Filament joiner for multicoloured printed 3D objects

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You can find more information on my blog at http://richrap.blogspot.com/2011_06_01_archive.html. This is the basic idea for making a multicolour 3D print using 3mm filament. People have different methods to achieve this, including: 1. Starting the print with one color filament, pausing it, reversing out the filament, loading a new color, and continuing the print. 2. Joining lengths of different colored filaments together and printing them in one go (using hot-air guns or flames). 3. Using multiple extruders with different colored filaments, producing complicated G-code to control them. I tried joining filaments with a flame (lighter) but it didn't work well. It's easy to snap the join after cooling, and it can char the filament, which is not something you want to feed into your extruder. Next, I tried using a flat heated block of aluminum, melting both ends and joining them. This works, but it makes a mess and is a little fiddly. After trying a hot-air gun (which didn't work out), I decided to make a temperature-controlled filament joiner. To build one, follow these steps: 1. Cut an aluminum block, drill a hole for the resistor (6.8Ohms), and slice it so you have joining channels. 2. Bond in the resistor (fire cement) and insulate the bottom of the block with something that won't catch fire, such as PEEK, PTFE, or silicon. 3. Wire it up like a 3D printer hot-end and add a thermistor (I also added an LED to tell me when it's on). 4. Mount it to a block of wood or something you can clamp down. 5. You can use your RAMPS electronics setup and a host program to control the temperature, just like with your hot-end. A good temperature for PLA is about 160 Degrees C, but ABS will need to be hotter. To join filaments, hold one in each hand, melt both ends on the side of the aluminum block, insert them into the groove, push together, and give a quick rotate. With practice, you should have a joined filament. If you decide to build one, consider these improvements: 1. Have a shorter heating zone, around 4mm for each side, to keep the filament more rigid when twisting it. 2. Have a bigger flat area to quickly melt both filament ends. 3. Have a cold block or wet sponge to rapidly cool the joined filament in place or a foot pedal controlled fan to blast cool it. You can even make the heating block clamp together like an electric plumbing pipe joiner (see picture). If you had a foot-pedal controlled one of these for filament joining, it might make the job even easier. Make one and print all sorts of cool-looking things with lots of colors.