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  1. #1
    Hi all,

    I nearly crashed my machine and have no idea how. Perhaps one of you guys may have some idea what went wrong. I was cutting a circular pocket in the plastic as per the photo. The plastic is 50mm thick I had cut 25mm deep fine in a series of 7 passes, it went fine I then cut another 25mm deep zeroing the z 25mm below the top of the part that was fine but I had not got quite deep enough so I had another go on the 6 or 7 pass things went wrong real quick.
    The only thing I can think is perhaps I touched my mouse or shuttle and it override the code if that is possible. The part was secure in vice so it did not work loose. I have tried the code again directly above the part 3 or 4 times I would think and all seems fine. Perhaps one of you guys will know where I most likely went wrong. It dived into the bottom right part of the job an tripped the machine which was very lucky

    Thank for any help

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  2. #2
    are you using mach3 ?

  3. #3
    Hi Blackrat,

    Yes, I am using mach3.



  4. #4
    Did you try sending it back to Zero after it happened.? This would tell you if it lost steps as it would go back to the wrong place. Which would be the most likely cause, if not then it's a little worrying because if G-code is fine it means Mach went Awol which shouldn't happpen.!

    Thou to be honest I'd be more inclined to say it just lost position thru missed steps maybe due to heavy load with possibly too high feedrate? I'd take a guess and suggest you may have the motors slightly over tuned possibly.?
    The fact it cut air fine doesn't mean your motor tuning is Ok. You could just be on the edge with motor tuning but not enough to stall motors but enough to loose steps when under a heavy load and/or too high feedrate.

    Post the settings for your motor tuning and give spec of the machine and I'll take a look.

  5. one thing i can think of is that you shifted Z0 25mm below the part and you did not change the quote of safe Z, where the rapids movements are.

  6. #6
    Quote Originally Posted by gianluca_g View Post
    one thing i can think of is that you shifted Z0 25mm below the part and you did not change the quote of safe Z, where the rapids movements are.
    No unfortunatly that wouldn't explain the shift to the side and also Safe Z is Machine coordinate position not Work coordinate. It has nothing to do with the parts your cutting other than it lifts the Z axis to a safe MACHINE coordinate position before rapid moves.

    This will be either Mechanical slippage of a coupler or motors are over tuned and it's loosing steps/position while cutting.
    Last edited by JAZZCNC; 05-06-2015 at 08:33 AM.

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  8. #7
    Hi Jazz,

    Cheers very much for your reply here mate as I am very keen to get to the bottom of things. Unfortunately, I did not return to Z zero my initial thought was to get up and out of the material. I will know next time to try and return to zero, not sure how I should have done that x zero, y zero was centre of the hole. It happened on my Denford Triac, it seemed to me like the plastic was being cut like butter as I had been taking it what I thought was real easy! I will get the following later: Motor spec, Motor tuning, Feed and cut rates and I may also take a video cutting above the job so you can hear the motors.

    Many thanks


  9. #8

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    Last edited by suesi34e; 05-06-2015 at 08:34 PM.

  10. #9
    Hi Jazz,
    I am well out of my depth here perhaps you can get my head above water!
    I have found out some info, as per the manual on the machine max federate is X,Y 2500mm/min with the Z being 1000mm /min.Is states feedrate override potentiometer 0 to 150% but I do not know what that means.
    The guy that converted my machine has done many Triac’s and set the X & Y at 3000mm / min, Z axis at 2000mm/min I am asking him for the spec of the motors.
    To cut out the rectangular shaped part in the vice with radiusedc orners I used a federate of 1900mm/min, s4000, cut depth 3.8mm per pass.
    When it all went wrong the cutter was not cutting anything as it was working down progressively to the bottom of the hole that had already been cut inorder to just cut the last 1mm of the bottom left behind and break through it went wrong on the 2nd to last pass so it did not reach the remaining 1mm to be cut.
    I have attached photos of the motor tuning, video of the part being cut above job so motor can be heard, the spindle is a 1.1kw, DC, 1.5hp
    The X,Y and Z ballscrews 16mm (5/8”) diameter x5mm (13/64”) pitch
    Many thanks
    Last edited by suesi34e; 05-06-2015 at 08:30 PM.

  11. #10
    Ok well nothing looks wrong or excessively over tuned here. Thou I'm not a fan of micro stepping at 1000ms (1000/5mm pitch=200 steps per) as I find for some strange reason this setting can give more resonance which can affect motors than 800 or 1600. That said I'm pretty sure this won't be your problem.

    What your problem is I'm not sure and without being at the machine it's difficult to diagnose.

    First port of call is checking all mechanical coupler connections or pulleys etc connecting to motors and ballscrews.
    Then check the machine returns exactly back to X0 Y0 in work coordinates. (Not Home position) Make a Ref mark or set a DTI before starting code and check it comes back to same mark when sent to G0 X0 Y0 using MDI or Goto Zero.

    If it doesn't then your loosing steps for what ever reason. I was trying to take note when watching the video because at first I thought it was stepping over slightly when returning to start of each step down but the camera is shaky so hard to see. Looking again a few times I don't think it is. Plus if it is it's certainly not enough to cause that amount of steppover you had.

    If it does return exactly to Ref mark then I'm afraid it may remain a mystery until it either repeats it again or you realise it was something you did by accident.!!
    Possibly could be electrical noise affecting the Machine but again with so much error I don't think so.!

    Sorry can't suggest anything else it could be.!
    Last edited by JAZZCNC; 05-06-2015 at 10:23 PM.

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