Making the Wind Turbine Blades.
The first part of the wind turbine I wanted to make are the blades. I previously made a test set of blades to be sure that they did indeed, turn in the wind. Success...I made a small video of the blades running on my test rig. (basically two bearings on a stick). The blades appeared to run very well in comparison to the two sets I'd made by hand a few years before. So I went ahead and started making a set.
I needed some blanks to machine the blades out of. Luckily for me, my father had some nice looking Pirana pine lurking in his garage. I managed to get enough out for a full set of blades. Each blank measures 600mm * 100mm * 28mm. The blanks will later be planed flat to a final thickness of 26mm. You may notice that the CAD model for the blades is only 24mm deep. The reason I'm cutting the blades from 26mm thick wood is that the trailing edge of the blade would be very, very thin if the blade was cut exactly to the CAD model. Basically the CAD model produces 2 surfaces to be machined. Whatever thickness you want the blade to be, you add onto the 24mm to get the blank stock thickness. So in my case there will be 2mm between each surface half.
If you've not got access to a CNC router. Now is the time to grab a hammer and chisel and start bashing away at a lump of wood. That's how I made my very first two sets of blades. It can be time consuming, but with some patience you can produce a nice set of blades for your wind turbine. If you do have a CNC router, put the blank in and go and have a beer while you wait for your machine to work it's magic.
I won't describe the CNC maching process for each and every part of the wind turbine, but seeing as this is the first one. I will give some details as to how I went about it. If you'd like to see the CNC in action, there's a small video in the video's section.
Firstly I resurfaced the sacraficial table top on the CNC router to ensure it was nice and flat. For this I used the Surfacing wizard in Mach2. Easy peasy so far.... Next up was planing both sides of the blade blanks to the correct thickness (26mm) and to make sure they sat flat on the table of the CNC router. I surfaced the blanks on the CNC, again using the wizard in Mach2. The blanks were secured to the table by using...... This may sound crazy, but double sided tape works great for this and saves having to make jigs and fixtures. So with the stock planed to thickness and held in place, it was time to load the gcode into Mach2 and begin cutting. There are two seperate gcodes for machining a blade, (one for each side). The first gcode cuts the profile shape of the blade out of the stock, it then goes on to shape the blade, firstly by (Horizontal Roughing), which removes the material in layers. A bit like a topographical map. After that it starts a (Parallel Finishing) pass, which smooths over the surface, in a back and forth motion following the contours of the blade. Once the machine has finished executing the first gcode, it's time to remove the blade and flip it over to machine the other side. When I made the first gcode. I purposely made the profiling pass cut too deep. This was so that it left an outline of the blade in the sacraficial table. This outline is what I use to align the blade in the correct position for machining the other side. The block you can see attached to the tip of the blade, is there to hold the blade level for maching the second side. When I made the test set of blades, I left small stumps on the first side to help support the under side of the blade after it had been flipped over. This seemed to create more problems than it solved. So to stop the unsupported section of the blade vibrating and deflecting away from the cutter, I pushed some small wooden wedges under the unsupported areas. Finally a picture of the completed blade, still on the CNC table. Just two more to go. The entire blade took just under 3 hours to make on my machine. If you want to see more of what I've been up to with my CNC router. You can have a look at my CNC website, here.