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Old 01-28-11, 12:03 PM   #30
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Join Date: Jul 2010
Location: East Coast of Florida, USA
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Default Prop with Twist

After Nibs latest post I decided to make a prop with twist. I used a bandsaw instead of the table saw for this one. If you want to duplicate it you will also need a rasp (rotary rasp optional), a hand saw, and some way to sand (I used a random orbital sander, but you could do it by hand). It took about 5 times as long to make this one as the one with no twist due to all the hand carving required.

Here's how to do it, step by step.

1) I ripped my board to 3" wide so it would fit in my bandsaw. You could go wider if your saw can handle it.

2) Mark the line for the leading edge on the top of the board (3/8" at the tip to full board width at the hub end. Flip the board end-to-end and do it again.

3) Set up a low fence on your bandsaw table. I used one of the cutoffs from ripping the board down to 3". Leave about 1/8" between the blade and the fence (this will form the trailing edge as the blade is cut).

4) Start with the line on the top of the board lined up with the bandsaw blade and the bottom edge of the board pressed against the fence. Turn on the saw and feed the board into the blade following your drawn line. Make sure you keep the bottom of the board pressed against the fence and the table and tilt the board as you feed it in. Stop when you reach the inside edge of the top of the board (where your drawn line ends). Turn off the saw and remove the board. Repeat for the other end of the board.

5) I used my router to get a start on the airfoil shape, but it's only good for the first few inches in from the tip of the prop on this design. You can do it all by hand with a rasp or a rotary rasp (see Step 7).

6) Draw a line squarely around the board where your bandsaw cut ends. Use the handsaw to cut into the board at an angle until you meet the bandsaw cut. This removes the waste piece. Repeat for the other end of the board.

7) Use the rotary rasp (or hand rasp) to carve the general airfoil shape into the back of the blade. You need to remove a lot of material near the hub, less toward the tip. When you get it roughed in, use the straight hand rasp to smooth it out.

8) Use the random orbit sander (or hand sanding block) to smooth out the rasp and saw marks.

9) Mark the center of the hub and drill the hole. I used a Forstner bit to fit 2 ball bearings to mine.

11) Balance it per Nibs' post.

10) Fly it.

I put mine up in the place of the 4-blade and it seems to fly well. I don't think the twist is right on this one, though (the blade angles don't match some online calculators that I tried). I'll post a video of it once I get some steady wind.

I can't upload all the pics in one post so I'll have a continuation . . .
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Last edited by Patrick; 01-28-11 at 12:17 PM..
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