Propellers, because I know it can be done;-)

[bryan]

I'm wanting to cut a 5 blade propellor for a wind driven pond aerator, I have everything but the blade to drive the air compresser. Looking at a size of approx 48", wanting to blow big bubbles in the pond. I have some ideas on cutting this but looking for other ideas to see if there is a better way. Which we all know there always more then one way to CNC. Ok, with that said any suggestions?

2388

[thewoodcrafter]

Bryan,
Can't help with cutting a prop, but are you sure a fan blade can develop enough static pressure to blow air bubbles?

[srwtlc]

Bryan,

Can't help with the prop either, but it sounds like a good two side Cut3D job. Surely there's someone out there that could model this. There appears to be quite a lamination process involved with your sample picture!

We've been thinking about blowing bubbles in our pond too, so I'd be interested in what you come up with. What did you come up with for the other components?

Roger, the "prop" is driven by the wind which in turn drives a compressor that pumps air through a hose that is extended out into the pond. Sort of a small version of the old windmills used for pumping water, but pumping air instead.

[Brady Watson]

Bryan,
If I was approaching this, I would 1st come up with the shape of one blade of the prop. I would either laser scan a similar prop (just one blade) or create one blade from scratch in Rhino with cross sections and rail sweeps, using known good cross sections. I'm sure there is software out there that can generate useable cross sections that can be adopted to your application. Then, after you have one blade, just rotate copy it around @ 72° apart and do a boolean merge with your hub. From there, export the model and machine in Cut3D using a 2-sided strategy. Laminated hardwood, and even treated 2-by material can be used for the prop.

Before even making a sample prop, I would investigate the gear reduction needed to get the required torque & RPM for your setup, and get an idea of the wind in your area and how much you can expect. You may find this link helpful in your quest: http://www.windstuffnow.com/main/blade_design_help.htm

-B

[bcammack]

I think I'd want to have separate blades that key into a central hub. That way I could just repetitively cut a single blade program instead of an entire propeller unit.

I can think of two upsides. First, if something goes amiss, you've only ruined one blade, not an entire propeller. Second, I suspect it'd be easier to balance with individual blades.

[myxpykalix]

Rather then reinventing the wheel, or in this case the propeller, It seems to me you might find at an industrial salvage yard some type of industrial air conditioning unit with the fan and shaft that you could adapt. I go to university surplus auctions and i have seen similar things there in the past. Those fans are lightweight tin i think already made so it would take it out of being a shopbot project though.

[kfitz]

http://www.princeaircraft.com/default.aspx

Lonnie uses a 'bot to make props. He's just west of Toledo, OH.

[bryan]

Scott, I'll keep you posted on what I finally decide to use, I'll be using a geared drive system to the small compress?


Brady, you are a walking resource of info, thanks for the great site, didn't even think about rotating the first blade of getting it drawn. I'm looking into the gearing ratios that will be needed based on the kansas wind patterns and speed.

Brett, good point on the balanceing the blades planned on removing material from the backsides of the blade to balance them,
Thinking that the blades as one piece unit it will be stronger and less stress on the center joint.

Jim, who emailed me off line, using a pump like a bicycle pump I had not thought of that, will have to look in to that to see if that would require less gear ratio to drive it.

Jack but picking one up at the salvage yard that take all the fun out of playing in the shop;-)

Kevin thanks for the web link I'll have to email and see if they have any suggestions

Thanks to everybody for idea and input, time for some drawing and research. Bryan

[myxpykalix]

I realize my solution takes all the fun out of creating your own propeller but think of it this way...it allows you time to be creative on some other project!
Seriously tho, when i was thinking about this I was concerned about the weight of the propeller and how much wind would be needed to spin a wood propeller versus a lightweight metal one. I'm interested in seeing what you come up with. Maybe a trip to Holland is in order to check out the ideas. I'm sure you could write it off as "research".