Converting to a Greg's-powered Bowden extruder

I started getting a little fed-up with the low Z clearance on Adrian's geared extruder design due to the rather large drive gear hitting the rails on very wide prints, so I decided to take the plunge to running a Bowden extruder. My goal was to not modify the original extruder or hotend in any way, in case the Bowden cable or its couplings failed and I needed to revert to the previous extruder setup.

Shown here, in working order.

The first hurdle faced was to acquire the PTFE tube that was to be used as a Bowden extruder, but that was going to prove difficult. At a total of something like 50 Euro all-up shipped in from the UK, I was wondering if it would perhaps be cheaper to just build a bigger RepRap...

However, the brilliant Vik Olliver (who does both the best price and best service for PLA and ABS filament over here in New Zealand through his company, Diamond Age Solutions) suggested to use PVC irrigation tubing from the local hardware store. This seemed like a great idea, so I went and got this:

Super-nasty, super-flexible, super-stretchy PPVC irrigation hose.

... not so good an idea on my part. Turns out the PPVC stuff is terrible, despite feeling OK when I tested it using a spare piece of filament. It is relatively stretchy, and when it stretches, it grabs the filament like nobody's business! I saw the more rigid PVC stuff out there, but I thought it would be too rigid; though after finding out that I didn't really have an option, I went and got some:

Super-better, super-rigid, super-not-stretchy PVC irrigation risers.

So far so good; they don't stretch, and they don't grab the filament when under pressure; they are also the perfect size to thread an M8 nut onto, and they don't let go of it under pressure. Looking good so far - though, yep, you probably need to remove those little wedge-shaped inserts screwed into the ends of them...

However, first problem - they are too short. I wanted to mount my extruder driver on the bottom-front-right of the frame (technically the rear-left - I've got my RepRap sitting bass-ackwards on my desk) and have the cable run out to the left, looping back around before entering through the top of the apex rails and going down into the carriage. This should facilitate good maneuverability of the carriage in both X and Z.

So, to join them together, I designed and printed one of these:

Assembled Bowden cable coupler.

This is my Bowden cable coupler. It takes the shape of two hollow plastic parts with a 7.4mm inner bore for the PVC hose, and two larger bores spaced slightly apart for the M8 nuts on the end of the hoses (STL files are available on the Thingiverse page). For a better view, here's a drawing of one half of this coupler:

Finally, the last hurdle to overcome was to attach the cable to the extruder and the hot-end, and to mount the extruder. To do this, I made three components:

1. A replacement base for the X-axis carriage, designed to be smaller for better airflow
2. A captive nut housing, holed for the PVC tube, to attach to the top of the base (identical one used on the extruder as well)
3. A small spacer for the PVC pipe to fit into the extruder body (I am using the MendelParts v6-style hotend mount).

STL files for these are available on the Thingiverse page for this project.

Here is the view of the re-jigged hot-end mount on the X-axis carriage - note how the coupler attaches using the M3 studs coming up from the extruder for the sake of simplicity.

The X-axis carriage, with Bowden base and clamp mounted

... and here is the view of the rejigged extruder cold-end:

Greg's Hinged Extruder with Bowden clamp on the bottom. Ignore the mounting blocks.

... if you will ignore my funky mounting, that is.

Note also that I am no longer using Adrian's Geared Extruder; its extrusion force was far too low to handle feeding filament through 900mm of PVC piping. Perhaps with PTFE, but not with PVC, so I had switched to the excellent Greg's Hinged Extruder design, skipping the obligatory Wade's Geared Extruder in the process. Why not upgrade to the latest, eh? 

In any case, the extrusion force provided by the Greg's far exceeded that provided by Adrian's (normally by a factor of 8, I am told) - so much so that I simply could not stop the extruder from feeding filament with my bare hands without damaging the filament. 

To get the printing going well, I had to change my retraction settings from 0.8mm up to 5mm. Unfortunately this does make printing a bit longer, especially when printing intricate parts, and since the Greg's is geared a bit taller, the retraction speed has to be a little less to prevent the motor from skipping steps.

Oh yes, and you can easily solve the slipping filament problem on the Greg's by using a couple of zipties:

What MacGyver would do if his imagination was broken.