Shear Pin Help!

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Eyeguy41

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I would like to add shear pins to mu LOC Hyperloc 300. It is phenolic tube, my concern is how do I strengthen the cardboard so that the shear pins don't continually ream out the hole that the pin is screwed into.
What hardware are you using and how are you installing it.
I was planning on using 2-56 nylon screws but didn't want to screw straight into the tube. I thought about tee nuts but I can't find them in the 2-56 size. Really curious what everyone else is doing. This forum is a wealth of knowledge and I could not have gotten as far as I have without it. Thanks in Advance.
 
I think a lot of guys are going to tell you to use CA to make the holes stronger. I know this is what I have used in the past and it has worked quite well. 2-56 nylon screws will work well for holding nose cones on or the lower part of the rocket above the fin can for DD. Again CA works good on paper tubes. If you are uncertain about the integrity, then glue on a piece of .005" thick brass sheet on the inside of the tube and use that to cut or shear your nylon. I think I would screw them in straight and not at an angle. At an angle you are increasing the amount of effort to shear, and could get something to tear instead. Don't forget your vent holes also if you are going to higher altitudes. I hope this helps, and feel free to ask more questions so that you can learn all you can. I am certain and for sure that others will chime in with their opinions also, so just wait for it, because they are coming.

BEAR
 
2-56 tee nuts should be readily available at any hobby shop that caters to the RC flying crowd. They're usually on a display raced with other DuBro products.
 
I machined two inserts that get mounted in the tube. One insert has a thru hole for the screw and the other is tapped. The insert has a very thin flange, about 0.015" thick by about 3/8" diameter. In addition the flange has a boss that is 0.050" deep x 0.125" in diameter, this is the part that goes in to the tube. I drilled a 0.125" hole in three places, through the body and the nose cone coupler. Then I epoxied the nut inserts into the nose cone from the inside. I repeated the same steps with the non-threaded inserts on the body tube. The nose cone and body tube now have a set of aluminum reenforced holes that line up perfect for shear pins. I am also making a set for 4-40 metal counter sink screw inserts that I will use to attach the upper body tube to the E-bay insert.
 
I will drill a 1/4" hole into the body tube and fill it with epoxy. After that has cured, I will take the tape off the inside and place the nosecone into the tube. I will take my tap and die tool and drill 2-56 holes through thr epoxy-filled holes and into the nosecone shoulder. The 2-56 shear pins screw in nicely and hold the nosecone on.
 
You do not have to tap the body tube or nose cone, just drill a hole a little smaller than the OD of the thread diameter and press the 2-56 in. If you thread it, then I will ask, how do you remove the sheared off part of the thread if it is screwed in. Whereas if it is pressed in then you can press it out.
BEAR
 
You do not have to tap the body tube or nose cone, just drill a hole a little smaller than the OD of the thread diameter and press the 2-56 in. If you thread it, then I will ask, how do you remove the sheared off part of the thread if it is screwed in. Whereas if it is pressed in then you can press it out.
BEAR

Good Point about the removal.

Making a hole and then filling it with epoxy will leave a nice strong and sharp edge for the shear pin to get cut with.

There are many ways to skin this cat and it seems that most will work reliably and effectively, I will, at some point, come down to personal preference and what you feel comfortable and confident with.
 
You do not have to tap the body tube or nose cone, just drill a hole a little smaller than the OD of the thread diameter and press the 2-56 in. If you thread it, then I will ask, how do you remove the sheared off part of the thread if it is screwed in. Whereas if it is pressed in then you can press it out.
BEAR

if you thread the body tube hole and then make the hole in the nosecone not threaded would that work. i have also read a lot of posts talking about putting a "cutter" on the tube or nosecone. is that needed and if so how can the shear screw shear without the cutter. not doubting just want to understand, i ask why so i can understand.
 
also where do you get the shear pins? is that what they are? or they just that for us?
 
IMHO, the name says it all. It is a "shear" pin. It shears or breaks from the force. The smallest I use are 2-56 nylon screws, about a 1/4" long. I drill the hole through the body tube into my nose cone. It is a little smaller than the thread OD of the screw. When the ejection charge goes off, it forces the nose cone off the end of the body tube and breaks the pins or screws, shearing them. Later, when I am cleaning up, I can take a punch or a drill and drive the broken screws out of the holes. You can also tap the holes in the tube. I believe you will be making a mistake if you tap the holes in the nose cone. If you are using a paper tube, then you make it stronger with CA or you can use epoxy. Then the paper does not tear, and it will be your cutter. In paper, I drill the holes, then I saturate the area with CA, then I drill the holes again. If you are uncertain, try it in a ground test to figure out how big a charge you need to shear the screws. Some people use bigger screws, depending on the size of the rocket. You are going to have to experiment to your comfort level. I hope this helps.

Oh, and for what it is worth, the tap makes threads in a hole. The die makes threads around a shaft. The tap will make a nut, the die will make a screw. You should not need a die for this project. I say this because you said you were going to "...take your tap and die tool to...". Forgive me if I get to technical here or get bogged down by the details.
 
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IMHO, the name says it all. It is a "shear" pin. It shears or breaks from the force. The smallest I use are 2-56 nylon screws, about a 1/4" long.

do you have a source for these "screws"
 
I go to an industrial fastener store. Depending on the size of your community, you should be able to find a "Fastenal" store. Some hardware stores will carry them in the fastener bins. You also might find them in the hardware/fasteners aisle at Home Depot or Lowe's. If not, they can readily be found on the internet, but frequently the hardware stores can get them for you within a weeks time. If you search the internet like I do, then I will start with Google, then on the horizontal tool bar where it says "More", click on it and then click on "shopping" in the drop-down menu. I would then type in "2-56 nylon". I just did it and on the second entry I found 500 pcs, of 2-56 nylon screws, 3/16" long (which should work and get through the nose cone). The cost was $6. See if that will work. I pay about $.02 each for mine, but I have paid as much as $0.25 each. I hope this helps. BEAR
 
IMHO, the name says it all. It is a "shear" pin. It shears or breaks from the force. The smallest I use are 2-56 nylon screws, about a 1/4" long.

do you have a source for these "screws"

McMaster Carr. Look up nylon screws.

What I did on my Iris was to cut out a couple layers of the paper, and epoxy in thin brass strip. One strip on the outside of the coupler, and one on the inside of the tube. Then drilled holes through both pieces. I use 1/16" styrene rod. Has worked well for me. However on the FG kits I'm building, I will switch to nylon screws.

Adrian
 
You do not have to tap the body tube or nose cone, just drill a hole a little smaller than the OD of the thread diameter and press the 2-56 in. If you thread it, then I will ask, how do you remove the sheared off part of the thread if it is screwed in. Whereas if it is pressed in then you can press it out.
BEAR

In my configuration I have plenty of left over screw to grab ahold of to unscrew it from the insert nut. However, if one was to use a shorter screw you can simply push the piece through. It will simply shear the threads since the insert is metal it is not a problem, it's only 0.065" worth of threads.
 
thanks guys. i don't think i explained myself clearly enough. now that Bear gave me the part, i see they are just regular hardware. with the picture i see they are really a screw, not something special, like the Apollo program exploding hatch bolts or something specifically for rocketry.

you guys are great, thanks for the help.
Lance
 
thanks guys. i don't think i explained myself clearly enough. now that Bear gave me the part, i see they are just regular hardware. with the picture i see they are really a screw, not something special, like the Apollo program exploding hatch bolts or something specifically for rocketry.

you guys are great, thanks for the help.
Lance

Pay attention to the plastic you choose, some are much tougher than you think. Good luck with your flights.
 
I get mine from McMaster-Carr ,they ship super fast.I use 2-56 on 3" dia. and smaller rockets and the 4-40 on larger ones. Suggest the phillips binding head type that are just a bit bigger head-wise of the pan head.
 
sounds good.
purpose of bigger head?
suggested length and why?

Bigger heads are flatter, thus less wind resistance and less chance of the head pulling through unsupported cardboard. Length would be the thickness of your inner and outer airframe together. 1/4" should be plenty long, as long as there isn't anything inside they will interfere with.

Adrian
 
Bigger heads are flatter, thus less wind resistance and less chance of the head pulling through unsupported cardboard. Length would be the thickness of your inner and outer airframe together. 1/4" should be plenty long, as long as there isn't anything inside they will interfere with.

Adrian

ok sounds good. what about the building in the "cutter brass" strips. are these needed? when i am ready to do DD i will of course ground test before launching.

if i wanted to make these screws work as a nosecone retainer without any pyro to shear the pins this would work also corect?
 
If you do not mind me injecting my thoughts, then yes, you can use the nylon 2-56 screws to hold a nose cone in place that is not going to have an ejection charge working on it. You could even go further and have two sets of holes in the nose cone, one set that you use for dual deployment and may take a red magic marker and mark those on the shoulder of the nose cone. The other set of holes are threaded so that you can hold the nose cone in place without an ejection charge, or you can use brass or steel screws in those locations. You can ground test your dual deploy set up and see if it shears OK as is with stiffened paper. If not, then add the brass. Sometimes it is a bit of work to get the brass installed correctly and still get the nose cone or coupler to slide easily so that you get your separation clean and smooth. The simpler you can keep it, the better it will be. BEAR
 
If you do not mind me injecting my thoughts, then yes, you can use the nylon 2-56 screws to hold a nose cone in place that is not going to have an ejection charge working on it. You could even go further and have two sets of holes in the nose cone, one set that you use for dual deployment and may take a red magic marker and mark those on the shoulder of the nose cone. The other set of holes are threaded so that you can hold the nose cone in place without an ejection charge, or you can use brass or steel screws in those locations. You can ground test your dual deploy set up and see if it shears OK as is with stiffened paper. If not, then add the brass. Sometimes it is a bit of work to get the brass installed correctly and still get the nose cone or coupler to slide easily so that you get your separation clean and smooth. The simpler you can keep it, the better it will be. BEAR


great help, thanks. the kids are in the "dad can we build it faster, higher, more bells and whistles" mode. all i hear is i need to get smarter to stay ahead of them. there's only a little more time of them thinking of me as smart, then they will realize the truth.
 
Education does not always equate to smart. Wisdom and patience, my young Jedi. The best lessons take years to accomplish. They never come fast. Teach the history, for it always repeats itself. By studying the past you can learn to predict the future. Then who is the smart one?
 
Education does not always equate to smart. Wisdom and patience, my young Jedi. The best lessons take years to accomplish. They never come fast. Teach the history, for it always repeats itself. By studying the past you can learn to predict the future. Then who is the smart one?

very true, but the most important thing you said is YOUNG. thanks for that. :wink:
 
For my Hyperloc 1600, I used four (4) sheer pins in the nose. It is a cardboard tube.

I first drilled through both tube and nosecone. I then cut some small squares from steel sheet. I used a Dremel to slowly sand out an area as large as the square around each hole, and epoxied the plate in place over each hole. I drilled the plates to be just a touch larger than the sheer pins. I then tapped the cardboard tube and reinforced it with super glue.

What this did was make the cardboard the part that the sheer pins screw into, but the pin passes snugly through the steel on the body tube and the steel on the nosecone. The two pieces of steel make a nice scissor to sheer the pins cleanly, and prevent the pins from wearing out the tube & nosecone.

So, I know that is probably about as clear as mud :facepalm:, but luckily I documented my complete build on my webpage. :wink:

You can see how I did them here:

https://cjastronomy.com/l3/holes
 
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