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http://www.thingiverse.com/thing:9850
Has anyone designed or built something like this? The link is to one that RichRap posted on thingaverse. I'm getting a Filastruder, so I think something like this may become necessary. I'm interested in full plans or a kit if anyone has info?

Haven't made something like that, but I have a way to do it that's quick and easy and probably just as effective...

I take a small length of PTFE tube - probably about 30mm - and put the 2 ends I want to join into it.

I then hold the PTFE tubing over my heat gun until I can feel the filament start pressing into each other. I push each end towards each other until about 2mm goes in on each side. Take it off the heat. Let it cool for 30 seconds or so and slide it out. The area where it joined will be slightly bigger in diameter, but I've never noticed any issue in printing with it.

A thin metal tube would likely do the same then?