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Thread: Extruders

  1. #21
    Quote Originally Posted by awerby View Post
    If you're building an extruder from scratch, why not build it with an auger screw, so it can handle pellets rather than just filament? Most thermoplastics come in pellet form, and are a lot cheaper that way than when extruded into filament. It would also give you more flexibility in terms of nozzle size - you can design a set of interchangeable nozzles, so you could switch between fast and thick deposition and slow and fine. If it works, let me know, because I want one...
    Augers are not super precise with their deposition, filament makers use an auger screw, but they use the tension on the filament to control diameter. Augers are not positive displacement pumps so they don't really such and push like you're thinking. Augers more 'suggest' which way things should go rather than demand, like how a filament extruder pushes or pulls filament.

    Anyways, onto the real issue. You'll need to use direct drive, since the plastic wont stay hot and molten through a bowden tube, and even if it did an auger would not be able to force the molten plastic through since it isn't a positive displacement pump. Next let's ramp up the heater block and cartridge, because you will need a much bigger melt zone to cover where your auger is. You'll also need a fairly big auger because of the size the pellets come in. Now add a big (and noisy) vacuum to feed this extruder with pellets from an outside source (or mount a barrel of them onto the extruder, but good luck moving it then). Basically, you end up with this.
    See that slightly larger than normal hotend? It's actually massive.
    Don't forget the shop vac to feed the pellets.

    You wont be using that on any desktop machine, no matter how rigid you want to boast your set up is. Filament extrusion is probably one of the few ways a bowden set up would work, and it allows direct drive to work without carrying too much material on the extruder at once. I think it's as good as it's gonna get for thermoplastic FDM, a couple of decades of R&D haven't found a better method for thermoplastic FDM.

    And you're right about the volcano having a standard heater cartridge, I just remember reading somewhere a while ago that they used a more powerful one. But I understand how the volcano works and why the heater cartridge is positioned the way it is and that incoming filament cools the hotend, this is why I said earlier which extruder would be able to push more filament, if we assume the hot end heating the filament is a non issue.

  2. #22
    I'm working on the extruder right now, one of my goals is to keep it within the face profile of a standard nema 17 (42x42mm). This of course comes with some space issues as I'm trying to make it geared. I'm considering making one gear stick out slightly as a sort of thumbwheel for manual extrusion/retraction to help with loading and unloading filament, any thoughts?

    Anyways, my current dilemma is how much of a gear reduction should I use? I'm wanting it to be usable with the pancake 20mm nema 17s, and I have two reduction ratios right now, a 1.8:1 and a 3.06:1. The E3D titan which people use with the stepper's I plan to use has a 3:1 ratio, is this "just right" or does it provide unnecessary torque? Would 2:1 or even direct drive work? I'm asking mostly for higher print speeds upwards of 100mm/s.

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