The parts were acquired through internet purchases, friends and stuff I already had from other projects. The 4 inch fiberglass tubing and matching coupler where purchased from Alan over at Hawk Mountain. I already had the nose cone that was for my Black Brant II project, but it was not to scale so I need another one for that rocket anyway. The 4-inch .125 wall aluminum tubing and 4-inch aluminum round rod came from OnLine Metals.com. The G10 for the fins and the alt bay boards came from Bill Begg's and the remaining hardware came from McMster Carr. I had the fiberglass cloth for the fin can glass other miscellaneous hardware. Now on the the fun part of actually building it.
The fin can consists of four 3/16th inch thick G10 fins and a fiberglass tube that I made using the combustion tube as a mandrel since that was the tube it was going to fit over anyway. Jeff gave me some very good instructions over the phone on the process to make a fin can using a mandrel. I have made paper tubes and various other items but never a fiberglass tube. For my first time it turned out great. I will describe how I did it for this project. Pictures are at the bottom of the page.
First step was to cut the fins using a Rocksim template from the sheet of G10 Bill Begg's let me borrow. As per Bill I used a jig saw with a fine tooth metal cutting blade. This worked well but it does eat the blade up quick. The first blade lasted for three fins (rough cut). During the first three fins I backed off pushing with moderate pressure and just let the saw cut and this seemed to be somewhat better. I finished up the last fin and some extra material for center rings and electronics mounting boards. Wow...there is still some blade left. Man that stuff is tough. Now I had to square up all the edges so all the fins would be the same size. Using the same technique with the Sponge Bob fins, I lined up the fins and clamped them together and drilled three holes. I then bolted them together so I could sand them all at the same time. I used a belt sander with 80 grit paper over all the straight edges until they were all even. MAKE SURE YOU WEAR A RESPIRATOR for this task. A dust mask will not do. The dust from this procedure produces a very fine fiberglass dust that is not good for you or your lungs. A good quality respirator will filter this dust whereas a dust mask will not seal completely against your face and allow these dust particle into you lungs. Please do not skip this step. Now all the fins are the exact same size.
The next step for the fins was to get out the fiberglass cloth and epoxy. The thought here is that I want to vacuum bag one layer of fiberglass to both sides of the fins to help later with a better grip for the overlay fiberglass when attaching the fins to the fiberglass tube. I don't know if this is necessary but I did it anyway. So I cut the fiberglass to match, two for each fin (both sides) and mixed the epoxy. I then glassed the fins and set them up with a bagging rig and let them sit over night. The next day I cut off the access glass and set them aside until I had the tube ready.
Making the tube was a little hard at first. Once I really got going it was much easier than I expected it would be. I may have to try this for a body tube sometime. The procedure from Jeff was slightly altered because I wanted to try something. I will talk the procedure I used and notate where I deviated you can decide. The first step was to debur the mandrel. This means to remove any sharp edges and major high spots. Since I was using an aluminum tube, this needed to be done. I just used emery cloth (or 200 grip sandpaper) to remove small burs or scratches. Use a file first for large burs then finish sand with the cloth. The next step is to wax the entire tube with carnauba wax and let it dry. Wipe it off with a clean paper towel and repeat the procedure again. Next get out some Christmas wrapping paper. You want to have enough so that it wraps around only twice and is about two inches longer that the tube you plan to make. Make sure the paper is tight with no wrinkles. Use two small pieces of scotch tape to hold the start and ending ends of the paper. This is harder than you think. Jeff says to wrap it so the picture side is down, but this is one of the times I deviated. I found that it was easier to wrap it with the picture side up that way it came off the tube. Next you are to wax the paper with the carnauba wax. Again harder than it sounds. Since the Christmas paper is already thin it can tear easily. When it gets wet, it tends to tear even more. So here is another place I deviated. I only used one wrap of Christmas paper with no wax and then one wrap of plastic wrap. The cheap plastic wrap that doesn't cling as well as the name brands works even better so you don't get any wrinkles. Same thing here for the tape to hold the plastic wrap. Two small piece of scotch tape for the starting and ending edges of the plastic wrap. Again another process that is hard to do than it sounds. Your mandrel is ready to make your tube.
Cut your fiberglass cloth so it is two inches longer than the root edge of your fins. You want at least five wraps but I recommend six. My 60 inch wide cloth gave my just under 5 wraps and so I cut another piece to give me six. Mix up your epoxy and apply some to the top of the mandrel just as you would like you are fiberglassing a body tube. Apply you fiberglass to the section of epoxy you put on the mandrel and slowly roll your tube. Add more epoxy and roll you tube some more (as in rolling up you fiberglass like you would with a roll of paper towels). When you are finished applying the fiberglass and it has enough epoxy (not dry spots), apply your next piece of glass if you are using more than one. Once that is done let it cure. I used my rotisserie setup to slowly turn the tube while it cured. This helps if there is any excess epoxy so that it doesn't pool at the bottom of you tube. Once it is cured come the fun part. Remember that your fiberglass tube is only a few thousandths bigger than the tube. Getting the tube off the mandrel. your tube will be a bit tight and may not slide off real easy but it may move some. I found that if I put the tube in freezer for about 10 minutes and then slide it off works very good. It two times of doing this, but it came off without too much trouble. I then cut the ragged ends off and set it aside.
Next I took two pieces of 1/2 plywood squared up the sides using a table saw so both are the same size. Then I drew diagonal lines from corner to corner. This gave me my center point to drill and the line to cut out for the fins to fit through. I then drilled a 3/16 hole in the center and used my circle cutting jig and slowly sized up the hole to fit the fiberglass tube I just made. Once the holes where made in both pieces, I matched up the edges of the boards and clamped them together. I then cut out the guide lines following the lines drawn on the boards. I made them about two inches deep and wide enough so a fin would fit. This was done for each fin. I then made angle cuts where the lines meet the round part of the circle to allow for the fin fillets. Then I put it all together. The holes for the tube where just a bit bigger so I used tape to shim up the tube to fit in the holes. I them put in the fins and used tape on them to hold them in the correct place on the tube at the correct angle. I taped the edges (tape dams) and mixed up the epoxy and started with the first two fillets. I repeated to procedure after the epoxy was cured until all fins had fillets on both sides. I have some sanding to do because a couple leaked while they were curing. The next step is to cut some fiberglass cloth to go from tip to tip of the fins two times and epoxy them. Don Spillman came over today to help me out a bit. He cut out the material to cover the fins over the fin can tip to tip. After he cut out the fiberglass he sanded all the fins and the high spots from when the tape dams leaked while making the fillets. He then start the glassing process by laying two pieces of glass over the fins. and set them aside. Thanks to Don, the fin can is much closer to being complete. We finished up the fin can by more sanding and putting on the fairing compound. We then put it on the rotisserie and let it dry. the finish came out great. it is nice and smooth and real shiny. just a little sanding here and there with some 400 grit and it is ready for paint.
