I need to figure out a way to sink a 10/24 screw into the wall of the airframe, and all the anchorage I have to work with is the thickness of the wall of the tube, period... I'd guess 1/16" or so?

PR convoluted G-10? Then, yep, 1/16." If you're not worried about turbulence or drag, just build up off the airframe with fiberglass (embed into airframe as much as you can) and thread into that. The buttons will stand out more, but they'll hold on okay. Just reinforce with glass or carbon fiber, etc.

Along similar lines, depending on the weight of the bird...

How about heliarc welding an Acme rail guide to the outside of a slimline retainer? The acme has less frontal area than a traditional button. If you're partial to the inherently non-binding nature of the regular button, get one machined up out of aluminum with a flange and get it welded up. Should be sturdy enough. For the top, just a standard button or an Acme with countersunk screws in the flange for good measure.

Just my $0.02.
-Ken

Interesting thought.... problem is the slimline is external, so now I have a lot more drag at the aft end... and I don't need the motor retention, because the motor is retained from the top. But this does have some promise -- I put on the slimline, and drill and tap into THAT? I wonder what the wall thickness of the slimline retainer is?

I checked GLR, and their 98mm Slimline's flange must be on the other side of a centering ring. Not that you can't modify it... Tim Thomas, Lawndartman, you there? I doubt if it's more than 1/16" in thickness. You only have two ways to go: build up on the airframe and put a threaded insert in, or add something aft--slimline, whatever--that you can thread in to. The reason this is such a good thread is that this is a situation that anyone who needs buttons on a min dia rocket will have. If the market were big enough, then this would be a "million dollar" solution... whatever it turns out to be.

When I started this post, I had a solution in mind... but I don't know if it is doable. See what y'all think of this:

a.) Cut a hole in the airframe about the size of a dime

b.) Have a piece of metal machined or milled that is that same size as the aforementioned hole. It would probably have to be milled so as to account for the curvature of the tubing?

c.) Glass over the entire area, probably three or 4 layers fin tip-to-tip, and then another couple of layers that are over the aforementioned plug

d.) Drill through the glass, and into the metal plug. Tap that. The glassing should keep things from pulling out.

My question... how do I make such a precise metal plate?

JW

My question... how do I make such a precise metal plate?

There has to be a machinist in the club, especially on the research end. Anyone who can machine a motor casing can do this, and yes, you'd have to match the curve of the airframe and not get in the way of the motor casing. First of all, I'd like to apologize for all the posts I've made on this site. I promise to get a life... eventually. John, that's a good idea, and it will work, providing there is enough to thread in to. This is what I hated when I was in engineering, my mind just won't stop until a solution is found. Another idea, going off what Ed suggested... this is difficult to explain without a drawing... so we'll imagine one... take this ), turn it 90 degrees to the left, an nice little curve of metal that matches the outer airframe. You can either thread into something for a rail button, or run a screw out and use a low-profile nut to hold the button on. Use this piece of metal and either weld a bolt thread to it or push it through a hole and use a nut to secure it from the other side. Now, going on what Ed said, just epoxy this between your fins and embed it in your laminating. This puppy will not move.

Almost everything I've read so far is about adding extra layers on the outside of the airframe to support/reinforce some thing - whether a band with some threads welded to it, or something else. All of these suggestions as good as they are rely completely on the added layers for structural strength. Should those layers peel away, there goes the button along with them. The PEM idea is good, but I would think that grinding away the flang would reduce the structural bond - it could easily pull right through the air frame. The dime size disk is a good idea also, however it relies on the added glass to support. Plus, when drilling into the disk from the outside of the tube, one risks separating the disk from the airframe. Also, 1/16" isn't much for a screw to bite into.

Here is another thought since there will be added layers of glass to the outside of the airframe. Take my original idea of using a machine screw. Taper the inside of the tube to allow the head of the screw to be flush with the inside of the tube. Use a t-nut (with the pointy tabs ground off) on the outside of the tube. Screw the machine screw from the inside out into the t-nut and tighten. Add the layers of glass over the t-nut and screw. Add the button with a nut on the outside. This gives the best of both worlds - support from the inside of the tube and support from the outside of the tube. No way that will pull out/off.

Should those layers peel away, there goes the button along with them.

Those layers aren't going to peel away, even with an N. But Ken is right. There are so many ways to do this. You do need a flange to anchor it. Use a "Nut-sert" upside down and epoxy the heck out of it. You only have to have strutural integrity for less than a second or so. John, for a min dia bird, you have to laminate a reasonable depth just to keep the fins on. ALL the suggestions are viable... can't wait to see what you do. The project that Tim Thomas and I want to do will come close to breaking the 30k waiver, which is what I'm assuming you, our resident "altitude junkie" regardless of where you end up living, are aiming for. Tim flew over our North site at 35k and thought there was no way we could recover such a high flight. You can however. Nice way to say, "See ya later!" And, we'll follow your lead. 😉

Thanks for everyone's suggestions. Keep in mind that all I'm trying to do is clear the rail-- I don't care if the button falls off at 5,000' and mach 2. All I want is for a safe departure from the launch site...

I can handle the machining John, you just need to get me an accurate drawing including the thickness, curvature, hole size and thread pitch.

My thought is you'd do it easier by using a Pem Nut and some epoxy. The rocket isn't that heavy.

Warren

Machine shop?? Machine shop!!!! Come on, it's time to start building rockets with angle grinders and nail guns.
🙂

I have a couple suggestions here JW. Using a piece of metal (like aluminum or even a nutsert thats been cut down) drill the holes where you want them. then JB weld them into place into the holes in the airframe for them. (them being the nutserts or aluminum pieces). using Masking tape from the inside to keep it smooth as it cures. When cured you have a threaded piece or a metal spot you can drill and tap. It will hold just fine. You could even use some liquid steel like JB weld to just fill in the hole drill a hole in the jb weld after and tap it. You will have to trim the screws that screw into it down to be just right in length but it would work. Other ideas would be doing something of the same and using it as a stronger way to hold Acme rail guides in place along with JB welding them in place. So the acme guide would be drilled and screwed down with the JB weld. into the inserts.

super glue. Base patch tapering over a square inch or so. Patch from CF or whatever mother material-best if is CF, seldom in the universe is a stronger joint than CF/CA/CF This excludes the strong nuclear force ;D

I figured it out (I think). Give a dumb farmboy enough time and he will usually cobble something together.

What about this. Get a .75" diameter wooden dowel, and some really coarse grit sandpaper. Orient the dowel perpendicular to the airframe and lay the sandpaper over the airframe. Sand until the dowel base is conformal (more or less) with the airframe. Cut the dowel with a bandsaw so there is about 1/4" substance to deal with. Epoxy this to the airframe. Drill, tap, and superglue Mr. Railbutton onto this peg (going thru the wall of the airframe for good measure).

Ought to work?

I would have done it with an angle grinder and a nail gun.

Use some of those cement coated 20d ring shank nails - that'll hold 'er. Maybe 3 or 4 of 'em. Probably be a good idea to put the motor in first though...