, what happens is if you had a piece of paper on the stopped spindle and a pencil in place of a cutter it would scribe two complete circles 1" in diameter.    The X axis goes in and out twice while the z axis goes up and down twice and then finishes up were you would expect at X.5, Z0.   

If I change the code to do the same thing in the X and Y plane  and substitute Y for Z it works correctly.

G0 X0 Y0 Z0
G17
G0 X-.1 
G0 Y-.5 
G1 X0 F5
G3 X.5 Y0 R.5  (This goes through 1/4 arc with a radius of .5")

Thank you

Lou Cetrangelo
Saint James, NY