Rando Bowden Extruder

by drandolph, published

Rando Bowden Extruder by drandolph Jan 3, 2013
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I have been using the minimalistic MK8 on my Replicator for a long time now and it's been perfect so I've converted it into a Bowen extruder. It uses the same bolt pattern for mounting as the airtripper extruder as well as the same bolt retention for the PTFE tubing.


Everything is on one build plate and with only 3 printed parts it is about as straight forward as you can get. This extruder is for 1.75mm filament.

It will work without the front plate on just fine and it's not really needed but I included it in case you want to close up the front and support the shaft from the motor. The front plate does have a viewing port so you can see the gear and filament.

This is part of an ongoing project for me to make a Bowden style conversion package for an MK7/8 or qu-bd extruder. I am currently working on the parts for the hot end conversion.

You will need

1 - Nema 17 motor (more power is better)
1 - M4 nut
1 - PTFE tubing with 4mm outside diameter and 2mm inside
2 - M6 bolts and nuts for mounting the extruder
4 - M3 22mm bolts (if not using the cover and 25mm if using the cover.
1 - Spring 1.25"L by .3"W McMaster #9657K331
1 - 10mm OD 3mm ID bearing McMaster #7804K128
1 - M3 10mm flathead
1- MK7 Drive gear from MBI or Raptor Universal Filament Drive Gear from qu-bd

(The file might throw you some errors while slicing it but it still prints just fine)

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@ punkti and koutetsu12, I have fixed the model and posted it here: http://www.thingiverse.com/thing:1391999.

All credit goes to drandolph.

Rando Bowden Extruder

also cant rpint ist because the .stl file is corrupt.. very sad as i really like the design of it..

Could you fix the STL file? I can't print it as is and Netfabb cloud takes the nut trap for the 4mm nut out.

You mentioned the QU-BD gear, and it looks like that's the one you have installed in the picture above. How have you been finding it in comparison to the Mk7?

I think they both can do an equal job however I think the Qu-bd one needs more pressure pinching it than the mk7. So a stronger spring is the only real difference I've noticed.

Looks nice - you aren't using push-to-fit connectors? I find them critical to my bowden success...

I thought about that and from what I've read people don't like those fittings. I have some so I may make another version with push to fit and test that out. It would make it easier to assemble but I'm afraid of the tension pushing the tube out of those compression fittings.