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New Nail Dart Design & Testing

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: boyntonstu » Sat Jan 16, 2010 7:26 am

This dart shoots well at 450 psi.

The secret was to add 1" of foam beyond the 3" nail head.

IOW Pierce a .33" thick foam disk with the 3" 10d nail and hot glue it to the head from below.

Add 3 more foam disks onto the head and the first disk.

It shoots very fast and straight at 450 psi.

My goal is to shoot them at 550 psi.

I am fairly certain that this design will take it.

Thicker foam would be nice.

I can make a new dart in the time it takes the compressor to reach 450 psi.

YMMV

BoyntonStu
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Closed Cell Foam Tail
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Unread postAuthor: qwerty » Sat Jan 16, 2010 7:31 am

looks good, you could try sanding them down to male it more aerodynamic.
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Unread postAuthor: boyntonstu » Sat Jan 16, 2010 8:12 am

qwerty wrote:looks good, you could try sanding them down to male it more aerodynamic.


Thanks, and I agree.

First function, next form.

I had a heck of a time stabilizing a nail dart above 200 psi.

A rocket shaped tail will be my next project.

However, even though the darts look ugly, they fly surprisingly straight.

Sanding is a problem. I chucked the nail in a drill press and it was a no go.

I am thinking of using heat and melting/cutting a shape.

Hints would be appreciated.
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Unread postAuthor: qwerty » Sat Jan 16, 2010 11:24 am

you could cut this foam rings from small to big then slide them on top od eachother.
But for my RC plane modelling i use hobby knives to carve EPP foam you could try that.
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Unread postAuthor: FighterAce » Sat Jan 16, 2010 11:37 am

boyntonstu wrote:I am thinking of using heat and melting/cutting a shape.


I was thinking of using a soldering iron and a bad tip for it. My guess is that the foam will start to melt and shrink as soon as you come close to it with the hot soldering iron.
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Unread postAuthor: boyntonstu » Wed Jan 20, 2010 2:45 pm

Image

I cut a piece of barrel material and drilled a hole for the soldering iron.

Notice how a cone shape is automatically produced.

I tried a few boat tailed shapes.

I also tried using a foam nose and a closed cell polyethylene pusher/sealer, not attached to the dart.

Just like using a wad. It produced the damage shown below at 200 psi.

The 10d nail penetrated 2 sheets of 5/8" plywood and the point sticking out was embedded in the third sheet.


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Cork Tail Nail Dart

Unread postAuthor: boyntonstu » Sat Jan 23, 2010 1:08 pm

A few photos of my new Nail Dart.

Corks are free or very cheap.

Easy to size with a drill press and a belt sander.

Grease them up an they slide easily.

This shot was at 250 psi driving a 3" 10d nail.

Finished Nail Dart


Image


Front side of carpet.

Image


Back side of carpet. (notice the hot glue)

Image

Nail head into 5/8" plywood.

Image

Out the back of the plywood.

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Cork Tail Nail Dart

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Unread postAuthor: psycix » Sun Jan 24, 2010 11:17 am

Not bad. Cork seems a nice material for ammo.
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Unread postAuthor: boyntonstu » Sun Jan 24, 2010 5:12 pm

psycix wrote:Not bad. Cork seems a nice material for ammo.


Thanks!

Like a greased piston in a pump cylinder.

One advantage over using a cone is that the cylindrical cork drives the nail straight down the center of the barrel.
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Unread postAuthor: paaiyan » Sun Jan 24, 2010 5:20 pm

I'd make a little effort to make the front of the cork a little more aerodynamic myself. Seems to work OK for you and it's a good idea, I just think you could round off the front a little and still retain the cylindrical shape towards the back for stability within the barrel.
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Unread postAuthor: boyntonstu » Sun Jan 24, 2010 8:47 pm

paaiyan wrote:I'd make a little effort to make the front of the cork a little more aerodynamic myself. Seems to work OK for you and it's a good idea, I just think you could round off the front a little and still retain the cylindrical shape towards the back for stability within the barrel.


Another way to get aero is to add a small paper nose cone transitioning the nail to the cork.

Boat tailing the rear of the cork may also help.
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Unread postAuthor: psycix » Mon Jan 25, 2010 9:24 am

Would the piece of paper hold all that force?
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Unread postAuthor: boyntonstu » Mon Jan 25, 2010 11:07 am

psycix wrote:Would the piece of paper hold all that force?


A conical nose cone ahead of the cork has very little force applied to it.

Think of model airplane wings covered with tissue paper.

I intend to fabricate a vertical lathe jig out of a drill press.

It will allow me to size the cork to the barrel and to taper both ends to the diameter of the nail head.

The remaining flat surface is the difference in diameter between the nail shaft and the nail head.


Not much of a transition.


A conical dab of hot glue should be fine, if needed.
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Cork Cutting Tool

Unread postAuthor: boyntonstu » Tue Jan 26, 2010 2:57 pm

Cork Cutting Tool



Image

I got a better idea than sanding/lathing the cork to fit the barrel.

The 3/4" cap is not soldered to the piece of barrel.

It was forced in using a vise.

I cut a composite champagne cork in a few seconds.

At 300 psi a 10d nail head went completely though 2 layers of carpeting, completely through the first 5/8" plywood, through the second 5/8" plywood, and it stuck out 1" beyond that.

This is not a cork gun with a string.

It appears that the cork may be reused at least few times.

The copper cutting tube was not sharpened and it did not burn the cork or get hot.

The hardest part was centering the hole for the 5/16" screw in the cap.
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Unread postAuthor: deathbyDWV » Tue Jan 26, 2010 3:55 pm

Great idea.

One way to figure out the center of a cap is to take a washer that's about half the size of the cap and set it inside the cap. Then push it up against the inside edge of the cap and use something like a super fine tip sharpie and draw an arc along the edge of the washer. Then just continue to do this several times going around the inside of the cap and you'll have the middle found.

If you don't understand I might be able to put up a picture...
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