The Mother of All Print Cooling Fans Revisited: Printable Blower

The biggest problem with the remote print cooling setup I tried here was that the blowers can be a little hard to get or expensive to buy.  At the suggestion of someone on the RepRap forums, I decided to try my hand at designing a printed blower that would mimic the function if not the performance of the CPAP blower.

The heart of the blower is a hard disk drive motor which most people can pull out of an old drive for free.  If you don't have one, someone you know does.  At the makerspace, some of the members work in IT and often bring in boxes full of HDDs to be scrapped.  They're mostly after the aluminum chassis to be melted down for casting, and the magnets.  I like to grab the bearings from the head positioning lever, and I grabbed a few motors for just-in-case.  It looks like that was a good idea!

I made some measurements and created a model of the motor first, then the impeller, and finally the housing.  This isn't a final final design- more of a proof of concept.  I'll be updating the design to some final form to fit the CPAP hose, etc., in the near future.  I want to experiment with a straight-through type design where the exit port will be on the "bottom" of the housing (should be easier to print).

Printed blower with the cover in place, held on with a few pieces of aluminum tape for testing.  The blower is 68mm in diameter and 41 mm high.

Cover off showing the impeller, held on the motor with 3 screws.  The impeller is 60 mm in diameter, and rotates CCW.  As it spins, air drawn into the center of the impeller is flung outward by the vanes, and goes down into the base where it is directed out through the exit port.

HDD motor mounts in the base using 3 screws.

Base has posts to mount the motor, and wires are fed through a hole in the side.  The posts are probably not very aerodynamic, so I'll look for ways to change the design for a little better performance.  It might be better to take the wires out through the bottom surface for the same reason.

3D printed blower for remote print cooling in a 3D printer from Mark Rehorst on Vimeo.


Ebay is littered with cheap drivers for HDD motors.

Update:  I reworked the design, made it much more practical, and it moves a little more air, too.  It's still not as powerful as the CPAP blower, but I suspect that's mostly because of the motor speed.

The new design prints in 4 pieces, the 80mm diameter impeller, top bottom covers, and the 22 mm diameter exhaust tube.  I decided to make the tube a separate piece so that it would print in very high quality.  It also allows the possibility for different sized tubes to be mounted on the same blower.

The assembled blower.

All four pieces: the base and top covers, the exhaust tube, and the impeller.  No support material is needed for any of them.

All four pieces print without support material.  I printed the impeller in 100 um layers, and the other pieces at 200 um.  I used PETG for the impeller and ABS for the housing, but since none of it gets warm, you could really use just about any materials you like.

The bottom side of the base (left) has slots for routing the motor wires.

I added mounting holes on all six sides of the housing, and some slots on the bottom for routing motor wires in case you screw the bottom of the blower down to a flat surface.

The output tube is 22 mm in diameter to match the rubber end of the CPAP hose.

The exhaust tube fits into slots in the top and bottom covers.  There are also bosses to ensure that everything self aligns when you assemble it.  The top and bottom covers are held together with plastic anchor screws.

While the box fits together tightly, it's a 3D print, so there's no guarantee that it's air tight.  It's probably a good idea to run a strip of tape around the seam in the box where the top and bottom covers meet to reduce any losses that may occur via that route.

How does it work?  See for yourself:

You can download the CAD files or just export the STLs here.

You can download the STEP file here...

Update  5/6/18:  I kept asking myself "why doesn't this thing move as much air as the CPAP blower?", so I did a couple basic tests.  Though I don't have a tachometer to measure the speed, setting them up side by side the answer was obvious.  The CPAP blower spins MUCH faster.  Another thing I noticed was that the clearance between the outer edge of the impeller and the housing in the CPAP blower was about 4 mm.  My printed housing was 83 mm in diameter and the impeller was 80 mm, so I designed and printed a 75 mm impeller to allow more clearance.  This impeller has 9 vanes instead of 12, which works nicely with the spacing of the 3 screw holes.

When I tested it again it didn't seem to move any more air.

That got me thinking- the CPAP motor is rated for 25W and when I'm running at full output, it's using about 12W to move the air (OK, some is moving the air and some is heating the motor).  The HDD motor is designed for low power- maybe 5 or 6W at 12V, so of course it isn't going to move the same amount of air as the 25W CPAP blower.  It's turning slower and it doesn't have the same power available to do the extra work needed to spin faster against the resistance of the air.

So, figuring that anyone who wants to use something like this for a print cooler for a 3D printer is probably going to have a 24V supply in the printer, I tried connecting it to a 24V power supply:

Printed blower with HDD motor running at 24V from Mark Rehorst on Vimeo.

Woohoo!  Look at that!

I decided to check the current:

Yup, about 1A which works out to about 24W.  The CPAP blower uses about 12W and it moves about the same amount of air.

I got out my handy-dandy IR thermometer and pointed it at the motor in the bottom of the case and it was reading about 60C after about 15 minutes of operation.  That's probably a bit excessive for a HDD motor and it probably won't last long at that temperature.  And you definitely shouldn't print the blower using PLA if you're going to run a HDD motor at that kind of power input.  Of course, in a normal 3D printer you don't need nearly that sort of air flow so it should be OK to run it for print cooling from a 24V supply.

I think this could be made to move air like the CPAP blower by using a BLDC motor used in RC cars and airplanes.  The CPAP uses a 4 pole motor rated for about 22k rpm and 25W.  That's about 2000 rpm/V.

In the RC world, they generally don't talk about voltage.  They think in terms of lithium battery cells connected in series.  Each cell produces 3.7V, so the closest thing to a 12V motor will be a "4S" (4 cells in series- 14.8V) motor.  So what we want is a 4S motor, preferably one that isn't rated for much more than 25W, which is similar to the CPAP motor spec.

The place to look for cheap brushless DC motors with similar ratings to the CPAP motor is RC hobby suppliers.  But you have to be careful when selecting an RC type motor is that they are often rated for huge amount of power in very small motors.  That means the winding resistance and inductance are. very low and they may take huge current (and run hot).  Those motors are usually kept cool by the prop-wash that is blowing over them whenever they operate.  The centrifugal compressor/blower I'm making copies the CPAP blower and puts the motor in the box with all the swirling air, so the motor should stay nice and cool.  Even at that, you don't want a motor that's going to suck too much current and you don't want it to burn up if you're running it from a 12V power supply.

If you're using this type of blower for a print cooler, it's never going to operate at full output, which means lower voltage motor should be OK even if you run the driver from a 12V supply.

A quick check at Hobbyking finds dozens of cheap brushless motors rated for 2000 rpm/V (2000kv in RC hobbyist lingo) or more, but only a few 4S rated motors.  If you use a lower voltage motor it will work OK, but if the driver ever fails it may burn up the motor.

Here's a promising motor for $7.42.  It's a 3100kv, 3S motor rated for 59W.  It should work fine from a 12V supply which will theoretically push it over 36k rpm, but again, we won't be running it nearly that fast for print cooling (PWM will keep the power and speed down) so it should work fine.  It's only 13mm in diameter and it weighs 10g!

UPDATE 4/1/20:

There's been a lot of interest in this post since the COVID-19 epidemic became a thing.  For anyone who is interested in trying something like this and doesn't know how to go about copying the curves in the blower impeller, I did a blog post that includes the technique I used here.