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Thread: G71 details

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  1. #1
    Join Date
    Oct 2008

    G71 details

    I'm writing a program that involves processing G-codes.

    I've tried to read up the details of G71 but am a little bit confused.

    If you look at the description, for example here:

    Fanuc G71 Turning Cycle - Helman CNC

    N50 G00 X106 Z5 M3 S800
    N60 G71 U10 R10 
    N70 G71 P80 Q90 U3 W0 F0.25
    N80 G00 X60
    N90 G01 Z-75 F0.15
    N100 G00 X200 Z100
    N110 G92 S1200
    N120 T3 G96 S150 M03
    N130 G00 X106 Z5
    N140 G70 P80 Q90
    N150 G00 X200 Z100
    N160 M30
    What happens after G71 stops executing line N70, i.e. after it has performed lines the lines/blocks 80 and 90 number times?

    Will the code then "fall through" those same lines as they 'happen' to be there?

    Is it customary to have profile there?


    And if they get executed doesn't that make G70 at line N140 superfluous as that has been cut already albeit at different speed?


  2. #2
    Join Date
    Feb 2011

    Re: G71 details

    the G71 is the ruffing cycle with the u leaving 3mm in the x and w leaving 0 in the z(second G71)
    the g70 is the finish pass to the programmed dimensions in line 80-90
    if you put 0 in the u (First G71)then the finish cut may not be needed but it will take a 10mm pass as the finish cut due to the U in the first G71
    when the G71 has completed the cycle with n80-n90 it will continue to n100 the n140 g70 should then read read the lines n80-n90 do them when finished it would come back to the line after the n140 - n150

  3. #3
    Join Date
    Aug 2009

    Re: G71 details

    G73 Example of different type cutting pattern...might help Fanuc G73 Pattern Repeating Canned Cycle Basic CNC Sample Program - Helman CNC

  4. #4
    Join Date
    Oct 2008

    Re: G71 details

    @rcs60 Thanks!

    Ok, that makes sense, but does this imply that the profile will always have to be after the G71 second line?

    This would also imply that any G-codes between the G71 the first block of the profile would be effectively ignored as the G70 would start and repeat from the block specified with the P word and after completion would continue, as you say, from the next line after the block specified with Q word?

    If the profile is not right after the G71 then after G71 completion this would effectively 'goto' the block specified by the Q word?

    I don't know why anyone would like to put it somewhere else but as an application programmer I need to look at all the corner cases...

    And I guess that there has to be a G71 before G70 although syntax wise it is kind of possible for the G70 to refer to a profile buried in some other part of the G-code file and not necessarily to the one just preceding it.

    To summarise if I got this correctly:

    After G71 completes the execution continues from the next line after the line/block specified by the Q-word.
    After G70 completes the execution continues on the next line after the G70 line.

    And actually the profile as specified by the P and Q words can be anywhere (but would be confusing).

  5. #5
    Join Date
    Feb 2006

    Re: G71 details

    May like to refer to this.

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