My first scratch built fins and centering rocket rocket

cjp said:

This is my first time cutting fins out of Baltic Birch Plywood(used a jig saw),and my first with making centering rings with my new drill press(29 mm mt)Used Semroc BTH70 tubes and a Loc nose cone.All built up it weighs in at 20.2oz. without paint and motor.The nose cone weighs 4oz.I papered the fins because I have the grain running the same direction as the root edge.My first mistake.The second was using lable paper to cover the fins.Pricey and I don't like the way it stuck to the fins.Will use white glue if I need to do this again.Epoxied all around the edges of the fins to make sure they stay on.Might call this The Flash after Kent Sate's Golden Flashes.My daughter has her degrees and Masters from Kent.She now works there as well.

Click to expand...

Sandy H. said:

I think its a good 'rocket' looking rocket.

I'm a little confused about your remark that you used ply and had the grain running the wrong direction. I have always been under the impression that the manufacturer flips the grain direction for each ply to give less directionality. If I'm off base here, someone please chime in! Then again, there's nothing wrong with papering the fins either, as it makes final paint prep easier.

Good job!

Sandy.

Click to expand...

cjp said:

I papered the fins because I have the grain running the same direction as the root edge.My first mistake.

Click to expand...

jeffgeraci said:

I do that time and again- how is that even possible? I get so into the design, and anxious to cut, and I just forget. You mentioned epoxy... why not just use a razor to squeegee epoxy over the fin surface? Then just sand with 220 and prime. Good for you attempting a first timer

Click to expand...

cjp said:

I thought the same thing this morning, I assume your talking about spreading epoxy over the fins instead of paper.I thought about Winwax wood hardener which I'm told is like CA glue,but the thought of sanding and losing my foil or getting a uneven surface made me go with paper lables(8 1/2" x 11").But I had to reposition one corner and was surprised how easy the paper came loose.That's the reason I put epoxy around the edges.I bought some Emers white glue yesterday and will go back to papering the fins off the rocket and placing them under a few books for a day or two until they dry(That's when and if I do this again).Also bought some Titbond III,and will use it for my next large build instead of epoxy.Heard and read great things about that product.

Click to expand...

MarkII said:

The only conceivable reason to use paper skins on plywood fins would be to make the job of finishing them a bit easier. The fins certainly wouldn't need them for strength. You might be able to flex the fins a little bit when they are cut out and loose, but once you have the root edge bonded firmly to the airframe, that flexibility largely goes away. If you mount them through the wall, it totally goes away. Paper lamination is a technique that is mostly just done on balsa fins. Conversely, laminating thin plywood skins onto foam core board, a technique borrowed from the model aircraft world, is a time-honored method to make strong and very lightweight fins for mid-power rockets. I have occasionally toyed with the idea of bonding very thin styrene sheet skins onto plywood, basswood or balsa fins but I haven't followed through on it yet. Although they would certainly boost the strength of balsa, mu main motivation would be to give the fins tough, mar-resistant and easy-to-finish surfaces.

Click to expand...

cjp said:

Do you cut your fins with the grain going in a particular direction or do you try to cut as many fins without wasting plywood?You have provided some very good imformation and I thank you for it.:handshake:

Click to expand...

MarkII said:

I usually orient the leading edge so that it is parallel to the grain on the side of the plywood that I happen to be drawing on, just out of habit. It truly doesn't matter, though. I have cut fins out with random (visible) grain orientations; all work, especially with the high quality Baltic birch plywood.

Click to expand...