Anyone got one? Or know where I can print a template out? Im at a stand still on the Ram Jet project untill I can get this. **Edit** I just downloaded the template widget, I Believe it will do the trick.

If you are in a computerless bind in the future, you can make a fin template without it. With four fins all you need is a pencil and paper. With three, you'll need a ruler. Wrap a piece of paper around the tube, mark where the edge meets. This gives you the circumference without having to do math.

With four fins, fold the paper in half where the mark meets the edge, then fold in half again. Don't use thick paper because it will throw off the marks. Thin paper won't make enough difference to worry about. Unfold. ( Optional: Mark the three creases you've made so you can see them better when you put the wrap around the tube again.) Wrap it around the tube, tape it down, and make your marks on the tube. With three fins, you will need a ruler to measure the length, then divide by three and make your other two marks. Finish out the same as with four fins. Forgot to add the line that you can do the same for six fins as you do for three. Just divide by six.

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I love sanding.

I didnt think about that, thanks man.

These might help. One is a .pdf and the other is a .jpg.

Greg

Attached Thumbnails

 

Attached Files

Guide3FinSetTemplate.pdf (21.1 KB, 133 views)

http://www.payloadbay.com/index.php

Go to tools, then the the Fin Wrap Guide, or the the Fin Guide Tool, which ever type you prefer.

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"Men and steel are alike. When they lose their temper they lose their worth." - Chuck Norris

Here's a trick that works with any rocket using any size tube and any number of fins...

First, wrap a sheet of paper around the rocket. Pull it straight and tight until it overlaps itself and the edges are square to each other, and mark where the paper overlaps. I usually put an arrow pointing back toward the other edge of the paper (under the overlap) so that I'm working with the right side of the overlap mark. (You can also use a strip of paper and this method to put a perfectly square 'ring' pencil mark around the rocket tube for cutting it to length, or to put fins or other stuff a certain distance up the tube from the end).

Take the paper off the rocket and lay it flat on your workbench. Measure the length of the paper from the end that was overlapped to the mark, which will give you the circumference. Make another mark on the other side of the paper at the identical length (you CAN just re-wrap the sheet around the tube again and do it that way too if it's easier) and then using a ruler, connect the two marks. Now you've established a line "square" (90 degrees) to the edge of the paper.

Now, take the number of fins you're planning to use. come up with some easily divisible number that is A) a multiple of the number of fins you plan to use, or easily divisible by the number of fins you plan to use, AND B) greater than the length you measured on the edge of the paper (the circumference). Once you've come up with your number (doesn't really matter what it is) place the ruler DIAGONALLY across the paper with one end right on the corner of the paper, and the number you chose laying EXACTLY on the line across the paper connecting the two circumference marks. Once it's lined up, go back and carefully mark each fin, by taking the number you chose and dividing by the number of fins. Mark both sides of the paper in this same method.

Use the ruler to connect the fin position marks from the diagonal marks on the paper to the edges, and voila!- instant fin marking guide!

Here's an example-- say you wrap your paper around a BT-80, which has a 2.6 inch diameter. Mark the overlap point and measure back to the starting point, which should be 8.164 inches, approximately (C=2 Pi x R). Now say you want to put 5 fins on this rocket. 2 inches would make a good number to use, since 5 x 2 = 10, and 10 is greater than 8. So, once you've connected the two overlap marks to establish a square line (which you CAN do with a drafting triangle if you have one, if not, using a square sheet of printer paper and wrapping it around to get the circumference works just as well). Once you have this square line connecting the two circumference marks, lay the ruler across the paper from the starting corner and pivot the ruler at the corner until the 10 inch mark intersects the square line. Now go back along the diagonal ruler and make a mark every 2 inches, at the 8, 6, 4, and 2 inch marks. Flip the paper and mirror the same marks on the other side (or use your handy drafting triangle from Hobby Lobby) and then connect each mark with it's mirror image on the other side of the paper-- connect all the 2 inch marks, 4's, 6's, and 8's-- you should now have a series of equally spaced parallel lines from one edge of the sheet to the other. Wrap the sheet back around the rocket tube and mark off the fin locations onto the tube by putting a mark on the tube at each line, and remember to include the overlap mark as well, since that's also a fin location (5 fins at 0/10, 2, 4, 6, and 8)

Now use the doorjamb or better yet your handy brass/aluminum angle to lay the fin lines up and down the tube squarely.

Sorry to be long winded, but once you do it, it's a piece of cake! Old drafting trick...

Good luck! OL JR

PS... say we use the same BT-80 rocket and we want four fins-- we can still use 10 since 10 divided by four is 2.5, which is easy to count off on the ruler-- pivot the ruler at the corner from the start mark til 10 is on the circumference square line, and mark off the 2.5, 5, and 7.5 inch marks, mirror on the other side, and connect the lines... instant 4 fins-- at the 2.5, 5, 7.5, and 0/10 overlap marks. Same with 3 fins-- only I'd use 9 in that case, because 9 divide by 3 is 3, and 9 is greater than 8.164, the actual overlap length (circumference). Line up the ruler start mark and corner, pivot to the 9 inch mark, and mark the paper at the 3 and 6 inch marks on the ruler, flip and repeat for the other side, and connect the marks, rewrap around the tube, and instant 3 fins at 3,6, and 0/9 lines...

Main thing is, keep everything square. Good luck!

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Similar method to Luke's, from my old drafting book. Line AB will be the circumfrence line obtained with the "wrap".

Attached Files

DivideLineGraphically.pdf (231.8 KB, 112 views)

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David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here

I just use the old yellow Estes thingie that is set for either 3 or 4 fins.

I mark the 3 fins as usual, plus one from the 4 set that's halfway between two of the fins. Now rotate the tube 60 degrees until that 4th mark lines up with one of the 3 fin marks, and mark the last 2 fins using the other 3 fin marks.

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don't know if this link has been posted yet, but here goes

http://www.rocketshoppe.com/info/fin_guide.pdf