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Move the bed up/down instead of the router ?

Discussion in 'Concepts and Ideas' started by KronBjorn, Aug 23, 2016.

  1. KronBjorn

    KronBjorn New
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    Hi,

    Are there any designs that move the bed up and down, instead of the router head ?

    Maybe with four lab-jacks or similar ?
    It would make the z-axis a lot simpler I think,...

    Thank you,
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Here's one I suggested a while back. It offers depth without the loss of rigidity from dangling down a long z-axis. The basic concept uses 4 C-beam actuators connected by a single belt to a stepper mounted at the base. Plywood sides attached to the vertical C-beams give the system its rigidity. It could also double as the world's most robust 3D printer although it probably wouldn't be very zippy.

    Suggestion.jpg
     
  3. KronBjorn

    KronBjorn New
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  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    The problem with using 4 separate motors is connecting them to a controller. Most controllers only have connections points for 3 to 5 steppers and such a design would require 7. While you could double tap a couple of the connections it can be a risky proposition should one of the steppers get out of sync. Using a single stepper and a connecting belt is also a far more cost effective method, a method which several of the larger printers over in the 3D Printer section use.

    Sketchup
     
  5. KronBjorn

    KronBjorn New
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    Those are very good points :)
    My 3D printer almost tore itself apart when two steppers got out of sync !

    What is the longest you can have a drive belt, do you know ?
    And could four lead screw carry the weight of the base plus material, or had you planned on some weights/springs ?

    Thanks,
     
  6. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You can get gt2 belts up to 2.2 meters from SDP/SI and 1.5 meters from Robotdigg. Other sizes have different max lengths.

    Just choose a screw appropriate to the load. I'm not a big fan of the TR8x8 screws for the Z-axis as they seem a bit too aggressive for an axis that doesn't go very far or need to get there very fast. I'd be more inclined to go with something along the lines of a TR10x2 which should carry just about anything and you don't have to worry about the screw turning the motor when the motor powers down.
     
  7. KronBjorn

    KronBjorn New
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    I think I might go for something like this:
    draft.png
    A wooden frame, with v-slot linear rails, and one NEMA with one or two belts driving the four z-axiz lead screws.
    I am a bit unsure if simple bearings can carry the axial load of the lead screws ?

    (I apologize for the rendering, I only know OpenScad (guitar for scale))
     
  8. Rick 2.0

    Rick 2.0 OpenBuilds Team
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  9. KronBjorn

    KronBjorn New
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    Ah, excellent, that's what I need :)
    Did not know they existed.
     
  10. dean knipping

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    I don't know how something like this would actually work because you are going to be limited by the height of the gantry. Yes you can have a long bit but you still have clearance issues. for a printer there wouldn't be an issue because you are doing an additive process then
     
  11. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You will only be milling the top surface of whatever you put in there. If you've got a 2" bit you will only be milling the top 2" of the object no matter how thick it is. The best example would be engraving the top of a fairly substantial (already assembled) jewelry box.
     
  12. Metalguru

    Metalguru Veteran
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    If you use separate stepper driver modules you can easily drive 4 modules/motors from a single set of Arduino outputs. Having said that, you may run into a bit of an issue with the maximum current sink capability of the Arduino outputs, but a simple transistor driver like a ULN2008 or even just discrete Mosfets would easily be able to do the job. Leveling the bed would be a challenge, however, since you could not independently control the motors. Leveling would be a manual process of turning the motors by hand.

    MG
     

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