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Thread: Arc Problems

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  1. #1
    Join Date
    Jul 2011
    Posts
    40

    Arc Problems

    Just got my new PCNC 1100 and am programming my first part on it and running into some problems. I am a 20 year veteran of G-Code programming but this is my first experience with Mach3.

    Heres a sample of my code

    G0G54X0.Y0.
    Z0.
    G1G41Y.25F20.
    G3J-.25
    G1G40Y0.
    G0Z.1
    G55X0.Y0.
    Z0.
    G1G41Y.25F20.
    G3J-.25
    G1G40Y0.
    G0Z.1


    OK. So what we have is cutting a .5 diameter circle in two locations using 2 offsets. The G54 cuts as expected with no problems but after I switch to G55, the machine will go to the correct G55 location but when it starts it's cut it goes to some crazy coordinates and makes movements that resemble nothing being programmed. This happens only in cutting movements. I have drilled in the multiple offsets with no problems. Am I missing something in Mach3 as far as format errors in my code? I know the code is correct for HAAS, FANUC, etc.

    Thanks in advance

  2. #2
    Join Date
    Jan 2012
    Posts
    714
    Check out screen 6 (Alt 6), and in the upper left hand quadrant is a setting for the IJ mode, there are two settings for it, I have had this cause the cutter to make large circles, nothing like what was in the program.
    mike sr

  3. #3
    Join Date
    Jul 2011
    Posts
    40
    Thanks. I'll check that out. But it still doesn't explain that it works with G54 and not G55. I haven't tried any other offset yet but I will this evening.

  4. #4
    Join Date
    Mar 2003
    Posts
    35538
    I think it may be a bug with G41 and offsets.
    Gerry

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  5. #5
    Join Date
    Jul 2011
    Posts
    40
    Quote Originally Posted by ger21 View Post
    I think it may be a bug with G41 and offsets.
    Is this a common issue with Mach3?

  6. #6
    Join Date
    May 2011
    Posts
    100
    Quote Originally Posted by bryanoates View Post
    Is this a common issue with Mach3?
    Yes, it doesn't work reliably with subprograms, G52, or G68 either.

    Part of the problem is that it works sometimes, just enough to make it useful. Then, when you attempt to do something else, it breaks, for no apparant reason, leaving you scratching your head and wondering why your code doesn't work.

    This drove me nuts on one particular program until I realized it. There is lots of discussion over on the Mach forum regarding this problem. Comp seems to be a particularily weak point of Mach. The workaround seems to be to calculate your own offsets directly, and don't use G41/42. If you code directly without comp, then multiple offsets, G52, G68, and subs seem to work OK. A bit of extra work, though, and tough on profiles with complex arcs.


    We can hope it will be fixed in V4, I suppose.

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