1. #1
    I have analogue drives (DQ860MA) and when switching on there is a thud from the steppers depending on how far they are away from a whole step and the ballscrew rotate slightly. Normally this is fine as I home the machine etc. but on a recent job I was surfacing a part and had to stop part way through. I wanted to keep the Z height exactly where I left off so I attached a DTI to the Z axis switched on (which moved the needle slightly) and then I jogged it back to zero.
    Out of interest is there any way of knowing before switching off how far the stepper is from a whole step? I know some drivers have the feature of remembering which micro step they are in but is there any other way of knowing using the drivers I have now?
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #2
    Clive S's Avatar
    Lives in Marple   Stockport, United Kingdom. Last Activity: 11 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 2,308. Received thanks 402 times, giving thanks to others 35 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    I would have thought that if you saved the fixture in Mach as you was shutting down then on restart homed the machine it would be correct.
    ..Clive
    The more you know, The better you know, How little you know

  3. #3
    Nope without the phase feature of the drive then it's not something easily done. Thou if you use the Enable of the drives then some times it can help or remove the twitch.!

    Best way is like clive suggests. Either save the Work offsets or write the Z axis position down and return to it after homing. It wouldn't be hard to knock up a on screen button to save the Z axis current location and another to return to it if required. Personally I'd write it down then use the MDI if need an exact location.
    Last edited by JAZZCNC; 28-12-2015 at 01:30 PM.

  4. #4
    Good info thank you - confirmed my suspicions
    On this occasion I was trying to get the most accurate position so used the DTI to be extra sure!
    I do normally write down the machine coordinates of the work origin as I've never got the save fixture on mach3 exit to work. Maybe I'm doing it wrong but when I switch mach3 on again the numbers in the DRO appear random.
    So I home the machine, MDI to the previous coordinates then zero the DROs.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  5. #5
    The numbers will appear random until you have homed. Then when you push go to Zero it will go back to XYZ Zero offset in work coordinates or if you type in the exact coordinate you finished at in mdi it will go there.

    Maybe your misunderstanding the Work Offset.? It doesn't save the exact location you turned the machine off at. It only saves the Work Zero offfset in relation to Machine coordinates. This is why you must home first. Then you can go to Work Zero offset or any location you type relative to Work Zero.
    Last edited by JAZZCNC; 28-12-2015 at 02:21 PM.

  6. #6
    Just tried it and it works! I was expecting it to pick up where I left off it doesn't work like that - homing and mdi to zero and I'm back. Part of my problem was that I often don't home the machine especially for small jobs
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  7. #7
    Clive S's Avatar
    Lives in Marple   Stockport, United Kingdom. Last Activity: 11 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 2,308. Received thanks 402 times, giving thanks to others 35 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    Part of my problem was that I often don't home the machine especially for small jobs
    It takes less than a minute to home and whatever if you don't. its a no brainer !!
    ..Clive
    The more you know, The better you know, How little you know

  8. #8
    Quote Originally Posted by routercnc View Post
    Just tried it and it works! I was expecting it to pick up where I left off it doesn't work like that - homing and mdi to zero and I'm back. Part of my problem was that I often don't home the machine especially for small jobs
    It's a good habbit to get used to homing the machine when first turned on. Most industrial machines won't do anything until the machine is referenced home.

    If you did want to save the location at shut down then it wouldnt be too hard to knock a script up which did this. Then have button to take you back after homing or even include it in the Homing script. (thou not good idea.!)

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