For those who don't want to have to download the attachment to open the PDF, see below (copy/pasted from the document, not my writing)
How to assemble the Flex E3D Extruder?
When assembling the extruder module, make sure the spring bolt is NOT
all the way through the threaded hole. It may definitely not touch the drive gear! (See red arrow)
You can turn the nut (See blue arrow)
to adjust the tension on the filament. Make sure the bolt itself stays in place when turning the nut. This is very important!
Most people print a thumb wheel to turn the nut easier… (haven’t done this on the example)
1) Now, how to assemble: first make sure the pulley is nicely centered between the two holes. This way the filament can run straight through without bending…
2) To do this, you can add two washers, or one thick washer behind the pulley. It’s possible you need a longer bolt, but you will probably find one between the spare parts.
3) Add a second PTFE Tube connector
on the lower side of your extruder, and put a tube through both connectors. Make sure they don’t touch the pulleys, but are as close as possible. (You can use the spare PTFE Tube connector of the standard extruder, or you can order some on AliExpress (very cheap, like $4 for 10 pieces))
4) Cut the end of both tube, on both sides, in a 60° angle. I find it easier doing this when already assembled, some people will do it before they put the tube into the connector… Next, push the tubes a little bit further inwards so they just don’t touch the pulleys.
5) Push filament through the tube, adjust the tension on the pulley and you’re done…
Made by Sam Vandenbulcke