Arc confusion


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Thread: Arc confusion

  1. #1
    joherl's Avatar
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    Question Arc confusion

    Hi!

    I am having trouble with G02/G03 with IJK method.

    This is the arc i am trying to define:



    This is my attempt at the gcode

    Code:
    M3 S4000 ;
    G90 G21 ;
    G0 Z0.500 ;
    G0 X5.900 Y0.000 ;
    G1 Z-0.700 F50 ;
    G18 G03 X4.100 Y0.000 Z-0.700 I-0.900 J+1.2 F50 ;
    G0 Z0.500 M2 ;
    It results in a tangetal arc like this:



    My mill does not accept M90.1 so I have to work with I and K as relative coordinates.
    I don't think i can use the R method since i sometimes need to move in Y as well.

    How can i alter my program to move in the arc shown in my first image?



  2. #2
    Community Moderator ger21's Avatar
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    Default Re: Arc confusion

    Not sure exactly what you are doing, but something like this.

    M3 S4000
    G90 G21
    G0 Z0.500
    G0 X5.900 Z-1.000
    G1 Y-0.70 F50
    G18 G03 X4.100 Z-1.0 I-0.900 K1.2 F50
    G0 Z0.500 M2

    Gerry

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  3. #3
    Flies Fast Superman's Avatar
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    Default Re: Arc confusion

    Mills use G17 for standard arcs where the centre point is on the same plane as each point on the arc...
    so G17 XY & IJ
    G18 XZ & IK
    the 3rd axis is sometimes used for creating a helical move

    so to correct your program... get rid of G18... or change to G17
    G2 is for clockwise movement.... G3 for CCW

    plus the M2 should be on the last line, by itself

    Try this for G17 .. using IJ
    Code:
    G21 ;    ( inch programming... by itself )
    G17 G90 ; ( safety lines.... XY plane, absolute )
    M3 S4000 ;
    G0 Z0.5 ;
    G0 X5.9 Y-0.7 ;
    G1 Z-0.7 F50 ;
    G02 X4.1 Y-0.7 I-0.9 J1.2 F50 ;
    G0 Z0.5 ;
    M2 ;
    Try this for G17 .. using R
    Code:
    G21 ;    ( inch programming... by itself )
    G17 G90 ; ( safety lines.... XY plane, absolute )
    M3 S4000 ;
    G0 Z0.5 ;
    G0 X5.9 Y-0.7 ;
    G1 Z-0.7 F50 ;
    G02 X4.1 Y-0.7 R1.5 F50 ;
    G0 Z0.5 ;
    M2 ;
    I also stripped trailing zeros, as they are not necessary

    Last edited by Superman; 06-12-2019 at 08:27 AM.


  4. #4
    joherl's Avatar
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    Default

    Removing feedrate from the G03 instruction seem to work in the simulator at least. I am writing a python program that generates this code thus the trailing zeroes. I will use it to engrave text in a groove. That is why i use G18 (XZ plane) and the additional Y coordinate.

    This code works in the simulator:

    Code:
    G21 ;
    M3 S4000 ;
    G90 ;
    G0 Z0.500 ;
    G0 X5.900 Y0.000 ;
    G1 Z-0.200 F50 ;
    G18 G03 X4.100 Y0.000 Z-0.200 I-0.900 K1.200 ;
    G0 Z0.500 ;
    M2
    Does it look OK?



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Arc confusion

Arc confusion