Download and print two template files from the links above. Make sure they're printed at 100% (200 dpi). When printed measure the distance between the dimension arrows, it should be 10cm on both pages. If it's a couple mm off that's probably ok.
Tape the pages together so that the 10cm dimension marks overlap as closely as possible. Best way to do this is on a window pane during the day, so you can see both pages showing through.
With a craft knife and the angle aluminium as a straight edge, cut out the outer border of the template.
Any time you're cutting, always make sure your other hand is never in front of the knife, so if you slip you're not going to slice yourself. The angle aluminium is good for this, as the vertical bit effectively shields the hand holding it.
Take an aluminium sheet and measure a box 42cm x 48cm. Draw a line half way up the 48cm length so you have two boxes measuring 42cm x 24cm. Score the outer lines with the Stanley knife and straight edge. You're not trying to cut through the metal, just create a line that can then be popped out later. A good method is to score once lightly, then a second time a bit deeper.
Do not score the 24cm halfway line.
Flex the metal so that it bends at a score line, then flex back the other way. Do this a couple times and it should split. Do the same for the other score and remove the outer metal. Keep it for later.
Tape the template to the metal rectangle (from now on to be referred to as a 'former') so that the long edge of the paper sits on the middle line and the right hand edges of both line up. Don't worry if the other edges don't align perfectly.
With blade and straight edge, score out the template curve, including the triangles at each end. It's not essential that this be 100% perfect, but try to get the first one reasonably nice as you can then use it as a template for the rest.
Score, flex, and remove the two triangles of metal outside the template.
Mark the centers of the little circles on the paper template with a marker pen so that they're visible from the other side and flip the paper over so that the printed side is down on the other half of the former, keeping the long edge on the middle line. Retape so it doesn't shift.
Give the curved score a couple of flexes and tear it out. Remove the two small triangles. Be careful not to bend the unscored metal too much as you're doing this as it may weaken it.
You now have your first former. Repeat steps 2 through 3 so that you have a total of 6 formers. You can use the first former as a cutting template rather than the paper. On three of the formers have the 24cm line drawn on the front, the other three on the back.
Take all six formers and peg them together so that they are as nicely aligned as possible.
Use tape to attach them if you don't have clothes pegs.
Drill each of the 16 holes through all six formers with a 4mm bit. Drill the center hole first, as this is the only one that needs to be reasonably accurate. It can help to put a bolt through that first hole to keep the formers from shifting around as you drill.
If the holes on your template are laid out a little differently than those in the animation it'll be because the template is more up to date.
Remove the template and unpeg the formers.
Place a former with the 24cm line slightly overhanging the edge of the table. Place the straight edge on the middle line and bend up to 90 degrees. Repeat with all six, with three formers bent shiny side up and three bent shiny side down.
Put the formers aside.
Take an aluminium sheet and flatten out any bends in the metal. Cut the long edge down to 67cm.
Draw a line 2cm from one of the 67cm edges, flip the sheet over and draw another line 2cm from the opposite edge on the other side of the metal.
repeat with 2 more sheets and peg all 3 together so that each drawn line is aligned to the edge of the sheet above it.
Mark the edge at 4cm, 6, 8, 10, 18, 26, 34, and then every 2cm up to and including 64cm
Keep in mind that one side has a score at 4cm from the edge, the other at 3cm.
Flip the sheets over, making sure they don't lose their alignment. Mark and score the same as the first edge. Make sure both have the 4cm gap on the same edge.
Tap the sheets on the table so that they are aligned on top of each other.
From the 4cm end draw a vertical line at 19cm from the edge, and one at 33cm from the edge.
Mark each line at 3cm and 20cm from both ends.
Drill all 3 sheets with 4mm holes at all 8 marks. If you're making a six vane turbine rather than three you can drill all six sheets at once as easily.
Unpeg the sheets.
Place a sheet so that the second 3cm edge is overhanging the table. Place the straight edge on the second score mark in and triangulate the edge as shown in the animation.
Triangulate the 4cm edge in the same way.
Pre-bend the sheet so that it'll be easier to place in the formers. Don't bend it so tightly that you crease the metal.
Flip the sheet upright and insert into the curve cut into a top former (the uncut half of the former should be pointing upwards).
The best way to do this is to first place the 4cm edge triangle into its slot, then the 3cm edge, push in the inner flap, then work the rest of the sheet through the cut.
Fold down the tabs so that the first three at each end fold out, then alternate. You will probably need to give the score marks a couple of flexes before tearing them, or use pliers if they're being particularly stubborn. If you find that you've bent a tab the wrong way leave it as it is, bending it back the other way will weaken the metal. Make sure the three long tabs alternate to each other.
Push up the former so that it's level with the bent flaps.
Place 2 bike spokes in the fold of the former and bend it closed. If you squish the edge of the metal around the spoke with pliers or similar it'll stop it from falling out.
Flip the vane, place the other former, and fold down the tabs in the same manner.
Slice and remove the former's two outer corners. Cut the smaller triangle level with the edge of the other former half, but give the larger triangle a 2cm offset, so that it overlaps.
Repeat for the other former.
Take one of the offcuts left over from cutting a former. Cut out a strip which is 7cm wide and then cut 4cm off the long length.
Triangulate the strip as shown.
Mark the rough middle of each end of the 3cm wide face with a line a couple of centimeters long.
Place the triangulated strut inside the vane so that the 3cm face sits on the row of drilled holes closer to the back edge. Sight the drawn lines through the top drilled hole to check that it's centered.
Drill the strut through the hole in the vane and attach with a rivet. Repeat for the bottom hole, then the two in the middle.
Take a fresh sheet, smooth out any bends, and cut the long length down to 67cm, then cut in half so you have two pieces 33.5cm wide.
Cut off 4cm from one of the short edges of both pieces.
Repeat so that you have four 33.5cm sheets (tho you'll only need three of them). Align and peg all three together.
From one of the long edges, draw three vertical lines at 1cm, 9cm, and 19cm.
Mark these lines in from both ends at 1cm and 20cm.
Drill a 4mm hole at each of the twelve marks.
Mark the sheet at 5cm in from the opposite edge.
Triangulate the edge as shown.
Place the half sheet inside the vane so that its un-triangulated edge is aligned with the vane's back edge. It's ok to have a small gap or bowl at either end if it doesn't fit perfectly in the vane.
Drill and rivet the row of holes in the half sheet closest to the back edge.
Stand the vane upright. Push the half sheet's triangulated edge in and forward so that it's against the other sheet and somewhat tight over the strut.
Drill through the row of holes on which the half sheet's triangulated edge is sitting and rivet in place.
Drill through one of the middle holes in the half sheet's back most row, making sure to keep the drill reasonably straight, and attach with a rivet and washer, so that the washer is on the inside of the vane. This bit is much easier with a second pair of hands. Try to keep the washer fairly flat on the metal.
Repeat for the other three holes.
Drill, rivet and washer the remaining row. The half sheet should be tight across the strut. You should notice that the vane is now a lot stronger and more rigid.
Fold up the overlap on both formers to 90 degrees.
These are pure aluminium sheets used in a printing process fairly common with newspapers and magazines. A medium sized printing company may recycle hundreds of plates every week, so it's usually easy to pick them up cheap.
Any size, thickness, or type is fine as long as they're larger than 67cm on the long axis.