My 6 input (5+1) mixing hot end

deckingman

Part 16 is now on YouTube if anyone is interested
https://youtu.be/h90vsaQSSj4

T3P3Tony

@deckingman thanks for the update. Its obviously disappointing that your mixing chamber had the disadvantages you have highlighted. I feel for how much time and effort you have put into the research, and in letting us "follow along" with the blog and now video updates. I think you have done a really valuable thing in documenting this, and as you say it will provide a start point for anyone who wants to try and work around those disadvantages.

Things like a constant pressure feed with nozzle flow controlled by a metering valve, active mixing to have a smaller chamber etc have been talked about in the past but are really hard challenges to solve with a hot plastic under pressure!

dc42

@deckingman, you have achieved a lot, even if you don't think you have been successful overall.

Did you see the message I sent you on Slack? I think you might be able to use the 6th input like a plunger, to more rapidly alter the pressure just before the nozzle and so handle short moves better.

deckingman

@T3P3Tony @dc42 . Thanks. I'm not overly disappointed. If it was easy to do, someone would have done it already. As you say, knowing what doesn't work (and the reasons for it) is almost as valuable as knowing what does work. I've learned a lot along the way and any knowledge is good IMO.

Also, I've ended up with a multi-input hot end that works better than anything I can buy. It might not be good at mixing but it has 6 inputs so I can print 6 colour objects with ease, I can use any M6 threaded nozzle, I can change that nozzle quickly and easily, so I can print with "exotic" or abrasive filaments, it's smaller than a 5 colour Diamond and virtually silent. So despite the fact that I never fixed the mixing thing, I have gained some nice improvements.

@dc42 I hadn't seen your message but I have now. I did try using up to 20% clear filament in that 6th input, mostly in the hope that it might "mask" the incomplete mixing to some degree. I can't say that I noticed any improvement. I suspect the only way it would work as you describe is if the 6th input used a much higher percentage of the whole. But even then, although that 6th input is a straight path to the nozzle, it's still a "tube" of molten filament about 70 mm long, and I doubt that the filament exiting that tube would behave in the same "dynamic" way as the cold rigid filament entering the top of that tube in what is effectively a series of varying pulses.

T3P3Tony

@deckingman crazy idea. What if that filament (as clear filament, as solid as possible) was used as a plunger to start and stop the flow out the nozzle?

So the path would need modification so it only entered the hot block as close to the nozzle as possible. It would be used as a sacrificial plunger to block the main melt chamber ooze, then retracted when printing continued. Obviously it would need different logic from a standard extruder to control, probably something based on the amount of force needed to keep the nozzle mostly block as it melted away.

Taking it one step further, if it worked well, it might be able to be used as a metering valve and get over the resolution issues. There would be a head of static pressure in the melt chamber which is topped up by the incoming filament, but released by the metering filament movement.

Even if that all worked perfectly! The big issue of course is still purging.

T3P3Tony

a chemically compatible but higher melting point filament would even further reduce the amount of "contamination" that this sacrificial plunger added to the output. it would still need to be slightly soft at printing temperatures in order to get a good seal.

PaulHew

Ian, I watched the print of your mixing hotend.
Incredible and fascinating and no purge block. (I did listen to how you purge)

I thought your machine was incredible when I saw it at TCT a couple of years ago but the 5+1 takes the prize.
Clever man.

P.

o_lampe

@deckingman
..that was heartbreaking. I hope you'll find something else worth to chase.

Based on your description of disadvantages I envisioned a mixing hotend with only one transparent filament, where the dry ingredients that are used by the filamentmakers. (pigments) are mixed together just before they enter the melting zone. (Cyan, magenta, yellow, black would be perfect)

It would probably require a stirring rod as other have used before, but oozing and slow spongy reaction wouldn't be such a problem anymore.
Purging would be no big issue, since you'd mix the colour on demand. Only sharp colour changes would need a purge tower.

No idea how to prevent the filament from climbing into the dry-mixing chamber, tho...it'll stay a dry dream I'm afraid.

deckingman

@o_lampe I'm sorry if you thought that was heartbreaking. I'm not heartbroken. I gave it my best shot but didn't manage to achieve all my goals. But I learned a lot along the way and ended up with a hot end that is better in many ways than the one I started out with.

deckingman

@paulhew Thanks Paul.

JawsN3D

@deckingman
Fantastic update. Imma have to read through this after seeing yer YouTube vids....

Regards, James aka Turbocharged400sbc

deckingman

Part 17 of my "journey" is now on YouTube for anyone who might be interested. https://youtu.be/fmz_SPbu7p8

I have a new innovation that I'm quite excited about and I think I have discovered the reason why a Diamond hot end requires high levels of pressure advance (circa 0.5), even with relatively short Bowden tubes.