Delta - 4th axis extruder

  • The recent addition of extra support axes for a delta, I have started to think about how to make optimal use of it. A couple of people seem to have played with the idea of mounting an extruder on such an axis à la flying extruder. In all the designs I have seen so far the extra axis was located between two regular towers, at the bed edge.
    If we assume the extruder is located perfectly at the edge of the printable radius and disregard necessary extra length for bends in the tube etc, the length of the bowden tube would have to be 1 bed diameter for this setup to work. For the delta I have been building for a while this would mean a 450mm bowden, which I still find quite long.

    This got me thinking about how this setup could be improved. First thing that came to mind is move the axis to the center of the bed. This would effectively cut the required bowden length in half to 0.5 bed diameter.

    A slightly more complicated approach would involve a rotating horizontal extension with a 0.25 bed diameter length. But one issue I could see arise here is the introduction of a severe twist in the filament. For example, printing a cylinder would keep rotating the entire thing, thus continually twisting the filament.

    In case 2 and 3 the axis itself would obviously have to be able to move up and down, not just a carriage riding along.

    /end wall of text 🙂
    0_1559081388920_2019-05-29 00.07.32.jpg

    What do you guys think?

  • administrators

    @nxt-1 An arrangement like a flying extruder, but actively lifted by the 4th axis which is a cable on a drum?

  • @t3p3tony said in Delta - 4th axis extruder:

    @nxt-1 An arrangement like a flying extruder, but actively lifted by the 4th axis which is a cable on a drum?

    In my plans I had only considered something like a pinion and rack. Assuming the length of the cable can be controlled perfectly, in theory it could even work for a direct extruder. That eliminates its usefulness to reduce effector weight, but it proves a point: the bowden length can be as short as needed.

    I would have to think about it some more, but as of now I cannot really comprehend how to configure the Duet correctly for a cable. Making sure the length is correct and homing I mean.

  • administrators

    @nxt-1 its was meant partly in jest. the issue with a cable on a drum is if it winds round more than one layer you get a changing length per rotation. Homing is possible is a number of ways, although synchronising that with the other three axis on the delta would be challenging.

  • @t3p3tony In jest or not, I like new idea's 🙂 It even gave me some new insights for other possibilities.

  • administrators

    To home it, you could pass the cable through a hole or slot in a plate or a printed part at the top of the printer, and have a knot or collet on the cable below that. Then either use a microswitch to detect when the knot pushes against the plate, or use stall detection.