Thursday, 17 March 2011

Hot-end for 1.75mm Filament (Push-fit Bowden)

My new push-fit 1.75mm Hot end is finished, it's based on similar designs like Adrian's new micro hot-end -

Here is how I made it -

I am a big fan of using off-the-shelf parts where possible in Reprapping, so using Pneumatic Push-fit connectors was an obvious choice for attaching the PTFE (bowden) tube to my extruder assembly.
The other standard part I always try to use is the metal rail mounts shown above. They work well as a clamp and  are low cost (£2 / $3) and easy to modify.
This 8mm mount above is manually tapped so I can screw in the Push-fit (1/8")

I'm using a simple Aluminium R/A piece to mount to my Repstrap, you could use something different to mount to Mendel, Prusa or Rapman machines.
10mm PEEK rod and block, 1.75mm Hot-end with 0.35mm Nozzle.

Turn down both ends of the PEEK rod (one 7.2mm and the other 8mm).
Then with a 4mm drill bore the barrel - the PEEK will expand and shrink so the hole will be undersized, but that's good.

Cut a length of 4mm (outer) PTFE tube.

Then you need to push the PTFE tube into the PEEK barrel, this is hard so taper the tube end with a pencil sharpener and force it in, you may need some PTFE spray to help this process.

Cut down the tube but make sure to allow both ends of the tube to compress slightly, one in the push-fit end and the other in the hot-end, you can tighten down the push-fit after it's all at temperature as the PTFE tube will elongate with temperature, you don't want any leaks.

Drill your PEEK block so it has the same spacing as the rail mount.

Drill your chosen mounting bracket.

Assemble with 55mm M4 bolts, washers and nuts, you can use a Nyloc nut at the top, it should not get hot enough to melt them.

You will need to tighten everything after it gets up to temperature for the first time, the PEEK will bend.

The other end of the PTFE tube is connected via a push-fit on the Extruder, so the 1.75mm filament can be driven down the tube to the hot-end.

I hope to have some examples of it running soon, I now have the last remaining Pololu stepper drivers, so I can start to wire-up the ScrewBall strap and get back to 3D printing (another 3D printer) !