Making a small plastic fan

I need to make a number of small fans. These are around 52mm diameter and at the thickest part are 10 mm thick. The blades are approx 6mm high and are around 1.5mm thick. There is a metal insert in the centre with a reamed hole.

The fans are for some smallish motors rotating at around 5-6000 rpm.

I had considered making an aluminium mold but its very tedious cutting the slots for the blades....

I have the central metal inserts recovered from the original fans which were destroyed when they were removed from the motor shaft....

So what is the best approach to manufacturing a few of these fans?

Edited By John Rudd on 21/04/2017 18:49:36

Edited By John Rudd on 21/04/2017 18:50:20

Could you take a silicon mould of the one illustrated and then cast them in G26?

Looks like an ideal candidate for printing if you only need a few.

John

Is this fan for a hobby activity or for a commercial venture?

At 5-6000 rpm as stated I would be concerned about 3D printed parts (by any method) staying together. Balance of parts, particularly large diameter parts, is critical at those sorts of speeds.

CNC mill...? Take quite a long time but just leave the machine to get on with it. Material aluminium or perhaps corian. The latter mills beautifully and quick, have just been making a part in it.

Brian,

I had considered taking a mold from this example.....still pondering, but what is G26? Some kind of casting resin I guess?

I had thought of injection molding, but have no IM facility, thought of reinforced polyester resin ( chopped fg strands?) but not sure if there would be enough strength in the little blades....

Journeyman,

Yup thought of 3d prints, not sure if they could capture the blade detail.....besides it would require a 3D cad program thingy creating for the printer ( stl file?)

Thanks for sharing your thoughts chaps....keep 'em coming...

Try this company www.brocott. co.uk for replacement fan, or just search for replacement fan on line.

David

Edited By David George 1 on 21/04/2017 20:05:38

Edited By David George 1 on 21/04/2017 20:09:34

David, et-al....

Time to come out! I have an affinity for a particular brand of power tools from the 60's-70's......

To date my collection numbers some 32 electric drills.....!!

I have painstakingly refurbished them to bring them back to life.....unfortunately in doing so I have had to destroy the original fan on some of them in order to get the motor cartridge out from the body.....hence having to make new ones, replacements are like that metal stuff Unobtanium that John S often refers to......

A couple of photos of a refurbed drill.....

Edited By John Rudd on 21/04/2017 20:24:48

Edited By John Rudd on 21/04/2017 20:25:40

Hi John - nice drills.

The aluminium bore was insert molded in the plastic fan so that the fan didn't slip on the shaft. The rest would have been plastic for ease of getting them balanced (light weight) and of course cost.

Later drills had straight knurls on the armature shafts I think and had fans that were just plastic. I'm thinking that GFN would have been a likely material ...... high softening point and quite stiff and strong for a plastic.

The thing is, if the fan bore cracks and slips, or the fan breaks, then it's not good news - the motor will burn within a very short time if being used in anger.

So really, if you wanted make fans that would allow you to actually use the drills in anger, then I agree with JH, the simplest way is to CNC a new aluminium fan of thinner section than the original to keep the mass down, unfortunately. I think Corian may be too brittle to reliably press on the shafts though, but I 'm only guessing here.

3D printing may be a light duty possibility, perhaps, if you never want to use them to do any real work and keep them cool, but they are not going to last long in my opinion. Perhaps that would be acceptable for you however, since they really look too good to get dirty.

One last point . perhaps some of the fans are repairable ? If for example the bores were destroyed, perhaps sleeving could work ?

Cheers - Will

Is that a Stanley Bridges "Wasp" ? I seem to remember destroying a couple of those by making them work for their keep.

me again ...... just realised the fan blades are straight, so no problem to machine new ones with a rotary table and a normal mill. No CNC needed.

Cheers - Will

If you know someone with decent high speed cnc mill it wouldn't take long to mill them from a high quality aluminium disk finished in other respects back O/D and bore approx half an hour each after set up , just get the blades cut as light as possible and locktite them to the shaft with high temperature locktite when assembled.

David

Will,

Agreed, Corian is too brittle, I've used it for something else other than a fan and found it fractured easily.

The original fans were a press fit onto the arm shaft, only way to remove them is to break up the fan and pull the steel sleeve off wth a puller.....

Chris, the model above is a DR4t model, much later than the Wasp, which was a single speed job. I have one of them too, no bearings in sight just bushes! Shows how simply built they were in the day....

Yup, Already tried that....took a looooong time.....looked good when finished, but my little mill couldnt cope....the motor packed up!

Might have to revert to that method of production and take more time.....

John Rudd

FYI. More information and one of several sources at http://www.johnburn.co.uk/product-range/polyurethane-pur-fastcast-resins/

Brian,

Thanks for the link ( bookmarked) will have to get my reading head on.....

Will, just found out what GFN is......the orig fans were definitely plastic with a lowish mp....I tried localised heat on the central bush in the hope of releasing from the shaft....the plastic started to deform!!

Edited By John Rudd on 22/04/2017 10:17:06

Oooops, sorry John. Yes, Glass filled nylon.

It's still a thermoplastic nylon, but filled with glass fibers. should be still OK at 200 to 240 degrees c.

You can tell if it's nylon by taking a small bit it and setting it alight. Blow it out and it would smell like burned wool. Of course, that assumes you have previously held a sheep over a flame as a reference ..........

If you gently cut a sliver off the fan with a snappy knife, you would feel the fibers cut if it was filled.

If it's not GFN, perhaps something with a lower temperature like ABS ?

Cheers - Will

John,

Having both CNC and 3D printing equipment, I would do these in 3D. From your description and some rough guesses, I drew the attached in about 20 mins, stl file comes out from the drawings (in Onshape, stored in public under "small plastic fan" if anyone wants to play further with them). Dimensions taken from your text plus some guesswork to be roughly right.

Get them printed at a 3D printshop from the web in 'whatever' - probably ABS or nylon would be best.

Definition is down to 0.1mm so detail should not be an issue.

Simon