Building The Blades. At last :-)
Right. First a bit about how I came to do things the way I have.
I have considered and rejected quite a few ideas for building these blades. A firm favorite at one point was to machine 2 part molds from foam and coat them in resin. Then inject expanding foam into the cavity. I produced the files needed for the CNC to cut them, but later rejected the idea in favour of machining the actual blades from the foam and skinning them with fibreglass.
Blade molds idea. Rejected.
However I decided to make the blades, they would have to be done in sections. One reason is that my machine cannot fit a whole blade on the table. Another reason is that it would waste a lot of material to machine it from one piece of foam.
The blades are each 1.1 metres long. They are designed with a "Tip speed ratio" of 6. Each blade will be machined in 4 sections and joined together, then the entire blade will be skinned with glass cloth and resin. The foam has no structural role and could be removed once the glass has set, but I shall leave it inside the blade because it'll be easier than trying to get it out.
Each section was modelled, toolpathed and translated into gcode. Then it was out to the garage to see how much mess I could make.
Cutting went much better than I'd expected. I was using a drill bit with the end modified, as a milling cutter. It was the only thing I had that would reach the maximum depth of cut. The stock foam was held in place with some double sided tape. In fact There's so little force reqired to cut the foam. I could have used a soggy corflake to hold it down. By far the most fun was watching it snow in my garage. I had my own foamy snow storm. Each section is taking about 4.5 hours to complete, which is longer than I expected, but it doesn't really matter as I can leave the machine to it's own devices while I drink coffee and watch TV.
Here's a piccy of the two sections just resting on one another. The square ends on each section were just to hold the parts flat in the machine, and as you can see in this picture, they get cut of once maching is finished.
I can't wait to make the next sections. Hopefully it won't be too long before I'm updating this page again.