JunkStrap’s Extruder

On my other printers (RoStrap as well als Sumpod) material feeding has always been one of the main causes of trouble. The “stock” cold end on the Sumpod was especially bad and had to be replaced with a geared bowden version. And on some point I even zip-tied that extruder to the carriage to reduce the necessary retraction distance to tolerable values.


As I did not mention it here before, this is a short video of it:

Most problems with bowden extruders are described in this E3D blog post, and if you aren’t printing ABS, retracting out of the melt zone (because you use a normal setup want to get rid of stringing) can quickly jam everything. And if I might add: there are “fixes” for underextrusion meant for Ultimakers out there. No, I won’t go for a bowden extruder again.
Mark Rehorst also describes a lot of issues here, but limits his reflections to single drive gear configurations.

You can use a single drive gear and still build a working extruder, but that is not easy to attain. There are also designs out there trying to grab the filament from two sides. It goes from using (gears and) belts on two sides to guiding the filament past the same wheel twice (“Saint Flint” Version). Commercial versions (from Bondtech and BQ for example) use intermeshed steel gears to get the drivegears rotating inversely – small and well made, but expensive.

For the JunkStrap I printed the Dual Drive Bowden Extruder of Colin Rose (former C_D, now invent3d) – which is already documented here. It is a bit funny to insert those tiny bearings into the massive frame (by soldering iron, so nothing cracks) and my “5mm” shafts were too thick for them, but threaded rod worked (somehow) provisorily to get it running. (Yes, the threads do push themselves to the sides during rotation a bit, but this is a JunkStrap and not a proper custom machine.)
Loosening the grub screws from my old Mk7 drive gears became a challenge, which could be handled by a Tx6 bit BTW.


Here is the first test:

Sadly though, the two drive gears have no chance of gripping 1.75mm filament properly. So I had to consult Jeremie Francois’ excellent article about how to modify those. Step one with my “no name” rotary tool and The little bolt hobbit by elk (instead of trying one of the Dremel mounts I used the flexible shaft):


Step two:


Mounting everyting (including this additional filament guide, as I had an earlier version of this extruder) and installing it into the Junkstrap can be seen below. The quick coupler was heated via candle, the tube is just the guide towards the Hot End. I don’t call this “bowden”.


Performance was not as good as imagined in the beginning as the gears had to wear a bit on each other. Trial-and-error calibration of the custom infeed was no trouble at all – read RichRap’s article on this topic if necessary.

And finally: this extruder skips steps instead of chewing away the filament (like all my previous ones did). ^^

The Sumpod is missing the E3Dv5 now? Indeed. It was converted to an E3D Titan Aero HotEnd and Extruder , which works like charm (yes, even with the “pancake” stepper)…

…if you read the entire assembly manual and observe the warning not to overtighten the screw through the large gear (which was not quite as red in the old wiki).


EDIT: Or was it the lubrication of that bearing? E3D just postet about the trouble they had with either their plastics cracking (because of the wrong lubricant in that ball bearing) or the bearings failing (because of another wrong lubricant in the same ball bearing).



I didn’t keep the jammed bearing, so there is no way for me to search for rust. The Titan Aero runs fine on the Reely bearings from Conrad since then.

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