Epoxy-ing Rail Button "weld nuts" to the outside of the Body Tube

[techrat]

Is there any reason I cannot epoxy the rail-button weld-nuts from the outside of the rocket, pointing inward? This will make it much easier to bond the rail button mounts properly, NOT get epoxy on the threads, and not completely screw this up. It's a 3" diameter tube, so I cannot get my hands in there. If it were a 4" tube, then probably no issue. The only thing I can think of is that the weld button flange won't have the tube to press against, so there is potential for it to be able to pull away and fail, but, with enough epoxy coated carefully around that outer edge, I should be OK for a rocket that doesn't even weigh 2 pounds. I've gotten away with glued-on launch lugs, this shouldn't be that much different. And note that I will be using the stronger "30 minute" epoxy, not the weaker 5-minute type.

 

[Steve Shannon]

Is there any reason I cannot epoxy the rail-button weld-nuts from the outside of the rocket, pointing inward? This will make it much easier to bond the rail button mounts properly, NOT get epoxy on the threads, and not completely screw this up. It's a 3" diameter tube, so I cannot get my hands in there. If it were a 4" tube, then probably no issue. The only thing I can think of is that the weld button flange won't have the tube to press against, so there is potential for it to be able to pull away and fail, but, with enough epoxy coated carefully around that outer edge, I should be OK for a rocket that doesn't even weigh 2 pounds. I've gotten away with glued-on launch lugs, this shouldn't be that much different. And note that I will be using the stronger "30 minute" epoxy, not the weaker 5-minute type.

You can try, but it may not hold well enough. There’s not much area to bond and the bond strength is directly proportional to the area. A rail button failure at the wrong time can be pretty serious.
Placing it on the inside with the threaded barrel extending through the body tube is much stronger and doesn’t rely on the epoxy. There are many ways to feed it through even though your hands cannot reach inside the body tube. You can use string or a piece of wire and slide it through the hole from the outside and then attach the weld-nut to the end of the string or wire and pull it through. I have done this and it helps to practice a few times without adhesive first.

 

[David Schwantz]

I like to make a ply plate that the blind nut mounts into. Just make a small plate with a little radius to match the inside of the tube. Install blind nut into plate and coat with epoxy. You have a predrilled hole in body tube in correct location, rough up inside of tube, stick an exato knife into ply plate as a handle, apply epoxy on ply plate, put over hole and use a screw to draw it up into place. Coat screw with oil so glue does not stick.

 

[Kane]

Stick with a magnet glued or taped to the end works for me to get the tee nut down into the tube. Also, I have never epoxied a tee nut into place. I make sure the screws are tight before every launch and leave it at that.

 

[Scott_650]

Like Steve said, you really need to get that nut inside the tube. Along with the thread the needle technique like he outlined you can use a spot of clay or poster tack putty (or a magnet as Kane posted) to hold the nut on a stick and insert it into the hole.

Another option for smaller diameter, lighter rockets is using conformal rail guides epoxied to the body tube. I’ve used rail guides on several already built rockets so I can launch them from rails at club launches as well as on new construction.

 

[jnmiller]

An alternative is Well Nuts (not Weld). These are surrounded by rubber that expand when a bolt is screwed in.
You don't need to attach anything inside the airframe. Just drill a hole from the outside and insert the well nut.
Attach your rail button with a bolt and screw it down. It won't come out. I've used these many times. None has ever failed.

https://www.amazon.com/gp/product/B0040D0MCY

 

[bobby_hamill]

You might get a long handle hemostat clamp you can choose from 3" to 24' lengths

https://www.amazon.com/SurgicalOnli...-lpcontext&ref_=fplfs&smid=A5Z3U5T7EU93P&th=1

 

[Steve Shannon]

My TARC kids epoxied their weld-nuts inside the body tube today. The aft most one they just held in place with their finger and then screwed on the button to hold the weld-nut in place while the epoxy cured. When they did their TMP rockets they inserted the front weld-nut by sticking it to a long stick and sliding it in place. For this rocket they just put it into the top of the body tube as far as their fingers reached.

 

[shockie]

What if you glued a half circle magnet on the insides of a body tube . Then used a metal rail button with a curved bottom to hold it place? And had some kind of stop at the top of a rail launcher that would prevent the rail button from continuing on with the rocket?

You can get magnets with various strengthd

 

[dr wogz]

work it so the button hits the upper centering ring. and tap / screw into that.. (no need to rely on an added 'thing')

add a doubler to the CR where teh button will be located so you have more 'meat' to aim for.. (it's easier to hit a 1/2" target than a 1/4" target)

 

[shockie]

Or how about a couple of small 5v powered electromagnets that are turned off by a flight computer and they just fall off?

 

[teepot]

I use a 10" long pair of hemostats to place the upper rail button. After the tee nut is in the hole the hemostat holds it while I put the button on and screw it tight. Then pull the hemostat off and tighten. I used to epoxy the nut on the inside of the tube. But have stopped doing it. Lock Tite the screw if you want. I like the magnet on a stick idea.

 

[seth_cooper]

An alternative is Well Nuts (not Weld). These are surrounded by rubber that expand when a bolt is screwed in.

I'll second that. It's all I use.

 

[Hobie1dog]

I'll second that. It's all I use.

+3

 

[lakeroadster]

Or how about a couple of small 5v powered electromagnets that are turned of by a flight computer and they just fall off?

or... explosive rail button bolts!

 

[lakeroadster]

I like to make a ply plate that the blind nut mounts into. Just make a small plate with a little radius to match the inside of the tube. Install blind nut into plate and coat with epoxy. You have a predrilled hole in body tube in correct location, rough up inside of tube, stick an exato knife into ply plate as a handle, apply epoxy on ply plate, put over hole and use a screw to draw it up into place. Coat screw with oil so glue does not stick.

Why not just use a wood screw then and forget the blind nut? Is it because the plywood isn't thick enough to secure a wood screw into?

 

[David Schwantz]

/tht would work fine. I just prefer blind uts.

 

[Dane Ronnow]

I'll second that. It's all I use.

Same here. I try to go throught the BT where a coupler is located. It'll never pull out

 

[DaHabes]

Is there any reason I cannot epoxy the rail-button weld-nuts from the outside of the rocket, pointing inward? This will make it much easier to bond the rail button mounts properly, NOT get epoxy on the threads, and not completely screw this up. It's a 3" diameter tube, so I cannot get my hands in there. If it were a 4" tube, then probably no issue. The only thing I can think of is that the weld button flange won't have the tube to press against, so there is potential for it to be able to pull away and fail, but, with enough epoxy coated carefully around that outer edge, I should be OK for a rocket that doesn't even weigh 2 pounds. I've gotten away with glued-on launch lugs, this shouldn't be that much different. And note that I will be using the stronger "30 minute" epoxy, not the weaker 5-minute type.

Inside for sure. I either use a small dowel or long, skinny iced tea stirrers tape together long enough to reach the hole, double over some masking tape to make double sided tape, tape the weld nut to the end and move the weld nut into place at the hole, insert the screw in the hole and turn to engage the weld nut (a couple of turns) and then use a pliers to pull the weld nut fully into the hole. Like some have said here, you probably don't have to epoxy them in, but I do because I'm anal.