sunderll
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One of the common issues when scratch building rockets is how to construct a light, strong and STRAIGHT fin. I've come up with a solution I'd like to pass on. It's pretty straight forward and may have been posted here before, but if not, I'll do it now.
Most of my rockets are 3" to 4" body tubes, weighing from 2 to 10 pounds and motors ranging from Gs to K's. I've used this on all of them.
One of the problems is always finding material that is REALLY straight and rigid. I gave up trying to find inexpensive AND straight plywood. So, I decided to make a simple 3 layer fin with 1/8" balsa sheets sandwiching 6 oz fiberglass cloth soaked in resin. The resulting fin is 1/4" thick incredibly strong and perfectly straight. When the resin has cured, the rigid cloth makes for the perfect center-line for sanding your taper on the edges. I'll include pics and explanations, although it's pretty self explanatory.
1) Print fin template from program. I use Open Rocket.
2) Trace onto a piece of card stock or 1/16" balsa, which is what I did.
3) I use 1/8" x 6" x 36" balsa sheet purchased from Hobby Lobby with their 40% off coupon found on their app. If you have larger fins, I just butt glue them together with instant glue.
4) I cut the long sheet into section large enough to border the template on all sides. Make two of these per fin.
5) Cut a piece of cloth ( I used 6 OZ in these photos) the same dimensions as the two piece of balsa sheet
6) On a very flat work surface ( I buy a 2'x 4' piece of sheet rock) cover the work area with waxed paper in case any resin oozes out the side.
7) Mix resin. In these pics I mixed 1 Oz. Pour half of it on the lower balsa sheet and use a piece of scrap balsa to spread it around evenly.
8) Lay the cloth in the wet resin. Using the same piece of balsa or spreading tool work the resin through the cloth weave.
9) Pour the rest of the resin on the saturated cloth and again spread it evenly over the cloth.
10) Lay the second balsa sheet on the top with the edges even. Using light pressure, slowly move the top sheet in circles to work the resin evenly.
11) I used a 1" x 8" wide pine, very straight, board to lay on top of the top balsa sheet and used a 5 Lb. weight to apply even pressure on the top board.
12) I let it cure about an hour minimum.
13) I then check to see that the resin is somewhat hardened. I then trace the outline of the fin, using the fin template on the sandwiched assembly.
14) You can cut on the lines any way you want. When the resin is still soft, I've used a single edge razor blade and straight edge. In my case I have a small table top band saw which works perfectly.
15) You can sand the perimeter of the fin any way you want, and the best part is the hardened resin center make a perfect center-line that the sanding bar stops at, making a razor sharp, perfectly straight tapered leading edge.
16) You can finish the balsa anyway you want. Any kind of a sealer fills the grain really nicely, then just paint. These are super straight and strong.
The next post shows the sanding bar and how it will taper nicely to the center hardened cloth.
Most of my rockets are 3" to 4" body tubes, weighing from 2 to 10 pounds and motors ranging from Gs to K's. I've used this on all of them.
One of the problems is always finding material that is REALLY straight and rigid. I gave up trying to find inexpensive AND straight plywood. So, I decided to make a simple 3 layer fin with 1/8" balsa sheets sandwiching 6 oz fiberglass cloth soaked in resin. The resulting fin is 1/4" thick incredibly strong and perfectly straight. When the resin has cured, the rigid cloth makes for the perfect center-line for sanding your taper on the edges. I'll include pics and explanations, although it's pretty self explanatory.
1) Print fin template from program. I use Open Rocket.
2) Trace onto a piece of card stock or 1/16" balsa, which is what I did.
3) I use 1/8" x 6" x 36" balsa sheet purchased from Hobby Lobby with their 40% off coupon found on their app. If you have larger fins, I just butt glue them together with instant glue.
4) I cut the long sheet into section large enough to border the template on all sides. Make two of these per fin.
5) Cut a piece of cloth ( I used 6 OZ in these photos) the same dimensions as the two piece of balsa sheet
6) On a very flat work surface ( I buy a 2'x 4' piece of sheet rock) cover the work area with waxed paper in case any resin oozes out the side.
7) Mix resin. In these pics I mixed 1 Oz. Pour half of it on the lower balsa sheet and use a piece of scrap balsa to spread it around evenly.
8) Lay the cloth in the wet resin. Using the same piece of balsa or spreading tool work the resin through the cloth weave.
9) Pour the rest of the resin on the saturated cloth and again spread it evenly over the cloth.
10) Lay the second balsa sheet on the top with the edges even. Using light pressure, slowly move the top sheet in circles to work the resin evenly.
11) I used a 1" x 8" wide pine, very straight, board to lay on top of the top balsa sheet and used a 5 Lb. weight to apply even pressure on the top board.
12) I let it cure about an hour minimum.
13) I then check to see that the resin is somewhat hardened. I then trace the outline of the fin, using the fin template on the sandwiched assembly.
14) You can cut on the lines any way you want. When the resin is still soft, I've used a single edge razor blade and straight edge. In my case I have a small table top band saw which works perfectly.
15) You can sand the perimeter of the fin any way you want, and the best part is the hardened resin center make a perfect center-line that the sanding bar stops at, making a razor sharp, perfectly straight tapered leading edge.
16) You can finish the balsa anyway you want. Any kind of a sealer fills the grain really nicely, then just paint. These are super straight and strong.
The next post shows the sanding bar and how it will taper nicely to the center hardened cloth.
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