Some thoughts on the HOT end.

A few thoughts on the heated end.

larger thermal mass is better - just like a flywheel - the thermal mass holds the energy ( heat ) better - so when the heat is transferred rapidly to the filament it doesn't suck ALL the heat out - so the heater barrel can maintain the proper heat without dips...

a heat sink is a BAD thing....

on the heater barrel, but not on the fillament channel

i.e. it's good if the inlet is coolled, but it shouldn't be connected to a highly conductive (thermally) part...

the heater barrel should not have to waste ANY energy heating what shouldn't be heated...

(the boards are taxed enough - so improving the efficiency by keeping the heating where it NEEDS to be is better, and not heating anything else (the room, the cold channel etc) is CRITICAL!

you should be able to heat the heater barrel with a minimum of energy and insulate it to keep it hot as well.

HOWEVER - because support material can now be used in the same material, there needs to be a way to COOL the barrel quickly as well... in order to speed up printing.

(cold support layers don't stick to cold object layers

so

the interface/support material is best laid down at about 20-30 deg colder than the object material, and the first layers (touching the support layers) should be about half way between the cold support and hot object layers.

it makes support removal OODLES better

EDIT:

Thanks for the comment, you're right - water cooling is something I was thinking about - but of course this is a DIY type thing, so water + electricity + human error = BAD SITUATION! :D hehe... so I was thinking it'd be better to move some air in there - through some copper piping or something like that.

I'm travelling right now with the bot - so I don't have access to all my tools - but plan on experimenting virtually in CAD.

I have a hot end that is working REALLY well - save the long heated channel - which I will be shortening eventually when I can make a coolable thermal block (instead of a long steel hollow tube). hmmm.... liquid cooled - I wonder if I could use some pieces from a liquid cooling system used for cooling overclocked PC hardware - certainly those are designed for liquid SAFETY! - maybe liquid cooling of the hot end IS possible!

Again, thanks for reading - I'll try and post more often!

UPDATE - this is working REALLY well - the pressure adjustment SUCKS but otherwise - I literally only have to adjust it if I'm changing filaments (which means they change diameter slightly) I'm working on a replacement assembly for the filament extruder body - will post pictures when it's closer to done. My main goal is to minimize EVERYTHING! pathways, plastic used, size, etc... can't wait to share!

OK - the theory was sound.

In practice? - yay, it works!

The following is a rigged up kinda like the paxtruder teflon idler not-a-wheel, wheel.

Prototype version - (note there are actually 3 pieces of scrap PTFE tubing, 2 for stabilizing, and 1 pressing against the filament - and this only worked for a while before the tubing started slipping)

Above is the current and PERFECTLY working version - a relatively simple retrofit of the MK4 Plastruder. The tensioning mechanism leaves a bit to be desired, however I have yet to have to adjust it and it's going on 2+ weeks of good printing (basically it's 7/3 right now and whenever I first posted the original post... ) --- also note the makeshift needle that shows if my motor is turning... it's just one of the little cone/piles of filament popped into the bearing hole. works like a charm.

Basically I flattened a piece of scrap PTFE tubing from the stuff I'm using to line the heater barrel. WOW this works - um... 100,000,000X better than the idler wheel IMHO.

the piece of flattened PTFE tubing on the near side (and another one on the back) prevent the idler from getting pushed to one side by the filament... and yeah that's a printed (failed) IDLER wheel.

Above and below here are the mocked-up extruder with PTFE lining.

• 5/16"-18 threaded hollow steel pipe (3/16" ID, and right now it's 5" long... TOO long. I need to shorten the actual "hot zone", but this proved a point.
• 3/16" OD, 1/8" ID (3.125 mm) PTFE tubing... with about 0.002-0.005" shaved off the outside to allow it to slip inside the hollow tubing without having to FORCE it in - which doesn't work when it's net fit.
• the rest is just for mocking up the extruder (the wooden blocks actually work really well over the metal - they insulate and really don't get THAT hot. (of course it's wood - so if you use wood on a heater barrel - do so at your own risk, as I didn't build your heater barrel, I don't know it's risks.

Yeah, I KNOW WAY too much plastic - but at the time it was better than NO plastic :D

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

Cupcake is Alive!

ok - well it was for about 3 prints.

Here's the short - and soon I will update with some pictures of the process and post some vids on Youtube. But for now - the long and short:

Cupcake cartesian bot - brilliant, few flaws in the design and went together SO easily. There were a couple of things not well illustrated in the online instructions that caused me to worry a little but when I went with my gut, all was fine.

The electronics and Replicator G work REALLY well to control the bot. I wish you could do absolute positioning in the remote control - but meh - whatever.... good enough. I feel like I should probably add an end stop for the Z axis - WAY too easy to hit that down button one too many times. (BE CAREFULY you can dent your little build platform if you're not careful.

The plastruder on the other hand - is fundamentally not flawed but the assembly of it is riddled with bad practice. things that need servicing require almost complete dismantling - this is just bad. So I'll be re-designing and working out my own.

I had to rebuild the extruder after only about 2 piles of plastic and a couple rafts because the idler wheel cracked. But I sandwiched the sucker between a couple discs of >PC< ,,, from a DVD heh.... nice - used some JB Weld to bond it all up and since then - BRILLIANT no flaws, and no chunks bitten out of the filament. However in the reassembly, the stress of screwing and unscrewing the M3 screws - some of the acrylic (GRRRR) developed little cracks and I am pretty sure if I disassemble the thing again - it's going to fall apart... for this I HATE ACRYLIC! it's Terrible - no thanks I don't like it... ick! For an extruder that takes these kinds of forces - it's just silly. (yes I know there are plenty of parts out there made from acrylic that work just fine - doesn't mean it's the best material for the job, by any means.

I've been looking at the Paxtruder - and while it looks interesting and potentially a lot better... meh - it won't be MY design so I think I'll do the extruder as a ME project!

The biggest problem with the extruder is the PTFE insulator it's nothing but trouble and you can't tell if it's failing until it's failed REALLY badly. there is actually a lot about the hot end I don't like, but in fairness - it's a complicated problem (I think) to solve. That is - heat up the nozzle and enough of the barrel, hold the barrel against something that protects the extruder and doesn't wick heat away from the nozzle and can withstand the pretty intense pressure from the extruder.

So - I'll try and post some images and vids from the build - and once I've done that I'll start posting my progress as I design my new extruder!

PS> Frostruder got here today - uh .... yeah it's a bit EXPENSIVE for what you get - but hey... the guys at makerbot deserve to maker some $ ? So support them! I did.