Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Cobra - Rear mounted cooler for Wanhao Duplicator i3.

by tahustvedt, published

Cobra - Rear mounted cooler for Wanhao Duplicator i3. by tahustvedt Oct 24, 2015
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EDIT - 20.12.2016

This cooler is still popular. I have changed the licence to let others adapt it to new printer designs.

EDIT2 - 29.11.2015

Updated again. More volume in the ducts and wider spacing between the exhaust openings. I hope it still performs like the old one.

EDIT - 29.11.2015

New design with a new blower orientation to clear obstacles better. Also has supports for the openings. I am printing it now myself. It doesn't need as much support to print. The walls are slightly thicker than before, but not quite as thick as the previous "fat" version.

EDIT - 31.10.2015

Added a duct with thicker walls. Only choose this if you have problems with printing the other one.

EDIT - 27.10.2015:

I added a picture of my own 70-80° overhang test which tests around all four sides, and it does equally well on all four sides. Also uploaded a duct with a slightly offset mounting hole to better align with the nozzle.

EDIT - 26.10.2015:
New and improved version with smoother ducts and more airflow directed towards the rear. The airflow feels very centered around the nozzle now. It performs better than any other I have tried on the Atom 80° Overhang test now.

A powerful cooler for 50x15mm blower fans. Being rear mounted means there's nothing obstructing the view of the print. The ducts are shaped to deliver a powerful blast from two sides without cooling the hot end too much, and a strong air flow can be felt all around the nozzle.

It mounts in the lower left hole of the lower bearing block. I recommend printing my plastic bearing blocks ( http://www.thingiverse.com/thing:1172838 ) and replacing the aluminum ones with them, because it lightens the printer considerably.

If you want to use the stock bearings, the hole might need to be tapped with a regular M4 tap, though you might get away with just threading in the screw if you use a shorter 10 mm screw. There is no need to remove the block to tap the hole, as there should be no screw in the hole originally. If you feel the flow is not centered around the nozzle try printing the little spacer to move the duct back a little.

Mounting it is not rocket science, and if you need to make some mods to adapt it to your printer because your printer isn't 100% equal to mine then deal with it. Just do it.

12V 50x50x15 mm blower fan. I use a cheap bushing fan with 0.18A rated current draw.
1x M4x10 mm to 12 mm screw for mounting the duct to the printer.
1x M4x20 mm screw for mounting the blower to the duct.

Print Settings


Doesn't Matter




Maximum 0.4 mm nozzle size.


Any. I used 0%


Use supports to the bed as necessary depending on your current overhang performance. Don't use internal supports, obviously.

I printed the prototypes using PLA, and they didn't melt despite printing at 230°C, but ABS would be safer.

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The clearance on my i3 Plus doesn't seem too good, any ideas?

I don't have a plus, but I assume they use the same hot end? The hot end is assembled slightly differently on each printer at the factory so some are higher and some are lower than mine. The hot end height can be adjusted by removing the stepper.

It's the same minus the little control board on the back with all the power connectors.. I'll have a look to see if i can alter it anyway. Thanks

Hey hey. Nice design! I really liked it, but the walls are soo thin. The "fat" version has the back fan facing at a 90 degree angle though and I worry it might not allow the wiring hub to be mounted in its place. Does it all fit or would it require some sort of adapter?

The walls on the latest version print just fine on a normal Wanhao Duplicato i3.

That's great, thanks! I'll give it a try

Is there any adapter for the Wanhao Duplicator i3 Plus for this cobra?

Carrier support for Wanhao Duplicator I3 Plus - for Cobra cooler
by jcheger

Would it be possible to obtain a .stp file? I'd like to adapt this for my Corexy printer

I don't see a way to fit this to the v2.1 bearing holder. The current spacer doesn't fit, and is too short to position the cooler correctly. What mounting spacer is everyone using for installation on the new v2.1 models?

Apr 20, 2017 - Modified Apr 20, 2017
TheBenBerman - in reply to rzkp78

It's elsewhere in the comments as well, just read

Wanhao I3 V2.1 Cobra Fan adapter
by raymnli

I can only say... AMAZING!!
This fan duct is outstanding, really. I can print out straight into thin air using this. Perfect surface finish even at overhang angles at 75 degrees. I highly recommend this to everyone.
The design is really good also from a "flow point of view", backpressure is kept low - so you use the full power of the 50 mm fan.

I printed it for the Monoprice V2 with the stock fan. Printed the fan adapter (too small) and then realized I also need another adapter. Found this remix that combines them all: http://www.thingiverse.com/thing:1982092

Wanhao - Monoprice i3 V2.1 Cobra Cooler for Stock Fan
Comments deleted.

Awesome design testing now. Definitely one of the best Ive seen

What support settings should I use on the v39 part?

Support to bed only, as internal supports will be impossible to remove.

Oct 17, 2016 - Modified Oct 17, 2016

I'm slightly confused by the 3 versions. Which is the latest?

EDIT: nevermind, 39 is the latest

Can anyone comment on whether or not this will clip the glass plate clips when near the corners? I recently built and sourced hardware to use this one: http://www.thingiverse.com/thing:1246425 but after attaching it I have found it fits the bed clips so bad it causes the Y axis belt to skip.

WANHAO i3 Fan duct
by Thorped

it would depending what you're using to clip it down with. binder clips? almost every cooler will prob hit those

Love this, printed as-is and mounted on my Duplicator i3 Plus.

Hey! Sorry guys, I didn't do anything special. I just unscrewed that bracket and let it sit on the cooler, the wires were just barely long enough to do it. I was going to print a replacement bracket, but it seemed happy just sitting there.

2nded, would love to see how you attaching this thing.


Any chance you can share a pic of how you mounted it to the I3 Plus? My plus has an extra bracket where this cooler would normally mount meaning its too far away from the nozzle.

Love your print setup.. great cable management and everything. Very clean.

Aug 11, 2016 - Modified Aug 11, 2016

Try this. Just design an adapter block for the V2.1 using Openscan. The spacer I mentioned below works but the fan can spin on the bolt axis. No need to tap the plastic bearing block. Link to the adapter.

Wanhao I3 V2.1 Cobra Fan adapter
by raymnli
Aug 10, 2016 - Modified Aug 10, 2016

Printed on, and then mounted to, a v2.1 but having some issues
1) The output of the ducts is not level front to back; the front is lower than the back by 0.5mm at least. I'm thinking of shimming the adapter block but worried if it sagged for another reason.
2) With only a single mounting screw I find that its tilting left-right. The single screw is a double edged sword, in that its easier to get it set just right on your own machine, yet more difficult to keep it set.
3) At 50% fan power I'm getting a +/- 2 degree C swing in nozzle temp. I have not yet autotuned the PID. With the stock duct, I rarely saw a it dip more than 0.1C so I don't believe I have the ground issue.

First overhang test was successful at 65 degrees, failed at 70 degrees due to warping (the layer curled up and kept snagging).

Aug 11, 2016 - Modified Aug 11, 2016
tahustvedt - in reply to LordKelvin

If it's loose even when the bolt is tightened then the bearing block is loose andneeds to be secured. One M4 bolt is more than enough to secure it permanently.

I can't make a thousand ducts to cater to all the different hot end placements. The hot end can be adjusted by loosening and repositioning, and no printer has exactly the same factory adjustment.

Oh no need to be defensive, I'm not expecting you to make more models. I was just commenting on the issues that I experienced.

The only model changes I would suggest are to improve manufacturability:

  • The fan mounting boss is rounded but when oriented for printing that results in a round overhang near the build plate. Suggest changing that to a square edge or 45 degree chamfer.
  • Similar note with the fan mount hole itself: making it a hexagon instead of round would eliminate support concerns.
  • For my install, there wasn't enough space to install a 25mm M4. I snipped out the back flange, but on a model revision I might enlarge that flange and then make a pass through big enough for the screw (not just an allen wrench).

On the left/right: the bearing block is not loose. It's possible the bolt is bottoming out before it completely compresses the bracket, but the issue would still be there even if it was tight; there is nothing to constrain rotation besides friction. Again, I might model changes myself to make a v2.1 version where the spacer is part of the model and a second oblong mounting hole is present.

If it's still loose then something is wrong. One tight bolt is more than enough to secure it.

hey tahustvedt,
I was wondering if it was possible for you to design a threedless screw to attach the duct to the printer as i don't have the knowledge or tools to tap the hole in the printer.

Adapter to fit Cobra cooler on Wanhao Duplicator i3 V2.1
by emila


I do not understand how to mount it? any video about it?
and as i see there is 3 STL file, what need to be print?

I have the original I3 with the cobra using a blower fan. It has given me many good prints. Recently, I upgraded the X-axis using the long Wanhao bearing kit to V2.1 with the plastic bearing block. The X-axis metal bearing blocks are gone. To compensate for the bearing block size difference, you need a 12mm spacer and a 24mm M4 screw or bolt. The spacer accounts for the bearing block size difference. Else if someone can design a spacer adapter for the V2.1.

12mm Spacer - http://www.digikey.com/product-detail/en/harwin-inc/R40-6711294/952-2193-ND/3728158

Loos awesome and I heard good comments about your design. Can you make one version aimed to e3dV5 and V6? Versions here are too small for the e3d heater block size (19mmX19mm)
Thanks for shareing

Anyone try this out on the 2.1 yet?

Here - this fits the 2.1 and uses the stock fan:


Wanhao - Monoprice i3 V2.1 Cobra Cooler for Stock Fan
Jul 7, 2016 - Modified Jul 7, 2016
tahustvedt - in reply to festaman

Looks like all you need to use it on the 2.1 is to make a C-shaped spacer between the Cobra and the threaded brass insert on the bearing holder.

Loks like they actually made some worthwhile improvements this time: http://wanhaousa.com/products/duplicator-i3-steel-frame

For those of us who still learn how to 3d design it would be great if that spacer was uploaded too :)

can't manage to fit m4 screws through the back of the blocks. they just get stuck. ideas?

Jul 2, 2016 - Modified Jul 2, 2016
nineismine - in reply to capze

having the same issue ...

I had a VERY hard time getting this to mount there were threads in the bearing block but in order to get the screw to thread I ran in into the hole once without the cooler. BE VERY CAREFUL you do not tighten this screw too much (with a drill for instance) as the rear exit for this hole is flush against the extruder and if you are a dummy like me you can actually bend this bracket by using a drill and not paying attention.

After I did this (and fixed my dumb mistake) I STILL couldn't get this cooler to mount. In order to get it to mount I used a dremmel and sanded the top of the area the screw mates into on the cool (Directly above the screw). EVEN after sanding that little bump over the screw until it was flat I sanded some more and it STILL didn't want to go in. To explain what I did next is kind of hard but here goes, I then sanded the 90 degree angle of the cooler that mates with the bearing block down until it was about 45 degrees, I didn't have to go too far but this let me angle the part in and get the screw to catch slightly off center. Ill post some pictures somewhere if anyone is in need of help and my explanation doesn't make sense.

Jul 4, 2016 - Modified Jul 4, 2016
tahustvedt - in reply to nineismine

-Get an M4 tap and run it into the hole first. This is the obvious answer. I even say this in the instructions
-Print a plastic bearing block and replace it. This is even better as the carriage becomes lighter.
-Use screws with a slightly smaller diameter, for example 3,5mm self tapping screws.
-Run a 3,9 mm drill into the hole first so that the M4 screws will form threads more easilly. I haven't tried this, but you're a maker, figure it out. ;)

Will this fit a Monoprice Maker Select v2?

Yes, nothing was changed that would impact this shroud.

Is there a version for the i3 Duplicator v2.1?

If this is the one, then all you need should be a C-shaped spacer: http://wanhaousa.com/products/duplicator-i3-steel-frame

Not from me. I don't have that printer.

Hello tahustvedt,
I have printed your cooler (latest revision) without a problem. I chose your design because i liked the idea of moving the fan to the rear of the rear of the printer giving a lot better view to the nozzle/print. So thank you for a great design.
I made an addition to your design, that might be useful to others as well. I had no 50x50x15 fan at hand, so I designed a duct that let me use the standard 30 mm fan. It works quite well: http://www.thingiverse.com/thing:1601940

Wanhao i3 standard 30mm fan-to-cobra adapter
by suneboe
May 11, 2016 - Modified May 11, 2016

Hello tahustvedt!
Good shroud but design needs an update!
1) i have printed a Fat version from ABS. Printed it like on screenshot.
2) Needs to have thiker walls of base ( where fan is inserted) Wal are so thin that they break when supports are dismounted. I have thikened them myself
3) air outlets need to be 1.5mm lower and about 2-3mm more apart. My heating block touches outlets and one melted a bit.
4) Air pipes can be made thinner and lifted a bit. Why? For example I find placing printed with back to me is better - because i see all the intenals and have aces to them without tossing printer around. Plus i have Z braces - accesing printe bed from Front is not very handy because of Z braces.
5) Would be very good if you could make a version for those wo has backorientated placement - fixing shroud to fan brackedinthe front.

Thank you for your item man!

Comments deleted.

I can't find a blower fan with .18a draw. I see .14a and .15a and up to .16a but no .18a

Someone have an Amazon or ebay link to an appropriate 50x50x15 blower fan for this project?

Apr 25, 2016 - Modified Apr 25, 2016
Dennish3D - in reply to JenniferG

Found on Amazon: 50x50x15 DC blower fan, 12V 5012, 0.1-0.2A, Made by YIDE, ASIN B00KNP794M. $7.65 (Prime)

Mar 15, 2016 - Modified Mar 15, 2016
JenniferG - in reply to tahustvedt

Okay thanks I guess I'll order the Delta fan now. Thanks for the link! Is it relatively light still?

It weighs the same as the other fans as far as I know.

Mar 15, 2016 - Modified Mar 15, 2016

Do I need an M4 tap if I print the plastic bearing blocks? Was planning on printing the one with recess so belt doesn't rub.

EDIT: Nevermind, I reread and found that they work great with the printed ones without tapping.. also found out you are the one that created the plastic bearing blocks as well -- awesome! :)

Am I going to have a problem with it coming loose with one screw like some have mentioned?

Is there room to add some meat to that bracket arm? Having a hard time printing it with any strength.

What orientation should it be printed?

Excellent cooling. I honestly avoided this one because it seemed a little too flamboyant, but it works extremely well. It seems to to a better job of cooling the part than any of the others I've tried, and doesn't seem to over-cool the hot-end like some others. I was also worried it wouldn't print very well because of the complex shape, but I was able to print it at 0.2mm with no supports and it came out perfectly usable.

Great design. Any chance you could modify it for 75x15 fan?

Jan 12, 2016 - Modified Jan 25, 2016

Great design, better than the other shrouds I tried. I do have a request for the next version. The shroud can rock slightly around the single bolt, this can easily put it in contact with the hot end. An fix could include an arm to reach the second bolt hole or perhaps a brace which formed around the bearing block to prevent it from rocking.

Even if this change is not implemented, it's a great design, very happy. Thanks.

Update: Jan 24,16. After several weeks of excellent service the Cobra shroud came to an end. :( I had a bad print, one end of the should must have caught a stray strand and got pulled downward putting it in contact with the hot end and everything went downhill from there.

I agree, that should make this one the very best!
I´m using plastic baring blocks which doesn't have as strong holes as the aluminum. Therefor I need another attachment point.

Thank you. Good idea.

Jan 11, 2016 - Modified Jan 11, 2016

Unrelated to the cooler, what is the piece in one of your pictures that you mounted to your heated bed to protect the heated bed wire from bending? I would love to have something similar. [Edit: this guy https://imgur.com/VTB2Kgm]

I just drilled a little aluminum V-profile and secured it to that so that the wires won't break at the soldering points. I used a piece of fiberglass between the bracket and the be to isolate it from the circuits.

What size fan is it fore? what are the dimentions?? looks awsom thx

12V 50x50x15 mm blower fan. I use a cheap bushing fan with 0.18A rated current draw. The parts list is listed under details.

Sorry dident se that :-/ but thx. it is under construction :-) looks greate so fare ;-) and i order a fan now to.

I want it for 60x60mm Fan :)

Great update, really like the new version, printing now, will try it later today :)

I printed the update. It works well, at least equivalent to the older version.

  1. It is easier to print, just make sure you disable "detect thin walls" if you are using slic3r
  2. It places the rear of the cooler much higher up, reducing the chance of accidentally knocking your print
  3. it probably has better flow than the old design
  4. the air outlets are slightly further away from the hot end for less melting potential.
Nov 25, 2015 - Modified Nov 25, 2015

I only use this cooler. Great results every time and never any cooling issues!

Would it be possible to make an adaptor or a new version that has the blower fan vertical mounted? Right now I find that the horizontal blower orientation often rubs on the heated bed plate wiring and knock the cobra off balance

I changed the blower orientation and angle now, maybe it works better for you. I don't want to angle it up more because the performance will suffer.

Thanks for taking the time to update your design. I will print it and give you feedback.

Just a tip- if you are having trouble with this print using slic3r, try disabling "detect thin walls" in the "layers and perimeters" setting menu. It gave me all kinds of issues with this model.

Nov 8, 2015 - Modified Nov 8, 2015

Strange because some people in the Facebook group also have this.

Thanks but I will have to pass since I am not sure I want to mess with the hotend.

Thanks again!

You can raise the hot end a tiny bit or lower the nozzles by doing some slight mod to the mounting hole/surface. I never had this problem.

Can you widen the gap between the nozzles? One of the nozzles melted because it was touching the heater wires.

I have same problem too) one nozzle melted

Is the duct level? Is the nozzle centered? You can adjust the nozzle centering by loosening the two screws under the extruder. The worst I have seen with a prototype was when the wire melted itself a little into the PLA nozzle, but the nozzle didn't droop or anything, and still worked fine. Can't you move the wire out of the way?

Nov 8, 2015 - Modified Nov 8, 2015
ericmoritz - in reply to tahustvedt

Yeah, that was the problem. I was able to bend the wires out of the way. Great cooler by the way. It is the only one that gives good cooling at 100% fan power without dropping the extruder temp by more that 10c

I meant one nozzle of CobraCooler was melted... maybe it has touched a nozzle during printing....

Maybe I just don't have my printer tuned well yet, but I struggle a bit with 0.8 mm wall thicknesses. Is there any chance of changing this file to have 1.2 mm wall thickness for a little more strength?

It's a lot of work to redo with thicker walls. What happens when you print 0.8mm walls?

surface finish isn't great, some delamination, and the underside of the "nozzles" where the support had to hold them up has holes/ incomplete shell

Oct 31, 2015 - Modified Oct 31, 2015
tahustvedt - in reply to chinkel

I uploaded a version with thicker walls. I haven't tried printing it, but I hope it works better. It doesn't have to be pretty to work well though. :)

Thank you so much it's awesome with thicker walls!

Nice! Had problems with the wall thickness aswell. Will print the fat one instead :)

How this cooler must be mounted? I tried to use m3/m4 screws, but they didn't hold in hole on back of the caret.

If the holes don't have M4 threads already then you need to run an M4 tap in them to make threads. I mention this in the instructions. Don't worry. Making threads in aluminum is easy.

Thanks! I have made threads with tap.
And set up cooler with M4 screw, but it is too low to hot table. Is it possible to made back part of cooler higher by a 4-5mm?

There is not enough room under the bearing block to raise the rear. The rear should be slightly higher than the nozzles, unless something is wrong.

yes, it slightly higher, ~1-2mm from heatbed, but cooler is touching clips that holding a glass on sides of my heatbed... And I still not found solution of this problem(

Ah, that's a common problem with all ducts. The solution is to use silicone pads to secure the glass: http://3dprinterbrain.com/pmwiki.php/DupI3/Tips

thanks for link! Already purchased silicone pads from ali, will try to use them in place of paper clips.

Keeping an eye on this to see if the design changes a bit to get max cooling then Im printing this!

I did some prints with this cooler...
...It's OK....
It's nice, to be able to see the nozzle while printing.
But it lacks of cooling capability in comparison with http://www.thingiverse.com/thing:1025471 .
Maybe, you could join the two outlets in the back of the nozzle, and make it a semi-circle?
I don't know...

DiiiCooler for Wanhao Duplicator i3 / Maker Select
Oct 25, 2015 - Modified Oct 25, 2015
tahustvedt - in reply to Bakak

I have wondered if I should make a third channel to the rear of the nozzle. I don't think it will work well if I make a semicircle, because the air will probably flow along the outer walls. I have ried that before with another duct, and there was no flow in the center. The Cobra does not rob the hot end of a lot of energy, which is a nice benefit in my opinion. :) Try the spacer. I will try using two spacers now to center the flos of the Cobra better.

I did a comparison print with Cobra and that cooler, and got very similar performance. I used the atom overhang test at 40 mm/s.

Maybe some LEDs?

Good idea.

So, what should we mount to the original fan bracket now that the fan is out of the way?

There's a clip to mount a dial gauge to the fan bracket.

Wanhao i3 feeler dial clamp

An LED strip

I already added a led strip design. Check my profile.

It's crying out to have a 40mm fan mounted on the top to cool the extruder motor.

That's a great idea.

I think it can benefit from moving a few mm towards the back. I will add a spacer to the files for tuning.

where this spacer need to be placed? thanks

Oct 29, 2015 - Modified Oct 29, 2015
tahustvedt - in reply to denis0k

The spacer was for the old version, but it still fits between the mounting face and the bearing block if you feel that you need to move the cooler back a few mm. The spacer is only for tuning.

Looks awsome! Printing it right now