LUNAR’clips 2002                        Volume 9, Number 3

Copyright © 2002 by LUNAR, All rights reserved.

How to Use a Book to Align Fins

Larry Deran, LUNAR #534

I have been struggling with the eternal problem of aligning fins, as has everyone else, and finally came up with what I think is the easiest method yet. Even better, it takes only immediately available materials, and produces almost perfect results.

The basic trick is to open a book and use it as a variable-thickness-plate by turning the right number of pages. You put the book next to the body tube on a table and leaf along until it is at the right place. Put a fin on top of the page and slide it over to the tube to check that the fin is at the right height.

After the height is right, make the usual three or four lines at the right spacing around the tube. For this, there are many techniques that all work fine. I use a circle drawn on cardboard with radial lines: place the tube over the circle and make tick marks at the intersections of the radial lines, then extend the lines while holding the tube in the notch of a door jamb.

Now get some Cyanoacrylate or "CA" glue. Don't bother with anything else, it's just a waste of time. CA hardens in seconds, and is a bit dangerous in that you can glue your fingers or eyelids together, so be careful and follow the directions. Wear latex gloves. (If you are allergic to latex, I think there are alternatives. But do find and use something.)

Lay a line of CA along the root edge of the first fin and place the fin on the book, sliding it over to the tube, which is on the same horizontal surface. Make sure that the fin-marking line is just visible above the fin, and that the fin is at the right position along the tube. There are only two degrees of freedom at this point, and everything is being held down pretty firmly, so it is not hard to get a perfect placement.

You can do another fin the way described above, but sooner or later you are going to come to a situation where a fin has to stick down into the table in order to allow the next one to be put on. To solve this problem, just slide the book and tube down to the edge of the table and allow both to project as far as

needed while remaining stable. This requires holding the book down rather firmly, but it is not hard.

After all the fins are on, fillet with a favorite strong glue. I use 12 minute epoxy, but probably elmers would work. The strength of the entire fin joint comes mostly from the fillets anyway. CA is rather strong, especially the 'gap filling' type, which has enough viscosity to stay put, unlike the original 'super glue' which was for china and other hard surfaces and which had a much lower viscosity.

The above technique has reduced my kit building time by at least one order of magnitude. I hope someone will try it out and tell me about it.

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