Tools
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Proline 4500 Mixing Chart (in grams)
HOW TO MAKE GREAT FILLETS
Hey everyone, I have been asked several times how I do my fillets. This is NOT the best way, just my way. When I started building high power, I dreaded fillets, but now they are the most exciting part for me.
Items Needed:
Carbon Paper
A ball to make the fillet size desired
Dremel with a deburring bit, or sandpaper for surface prep
Masking tape
Epoxy
Finding carbon paper may be the hardest item to source, a bit of a product of yesterday. I got mine at OfficeMax. If the person behind the counter is under 40, they will have no clue. I ordered mine online and had it ready for pick up at the desk. Or I would imagine Amazon would have it. I use a deburring bit in my Dremel for surface prep, but you need to score/scar the surface of the fiberglass, and if a cardboard rocket, remove the glassine outer layer.
I use the orange, heavy-duty Scotch tape for taping the area off, but any Scotch tape or painter’s tape will work.
A ball is the biggest trick. Not a pipe/tube/socket or craft stick. All those create variable depths and will not give you a consistent fillet. You can find all different sizes of wooden balls at Hobby Lobby. Find a size that matches the size of the fillet you want to create. I bought them all, and make the decision when I am ready. I use one per rocket, then just toss it when done. Simple and cheap.
Steps:
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Take the carbon paper and your ball and mark a line where the fillet will go. Lay the carbon paper in the valley of the fin/tube and drag the ball back and forth making the black carbon line.
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Prep your material for the best adhesion. I scar the surface with the Dremel. The sandpaper will have the same effect. Again if cardboard, remove the outer layer of paper or glassine.
Then remark your lines with the carbon paper as in Step 1.
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Take your tape of choice and mask off the area to receive the fillets. It is very important to place the tap the OUTSIDE of the black line. If you place the tape on the line, you will create a ledge in the epoxy when you pull the tape off. You want the ball and rocket surface to make contact in the following step, and the black carbon line represents where the ball the rocket surface meets. Tape to the outside so the ball drags the surface, and the tape will aid in the removal of extra epoxy that squeezes out.
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Adding epoxy. When you have your epoxy to the consistency desired, you are ready to pour. I prefer a fairly stiff epoxy (warm peanut butter). This can be achieved by letting the epoxy set a bit or adding a thickening agent (see manufacturers’ recommendations).
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After your epoxy is added, you are ready to shape the fillet. Take your wooden ball and wet the ball with a wet paper towel, and start on the fins leading edge and pull the entire distance in one SLOW pull. This will allow the epoxy to push ahead and fill in as needed. If you are short or run out, just add more to the fillet and re-pull the entire distance. It is important to clean the ball after every pull, as epoxy on the trailing edge of the ball will create uneven lines behind the ball. It’s best to add a bit of epoxy at the leading edge and just pull the entire distance anytime you need to redo a shape.
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After you are happy with the fillet, pull the tape. It’s best to do it now as the epoxy set up on the tape edge will make them hard to remove later. Just take your time, pull all the tape off, taking care to not mess your near-perfect fillet.
You also want to do this now, so that the extra epoxy on the tape will not run down onto your fillet.
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To close out, keep an eye on the ends of the fins to ensure epoxy does not run down before it sets up enough to not run. If you don’t want to babysit this area, be warned it can run and taper the fillets on the ends and make a mess on your rocket. Tape in the “run zone” is a good way to ensure it stays clean while it sets up.