Shear pins?? what are they?

Can someone please explain in sufficient detail what a shear pin is used for, and how it is PROPERLY used? What applications call for shear pins?

I've got a 6" dia airframe in 3 sections. I was going to pop rivet them together, but that means I need to drill them out after I launch it, to fit it in my car. I was thinking of using shear pins, if that's what they're for. My impression was they're used to break on purpose when your rocket separates? I don't know:confused2:

Shear pins are small nylon screws, you drill a hole through the airframe into the sholder of the NC and insert the screw, once the screw is in it holds the nosecone to the rocket to prevent drag seperation. When the deployment charge fires, it shears apart and allows the NC to come off. For your application I would install tee nuts into the coupler, and grind them flush on the exterior side of the coupler. Drill a hole through the tube that lines up with the tee nut, then insert a bolt into that. When you are done, simply unscrew the bolt.
Hope this helps,
Ben

In strict definition, shear pins do exactly that. They 'shear' under (ideally) a specific load. Obviously different diameters will have different strengths so you can tune your ejection system to that standard. I use the removable rivets to hold nose cones and even av bays if I'm using motor only ejection. I would recommend some t-nuts and screws if you just want to break things down after a launch, but you could also certainly incorporate those into a dual deploy system, with ground testing obviously to ensure complete separation. One trick is to epoxy a thin metal shim so you can get the 'guillotine effect' when the shoulder slides out of the body tube and cuts the rivet (or nylon screw) cleanly. It also reduces the tearing effect that just putting them thru cardboard mite have. I use thin shim even in FG birds, but fitting them may be a little problematical given the tighter tolerances you may face. McMasters-Carr have these available as well as many local industrial supply houses. Straight smoke and good chutes!

obviously I type much slower...what he said oint:

Either of these styles of nylon fasteners could be used as shear pins (the first being more common)





From what you are describing that you are looking to achieve, I don't think that this is what you are looking for. If you want to use this to assemble and disassemble the rocket for transport you will want to use a button head screw or something similar.

The reason for the nylon fastner is that it will shear when the ejection charge fires thus allowing the components to separate (the reason they are called shear pins). This is done to keep the components together until the ejection event to prevent drag separation.

fyrwrxz said:

obviously I type much slower...what he said oint:

Click to expand...

Me? Type fast... yep, the same way i fly O motors every month:gavel:

Jeff, i have some 1/8" diameter 2 part expanding rivets I can give you for your rocket in February. I also have about 100 shear pins if you need any of those.

https://www.missileworks.com/index.php?main_page=index&cPath=3&zenid=00qlh3nnscguh41ms0k97kmnr0

I bought 100 shear pins for 10 bucks there, the 2-56 kind.

I also bought 100 click lock rivets from
https://www.mcmaster.com/#standard-rivets/=g0afdm

for 13 bucks (I had to order some end mills for my CNC as well, so it worked out alright, otherwise tax and price were a little much), but the parts are very high quality, and very reusable

WOW those prices are unreal,, go to Mcmastercarr,, https://www.mcmaster.com/#nylon-machine-screws/=g0i2nh $4.92 for 100 2-56.

Tom