Part 2 of this series documents my conversion to a Bowden tube system for the Printrbot.
Part 3 documents the special considerations of getting the Printrbot to dual extrude.
There's more than one way to add dual extruders, but no matter which path is picked there are some significant blocks that have to be overcome. The main one is that the Printrboard simply doesn't support two extruders. There are some clever hacks that come close, but the real way to do it is to replace the Printrboard with a controller that natively supports dual extruders.
Here are the steps that I've planned out. I've gotten past Step 0 and Step 1, but the big ones are still coming.
- Step 0: Tighten everything up
- Step 1: Convert to Bowden Tubes
- Step 2: Replace the Printrboard with a Ramps 1.4 board
- Step 3: Add second Extruder and Hotend
Step 0 consisted of making sure the PB+ was rigid and ready for expansion:
Printrbot X-Axis Belt Tensionr
Printrbot Y-Belt Tensioner
Printrbot Y-Axis Bed Stabilizers
Printrbot Plus V1 Z bar stabilizers
GT2 20T Pulleys and 2GT Belt
M8 Threaded Rod and 5mm to 8mm Shaft Couplers to get around the Z-axis Ribbing problem.
Additionally, this included tightly calibrating X, Y, Z and E as well as learning how to make the most of the slicing settings of Slic3r. Here are the KISSlicer INI files I'm using: (I'm positive they'll continue to change as I improve.)
Step 1: Bowden Conversion
The weight of a Wade's Extruder on the X-carriage is non-trivial. There is very real inertial momentum that has to be managed when choosing speeds and handling things like the vibration created during rapid short zig-zag fills. The solution to this is to move the extruder off the moving part. The most common way to do this is via a 'Bowden Cable'. This is a tube that connects the stationary extruder to the moving hot end, allowing the filament to be pushed into the hot end from a distance.
Adding a second extruder either means increasing the weight on the carriage or leveraging Bowden cables for two hot ends. I chose the Bowden approach. It's used on a lot of different printer designs and doesn't require trying to constantly optimize the size and weight of two extruders.
I stand on the shoulders of giants in the 3D printing community who have created Bowden conversions for the Printrbot. Thingiverse is packed with great models and ideas. For a variety of reasons, I ended up modeling my own conversion pieces in OpenSCAD to fit my various parts:
Printrbot Plus Vert. Shaft Extruder Mount for Bowden
Ubis Hot End Bowden Mount (Printrbot)
For the Bowden tubes and connectors I purchased:
- SPC-06-01 Pneumatic Push to Connect Fittings (also sold as Pneufit fittings). This fitting uses a British Standard Pipe Taper Thread R1/8". Tap size is 8.4mm for this thread, but I'm 'self' tapped with the thread itself into the plastic. I used 9.45mm for the base and 9.15 for the tip (it tapers.) I bought these from eBay.
- PTFE/Teflon Tubing/Pipe OD 6mm ID 4mm purchased from eBay.
The position of the extruder remains significant. Getting the right mix between tube length and tube bend is important.
- It can be placed stand-alone. This is easy but lengthens the tube between the extruder and hot end. Bowden rigs are notorious for 'ooze'. I'd love for others to provide more insight, but my theory is that this is a function of the slight additional length of filament that bends in the tube as the extruder pushes the filament. The bend serves to store potential energy like a spring that continues to force filament into the hot end. The longer the tube, the more stored energy. I created a standalone mount for free standing extruders.
- It can be placed to ride on the X-rail. Thingiverse user sponnet has created a [urlhttp://www.thingiverse.com/thing:26963]mount [/url]that lets the extruder ride up and down with the X-axis. This has the advantage of only needing the tube bend to accommodate the back and forth movement of the hot end since the extruder raises and lowers with it. Downside is that it adds weight to the Z-motors, but they're doubled so that may not be an issue.
- It can be placed at the top of a Z shaft. This is the mount I created and listed above. This is problematic when the X-axis is homed and the Z-height is very high. That creates a pretty aggressive bend (taunting Lady Friction.) But my PB+ rarely has the Z-axis very high. This has been working very well.
- It can be placed somewhere else. Later I intend to create a bridge between the two Z-shafts (adding rigidity,) and mount the extruders up there.
Printing with the Bowden setup has been like starting over from scratch. The 'ooze' issue is huge. I've upgraded to KissSlicer and finally found a set of parameters that leverage the 'suck' function to minimize the ooze. I've been getting greast looking prints again, not quite as good as my stock extruder/hot end arrangement, but very good.
I'm on to Step 2, Replacing the Printrboard with Ramps 1.4 setup. I purchased the Ramps 1.4 boards (Arduino, Ramps shield, Stepper motor shields, LCD Smart controller,) from eBay. It should arrive soon and I'll document the next steps towards dual extruders!
What are your experiences with Dual Extruders, Bowden Coversions or Board replacements on the Printrbot?
) That's a lot cheaper than a 
