Anatomy of the multi-material filament pathway  

Re: Anatomy of the multi-material filament pathway

Blimey. You don't want much... How long have you got???

Stainless Steel "Cooling Tubes". They do exactly as described.

Bondtech gears to add torque to the filament drive - and they are much more precise than the previous brass drives (where different E-Steps were required for each ,extruder)

Special 1.9mm ID PTFE to form the end of the filament for the next load.

Adjustment to the heat break to help cater for stringing on unload.

Requirement to get filament tip into cooling tubes as quickly as possible.

You should have been part of the beta testing!

Peter

Re: Anatomy of the multi-material filament pathway

Thanks Peter. I don't suppose you know if Prusa will ever write this up and/or present it at come conference? It'd be a really interesting read to see how they walked though the various engineering compromises to get to the final product.

Re: Anatomy of the multi-material filament pathway

No, sorry; I have no idea what PR will or will not document.

I only know what we were told during beta tests. And of course, things are still being changed/improved.

Peter

Re: Anatomy of the multi-material filament pathway

I think it's interesting to watch the extruder move the filament back and forth in the cooling tube to form it into a nice round shape with a rounded tip as it cools. I'll bet coming up with that was a good light-bulb moment.

Re: Anatomy of the multi-material filament pathway

I think it's interesting to watch the extruder move the filament back and forth in the cooling tube to form it into a nice round shape with a rounded tip as it cools. I'll bet coming up with that was a good light-bulb moment.

Yes, it was in interesting moment, but strangely, using PTFE cooling tubes, no movements are necessary.

Peter

Re: Anatomy of the multi-material filament pathway

Blimey. You don't want much... How long have you got???

Way too much time on my hands 🙂

Stainless Steel "Cooling Tubes". They do exactly as described.

Bearing in mind I know almost nothing on this subject, I though the idea was that the filament was cold once it left the cooling part of the hotend, so why the specific steel cooling tubes? And given that they're are obviously necessary, why metal tubes at all - ptfe wouldn't work as well?

Bondtech gears to add torque to the filament drive - and they are much more precise than the previous brass drives (where different E-Steps were required for each ,extruder)

I do rather like the bondtech drivegears, but given the cost compared to the alternative (I'm sure Prusa didn't pay the $50 they charge on their website, but still more expensive than the old system) I assume its just necessary to push filament though such a long bowden tube?

Special 1.9mm ID PTFE to form the end of the filament for the next load.

Is this a tolerance thing. If they use 2mm here, the chances are that it'll stick in other 2mm places?

Adjustment to the heat break to help cater for stringing on unload.

Okay.

Requirement to get filament tip into cooling tubes as quickly as possible.

So why is that? Couldn't you let the filament cool in the cold bit of the hotend before yanking it back into the splitter?

You should have been part of the beta testing!

I know far too little to have been helpful.

Thanks

Re: Anatomy of the multi-material filament pathway

Tim

I will cover things in a little bit more detail...

The ID of the PTFE is 1.9mm and that of the cooling tubes is 1.95mm. Initially the former was 2.0 and the latter 1.85, so the tip forming was carried out inside the cooling tubes. The problem there was filament diameter.

Note that the PTFE is initially nominally smaller ID than the cooling tubes

So things were switch around and the PTFE became the primary tip forming place, and the tubes just for cooling.

This method ensure that the filament will feed into the hot end on the next load (maybe 99.99% of the time...).

PLA has a "glass transition temperature" of around 62 degrees; it's pulled out of the hot end at maybe 215 degrees and is malleable for quite some time. This cooling process must be carried out in a "controlled" manner in order maintain a nice clean end.

Regarding the use of PTFE, see my earlier comment. But, there is a problem with PTFE in that it is abraded by filament - even quite soft stull - and it will wear.

The additional torque provided by the Bondtech gears is more to overcome the stiction of the filament inside the cooling tubes and any stringing that may have occurred during unload. There were quite a few models printed with the brass drive gears (I had even written a post-processor to handle the differing E-Steps) before the Bondtech ones were introduced.

Hope this covers your queries.

Peter

Re: Anatomy of the multi-material filament pathway

Hi,

Where can I find spare cooling tubes? They don't seem to be listed anywhere...

Re: Anatomy of the multi-material filament pathway

http://shop.prusa3d.com/en/multi-material-spare-parts/167-mmu-multiplexer-stainless-steel-tube.html

You will need to speak with "Live Chat" ask them for access and then ask them to put some in stock for you.

Peter