“Hey Mark, what the hell is that weird looking thing again” ? To put it simply, the extruder driver of a reprap /repstrap machine is the part that MOVES the plastic filament that is going to be melted, using different  methods (pinchwheels, cogs, you name it).

This was the part i feared the most from the beginning , since its almost the only part of the machine (with the extruder itself) that requires really specialised/more complex parts , or so i thought!

Here is how it actually went:

The good:

  • this version you can see above was done after a bit of experimenting with all the cogs i managed to salvage from a few printers (i should call those goldmines, really)
  • in the end these were the only two “compatible” cogs i could use in this design, as the one mounted on the motor’s axis , is the only one i could modify to ensure that the cog does not “slide” on the axis when a lot of force is applied to it .
  • the second cog (idler), is rotating freely thanks to two ball-bearings salvaged from my old roller-skates

The bad:

  • i wanted to re-use one of the stepper motors i salvaged as well, but those clearly don’t have the necessary torque unfortunately
  • while it works surprising well with a PLA plastic filament, for some reason, i was never able to reliably make it work with ABS (another type of plastic, think legos) , it might be because of the plastic itself , the slightly larger diameter of the ABS filament , or perhaps simply because of the shoddy construction
  • i will frankly say i don’t believe this system will work reliably in the long term, so one of the FIRST things i will print on the machine as soon as it works, is simply all the replacement parts for a better extruder

The ugly:

  • while you will find proof in the video below that it is indeed possible to have a working, semi-reliable extruder driver from scrap, it can never go beyond a temporary solution
  • the whole thing is approximate at best, and not practical to mount on the machine itself
  • if i do not manage to print out replacement parts quite fast and this mechanism breaks down, i will really be in trouble , since i would really like to avoid having to shop for some additional parts again

To give you a better idea of how it works here is another picture and a video:

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2 thoughts on “Building a Repstrap (5): plastic filament extruder driver from scrap

  • August 25, 2010 at 18:12

    the only issue with your extruder is that i don’t see how you can adjust the pressure that your applying to your filament, i would look into that

  • August 26, 2010 at 11:24

    Hello Mike!
    Actually , it is not visible on these shots and video, but the position of the stepper motor and its cog, and therefor the pressure on the filament, is adjustable (left-right) by about 2-3 milimeters , simply by loosening the mounting screws a tiny bit.
    Or did you have another method in mind?


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