Kossel Bowden Extruder

thingiverse

I tried a number of different bowden extruders before i finally sat down and picked all the features I liked from the better ones and amalgamated them in this one that I use on my two Kossels. This extruder mounts on a 2020 open beam on the Z tower of the Kossel (Delta) and extends to the right side of the printer when viewed from the front. It's a very strong driving extruder and if there's clicking or skipping, it's probably a problem elsewhere. Printed .3 layer height, 50% infill, PLA. Print Settings Printer: Kossel Rafts: No Supports: Yes Resolution: 0.3mm Infill: 50% Notes: For the main body of the extruder you shouldn't have to add any supports, there are some in there from Meshmixer and it's all I found was needed. For the extruder ARM, supports are needed where the bearing will go. I use the default settings in Slic3r for support when printing it. Takes a matter of minutes to chip out the supports. Post-Printing Steps and Parts I drill out the filament entry and exit holes in the main extruder body with a 2mm bit. Gives you a little wiggle room to work with. The filament connector is a 1/8" 27 NPT type since it's far easier to get the bowden tube in and out of in place of those 5mm ones. Plus it makes threading the filament a lot easier (for whatever reason). I use a tap set to pre-thread for the connector. Bearing is a 625ZZ and held in with a M5 x 20 bolt and nut. Don't over tighten the bolt, the bearing should turn freely without binding. The knob design is a press fit, but the STL file also has the insert for the ARM. The insert fits inside the arm as a pivot then the arm mounts to the stepper with an M3 x 25. The other stepper mounts use the standard M3 x 6. Tension is provided by a compression spring. Use a M3 x 25 with washer to retain the spring. The compression spring is 20 x 5 ID, 7.5 OD. eBay labels them as "20mm x 7.5mm x 5mm Alloy Coil Stamping Compression". These springs are fairly stiff so I compress them about 5mm tops. The hobbed gear is a typical MK8 one. Extend the flat spot on the stepper motor shaft to give the gear something to seat into. Last is the "guide". I mount the guide 30mm or so above the extruder, it helps keep the somewhat floppy Bowden tube in a better position during printing.