Extruder Problems...

The Plastruder MK4 has, honestly, been nothing but problems...

For the filament pusher end, I've got it relatively working as long as the heater barrel assembly doesn't get all jammed up... but it DOES get all jammed up.

When it gets jammed up - the generous forces from the pinchwheel motor can crack (easily) the idler wheel when there is too much forces backing up. so the filament when it buckles tends to like to force the idler wheel sideways and either crack it loose from the bearing - or worse CRACK it, because it's ACRYLLIC! (has anyone tried making the plastruder out of lexan? expensive, a little, but, uh... not as expensive as repeatedly rebuilding and replacing parts on the acrylic version... just a thought.

anyway - when I first started building the cupcake and plastruder - I thought the whole heater barrel design was just STUPID. Of course - as I've mentioned before it's not stupid, it's just a complicated problem, the way it's being solved. and trying to make a 3mm diameter tube/guide that is COLD, and butts right up against the 3mm diameter HOT, is TRICKY.

So, and we'll see if it works out, but, my thought here is use a larger diameter heater barrel, and line it with PTFE tubing. 3/16" OD and 1/8" ID. The PTFE tubing will provide a non-stick surface that, hopefully, has no problem being heated to 240-250°C (since it's upper limit is 260° C) .... I still need strength and stability leading in to the heater barrel, so I'll still be using a PTFE insulator spacer, but this will not cover much if any of the heater barrel. I'm actually hoping to butt them together. I might dog-point the end of the barrel by 3-6mm just so it's easy to center, but I don't need a compression fit between barrel and PTFE - so I don't really need to even clamp the PTFE to the hot end... it's more like a sleeve for stabilizing.

Also I want to have as little metal on the heater barrel assembly, I want to keep the thermal mass as small as possible and keep as much heat right at the nozzle. So I'll be using a pair of thin nuts and a single small 3mm thick plate of aluminum (similar to what Charles Pax is using on his paxtruder - which is pretty nice looking, and if there were a kit, I probably would have tried that first, but... I'm excited to try out my experiment here.

Of course - I can already see there MAY be some problems with the design, and will follow up and to let you know if any of them pop up...

• what if the PTFE lining wants to push out? (hopefully the PTFE insulator/spacer will help prevent that, but I don't know - I also have some glass filled PTFE which should prove stronger and more stable than standard PTFE, we'll see )
• what if the ABS / PLA squidges between the PTFE tubing and works it's way up and out the top of the barrel. that's no good.
• what if 240°C PTFE tubing is too close to it's maximum limit and is weak and gets CHEWED to shreds by the filament with it's teeth created by pinch-wheel?

there are probably a few more things that could go wrong - we'll just have to see.

until the parts get here - I'll be workin' on real work :D