Hybrid Volcano / Bondtech CHT Nozzle

CNCModeller

Hi All,
So I thought the community might be interested I got a pre-order Bondtech CHT Nozzle at great expense from 3DJake last weekend, and surprisingly it seems to be worth it.

However I am running it in a unorthodox setup. I've kept my volcano heat block and turned down a volcano nozzle shaft to fill the gap between the heat break and the CHT. After some initial leaking which was cured by tightening the heat break while hot, I can confirm much better flow rates. This is assessed anecdotally as I can print faster without gaps appearing in thin walls.

I've now got some accurate miniature scales so will try and do some flow rate testing over the weekend.

Anyway hopefully the feedback is useful.

All the best
Barry M

Phaedrux

Very interesting. I've been wondering about this myself. I don't suppose you could do some testing using the flow rate measurement method?

https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+4:+Calibration/40#s177

deckingman

Also for info, Bondtech are sending me a 1.8mm CHT to try on my 6 input hot end. Neither I nor Bondtech are hopeful that it will improve on the 73mm^3/sec average flow rate that I've thus far achieved because the filament is already molten before it reaches the nozzle. But there is only one way to find out for sure....

CNCModeller

@phaedrux said in Hybrid Volcano / Bondtech CHT Nozzle:

Very interesting. I've been wondering about this myself. I don't suppose you could do some testing using the flow rate measurement method?

https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+4:+Calibration/40#s177

I'll give it a try. I was planning to use CNC kitchens approach to see how it compares with his setup.

https://youtu.be/UNJdv5bFGOg

Will be back when I have some results.

CNCModeller

@deckingman said in Hybrid Volcano / Bondtech CHT Nozzle:

Also for info, Bondtech are sending me a 1.8mm CHT to try on my 6 input hot end. Neither I nor Bondtech are hopeful that it will improve on the 73mm^3/sec average flow rate that I've thus far achieved because the filament is already molten before it reaches the nozzle. But there is only one way to find out for sure....

That's interesting @deckingman , so what aspect of the design do you think is restricting flowrate, if not filament melt rate?

deckingman

@cncmodeller said in Hybrid Volcano / Bondtech CHT Nozzle:

@deckingman said in Hybrid Volcano / Bondtech CHT Nozzle:

Also for info, Bondtech are sending me a 1.8mm CHT to try on my 6 input hot end. Neither I nor Bondtech are hopeful that it will improve on the 73mm^3/sec average flow rate that I've thus far achieved because the filament is already molten before it reaches the nozzle. But there is only one way to find out for sure....

That's interesting @deckingman , so what aspect of the design do you think is restricting flowrate, if not filament melt rate?

I think you misunderstand - you might want to take a look at my recent YouTube videos.

In my multi-material design, six individual filaments get fed into the top of a heated combining block and exit at the bottom before they enter the nozzle block. So by using a mixing ratio which uses all 6 filaments in equal proportions, I essentially have 6 melt chambers (one for each filament) which are about 35mm long. This is how the high filament melt rate is achieved.

Only after the filaments are molten are they then combined before they enter the nozzle block. So if the filament is already molten before it reaches the nozzle, then it is unlikely that the nozzle geometry will have any further impact on the melt rate.

Or to put it another way, the main difference is that with a "conventional", single input hot end, much of the melting happens within the nozzle - that's the fundamental premise upon which Core Heating Technology is based. But with my multi-material design, the filament is already molten before it reaches the nozzle. Which is why both myself and Bondtech believe that a CHT nozzle will have minimal impact on the overall melt rate. But I'll find out for sure in due course.......

CNCModeller

@deckingman

Hi yes I understand, but I was wondering what aspect of the design is limiting you to 73mm3 at the moment if you're confident that it's not unmelted plastic reaching the nozzle?

If it's not melt rate, is it back pressure due to the small diameter of the galleries and the viscosity of the molten plastic?

Just interested in the bigger picture really, e.g. what's the next problem to consider if melt rate is not the primary factor any more.

deckingman

@cncmodeller said in Hybrid Volcano / Bondtech CHT Nozzle:

@deckingman

Hi yes I understand, but I was wondering what aspect of the design is limiting you to 73mm3 at the moment if you're confident that it's not unmelted plastic reaching the nozzle?

If it's not melt rate, is it back pressure due to the small diameter of the galleries and the viscosity of the molten plastic?

Just interested in the bigger picture really, e.g. what's the next problem to consider if melt rate is not the primary factor any more.

Well to be honest, the primary goal of this hot end was never to achieve maximum melt rate - it's to be able to print multiple materials. The fact that it is capable of 72mm^3 sec is an added bonus.

I hadn't really given much thought as to why that is the limit - it's getting into the realms of auger driven pellet extruders so fairly respectable by anyone's standard. But given that I could only achieve 44mm^3/sec with PET-G, I suspect that viscosity is having a big impact. So perhaps increasing the temperature would help to increase the volume flow rate as it will lower the viscosity of the molten material. Most people run elevated temperatures when they demonstrate high flow rates, but I didn't in my tests. Obviously, the larger the nozzle the more easily a viscous fluid will flow through it, so something bigger than the 1.5mm that I used would help too. Perhaps polishing the inside of the filament path might help, as would lining the walls with a low friction coating. It becomes a case of diminishing returns though.

But there are downsides of focusing on simply achieving the highest possible volume flow rate. One needs to use a large nozzle with wide layers and large layer heights which precludes printing highly detailed parts. Also, it takes a significant amount of time for the plastic to cool. Even with vast amounts of part cooling air, if the part is on the small side, then one has to slow the print down in order for one layer to cool before the layer is deposited on top. Otherwise the part will simply collapse into a spongy mess on the build plate.