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  1. #1
    See before and after pic :D

    I'm adding a new cpu to get absolute positioning from cheap Chinese digital scales rather than relying on the lead screws. A second opinion as to the tool location, one that can see backlash and compensate for it, I have about .003" in X and Y.

    The wiring was a mess and about to become a disaster so I moved all the electronics on to the back of the cabinet door. Tidy with easy access. Still need a fancy fixing for that conduit on the X axis motor, luckily the machine still works so no probs.

    Changed to solid state relays for the motor and suds pump so I'm switching 15 volts DC rather than 240 AC. Well, that was the plan, but then I realised I often want to be able to kill the steppers without having to turn on the PC so I stuck in a switch to off the 40V PSU. Back to switching mains, whaddya do?

    Next is handing control to the new cpu so it works on the USB rather than the printer port, then I can start fitting the scales.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. Quote Originally Posted by Robin Hewitt View Post
    See before and after pic :D

    I'm adding a new cpu to get absolute positioning from cheap Chinese digital scales rather than relying on the lead screws. A second opinion as to the tool location, one that can see backlash and compensate for it, I have about .003" in X and Y.

    The wiring was a mess and about to become a disaster so I moved all the electronics on to the back of the cabinet door. Tidy with easy access. Still need a fancy fixing for that conduit on the X axis motor, luckily the machine still works so no probs.

    Changed to solid state relays for the motor and suds pump so I'm switching 15 volts DC rather than 240 AC. Well, that was the plan, but then I realised I often want to be able to kill the steppers without having to turn on the PC so I stuck in a switch to off the 40V PSU. Back to switching mains, whaddya do?

    Next is handing control to the new cpu so it works on the USB rather than the printer port, then I can start fitting the scales.
    looks a lot better Robin. Wish I had that much space to start with!

    Can you explain 'cheap Chinese scales' further and how you plan to use them... I assume in place of encoders on the leadscrews? I was thinking on the lines of hacking apart a couple of cheap 200mm digital vernier units - that would give 0.01mm resolution (.0004thou), were you thinking along the same lines? If so, have you opened up one yet to see whats inside?

  3. #3
    Quote Originally Posted by Kip View Post
    Looks tidier for sure! Did you lose any traverse on the "X" when you mounted the motor?
    Good spot :D

    I lost 70mm, but I will get it back.

  4. #4
    Quote Originally Posted by irving2008 View Post
    I was thinking on the lines of hacking apart a couple of cheap 200mm digital vernier units - that would give 0.01mm resolution (.0004thou)
    The cheap chinese digital scale resolves 20480 lines per inch but it's hard to get the jitter down to less than 3 counts. I simply dump the bottom two bits and accept a stable 5120 counts per inch (approx .005mm res). Don't forget to clean the grit out if you buy one :D

    It's 2x24 bit two's compliment, here's a link...

    http://www.yadro.de/digital-scale/protocol.html

  5. Quote Originally Posted by Robin Hewitt View Post
    The cheap chinese digital scale resolves 20480 lines per inch but it's hard to get the jitter down to less than 3 counts. I simply dump the bottom two bits and accept a stable 5120 counts per inch (approx .005mm res). Don't forget to clean the grit out if you buy one :D

    It's 2x24 bit two's compliment, here's a link...

    http://www.yadro.de/digital-scale/protocol.html
    Thanks for that. Do you have a link to the 'scales' themselves? I was thinking on the the lines of creating a DRO for the lathe initially, then possibly CNC-ing it later but was being put off by the high prices charged for DROs generally. I have the means to write the software for myself and plenty of hardware available.

    Incidentally have you seen http://www.mysmart-tools.com/. Seems like a work in progress, but interesting nonetheless...

  6. #6
    I shopped around then bought my scales from Allendale

    http://www.allendale-hosting.co.uk/

    I made the mistake of buying a vertical mount scale for the Z axis, found you can't turn the display on without resetting the whole thing, I thought this might turn out to be a pain when testing so I dumped it.

    Allendale also do pretty anodized aluminium covers for scales. Means you can't see the display but does make them drip proof. The end mounts for the scales are a bit naff in pressed steel, so I remade them in aluminium.

    OTOH they do work...
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  7. #7
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,545. Received thanks 161 times, giving thanks to others 652 times. Made a monetary donation to the upkeep of the community. Referred 10 members to the community.
    Quote Originally Posted by irving2008 View Post
    a DRO for the lathe initially,
    Whats a DRO?

  8. #8
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,545. Received thanks 161 times, giving thanks to others 652 times. Made a monetary donation to the upkeep of the community. Referred 10 members to the community.
    Quote Originally Posted by CNCUK View Post
    Whats a DRO?

    Digital Read Out ?
    www.machine-dro.co.uk

  9. #9
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,545. Received thanks 161 times, giving thanks to others 652 times. Made a monetary donation to the upkeep of the community. Referred 10 members to the community.
    Quote Originally Posted by Kip View Post
    I managed to keep the traverse on mine with the casting I made. I'll make a new one soon to mount the nema34 motors.
    wow thats a really nice mount kip !

  10. #10
    Nice :D

    Did you make that without cnc? That was my problem, needed cnc to make cnc.

    I currently have both axial bearings at the handle end, want to change that to one either end so I can stretch the screw with cup spring washers.

    Haven't figured out how to do that on the Y axis yet, I think it will have to include it's own braces all inserted through a much enlarged hole where the spindle enters.

    How did you do the Z? I replaced the depth stop with a screw. I insert a fat bolt when I want to fix the quill to it. I nearly demolished it once, locked the spindle but forgot to remove the fat bolt before applying a sledgehammer to the drawbar. Luckily the screw was up to it. Jap screw :D

    best

    Robin

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