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styrene shear pins
#1
I am building a mad Cow 54mm fiberglass Frenzy.  I usually use 2-56 nylon screws for shear pins but I like to try new things and I hear some people use styrene rod for shear pins.

What size styrene rod is good for shear pins?  I have some 1/16" laying around.
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#2
(11-05-2015, 12:11 AM)squawsach Wrote: I am building a mad Cow 54mm fiberglass Frenzy.  I usually use 2-56 nylon screws for shear pins but I like to try new things and I hear some people use styrene rod for shear pins.

What size styrene rod is good for shear pins?  I have some 1/16" laying around.

That'll work.

I did the opposite. Started with styrene, then switched to nylon screws.
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#3
One caution... Old strength of materials testing by Drake Damerau found that styrene rods were inconsistent in shear force likely due to manufacturing tolerance and stretching in our particular application. On the other hand 2-56 and 4-40 nylon screws tended to be consistent and over a grouping of 2 to 4 typically used, the average force was very predictable.
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#4
I've used 1/16" styrene shear pins on most of my papertube rockets. I usually use three equally spaced around the perimeter. For fiberglass tubes, I use the 2-56 screws. I have always had problems with the 2-56 screws in papertubes, even with it hardened with CA.
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#5
I would stay with the nylon. I don use sheer pins. I friction fit and if I was to go with pins it would be nylon.
Bill Fields
L2
TRA
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#6
I've read the Drake Damerau shear pin testing article, and it seemed to me like the styrene rod testing he did was just a throw in  to say he tested them, while his primary focus was on testing  nylon screws.  He was using styrene tines (square), in round holes for one. 

Anyway, just to form my own opinions on the matter I've tested the 1/16" rod and the 0.080 " rod.  I had consistent and repeatable shear with both.  The 1/16" took  about 25 pounds and the 0.080" took about 35 pounds for one pin.  See attached photo for totally scientific Wink test setup.

I always use styrene on cardboard airframes and have never had an issue.  For fiberglass I use nylon screws.

Here's another interesting article on the matter from Stu Davis.  Hopefully Stu doesn't mind me reposting it.


Attached Files Thumbnail(s)
   

.pdf   shear pins.pdf (Size: 642.61 KB / Downloads: 11)
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#7
I still use the 1/16th styrene rod on my phenolic rocket and on my quantum tube rocket with great success. For my fiberglass rockets, I switched to 2-56 nylon screws for my 4" rockets, and for my 8" rocket, 4-40 nylon screws.

Adrian

Adrian Butler
NAR 73787 L3
Tripoli 13524 L3 
QCRS, Princeton, IL
Chicago Rocket Mafia "The Mechanic"
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#8
Back in the day...lol lots of fliers used the styrene rods. I tried it myself before the pins. Heck i used to see plastic picnic fork tynes [prongs] beings used.

I switched to 2-256 screws for simplicity [for me anyhow] getting the rod became harder to find & I had to order it. I didn't care for to ends sticking out of my rocket and it just seemed much easier to push a pin'/screw in and be done with it. When using the rod, I had to try and cut even lengths etc..etc.etc.

I will agree that both types work equally well, but I think the learning curve is shorter with pins due to mainstream use.
As long as you can get reliable info on placement/use of styrene...go for it.
There are lots of ways to get the job done, as long as it works....great
Me, I don't see any need to re-invent the wheel.....as long as it doesn't get a flat.LOL
Jim Hendricksen
T 9693
L-3 Savannah Ga
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#9
On a lighter note....

I had styrene pins as the hinges on my front screen door for 20 years or so.
And sure enough, when they tried to move the new couch in through the front door, they removed the pneumatic break cylinder, and let the screen door flop all the way back...
and those polystyrene pins proved that they were sheer pins...neat as you please, they sheered right off...and my aluminum door fell off those hinges, struck the porch floor and then fell forward to shatter the glass all over the concrete steps.... just like clockwork.

(Of course the delivery company denied that they had caused the problem...."Those hinges were worn out". They refused to pay for the damage their men had caused us... $109 for a new door that we had to install ourselves...)
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