Why the Angst about a fan on the hot end?

Maybe angst is too strong a word but I thought it might provoke a good discussion. Seems like there is a general consensus (?) that it is good to have an abrupt temperature transition from the melt zone and the "barrel" of the hot end. If I can start with this premise, one of the technologies to achieve this is active directed air flow over the "barrel"/feed tube, including a finned heat sink. So, a fan can be used. Now the downside of a fan would include:

* Another mechanism to wear out
* Incremental cost
* Extra weight on the extruder to accel
* Noise
* Cooling of the part and/or head where you don't want cooling

Several people on this forum have stated that a fan design is a "deal breaker" or have similar strong, negative feelings about it.

I was wondering what their thinking is that leads to this fairly strong position. I, possibly naively, think it is not all that bad, though it is not as elegant as a design that does not need one. So what is so bad about a hot end fan?

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Several people on this forum have stated that a fan design is a "deal breaker" or have similar strong, negative feelings about it.

Heh, that would be me.

For me, my print head is already a very crowded place. The last thing I want to do is add another component that takes up a fair amount of space when my experience says it's not necessary.

Secondly, I think it's possible to get a sufficiently sharp thermal gradient without active cooling with a good design. Not to insult Sanjay or any other hotend designer, but requiring a fan says to me "We couldn't figure out a clever way to make this work without adding a fan". It feels like a kludge.

So there's my 2 cents.

the "deal breaker" i've heard this one a few times,

it's not so much about clever design and avoiding the use of a fan, there are only so many ways to keep the cold side of a hotend cold,

if a hotend maker says use a fan on the cold side it's usually for a good reason, my hotends don't particularly need a fan to function however for best results it's something i recommend doing, general reliability and control over things like extrusion rates and retraction are generally better , for those who are dead against fans, i've got the better half to a water cooled hotend,

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Has anyone tried a Peltier device?

thejollygrimreaper Wrote:
-------------------------------------------------------for those who are dead against fans,
> i've got the better half to a water cooled hotend,


If you feel like sharing some details about your water cooled hotend, I'd definitely love to hear them.

I like the fan and think the weight is negligible, at least for my overbuilt structures.
Geared steppers are the big weight culprits for my designs.

I'm not able to use bowden concepts as my filament tubes are 2-3 fee long.
I'm also not keen on the Wades designs with a plastic gear on big plastic gear, with springs, bolts, bearings etc.

Integrating the coldend fan and part cooling fan function seems to be a win/win.

I believe that the coldend section can benefit from getting melty, when desired, to help clear jams by melting them.
If the coldsection is always able to shed heat, jams that occur from heat soak (PLA softening up the length of the material itself) are harder to clear. a coldend that can be either hot or cold based on a simple fan on/off can't be a bad thing IMHO.

I've noticed that my Uprint has a fan off and extra high (330C) cycle, and I've concluded that it is a jam clear method, which also moves the melt zone down into the heatblock sweet spot. Then the fan on provides cooling for both the tube inlet and the road/nozzle tip area.

I may be wrong on this, but my next setup will be exploring the thoughts above.

dave

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Integrating the coldend fan and part cooling fan function seems to be a win/win.

I don't think this will work as well as you think. The problem is the fans have different requirements.

The hotend cooling fan has to run all the time. If it doesn't you *will* get inconsistent extrusion because the thermal environment inside the hotend will change drastically every time the fan cycles on and off. It will be worse than having no fan at all.

The part cooling fan needs to run only when needed to solidify the current layer. If you run the fan all the time, you will cool the part too much and it will warp - even PLA wants to warp more if it is cooled too much IME.

A peltier cooler would work, but the're no lighter than a 1 inch (25mm) fan. And of course you have to get that heat off the hot side of the peltier which likely means...a fan.

A peltier element will just move the heat 3 mm away and add a whole bunch more on the way. Then you have all that heat still right in your print head. Not really useful unless you need to cool something below ambient.

I haven't used a part cooling fan since I stopped using PLA. I think I would have more need for a part heating fan than a cooling fan, now that I'm using PC pretty often.