Basic shear pin know-how needed

[J Blatz]

I am slowly finishing my Doug Stout Arcas kit. For those who don't know, which is probably most, this is a 4.08" paper airframe kit with a solid wood cone. I am looking to do dual deployment and need info on how to use shear pins with these materials (ie, making a shear pin work with paper airframe and wood NC). Any general info on shear pins and their usage is also appreciated.

[COrocket]

check out this webpage for info http://www.info-central.org/?article=174

I'd imagine drilling the nosecone to the depth of the screw would be fine. Other people might have some good ideas for reinforcing the hole in the airframe (I've never done it)

[jsargevt]

Funny I am finishing my stout arcas as well and I was contemplating the shear pins as well.

I got some 4/40 plastic screws from microfastener.com. I think that 2 will probably be good for this rocket. I also picked up some threaded brass inserts at lowes or home depot (forgot the size I'll check tomorrow). The 4/40 screws fit in nicely, so nicely in fact, a am trying to figure out how I am going to get the remains out of the insert. They push in but the screw threads catch on the metal threads on the insert. I think some CA on a toothpick might help. I'll let you know once I finish up the install and do some testing.

I will CA the holes in the paper airframe and that should be enough to keep the hole from enlarging.

If this doesn't work as expected I'll probably use some kind of metal "cutter" on the nose but the insert looks promising.

Awesome kit, isn't it? I am excited to wrap it up in the next few weeks and hopefully get my L2 before the end of the year. Only time will tell...you can't rush these things....

[DM1975]

I would look at getting something smaller than 4/40 for the shear pins. I use #2 on my 4" rockets and their are smaller than that available.

CA the holes in the airframe. You could even back it with very thin brass shim stock to help cut the pins.

[chadrog]

I would look at getting something smaller than 4/40 for the shear pins. I use #2 on my 4" rockets and their are smaller than that available.

CA the holes in the airframe. You could even back it with very thin brass shim stock to help cut the pins.

Agreed - #2-56 nylon screws are a better bet in paper rockets. #4-40's will not break without an additional "cutter", and will rip through the tube. I use 2-56's in my DD setup on my Minnie-Mag (5.5"), along with a pin cutter. The cutter is a sharpened washer glued into the nose cone shoulder.

[AlphaHybrids]

To get the pin out just heat a screwdriver with a flame and press into the nylon screw and let cool. The just turn out/pull it out.

Edward

[jsargevt]

I sit corrected - I checked the package and the screws are 2-56. Serves me right for posting later at night without checking the facts. Also - the brass insert should act as a "cutter" once I screw it into the nosecone. That is the idea at least....

[davdue]

Agreed - #2-56 nylon screws are a better bet in paper rockets. #4-40's will not break without an additional "cutter", and will rip through the tube. I use 2-56's in my DD setup on my Minnie-Mag (5.5"), along with a pin cutter. The cutter is a sharpened washer glued into the nose cone shoulder.

What size washer and how/where is it sharpened?

[DM1975]

You can use a thin brass sheet to do this with. I carv out a spot and glue it in place with some JB Weld and then drill through it. Works really well.

[chadrog]

What size washer and how/where is it sharpened?

I believe that particular one is a #10, the inside diameter is sharpened with a small grinding stone/dremel. This might be a better example:

[Disaster_Guy]

I have bought my #2-56 shear pins in low quantity (and paid way too much as a result). What is the best source for #2-56 nylon in quantities of around 50?

[chadrog]

I have bought my #2-56 shear pins in low quantity (and paid way too much as a result). What is the best source for #2-56 nylon in quantities of around 50?

Mcmaster-Carr is the best place that I know of. It's only a few bucks/hundred.

[jsargevt]

I have bought my #2-56 shear pins in low quantity (and paid way too much as a result). What is the best source for #2-56 nylon in quantities of around 50?

I picked mine up at http://www.microfasteners.com/ - fast reasonable shipping on top of good prices.

[DM1975]

I get mine from the local Fastenall by the 100 count. I'll probably buy some from McMaster Carr when I make an order from them next month.

[degreaser]

Here are mcmaster pn for 3/8" 2-56 nylon screws. They work great. $5/100.

93135A015 phillips
93135A079 slotted

[JordanT]

Here are mcmaster pn for 3/8" 2-56 nylon screws. They work great. $5/100.

93135A015 phillips
93135A079 slotted

Note: if you're on a budget, shipping is about $5 for McMaster. They don't say upfront. Also, if you order and all your screws aren't in stock at one location they'll charge you twice for shipping. I only know because I ordered some #4-40s and some #2-56s and it came to $9-10 total so I tried to charge it with a prepaid card that had about $16 left on it. The charge was denied because the total was $19.xx. At least, I presume shipping was $10 since it came from two separate warehouses. They may charge $10 to ship anything. (Note: they shipped immediately, and called about the card denial a day or two later, so I could charge it on a regular card)

[degreaser]

Note: if you're on a budget, shipping is about $5 for McMaster. They don't say upfront. Also, if you order and all your screws aren't in stock at one location they'll charge you twice for shipping. I only know because I ordered some #4-40s and some #2-56s and it came to $9-10 total so I tried to charge it with a prepaid card that had about $16 left on it. The charge was denied because the total was $19.xx. At least, I presume shipping was $10 since it came from two separate warehouses. They may charge $10 to ship anything. (Note: they shipped immediately, and called about the card denial a day or two later, so I could charge it on a regular card)

I've never had issues with mcmaster. I add stuff to the basket until it's full enough to justify an order. Their website is among the easiest to use in the industry and stock status is given at order time. They ship very promptly, I usually have the order in hand within 48 hours.

[EDIT] - if you are an amazon prime member, the small parts store has them with free shipping. But then again prime membership isn't free...

[JStitz]

Jason, I was going to comment on how Tom Blazanin use to use just plain styrene rod from the hobby shop, but these guys have the nylon screws figured out.
I still like the brass or metal "Cutter" that some have used and would like to know how many deployments they got before the epoxy gave way..or does it?
Also what about the left over styrene rod from Models? is it soft enough if the diameter is right? I plan to retro-fit several rockets, from cardboard..to unglassed PML..to glassed PML.

DM1975,how long has your cutter lasted?..do you sharpen it with a file ever?
I'm sick of peeling off old masking tape.

[JordanT]

I've never had issues with mcmaster. I add stuff to the basket until it's full enough to justify an order. Their website is among the easiest to use in the industry and stock status is given at order time. They ship very promptly, I usually have the order in hand within 48 hours.

[EDIT] - if you are an amazon prime member, the small parts store has them with free shipping. But then again prime membership isn't free...

I should say that I have no quibble with their service, it's just a bit annoying that shipping isn't calculated by the website. Good to know about small parts and Amazon Prime. I have it and it's well worth it for me (well, my business pays for it). Way back when (10 yrs ago) Smll Parts was on the expensive side, but were a rare source for pre-internet parts and had great customer service.

FWIW, I just installed my first set of shear pins yesterday. Drill a #4 hole for #2 screws. Oops.

[DM1975]

Jason, I was going to comment on how Tom Blazanin use to use just plain styrene rod from the hobby shop, but these guys have the nylon screws figured out.
I still like the brass or metal "Cutter" that some have used and would like to know how many deployments they got before the epoxy gave way..or does it?
Also what about the left over styrene rod from Models? is it soft enough if the diameter is right? I plan to retro-fit several rockets, from cardboard..to unglassed PML..to glassed PML.

DM1975,how long has your cutter lasted?..do you sharpen it with a file ever?
I'm sick of peeling off old masking tape.

I have only launched each of my rockets with the brass shim on it once so far. The brass is recessed and JB Welded in place. I don't thin it is going anywhere any time soon. Also, I don't sharpen it, it is not needed. The brass just keeps the holes from getting bigger and gives a more solid shoulder for them to push against. You can yank the nose cone real hard and shear the pins yourself and see how it works. For me the nylon screws are perfect as they are consistent in size and strength, they can be trimmed off flush if you want, and they just look right having the screw head there.

Shear pins were really spooky to me at first but once I did my first rocket up with them I'm hooked. No guess work, no masking tape, no drag separation or pre mature main deployment, and it is all stupid simple once you do your first one. I don't think I'll ever build a rocket without them again.

[Wiley]

Not to hijack this thread, but I had a couple of questions on this same subject. I'm currently building a 4" blue tube rocket with a plastic nose cone. I have the means to reinforce the holes in the nose cone, but I was wondering if the blue tube needs to be similarly reinforced. Blue tube is pretty tough, but I want this rocket to last, so I can't have shear pin holes turning into shear pin slots . Also would you recommend three 4-40 or three 2-56 screws for this size nose cone?

[DM1975]

Not to hijack this thread, but I had a couple of questions on this same subject. I'm currently building a 4" blue tube rocket with a plastic nose cone. I have the means to reinforce the holes in the nose cone, but I was wondering if the blue tube needs to be similarly reinforced. Blue tube is pretty tough, but I want this rocket to last, so I can't have shear pin holes turning into shear pin slots . Also would you recommend three 4-40 or three 2-56 screws for this size nose cone?

I use two 2-56 on my 4" rockets. Soak the holes in the tube with CA to harden them. That should help it last quite a while.

[Jogetorenk]

dont have much idea regarding this but you can look up for this at http://www.microfasteners.com/ as this would help you a lot

[isobig]

Building my first fiberglass rocket (4") and the instructions say to use shear pins. I think the FG would be strong enough so as not to need a cutter as mentioned above? Also, do you drill same size hole in airframe and coupler, or make the coupler hole slightly larger so that the screw only screws to the airframe and not the coupler?

[chadrog]

Building my first fiberglass rocket (4") and the instructions say to use shear pins. I think the FG would be strong enough so as not to need a cutter as mentioned above? Also, do you drill same size hole in airframe and coupler, or make the coupler hole slightly larger so that the screw only screws to the airframe and not the coupler?

Correct on all accounts. I drill my holes in fiberglass like this - first drill hole sized for tap - tap hole through both components - insert a screw - repeat for the rest of pins - remove screw - take parts apart - drill slightly larger hole in inner part. Piece-O-Cake in fiberglass.

[isobig]

Correct on all accounts. I drill my holes in fiberglass like this - first drill hole sized for tap - tap hole through both components - insert a screw - repeat for the rest of pins - remove screw - take parts apart - drill slightly larger hole in inner part. Piece-O-Cake in fiberglass.

Drats... now I need to go buy a 2-56 tap. LOL

[DM1975]

You don't have to tap it. As long as the shear pin fits in tight it will work fine.

[Budzilla]

Just to chime in. My 3" Blue Phenix cracked so I would definetly reinforce or glas the Blue tube.
After I glassed it my first attempt at dual deploy the main chute fouled so the rocket hit pretty hard. No damage what so ever.
On this bird I used plastic body rivets to attach the payload section to the ebay. The main chute is in the payload section & I ensure the nose is friction fitted fairly tight.
The drouge is below the ebay and I use the motors ejection charge as a back up.
I have had 3 succesful flights afterwards and no need for the shear pins.

[MackDiesel]

You don't have to tap it. As long as the shear pin fits in tight it will work fine.

How do you not have to tap it? Wouldn't the nylon be too weak to screw itself into even a paper tube? You don't have to tap machine screws going into wood, but this nylon can't gouge itself into the airframe, right?

[chadrog]

How do you not have to tap it? Wouldn't the nylon be too weak to screw itself into even a paper tube? You don't have to tap machine screws going into wood, but this nylon can't gouge itself into the airframe, right?

He's saying use a bigger drill - same size as the O.D. of the screw. I like the added security of the threads.