This is a hotend fix for the BIQU B1.

#How it works:

Filament travels from the extruder, through the bowden tube, down the hotend, through the heatbreak and into the melt-zone where it is pushed out of the nozzle.

In most printers this whole path is lined with PTFE (or bowden) tube as it offers very little resistance to the movement of the filament. If the PTFE tube is not pushed very tightly against the top of the nozzle then it is possible for filament to leak out and make contact with the metal walls of the heatbreak.

This filament then gets stuck there and starts to create a bulge which interferes with the flow of the filament that is being extruded. If this happens then the net result is that you get inconsistent flow and regular jams. To prevent this from happening it is best to not rely on the teeth of the bowden coupler at the top of the hotend to hold the PTFE tube in place against the nozzle. Instead, it is better to force the PTFE tube against the nozzle using the far more powerful and reliable pressure that is created when you screw the bowden coupler into place.

This is precisely what this mod does.

#How to use it:

Measure a length of PTFE tube that is 32.3mm long and cut it using a PTFE cutter (see the last point). Note that some users have reported that they needed a slightly longer tube. The ultimate test is to make sure that you take careful note of the text in bold below.

Remove all filament from the hotend and then remove the bowden tube from the hotend.

Allow the hotend to cool.

Unscrew the bowden coupler from the top of the hotend.

Shine a torch into the hotend and check that no filament has leaked out on the sides of the nozzle. If it has then you will need to unscrew the nozzle and clean it (never do this with the power applied. Rather heat the hotend up to 230, turn the machine off and then unscrew the nozzle). If it has not then you can continue.

Insert the section of PTFE tube that you have cut into the hotend and place the washer on top of the PTFE tube. The PTFE tube should extend just a tiny fraction above the ridge where the hotend opens up. Some users have also reported that using a phillips screwdriver to open up the PTFE tube at the top (a little) helps to make the filament insertion a little easier because it reduces the chance of the filament catching on the edge of the tube.

Start to screw the bowden coupler back into the hotend but don't screw it down so much that it presses against the washer just yet.

Cut a small piece of filament from a spool and push it down through the bowden coupler, through the washer and down to the end of the hotend leaving a section sticking out the top of the hotend. This will help to keep the washer aligned as you tighten the bowden coupler.

Tighten the bowden coupler against the washer.

Remove the short piece of filament, reinsert the bowden tube into the coupler and print without the worry of irregular flow.

#Other side effects:

From time to time your bowden tube in the hotend will perish due to heat and need replacement. With this mod you will not have to replace the whole bowden tube from extruder to nozzle but rather just the short section within the hotend.

#Am I going to make a PTFE cutter that makes it easier for you to cut a section that is exactly 32.3mm long?

No because @thisiskeithb has kindly done that already. See: https://www.thingiverse.com/thing:4626725

I've not tested it so you may need to account for shrinkage in the material that you use but that should get you 99% of the way there.