This DIY PTFE hotend tube will be most of all useful for RigidBot / RigidBotBig extruders, but also will be useful for J-head hotend, Delta Rostock extruder and may be some others but this all I know.
The idea is to use 2 PTFE tubes one inside another, first is ID 2mm and OD 4mm, second is ID 4mm and OD 6mm.
Tubes can be purchased on ebay for 5$ per meter which is waaaaaay cheaper then 4$ per 20mm tube, and then you can make as many as you need.
How to do:
Insert smaller tube into larger, align ends of tubes. measure 16 mm for RigidBot hotend and 20mm for J-Head, cut with exacto knife! Just make sure you cut is straight and even, both tubes ( inner and outer is same width. ) You can even sand both ends on 220 grit sand paper just to smooth it if necessary.
Align ends of the tubes before cutting
Smaller tube inserted into bigger.
As you can see on this photo, there is some gap between 2 layers, I believe this allow to compensate contractions of PTFE tube preventing reduction of inner diameter.
Here is comparison of old and new PTFE tube. Before you going to install you new tube please compare it with old one just to be sure lenght is proper.
I don’t have long term test at the moment I just replaced this in my hot end, first impression is pretty good. Will do some complex prints and will post results.
Also currently I print exclusively with PLA, so max temperature is 200C. but still original PTFE tube was shrinking even at this relatively low temperature, so I pretty optimistic with this design.
Edit ( Jan 27th, 2015 ):
After running this tube design for almost 2 month, I can say this is successful design and worth doing, especially if your Teflon tube is busted. Also PTFE shrinking is much less with composite tube.