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3D Printing an armature fan for a router

C

calgaryguy

Chris
My recent (and semi-stalled by my fault) efforts on prototyping a NEMA-IEC motor adapter flange with @Janger reinforced for me the value of 3d printing.

I have a 3.25 HP Porter Cable router, model 7518. I actually have 2 of them. Most people in the wood working hobby and commercial space know of these routers for their durability and the fact the model has been around for 30-40 years. Porter-Cable, sadly, is basically a dead company and parts for these routers are discontinued/out of stock. Watching ebay is an option but its hit and miss. These routers are very heavy duty and were also sold re-badged under the DeWalt brand after DeWalt acquired some assets of PC. They are sought after in the used market and are almost a 'buy it for life item'.

The issue with one of my routers is that the plastic armature cooling fan exploded. The router is 100% fine but wont last very long without its cooling fan. Here's a pic of a similar one. Note that it has a steel ring inside it for press fit on the armature.

Capture.PNG

Here's pics of the ring and separated/destroyed fan plastic from my router

IMG_0054.JPG

If you are cirous as to why I had to dremel/die grind the ring off - the ring had slid very close to the armature windings and I couldnt get a puller on it to remove without contacting the windings and possibly damaging the armature. At the time i was trying to preserve as much of the router as I could without damage so it could be used to parts at the very least.

The plastic fan is either molded onto, or press/shrunk fit onto the knurled surface of the steel ring. How exactly that process happens I'm not sure. The failure, if you are curious, happened when the steel ring moved slightly on the armature and made contact with the inside of the router body/housing.

SO, my question is: would it be possible to model a fan and 3d print it and attach/press onto/adhere it onto a new steel ring for this application? This router has speeds up to 28,000 rpm I think - will hobbyist 3D printed material handle this kind of speed/force? Modelling the curved shape of the blades looks to be a difficult task/ask: how would someone go about doing so?

As I stated up above, I have another, Identical router that has an intact fan - this could be used to do the modelling. Modelling the curved shape of the blades looks to be a difficult task/ask: how would someone go about doing so?

This is more a 'what if' or 'is this potentially' doable question. We can expand the discussion if its doable/possible...

Cheers,
Chris
 
Folks print collet fans for CNC routers on a regular basis.
Other folks always freak out about the explosion potential but I've not heard of one letting go.
Search Thingiverse for collet fan for examples.
I would print it in PLA or PETG. and see how it goes.
 
David said:
Folks print collet fans for CNC routers on a regular basis.
Other folks always freak out about the explosion potential but I've not heard of one letting go.
Search Thingiverse for collet fan for examples.
I would print it in PLA or PETG. and see how it goes.
Click to expand...
Good info, thanks!

And yes, I had seen some 3d cad examples of armature fans but wondered about the durability.

I'm not overly concerned about a fan coming apart as its internal to the aluminium housing - I mean except for the potential damage to other parts inside the housing
 
Hard to say how much engineering is in the router blade design from an air flow perspective. From across the room it generically looks like this article link. CAD wise it illustrates a likely method, a few 'airfoil sections' each at a certain angle & lofted to become a blade. Repeat the blade pattern around the hub. RPM & airflow & dimensions obviously factor into this. I have seen CAD examples of low speed fans for computers & such that are a more rudimentary constant thickness foil but who knows how much thought went into them. Even low RPM, low CFM cheapo PC fans have curved foils, progressive pitch even if more or less constant thickness. But others have an airfoil, maybe noise is a bigger design factor.

On a router, higher RPM & power levels for sure mean increased blade load. Maximum blade stress is adjacent to the hub which is why you typically see thicker sections or generous fillets in that area, but at the expense of airfoil efficiency. Blah-blah, I'm just trying to say at minimum you would want to replicate the type of plastic. Often these kinds of blades are injection molded but the plastic contains micro fibers for strength. I'm confident a home shop 3DP could make a suitable shape that would work, but I think you would have to define no infill (as solid as possible) & select a strong-ish filament. If there is no harm it it exploding in a contained environment then its basically trial & error. But if shrapnel can damage things, well that's a different safety aspect.

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Design and Testing of a Cooling Fan for Electro-Mechanical Actuators for Aerospace Applications

Air cooling with wing bay air circulated by axial flow fans is the most suitable and viable way in cooling aircraft Electro-mechanical Actuators (EMAs) used for flight control surfaces. The main objective of the cooling fan is to deliver high static pressure head and high volumetric flow rate...
vibgyorpublishers.org vibgyorpublishers.org
 
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Reminds me a lot of RC EDF (electric ducted fan) Chances of retrofitting probably slim but just mentioning more for comparison purposes. They look like injected plastic but I'm not too familiar with EDF power & RPM levels. RPM might be comparable or higher. But 3.25hp router is 2400 watts so getting up there.

1742930032900.png


 
ok that was surprisingly simple. I drew two blade "profiles" inside and outside out of some arcs in two sketches 50mm apart. I then used the "Loft" command to build the blade between the sketches. Then used the circular pattern function to wrap the blades around a cylinder shape, added a hole. With some more specific dimensions I think this would be easy to fabricate. Funny how "simple" things like a box with a lid that fits can be so troublesome but a "sophisticated" fan is 5 min. I spent more time writing this than doing the part.

1743043555214.png
 
Based on the krurling, the original was most likely injection molded over the ring (we made a few parts this way at Raymark back in the 90's).

3D printing (I think?) can also be done over a core, or at least enclosing a core dropped into a close-fitting cavity before the print is complete.

I would use a glass or carbon filled material for strength (and to minimize the potential for explosions). These materials may also work with an interference fit over the shaft.
 
Was the knurled steel collar no longer useable or that needed to be re-made anyway? The knurling wouldn't really help a 3DP fan hub if we are guessing the fan was injected molded around it, which looks to be the case although hard to see the IS surface of the broken plastic part beside it. I would not try to heat the ring & melt it into the 3DP like a screw insert because a) I don't think it would melt uniformly b) any off axis imbalance is asking for a blow out at 24K RPM

A new simpler 'plain' ring could be made if for example the plan was to drill some pin holes on the intersecting diameter line for steel dowel pins to act as circular section 'keys' in combination with a good glue. You could easily 3DP any kind of torque retention features on the fan hub side, but now you have the job of matching that by machining the steel ring.

Maybe someone smarter can help with the math to check shear force. For example if T = P * 5252 / RPM = 3.25 HP * 5252 / 24,000 rpm = 0.711 ft-lbs torque. Then relate that to hub diameter & shear strength across a pin. Or surface area * glue strength rating if you dare, LOL.

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