PDA

View Full Version : Rocket Ship build: homemade ply?


stefanj
07-07-2010, 07:52 PM
I'm starting work on a classic "rocket ship" rocket. Essentially, a variant of the Silver Comet.

I plan on making a whole bunch of fin templates and testing them out for looks by making "falsies" out of cereal box cardboard. Just drawing the model doesn't give me a true idea of what the final product will look like.

They may or may not have pods on the tips.

One thing is for sure: I want the fins to be thicker than 1/8", which is the width of the slots in the V-2 / Silver Comet boat tail.

I'm thinking of laminating a 1/8" piece of basswood with 1/16" pieces of balsa. The TTW tabs would not have the balsa plys. I'd use a belt sander to carve out the airfoil.

Any ideas what to use to laminate the pieces? Epoxy? Wood glue?

Should I use basswood for all three layers?

sandman
07-07-2010, 08:53 PM
I'm starting work on a classic "rocket ship" rocket. Essentially, a variant of the Silver Comet.

I plan on making a whole bunch of fin templates and testing them out for looks by making "falsies" out of cereal box cardboard. Just drawing the model doesn't give me a true idea of what the final product will look like.

They may or may not have pods on the tips.

One thing is for sure: I want the fins to be thicker than 1/8", which is the width of the slots in the V-2 / Silver Comet boat tail.

I'm thinking of laminating a 1/8" piece of basswood with 1/16" pieces of balsa. The TTW tabs would not have the balsa plys. I'd use a belt sander to carve out the airfoil.

Any ideas what to use to laminate the pieces? Epoxy? Wood glue?

Should I use basswood for all three layers?

Balsa for all three layers will be plenty strong.

Use wood glue and a lot of weight on top to laminate.

Doug Sams
07-07-2010, 09:03 PM
I'm starting work on a classic "rocket ship" rocket. Essentially, a variant of the Silver Comet.

I plan on making a whole bunch of fin templates and testing them out for looks by making "falsies" out of cereal box cardboard. Just drawing the model doesn't give me a true idea of what the final product will look like.

They may or may not have pods on the tips.

One thing is for sure: I want the fins to be thicker than 1/8", which is the width of the slots in the V-2 / Silver Comet boat tail.

I'm thinking of laminating a 1/8" piece of basswood with 1/16" pieces of balsa. The TTW tabs would not have the balsa plys. I'd use a belt sander to carve out the airfoil.

Any ideas what to use to laminate the pieces? Epoxy? Wood glue?

Should I use basswood for all three layers?Stefan,

I've made several batches. I use my radial arm saw deck because its base is fairly true to plane - there's neglible warp in it. A layer of aluminum foil keeps the fins from getting glued to the table :)

I use balsa, and like you suggested, laminate outer layers of half the thickness of the inner layer. In my case, that's usually 1/32" outers with a 1/16" inner for a total of ~1/8". Your 1/8" + 2x 1/16" sounds like a fine 1/4" board. You'll be surprised at just how strong balsa can be in this configuration. (BTW, A company called Mach-1 used to make balsa ply. BMS used to offer fins made with it. I still have a little in my stash.)

I wouldn't worry about using this for the tabs - they'll be quite strong. As for the belt sander, that'll probably be too aggressive. Some 100 grit in a sanding block would be my starting point.

I use yellow glue and apply it with an acid brush. I apply it to both faces, then place the pieces in contact, separate them, then re-connect then. (This is called booking, and seems to be a key step.) After all the layers are built up, I clamp them together. I use a piece of 1x6" birch hand picked for its planarity, covered in foil. This is clamped over the material in a sandwich with the table saw deck as the lower bread. Alternatively, use two pieces of birch (sans table saw :) ).

A bit of glue will ooze out when you clamp it, so make sure you have sufficient foil down to keep it from getting where you don't want it. Once the plywood's in the sandwich, it'll be hard to wipe up the excess, so you need the foil to act as a barrier.

I've never tried this using epoxy, but here's my two cents. If you make it with wood glue, you can attach the fins with wood glue or any other glue. If you make it with epoxy, you'd likely need to use only epoxy with it from then on.

I've made several batches over the years, and have even started making it in small batches for making one fin or a couple of centering rings. I can whip up a small batch very quickly so it's something you can work into the flow without lots of extra time/effort.

Also, I've mixed materials doing this and used 1/64" birch ply over 1/8" balsa. It makes for a very stiff and sturdy fin.

HTH.

Doug

.

LeeR
07-07-2010, 09:07 PM
What sandman said ...

Plus, I'd suggest not using a belt sander on balsa, unless you are a master at using one. Balsa is easy to hand sand for airfoils, even basswood is not too bad to hand sand. For plywood, a belt sander is almost a must. I've got a fin sanding jig for a Dremel, but it's home made, and not sure anything like it is commercially available.

http://i265.photobucket.com/albums/ii220/hobbes_pics/tools/fin%20sander/th_fin-sander.jpg (http://s265.photobucket.com/albums/ii220/hobbes_pics/tools/fin%20sander/?action=view&current=fin-sander.jpg)http://i265.photobucket.com/albums/ii220/hobbes_pics/tools/fin%20sander/th_ply-fin002.jpg (http://s265.photobucket.com/albums/ii220/hobbes_pics/tools/fin%20sander/?action=view&current=ply-fin002.jpg)http://i265.photobucket.com/albums/ii220/hobbes_pics/tools/fin%20sander/th_ply-fin003.jpg (http://s265.photobucket.com/albums/ii220/hobbes_pics/tools/fin%20sander/?action=view&current=ply-fin003.jpg)

When I built my Phoenix, I did not have this fin sander, so I used a small hobby plane to shave super sharp leading edges on the balsa fins, then used CA to toughen them. That was about the only time I recall using any technique other than hand sanding for shaping balsa fins. I've put a small cordless Dremel on this jig (to "underpower" it), and used it for balsa, but frankly, I prefer hand sanding, since I can make much more complex airfoils, vs. a simple straight taper.

stefanj
07-08-2010, 01:02 AM
Thanks all.

The complication is that the tabs have to be 1/8" thick to fit in the slots. This might mean a complicated laminating job, with a bit of the center ply sticking out. Or laminating the rough cut fin pieces and sanding the edges square afterwards.

I use sanding blocks and sheets for balsa and thin basswood. The fine grit belt on my sander does help with thick basswood.

mojo1986
07-08-2010, 07:25 AM
I have laminated balsa with white card stock..................also extremely strong with the benefit that finishing is easy.

Joe