Interested in using two Z axes



  • Hello,

    I have been using a custom clay printer in which the print bed moves in the X and Y axes and the Z moves up and down. I am interested in building a dual extruder version of this design and would like to have whichever print head is not in use move up and out of the way a few millimeters. Is this possible? How would I go about this? I have attached an image of what the machine would look like.0_1541606402279_42992430_1960274954086958_6605468715855478984_n.jpg


  • administrators

    Currently we don't support remapping the Z axis as we do for the X and Y axes. However, I think you can accomplish what you want to do using M584 commands in the tool change files. You would assign both motors to Z, also assign the individual motors to U and V axes, but hide the U and V axes using the P parameter in the M584 command. When selecting a tool, un-hide U and V, move U or V down a few mm to lower the tool, then hide U and V again. When freeing a tool, do the same except move U or V up the same distance.



  • Many thanks, this sounds like a great solution. I will get to work now.



  • If the motion is just a few mm, could this not be accomplished with a servo?

    I would maybe drive two Z screws with a single motor, and use a bearing to allow the Z nuts to turn. Put gears on the nuts to mesh them together, and use a servo to drive the gears. When the servo rotates, the nuts turn in opposite directions, moving one head down and the other up. The gears would only need 1/4 turn range (Assuming T8*8 Z screws) to give a 2mm range, making for a 4mm difference between the two extruder heights. It seems like unnecessary complication to keep track of 2 different screws, and a potential to have things drift out of synchronization.

    A servo can have a relatively binary position, and even in the event of power loss, it will go to either one or the other position.0_1541610589143_gears.png

    Only a portion of these are actually necessary to get the required differential between the two heads, as I said, a quarter turn would achieve 4mm.
    0_1541611253009_partial_gears.png



  • @supraguy Many thanks for these insights. I will admit to having no experience working with servos - having always used stepper motors in the context of 3D printing. I will look into this as well with some students in engineering (I am an artist/teacher who ended up building printers).

    Each Z axis weighs a lot - not sure if that matters - I would guess there are various size servos and some can carry a lot of weight. The print arm is made of aluminum and it carries a large tube of dense heavy clay. I have attached an image of the single extruder version. 0_1541612916290_00000PORTRAIT_00000_BURST20181006111145298 (2).jpg



  • The servo need not carry any weight at all. In this case though, the bearing that allows the gears to rotate will need to bear the weight. Since the servo would be raising one, and lowering the other, it should only ever have to lift a difference in mass between the two. It would also be using the mechanical advantage of the lead screw in that (Plus a 2:1 gear reduction if it's as per the diagram that I have here.)

    This would have the gears being attached to the Z lead screw nuts along the large holes in the centre. The gears would then attach to the extruder gantry via a bearing that would allow rotation.

    When the servo (Attached to the small gear) rotates, it would turn the two large gears. One of these would raise by 2mm and the other would lower by 2mm.

    One drawback to this is that the gears would be relatively large, to span the gap between the 2 Z screws, and there would need to be room to allow this for the towers, however, you might be able to make those gears smaller if for example a smaller difference in height is acceptable, and you only need 1/8 of a revolution instead of 1/4.

    This might be overcomplicated as well, and a simpler see-saw configuration balanced on a single lead screw tower might be enough. It would certainly be easier to build.



  • On another note, the clay extruder is brilliant, I love it. I assume that the resultant prints would be kiln fired to make ceramic objects. Do you find that there is any issue with trapped air in between extrusion lines/layers?

    At one point, I was looking at trying to extrude paraffin wax in order to do lost wax casting of metal objects, and thought of something like this as an alternative to a pellet hopper extruder which just doesn't seem to work tot he same kind of tolerances that I'd like.



  • @supraguy Many thanks! Yes, the pieces get fired, glazed, etc. We use typical clay you might use for pottery making or sculpture from our ceramic studio. The material is incredibly cheap, so we are looking at scaling up a lot. No problems with trapped air - usually those issues in clay have more to do with excessively thick clay that is unable to dry properly. With printing we can be super specific about wall thickness. If you are interested here's a bunch of objects made with this tool: link text . . . and a forum with tons of info on clay printing: link text

    Many thanks again!



  • Clay printing is so cool. I'd love to get my hands on one. Thanks for the links.


 

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