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  1. #1
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    Default Anyone used Power Feed setup for CNC?

    Factory neighbour has a large Hafco mill (BM-40 or 30) that he has asked about adding some CNC abilities to. He is not real computer savvy, so I will be looking for a non-PC based solution. Maybe a tablet, or LinuxCNC on an embedded device.


    The easy way would be to add big stepper motors and some toothed belts, but that prevents manual use unless they are disconnected again.



    I'm looking at the Power Feed motors, and DRO scales, and wondering if LinuxCNC could be configured to use these already attached motors instead of steppers?




    (I know real CNCs use DC servos, and high end ones also have additional closed loop feedback, but has anyone ever heard of one without direct feedback from the screw motors?)

  2. #2
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    Default

    I can’t see that being possible - backlash and lack of ability to control small movements would be the killer.
    While it may be possible to control large movements with feedback from the scales, I can’t see it working with the relatively large on/off movements from a typical feed motor.

    Aside from the technical challenges, there would be a huge time investment to get a DIY machine to the “unskilled operator” level.
    If you didn’t get it all the way there, you would be supporting it forever.

    Personally - I wouldn’t touch it with a barge pole!!

    Proper conversion with ball screws etc for your own shop - maybe, but definitely not for a customer.

    Steve

  3. #3
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    Default

    As Steve said, without knowing either how many steps the motors are doing or having any way to repeatably and controllably energise them like a servo or stepper you can't make anything remotely functional. Even if you have the positional feedback from the scales.

    Sent from my SM-G973F using Tapatalk

  4. #4
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    Default

    Thanks Steve. Backlash is indeed the issue with existing (Acme thread?) screws.

    (and "hunting" would be the issue with scale based closed feedback)



    Some of those power feed enclosures have speed control levers, instead of the old left/off/right lever.
    I'm not sure any of the free software supports speed control, plus backlash compensation, plus closed feedback, though



    The only CNC machining actions he asked for are milling circles and rectangles. Which is why I considered the hackiest solution.

  5. #5
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    Default

    Milling an accurate even accurate ish circle is the hardest part of a 3 axis cnc machine. All the early point to point machines that still used trapezoidal screws could do lines and pockets okay a lot of them used multiple electronic clutch packs to take the drive from a single DC servo. Moving multiple axis simultainiously was impossible. To avoid hunting the clutches released very quickly triggered by the control. They also had hydraulic axis clamps that clamped all the non moving axis.

    I suspect with your proposed idea entering corners of pockets would be a regular hand grenade experience of smashed endmills and he would be having to manually lock all the non moving axis all the time.

    Sent from my SM-G973F using Tapatalk

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