Shear Pins

Who uses pins in the boster section ??

My tubes are basically home grown G10 so I am seriously considering it. It seems like very little premium for a great deal of insurance.

I would use them on anything using electronics. If you use motor deploy just use tape to snug it up.

If you do use them use #4 nylon screws and ALWAYS ground test!

thanx, Ben

Based on the book I have I picked up a bunch of #2 nylon scews. I am using electronics so I will probably put a couple in for insurance.

I second that- ground test

I definitely use them. I like #4 nylon screws, though #2 work well too.

with g10, likely not an issue, otherwise I suggest starting with #2's and as the holes enlarge, can always upsize to #4.
J

Hi Paul

Yes, I use them to hold the nose cone and (in dual deploy mode) to pin the booster to the upper section of the airframe. The reason to pin the booster to the upper section is to prevent drag separation -- like you said: its cheap insurance.

Two 2-56 nylon screws work well in my 4" min diameter bird (which has flown on K, L and M motors) with 2 gram ejection charges.

Kevin.

Originally posted by denverdoc
with g10, likely not an issue, otherwise I suggest starting with #2's and as the holes enlarge, can always upsize to #4.
J

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Hey Doc,

I have a great technique to re-work the shear pin holes as they enlarge. Place a piece of painters tape over the hole on one side of the airframe tube. From the other side of the tube fill the hole with fine saw dust (I use course sand paper on birch plywood to create a small amount of wood dust). Flatten down the little pile a bit with your finger, then apply a drop or two of CA glue. Let it set up them peal off the tape and re drill the hole. Works great and leaves a very durable surface for shearing the nylon screws.

SE

Ok...since this is already started...

I will be using motor ejection on my expediter. Do I need to use these screws on my NC and transition?

I think the idea is sound no matter what type of ejection system you employ. In single deployment it can stop drag seperation and thus prevent a zipper. In DD it will keep the NC on until it is time for the main to be deployed. They are basically insurance.

Here's a photo of my "Nuclear Stonebreaker" nose cone showing one of the three brass shear plates that I installed in the shoulder of the nose cone. I used a Dremel Tool to sand out shallow holes in the shoulder of the nose cone for the brass plates. I bent the top 1/4 inch of each brass shim stock plate at a 90 degree angle so that it can be inserted into slots cut in the shoulder of the nose cone. I roughed up the back side of the brass plates for better adhesion and used JB Weld to attach them to the nose cone. The shear plate holes match up with 3 holes in the forward airframe. I reinforced the holes in the body tube with CA glue and used #2 nylon screws as the shear pins. The setup has worked perfectly for numerous DD flights.

Here's a shot of the #2 nylon screw shear pin and associated hole in the airframe.

I did pretty much the exact same thing.

what is the rocket you have as an icon?

That's his own scratch design, the Top Secret.

Here is one of his build threads on one of his many scales of TS

Originally posted by plasticpaul
Who uses pins in the boster section ??

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Since you ask - I do.
As said - seems like cheap insurance.

I've always only used them for the NC, whether doing DD or not...
I'd used #4's once, one each on both booster and NC... the booster one didn't shear and my 3" AMRAAM was heading in directly over the parking areas at Springfest... talk about a Sphincter factor!!! Fortunately, the NC ones DID shear, and although it zippered the payload tube, it landed safely. Since then, I do a decent friction fit for the av-bay/booster and use one #2 nylon screw for the NC.
That said, I will more than likely start using 1 #2 for the booster and 2 of them for the NC... I HAVE seen a single #2 screw on an NC shear and the main come out at apogee from the shock of the leash being fully extended and the payload section jerking to a halt...

I think using two 2-56 nylon screws on either/both sections is plenty. Maybe I'm just a bit shy about using the 4-40's now after my AMRAAM scare...

Cheers!

Ron

I do. Both the nose cone and the booster.

So what size hole should I drill to install these? And what length screw is ok?

The hole needs to be just big enough for the screw to thread in... you don't want it sloppy... on some of my birds, I've drill the hole, then soaked it in CA, then run a 2-56 tap through it...
Don't recall the drill size though...

R

Any length should be fine as long as it goes fully though both pieces of airframe or airframe/nc...

R

Where do you guys buy your 2-56 nylon screws from???

I found these on mcmaster carr: $5.03 pk/100 2-56 x 1/2"

Is that cheap enough???

Originally posted by bigone5500
Where do you guys buy your 2-56 nylon screws from???

I found these on mcmaster carr: $5.03 pk/100 2-56 x 1/2"

Is that cheap enough???

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Seems like a decent price to me.

that's where I got mine. 100 screws for $5 seemed like a good enough deal to me. Even if it's high, it won't come out to more than a couple extra cents per flight :shrug:

I got mine at McGuckin hardware, and I recall a price of about $3.50 for 50 #4-40 nylon screws. I don't remember what I payed for the #2-56.

A 5/64 bit works just right for the 2-56 nylon screws. Still tight enough that you'll need to screw them in.

FWIW, using just one shear pin runs the risk of causing the NC to cock slightly and bind in the tube. At the very minimum I would use at least two, I always use a minimum of 3.

I have a rocket (my L2 rocket) that is plain unglassed LOC 4" that has 22 flights as of yesterday, that uses the same recessed shim stock arrangement as posted earlier in this thread for the NC. The shear pin holes in the BT are still in great shape. A little CA dribbled into the hole when it's drilled makes them very durable.

Originally posted by cjl
I got mine at McGucken hardware, and I recall a price of about $3.50 for 50 #4-40 nylon screws. I don't remember what I payed for the #2-56.

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Dude, they have everything at McGuckin. EVERYTHING. it's the coolest thing ever!

Exactly - I love the place

(ah crud - I can't type today)

Originally posted by plasticpaul
what is the rocket you have as an icon?

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Sorry for the slow response Plastic, looks like some one else answered your question. The rocket in my avatar is one I designed back in 1972. It won the Estes Design of the Month contest sometime in 1973 (https://www.dars.org/jimz/eirp_78.htm).

I scaled it up and got both my L1 and L2 certifications with it on the same day in March of last year. See thread:

https://rocketryforum.com/showthread.php?s=&threadid=22387

I got my shear pins in today and need some advice...really a yay or nay...

I plan on using 2 in the nosecone and 3 each in the forward and aft sections of the transition/ebay. Is this sufficient or not? They are 2/6 x 1/2" nylon with a binding head if it matters. I'll drill the holes with a #50 drill and harden the hole with CA then run a tap through the hole.

Game plan or not???