Extruder Nozzles - 3.2mm vs 3.5mm Holes...

Hi,

I hope all on the forum are well.

I''ve made a new nozzle for my Mendel as my old nozzle is no more . I have followed the design shown here (http://reprap.org/mediawiki/images/6/69/Better-nozzle-machined-parts.png) and have finished my first nozzle. See attached.

I wondered if any people have some input into what is size hole is best the thermal barrier and brass hot end?

The design above uses a 3.5mm hole for each but this seems a little large and i'm worried this could result in plastic being pushed back up the nozzle and not out of the end. I have used a 3.2mm hole instead as it may reduce the risk of this but if anyone has any input into the benefits of using a 3.5mm hole, the guidance and input would be most appreciated.

Let me know your thoughts.

Regards to all.

Raj

I use 3.5mm without any issues. I have run 20+ lbs of filament through it at speeds of 50mm/s - 120mm/s

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3.5mm is good. The reason being that filament expands as it get closer to the hot end, and expands even more as it approaches the melt transition point. 3.2mm is more likely to bind higher up causing too much resistance, or jamming.

This is true for abs plastic as it does swell as it heats up to a glass transition state. I don't think PLA expands as much, so some care needs to be taken to ensure that PLA does not melt and make its way back up beyond the heated section of brass. I have gone thru 4 rebuilds of hot end just because of PLA..... If you use PLA with the wider diameter be sure to remove PLA each time before you start cooling down extruder, otherwise PLA will harden and become jammed, and it may never get hot enough where it is jammed, to allow it to flow again. This of course can be resolved by disassembly, but it is far easier to just remove PLA after use....

jamesdanielv Wrote:
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> This is true for abs plastic as it does swell as
> it heats up to a glass transition state. I don't
> think PLA expands as much, so some care needs to
> be taken to ensure that PLA does not melt and make
> its way back up beyond the heated section of
> brass. I have gone thru 4 rebuilds of hot end just
> because of PLA..... If you use PLA with the wider
> diameter be sure to remove PLA each time before
> you start cooling down extruder, otherwise PLA
> will harden and become jammed, and it may never
> get hot enough where it is jammed, to allow it to
> flow again. This of course can be resolved by
> disassembly, but it is far easier to just remove
> PLA after use....


I only use PLA, NEVER clear the nozzle and like I said before have run 20+ lbs of it through my extruder at 60 - 120mm/s. It have found it helps to have some cooling on the thermal barrier when using PLA because of its expansion being at such a low temperature. Heat sink or fan blowing across it.

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well that is good to know. maybe technology is different than it was a year ago.... what kind of pla are you using? how much does it swell compared to abs? thx

I use 4043 PLA from ultimachine. My extruder design is in the links below. The videos on my blog of my machine printing at 120mm/s were with a heatsink on the thermal barrier but no fan.

I can't compare ABS and PLA because I have never printed with ABS due to the smell and need of a heated bed.

Without the heatsink in my early testing I found the heat moved up the thermal barrier after about two hours of being on which caused more friction as more of the filament expanded and made contact with more of the thermal barrier.

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here is the link to the video i think he was talking about [www.youtube.com]

that is an interesting x carriage. it seems to ride smooth as well.

jamesdanielv Wrote:
-------------------------------------------------------
> here is the link to the video i think he was
> talking about
> [www.youtube.com]
> =player_embedded
>
> that is an interesting x carriage. it seems to
> ride smooth as well.

Yeah the X-carriage is the result of the hotend not fitting through my original one and figured if adding a heatsink I may as well use it as the carriage itself. A few L backets and bearings later I had a finished carriage.

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