To Duct or not to Duct?

Hey All,

Is there a stance on using the fan ducts with 40mm fans?
I have been running but have been having a really hard time getting bridgesor overhangs to come out.
Any suggestions or ideas are greatly appreciated.

Thank You

Me too. The 2 9CFM 40mm fans I have aren't doing nearly as well as the single one on my Prusa's X carriage. I have 2 15CFM 50mm fans to see if that will make a difference.

As far as the ducts, they made no difference for me in print quality.

Edited 2 time(s). Last edit at 10/12/2012 10:20PM by pokey9000.

I still run them on my printed machine but I do have really powerful fans on it. They are extremely loud above 150 (60%) and the ducts do seem to work well. I did find the 50mm fans on the laser cut machines do not need them.

Have you tried turning up the fan speed?

I also have an RC filter on all the fans I use, it consists of a 1R 1/4w resistor and a 470uf cap.

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I thought about throwing some 40mm server fans I have around here in, but I really am enjoying how quiet Tantillus is. I plan to switch from using the heated bed FET for driving my fans to the scheme I use on my Prusa: spare PWM going through a low pass to a Darlington. That's been great at quieting the fans.

Hey All
So I have been running some tests but while they are going on, here are some pictures of the problem. I might have something else going on....

This is the extruder small gear, so we should all have a pretty good reference of how it prints and that it is not that hard of an overhang.

@Sublime
Here is what I am at spec and setting wise.
I am running two 40mm fans, 4.11 CFM with the ducts and at 255 there is no difference in the problem.
Both Fans pointing inward, (I'm not sure if this matters)
Barrel Temp (Actual) 175.
Layer Height - .15mm


Thank you all for the help and suggestions.

Edited 1 time(s). Last edit at 10/13/2012 10:27AM by tjhj2.

tjhj2 Wrote:
-------------------------------------------------------
> Hey All
> So I have been running some tests but while they
> are going on, here are some pictures of the
> problem. I might have something else going on....
>
>
> This is the extruder small gear, so we should all
> have a pretty good reference of how it prints and
> that it is not that hard of an overhang.
>
> @Sublime
> Here is what I am at spec and setting wise.
> I am running two 40mm fans, 4.11 CFM with the
> ducts and at 255 there is no difference in the
> problem.
> Both Fans pointing inward, (I'm not sure if this
> matters)
> Barrel Temp (Actual) 175.
> Layer Height - .15mm
>
>
> Thank you all for the help and suggestions.

First off the finish on the rest of the gear looks really good so I think you have the cables installed correctly and nice and tight.

That gear is a little tough to print in the orientation I have it because of the area right above the teeth is actually a 90deg over hang and the outside has a curve. This means it never prints 100 perfect but should come out better than what you got.

Suggestions:

Print four at once.
Slow down the print to 75% or 50%
Remove the ducts and see if it helps.

Also the ducts were made to line up with a hotend I had made for the first Tantillus and that Tantillus now has a J-head mk-IVb which is a lot longer than the mk-Vb. The duct may not line up correctly with the hotend and object being printed because of this. The mk-IVb is actually to tall and the mk-Vb may be a little short for it to line up correctly. The mk-Vb's I supply are in between the two lengths and line up correctly to cool both the thermal barrier and the printed object.

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The fans in the LC kits are rated at 15cfm for reference.

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
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So after some testing I am not sure what I have learned, but I will share and see what everyone thinks.

Setup
I took a large 5inch case cooling fan that puts out around 75 CFM and zip tied it to the front window. Which in my mind should be more than adequate.
I taped the lower duct off on the 40mm fan duct because it lines up under the build table due to my MK-Vb nozzle height. Now all my airflow should be directed at the build surface.

Additional Info
In the past I have found my minimum print temp is 160deg.
Both prints performed at 45mm/s perimeters and 60mm/s infil.
Infill 0.9


Tests
I printed one at the normal temperature I use of 175, with both 40mm fans at 255, and the large fan full power.
I printed a second one at 5 deg above my minimum print temp. Temp 165, 40mm fans at 255, large fan full power.


Results
The side facing the large fan printed well, but the side facing away came out badly again. There was no noticeable difference between the one printed at 165 and 175.


Thoughts
Yes cooling seems to matter, but is there ever going to be enough cooling? Is more cooling really the solution to my problem? If 75 + 10cfm of air flowing over the part in all directions doesn't cool the entire part, what will? Is it incorrect to say that the three fans should provide enough airflow to cool the entire part...

The direct cooling helped on one face but was not adequate enough to cool the entire gear.

I could cut the back of the case and install a rear fan to blow over the part, so get cooling on all 4 sides, but this seems to be overkill and I think I am fighting the wrong problem.

Any other suggestions on what it could be.

Edited 2 time(s). Last edit at 10/14/2012 10:42AM by tjhj2.

I think two stronger fans from the sides will give more even cooling than the large one from the front that would most likely be strong enough to make the side ones useless.

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Hang on tjhj2. Time permitting I'll be trying out 2x 15CFM 50mm fans tonight, and I'll post my results here.

Thanks Pokey9000 let me know how it goes.

I ordered 4 50mm 12.5 cfm fans. I couldn't find any 15cfms so well see where this leads.

Time didn't permit, but I did SCAD up a 50mm holder this morning that I'll print tonight.

These are the fans I bought: Link Depot FAN-5015-B .

edit: Printing the 2nd mount now. The first one fits perfectly. SCAD and stl attached.

edit 2: Don't print it just yet, Airflow seems to spread too far under the bed when the Z is homed. I'm redoing the mount with the fan 4mm higher (as far as it can go) to direct more air at the thermal break and the bottom of the nozzle.

edit 3: Updated part - fits great. Whether or not it cools better than the 40mm remains to be seen.

Edited 3 time(s). Last edit at 10/17/2012 01:03AM by pokey9000.

5015b is the same part number as on the fans I have in the kits. Mine are 2 wire and the ones from newegg are 3 wire but that should not make a difference.

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Did a print with the 50mm 15cfm fans, and it definitely makes a difference on overhangs. I still need to play with temps and feed rate for small layers, but I am seeing much less curling than before.

As a side benefit these sound less grating to me than the lower flow rate 40cfm ones I had on before.

Pokey9000,
Thanks for the info Ive got some of the 15CFM's on the way, I hope it works as well as yours.

Edited 1 time(s). Last edit at 10/18/2012 02:21PM by tjhj2.