Practicing shear pin threading

[RocketSquirrel]

Im messing around with a carboard mail tube trying to get it right, i think ive got it but since ive never used shear pins before, im not sure if the ejection force will pull out this tiny washer. It fits m2 screws. (It wont be this close to the edge, just practicing)



I tried different ways and what ive landed on is;

1-ca both sides of the tube. (Not sure this even helps)
2-drill 1/16th hole
3-sand around the hole on the inside so the washer lies flush
4-tap the hole
5-dab epoxy over the counter sunk hole
6-place washer over it and thread the nylon m2 shear pin, wiping away excess and ensuring the washer is flush
7-let it dry, back out the screw.
8-sand any exess.

Ive seen someone on here do it similar with a larger piece of quarter size thin sheet metal, then thin layer of fiberglass over the metal.

This will be for my L2 dual deploy flight on a 5.5" LOC big nuke. I feel like its got to be a little better than trusting the threaded cardboard to shear the pin... I'm just asking for thoughts on it

 

[mrwalsh85]

Why tap the hole? If the holes are threaded, you're asking for trouble. Any change in the distance between the airframe and coupler/nose cone shoulder will change your pitch between your two threaded holes, and you'll struggle to screw them in.



All of my shear pins are drilled to the next size down from the major diameter of the screw. This typically results in a "z-z-z-z-zippp," as I insert the pin, without much resistance. But it won't back out.

I treat the threads of nylon screws as a similar concept to this.

Now, keep in mind that I typically fly FG airframes, but my WAC Corporal uses 7.5" LOC tubing which is thick wall, and it is a rule of thumb that I drill the hole small, saturate with CA and let dry, then drill out to the size I want (as per below), saturate with CA again and let dry, then drill out one last time. This gives me a nice solid edge for shear pins to break against. This method kind of works on smaller airframes but you're asking a lot of thinner wall cardboard airframes.

My sizing method is as below.

For example, a 2-56 screw is 0.086" Diameter. Reference the chart below for a 2-56. Same concept applies to #4-40.



I'll start out with a #92. If it's too tight for my liking, I'll open it up to a #91 - I like to get as few tools out as possible to fly my rockets. If it's still too tight, you're taking a big gamble with a #90. At that point, I'll run the #91 again to try and give it a smidgen more, but I've found sometimes going to a #90 is what is needed. Most times, I can push the screw in by hand, which is my goal. Sometimes, I need a little help with a solid object (read: not our flexible skin), so I'll use the wide edge of a flathead screwdriver, the pivot point of a pair of pliers, etc... Whatever is handy.

Works and I almost always still have the head and a very stubby length of threaded body left on the shear pin still in the hole when I get the rocket back.

 

[KenECoyote]

https://www.rocketryforum.com/threads/shear-pins-with-light-cardboard-tubing.183626/post-2521713

 

[Rocketjunkie]

#2, 5/64" drill, #4, 7/64" drill. Press in, no tapping. Poke out the pieces after flight. Usually with cardboard rockets, I use masking tape for a friction fit and save the shear pins for fiberglass rockets.

 

[JoePfeiffer]

I tap the body tube but not the coupler (the hole in the coupler is a tight clearance hole) because it just seems tidy. But yes, after a couple of flights it isn't threaded any more....

 

[lr64]

Round toothpicks or, at least, the ones I have, are a nice press fit into M2 holes.