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Printing a fan nozzle  

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scott.b47
(@scott-b47)
Trusted Member
Printing a fan nozzle

I have a Mk3 fan nozzle that I'm trying to print in a polycarbonate blend. The blend is relatively low temperature for polycarbonate, seems to print anywhere from 235 to 260. Probably prints even higher than that, though I see no need. Prints fine without an enclosure. Doesn't warp.

The part visually looks fine if I print it with the cooling fan on, but the manufacturer specifically recommends against doing so. My own tests show that printing with the cooling fan on leads to poor layer adhesion. Unfortunately as soon as I try printing with the cooling fan off, I end up with a mess around the mounting tab/hole. Pictures are attached. The rest of the print is more-or-less alright.

I'm tried numerous ideas, including going higher or lower with temperatures, higher or lower with speeds, increasing retraction, turning the fan on for bridging only, etc. There's just no way I can get this particular portion to print correctly without full-time cooling fan operation. Does anyone have any suggestions?

Thanks

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Napsal : 25/04/2019 8:11 pm
scott.b47
(@scott-b47)
Trusted Member
Topic starter answered:
RE: Printing a fan nozzle

Second picture, I couldn't figure out how to upload two pictures to the same post.

Attachment removed
Napsal : 25/04/2019 8:12 pm
vintagepc
(@vintagepc)
Member
RE: Printing a fan nozzle

The layers have very small areas in that region. - there is a setting to increase the minimum layer time and give it more time to firm up and avoid sagging. 

Additionally, print a second one on the opposite end of your build sheet at the same time. This makes the head move away from the first one and also gives it more time to cool; just slowing down still keeps the nozzle above the part which can radiate heat into it and aggravate the issue. As an added bonus, you'll have a spare in case you encounter a blob of death down the road! 🙂

Napsal : 25/04/2019 8:37 pm
scott.b47
(@scott-b47)
Trusted Member
Topic starter answered:
RE: Printing a fan nozzle

Thanks. Where do I find this minimum layer time setting? The only thing I've run across so far is related to the "Enable Auto Cooling" setting, which I suppose I could use in conjunction with setting a very low fan speed.

Napsal : 25/04/2019 9:04 pm
vintagepc
(@vintagepc)
Member
RE: Printing a fan nozzle

you need to be in expert mode under 'cooling' on the filament settings. 

Then, there should be 'slow down if layer print time is below...'

Napsal : 25/04/2019 9:50 pm
scott.b47
(@scott-b47)
Trusted Member
Topic starter answered:
RE: Printing a fan nozzle
Posted by: vintagepc

you need to be in expert mode under 'cooling' on the filament settings. 

Then, there should be 'slow down if layer print time is below...'

Yes, but that option is greyed if I uncheck `enable auto cooling` (at least in my Slic3r PE, which may be a version or two behind). I think I could get around this by enabling auto cooling and setting the fan to very low numbers.

Printing two of them has met with some success. There's still some nastiness right around the midpoint on that hole, but the molten sagging is much reduced. This was only changing from one to two models, I'll try adding some slowdown to it as well.

Attachment removed
Napsal : 26/04/2019 12:43 am
vintagepc
(@vintagepc)
Member
RE: Printing a fan nozzle

That looks like bridging. Make sure you have 'detect bridging perimiters' enabled, and enable *some* fan when bridging. That should help immensely. But that looks decent enough I'd probably just drill out the hole and call it good 🙂

Napsal : 26/04/2019 12:54 am
scott.b47
(@scott-b47)
Trusted Member
Topic starter answered:
RE: Printing a fan nozzle

What would a good definition for "some" be? maybe 30% ?

I've printed 13 fan nozzles so far, a few more couldn't hurt. I'm probably going to pause a moment and simply make a model that has the little tower with the countersunk hole through it. That would have made a lot more sense, ten fan nozzles ago.

Napsal : 26/04/2019 2:38 am
vintagepc
(@vintagepc)
Member
RE: Printing a fan nozzle

Unfortunately it depends on your filament and what temperatures it starts to solidify at. So I couldn't tell you an exact number... you'll have to experiment :-/ For example, filament printed hotter or that is droopier will need more fan to cool enough to keep its shape than something that is stiffer when molten or not too far above its melting temperature.

 

Napsal : 26/04/2019 12:06 pm
GeorgeE
(@georgee)
Trusted Member
RE: Printing a fan nozzle

You could just fill in the hole with a very thin cylinder at the midpoint  to remove the bridging then drill it out when the print is finished.

Napsal : 28/04/2019 11:22 am
Vojtěch
(@vojtech)
Honorable Member
RE: Printing a fan nozzle

Indeed, the "minimum layer time" options are what you're looking for. Enable 'auto cooling', disable 'always on', set the minimum fan to 0, maximum to whatever you need and a large enough minimum layer time. That will allow the whole print to be printed without fan and only the small part that requires cooling will have the fan turned on.

Aside from that, I do print filaments that explicitly say 'turn fan off' with a fan running quite often to avoid temperature artifacts on details, but then you need to print at the upper end of the temperature range to get decent layer adhesion and print quite slowly.

Napsal : 28/04/2019 4:00 pm
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