Sunday, 13 March 2011

Bowden Extruder - DIY RepStrap build for 1.75mm or 3mm Filament.

So for my new Repstrap (ScrewBall Strap) I am going to be using both 1.75mm and 3mm Filament, with a dual extruder set-up (eventually).
I wanted a bomb-proof extruder so I can print fast and reliably, so I hand-made one. That's the plan anyway...

I will of course print one of Adrian's new Mini extruder's and have a go at using a NEMA11 motor in a Bowden configuration at some point, but for now here is how this one was made and assembled.

Top shows the filament drive path and Pneumatic Push-fit connector for standard 4mm or 6mm PTFE tube.
Middle is Idler bearing block.
Bottom right is Nema17 motor mount.

Close up of Pneumatic connector - tapped and screwed, PTFE tube can easily be fitted and removed.

 I decided on a 10mm belt-driven drive-train (belt is 280mm) Pulley's are 16 and 40 teeth.

I wanted a straight-through filament drive so it's easily mounted on my RepStrap and could be made to tilt as printed build-height increases.

Underside - Excessive use of bearings for a belt-tensioner I know.

I mounted the 4 springs recessed inside the bottom block, so I can just use normal wing-nuts on the top idler block, this makes it much easier to take apart to clean and reduces the total height by using dead space for the springs inside the extruder body instead of sticking out the top.

This has 3mm ABS coming out of the 6mm Push-fit Pneumatic connector, but it's just as easy to screw in a 4mm for 1.75mm Filament drive.

I'm sure this design could easily be printed so If it all works well I will try to print a copy of itself and post some design files. And I really like the Herringbone Gears, so I expect that will replace the belt-drive in a printed model.

I also think the internal compression springs idea could be incorporated into other extruder designs, it really makes filament change and cleaning a much easier job than having to remove the springs each time.

I have also made a new 1.75mm hot-end for this Bowden driven Extruder, I'll post that and how I made it tomorrow.



  1. Hi Rich,
    Nice bit of construction. What's the purpose of the push-fit connector?
    Is that a high-density ply or some kind. Haven't seen much of that round here. What thickness is it so I can get a scale?

  2. Hi #6

    The push-fit pneumatic connectors allow the very slippery PTFE tube to be held (but also easy to remove) so you can pass the filament via the tube to a very light weight hot-end.
    Other people glue the PTFE tube, but that's not great and a few screw the tube onto a nut or stud, bit I like the push-fit's.

    It also means I can use the same remote extruder body to drive 3mm or 1.75mm filament, and just change the push fits and hot-end.

    It should be easier to see what I'm doing when I post the finished hot-end (I'll try to do that tomorrow).

    And yes, it's high density ply made from laminated wood veneer and resin, it feels like Tufnol and machines easily like Delrin/Acetal and is very strong and light weight.

    I do all my photo's on the same green 10mm grid, so the ply is 12mm and 14mm in this extruder.

  3. Hi Rich,
    Tks for the reply. I understand what you are at now. I couldn't figure where the hot end would connect, but you are positioning the extruder "cold end" remotely, and clever use of the pneumatic connector.

  4. good work bro

  5. Hi Rich,
    Did you have to change anything with your nozzle geometry or hotend now that the filament is placed in compression over a longer distance and may tend to buckle?