Mounting a rail button on a minimum diameter project

This topic has 30 replies, 7 voices, and was last updated 18 years, 3 months ago by Conway Stevens.

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June 21, 2007 at 9:59 pm #44771
new2hpr
Participant
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
June 21, 2007 at 10:30 pm #44772
Anonymous
Depending on how you’re retaining your motor casing… you could make a plate (with a hole in the center to allow the nozzle through but small enough to retain the motor) and weld either a 1/4×20 nut or bolt to it to screw down the button. Just use 4-6 screws to bolt the plate to the aft;

Nope, no room… 4″ motor in a 4″ airframe. The only thing protruding is the aft closure. The nozzle is well up inside that. There is no “aft” to put the 4-6 screws you refer into. No centering ring, no fin tabs, just a 98mm aft closure hanging out the back end. I’ll retain the motor from above….

JW

PS What is a “fin tab” ? 🙂
June 21, 2007 at 10:35 pm #44773
Bruce R. Schaefer
Duck tape, lots of duck tape… do the PEM thing, that should hold it fine. I’m glad you started this thread, John. Tim Thomas and I will be faced with this problem next year…
June 21, 2007 at 10:37 pm #44774
Anonymous
Upon reading the initial question, I assumed the problem was only how to attach the button to the airframe securely, but I think there is more to it. How do you attach the button or something similar to the airframe while keeping the drag and turbulance induced by the button to a minimum.

John, can we have more specifics about the rear end of the rocket?

This is similar to all my rockets, with one exception — this one is 98mm. The fins are surface mounted. The airframe is 4″ diameter, and the motor is 98mm. I’m not at all worried about drag or turbulence… I’m worried about the button falling off at an inopportune time.

There are no centering rings to tap into, since this is minimum diameter. Think of this as a giant Estes rocket that uses the airframe as a motor tube. 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?

Hope that helps. This is a toughie.

JW
June 21, 2007 at 10:40 pm #44775
Anonymous
Here’s another thought. Position the end of the motor about 1/2″ into the tube – or – at least leave enough airframe exposed for a screw.

It won’t fit — the motor won’t go into the tube, because the aft closure will preclude that. Minimum diameter rocket….
June 21, 2007 at 10:44 pm #44776
Bruce R. Schaefer
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.
June 21, 2007 at 10:47 pm #44777
Anonymous
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?
June 21, 2007 at 11:18 pm #44778
Bruce R. Schaefer
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.
June 21, 2007 at 11:24 pm #44779
Anonymous
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
June 21, 2007 at 11:54 pm #44780
Bruce R. Schaefer
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.
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