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  1. #1
    First had this problem in January on a Denford Microrouter driven by Mach3.. http://www.mycncuk.com/threads/13372...osing-position

    Replacing the BOB fixed the problem last time (or so I thought) but now it is back. The router has been in use about 8 hours a day 6 days a week since replacing the BOB. A few weeks ago the X,Y&Z just stopped mid cut with the spindle still running (spindle is controlled via a plugin) pressed the cycle start and the program ran fine. All appeared to be well until last week when it started losing steps again on all axis but more noticable on X.

    The fault is now present all the time except every now and then after turning everything on I can sometime jog smoothly for a few minutes before it shows. All connections to the BOB checked and the power supply is a constant 24volts. Nothing has been changed or moved and there is nothing else running in the workshop. The only other thing I can add is that since the fault has returned

    After searching the forum for a day the only pertinent commet I can find is one left by JAZZCNC
    Bob's are sneaky bastards they trick you into thinking they are fine so you go round in circles chasing other things but then you end up back at the BOb and soon has you change them out every thing works fine.!

    So would I be better off investing in a better BOB, and if so which one? This is what is in there now
    https://lozharroplures.co.uk/my_images/1.jpg

  2. #2
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 15 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 7,689. Received thanks 1,327 times, giving thanks to others 86 times.
    That still holds true but there are things you need to check and procedures to go through before you condemn the BOB.

    If it's just missed steps while in use and not when things turn on like Vacuum or Spindle etc, which could be electrical noise, the first thing to check is the mechanicals.
    It doesn't take much binding to stall a small stepper motor when rapidly moving from position to position so if you have a sticky axis this could be the cause. Try to take note which axis loses steps and whereabouts in the Job it loses steps, ie: Rapid moves, etc.

    If the mechanicals is good then it could be that you just have it over tuned and it's close to the edge where torque drops away, but only on certain moves like rapid moves.
    An easy test is to just lower the velocity in motor tuning slightly and see if it still loses steps.

    What is the velocity and acceleration in Motor tuning for each Axis.?

    I would check out the mechanicals first before doing anything else.

  3. #3
    Cheers,

    No vac on and tested today without power to VFD so I think I can rule that out.

    As it is losing steps in all directions (though X is most noticable) I am tempted to also rule out mechanical binding?

    I will look at the velocity and acceleration tomorrow and post settings/results.

  4. #4
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 15 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 7,689. Received thanks 1,327 times, giving thanks to others 86 times.
    Quote Originally Posted by ngwagwa View Post
    As it is losing steps in all directions (though X is most noticable) I am tempted to also rule out mechanical binding?
    It would be a mistake not to check it out.

    What machine is it again.?

  5. #5
    Denford Microrouter.

    Last time it was faulty I did clean all the nuts but it was only when I fitted a new BOB that it stopped knocking and losing steps.

    I have just been over to the workshop and regarding the velocity and acceleration settings X and Y were set at 3000 and 150. When first turned on (lo and behold) the machine jogged several times along X with no knocking. Set them to V=1000 and A=50 was knocking when jogged, Also tried 500 and 20 still knocking.

  6. #6
    I had a PC that would knock / lose steps on every 360 degree rotation of the screw on every axis.
    I re-installed windows and the issue was gone.

    It was an error with NT driver in windows that came up every so often.

  7. #7
    Quote Originally Posted by dazp1976 View Post
    I had a PC that would knock / lose steps on every 360 degree rotation of the screw on every axis.
    I re-installed windows and the issue was gone.

    It was an error with NT driver in windows that came up every so often.
    When I first had this fault I did try a completely different PC and it didn't solve the issue. On the other hand if the problem was as consistant as yours it may be easier to solve.

  8. #8
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 15 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 7,689. Received thanks 1,327 times, giving thanks to others 86 times.
    Maybe worth taking a video because missed steps don't really knock.? A knocking would certainly make me think mechanical.

  9. #9

  10. #10
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 15 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 7,689. Received thanks 1,327 times, giving thanks to others 86 times.
    Quote Originally Posted by ngwagwa View Post
    That's not missed steps. It could be something electrical or computer related with parallel port causing problems with the pulses, possibly? However, the first place I'd start is with Motor and pulley couplings, belts etc and checking out the mechanicals.

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