Pull pin smoke design

[Spudgun]

Ok. I know there was a long archive file on pull igniters but didnt want to awaken that thread again.

I have been thinking about pull igniters mainly for use in smoke bombs and here is the design I have come up with (see attatched). I have tried to make the design as reliable as possible but would like to know if any of you guys can see any improvements that could be made.

I have tested the nail striker and it detonates the cap fine (these are childrens' 8-shot caps by the way) but sadly I have got no fuse at the moment. I would be using 2mm flying fish fuse as it is the easiest to get hold of for me. Flying fish burns at about 0.8 seconds/centimetre so I would use 5cm of it to give a 4 second delay.

Can anyone spot any flaws?:cool:
(image not to scale ;)

[Lewis]

Seems feasible, but I think there's lots of room for error with the cap. I don't think an 8-shot cap would be capable of igniting fuse reliably.

[Spudgun]

My thoughts exactly.....Thats why I have taken the powder from another cap and put it into the first one, this creates a high power cap that on testing in the pen tube ignitor shot a flame out the back of the 'nozzle'...This should I think ignite the fuse but if not maybe I could coat the end in BP or a small amount of powder from an estes rocket motor?

[Hirudinea]

Thats why I have taken the powder from another cap and put it into the first one, this creates a high power cap that on testing in the pen tube ignitor shot a flame out the back of the 'nozzle'...This should I think ignite the fuse but if not maybe I could coat the end in BP or a small amount of powder from an estes rocket motor?

What about using the powder from the head of a strike anywhere match in your cap, that should give you some flame.

[inventorgp]

What are you going to use for the smoke composition?
KNO3 and sugar? Or some thing a bit more exotic?

[Spudgun]

Hirudinea: Thats a good idea, some of my earlier designs involved using the head of a match instead of a cap but I never thought of using the powder in the cap as well....I will give it a go.

inventorgp: I am sticking with the KNo3:sugar mix at about 4:3. I might also try adding some shredded rubber to give it a bit of a kick.

[c.Tech]

A couple of little tips:

Your fuse seems to be layered, make sure there is no chance the fuse could touch or let sparks jump to other parts of the fuse making the time shorter.

Make sure the fuse is exposed to enough air so it won’t burn extremely quickly reaching the cap within less than a second.

[Spudgun]

Thanks for the imput c.Tech. Sorry for the crude diagram- the fuse will not be layered, I shouldn't have shown it like that, in reality the fuse will be in a shallow 'u' shape, going from the cap to the filler.

I have just received my fuse today in the post and it is green flying fish. I'm not sure if anyone is familiar with it but it is pretty much the same as regular visco, containing a slightly different core material instead of BP, this gives it colour when it burns and allows it to zip around the sky erratically, hence the name.

"Make sure the fuse is exposed to enough air so it won’t burn extremely quickly reaching the cap within less than a second"
I assume you mean reaching the filler in less then a second :) . There are air vents to let in air for the fuse and to let the smoke gasses out, but I dont think the burn rate of the fuse will be greatly effected considering it burns underwater anyway....

After testing the reliability of the cap igniting the fuse I have discovered an issue- The force of the cap detonation shoots the end of the fuse out from the pen 'nozzle' without igniting it. This means I need to use an adhesive to keep the fuse inside the nozzle. I have used locktite instant adhesive but as it is so runny gets soaked up by the fuse and may affect the burn rate(?)....Would a 2 part epoxy resin be better?....When the fuse does not shoot out it lights every time :)

Here is the design mark 2

[nbk2000]

Use .GIF format for saving your computer drawings. Much smaller size and clear lines instead fuzzy like with .JPG.

[Alexires]

Spudgun - Congratulations on it working, I was dubious as to whether it would.

2 Part epoxy holds stuff pretty well. If you use 5 minute epoxy, mix it until it becomes rather thick, and then apply it. That should stop it from soaking into the fuse.

I was thinking, why not have a 9V battery with one terminal attached to the nail and another attached to some nichrome wire inserted just inside the smoke composition, or attached to the fuse?

Ofcourse, there might be a problem with the cost of the battery and all...

[Spudgun]

yes, I have some 'permabond' which sets in about 5 minutes, it goes a pearly colour when mixed.

Good thinking about the electrical detonation idea, it would be much more reliable then the cap method but sadly is not the most cost effective way of doing it:(

[Alexires]

You could always have a small capacitor that melts a thin nichrome wire, and hooks to the battery.

The smoke devices are on the belt, all charged from the battery, and when you pull them off the belt and pull the pin, the capacitor discharges and sets the smoke off.

Or, you should just use a pin, a cap and a piece of fuse *wink*.

NBK had a thread on pull strip grenades utilizing match heads and the striker IIRC. Maybe try a few experiments like that?

[teshilo]

Intresting design had US grenade with double action fuse delay/impact(i dont remember his mark). After as safety pin pulled and powder in fuse burn ,heat from it produce electic current by mean small heat- electric battery and switched second firing chain with impact sensor as "ball in tube"Grenade explode after five second delay or after impact.

[Spudgun]

Ahh ok, so after the pin is pulled it detonates on impact or after the fuse delay, (Which ever occurs first). Thank you for that, an interesting design, it has got me thinking.....

Alexires: Thats also a good idea, that way you don't have to destroy the battery and keep the reliability of the first idea you mentioned. Hmmm....:rolleyes:

[inventorgp]

For a capacitor you would need a high capacity low ESR (equivalent series resistance) capacitor . About 1 Farad would do nicely (anything from 5000µF – 1F), with a resistor to charge the cap and a resistor to limit the current flow to the nichrome wire. Using an ESR cap isn’t necessary but, also make sure the cap doesn’t have a internal bleeder resistor.

Cap, referring to capacitor.

[inventorgp]

The first resistor (to the cap) is to prevent draining the battery. The second (to the nichrome wire) is for limiting current but, it’s also used to stop the cap dying from instant discharge.

[w22shadow]

Has anyone entertained the idea of using the springs from hole-punchers (http://img.shopping.com/cctool/PrdImg/images/pr/177X150/00/01/6f/76/1e/24081950.JPG) in spring-based designs? They seem rather well-suited to such a purpose. :)

[Spudgun]

Today I tested the whole detonator at school (had to show my friend :)) and it works perfectly. I am using a split-pin as the pin with a keyring through the hole in the end.

The spring I used is just one I found in a box in my garage but sadly there are only about 3 more left :(, this means I need to find a new renewable source of springs. The one in my 'prototype' is about an inch long (uncompressed) an just under 1/8 of an inch in diameter, it is very strong for its size as I can bearly fully compress it with one hand. Has anyone got any ideas where I could get some of these?

[nbk2000]

A hardware store would be my first suggestion. ;) :D

[Spudgun]

I finally got the chance to test the whole detonator + smoke device and am pleased to say it was a success!:) The delay was even accurate and set the thing off after 4 seconds:D. The success of the prototype has created some more ideas to my mind. I hate the way the cardboard tubes I am currently using burst into flame once the filler has finished burning and would set anything they are touching on fire. This is why I would like the device to be encased in a non-combustable material ie steel tubing, however would this affect the stability of the KNO3+sugar mix?

[nbk2000]

Make a saturated solution of Borax, and soak the tubes in that.

This will make them non-combustible. :)

You'll have to test how long you can soak the tubes without them falling apart on you.

[Alexires]

Spudgun, you are in luck!

During my long and boring days, I have tested just that. The best that I have found is either making the smoke composition burn for longer by the addition of Sodium Bicarbonate, or by soaking one of those postal tubes wrapped in cloth in a PVA+water solution.

Even with the normal 50/50 KNO3/Sugar (w/w) smoke device, it easily withstood the temperature. The tube even remained together to some degree.

I'll make one up tomorrow if you like, and test a BP composition in it (no sugar around).

Also, I have some borax lying around NBK, so I'll try that.

I think by using cloth, you don't have to worry about the tube falling apart on you when you soak it.

[GibbsFreeEnergy]

I am unable to view the images in this thread so I hope this isnt too similiar to what is being shown. This design was drawn very roughly in a short period of time in Rhinoceros 3.0. I think it is pretty easy to see how it works from the picture. Essentially, the pin is pulled and the pointed hammer (which could likely be a large penny nail cut off-bronze) is propelled forward by the loaded spring behind it, which then collides with the primer of a cut off shell casing (yellow). Underneath the primer is black powder (black) or any other flammable powder that would then ignite and ultimately ignite the wick that is inside of it (green).

Since most of us do not have access to advanced machining tools, I attempted to draw this so one could make it using only different sized drill bits in a simple drill press. The holes are made to be drilled all from the top, and then the pieces are inserted. Next, one would insert the wick, and then a small amount of epoxy on the bottom of the powder chamber in order to ensure powder can not spill through past the chamber. Powder can now be added to fill the chamber, and then the shell casing can be placed on top (the hole should be drilled to the proper size to accomodate whatever caliber shells one would like to use). Afer this is complete, one can drive the pin through the side and then place the hammer in from the top hole. The spring can be compressed underneath an epoxy resin or one could thread the top hole.

Well, hope this makes some sense. The instructions are rather vague but essentially every stage is done from the top of the device (large hole) and then it is either sealed with epoxy or a threaded plug. Sorry if this is rather rough.

http://i100.photobucket.com/albums/m27/GibbsFreeEnergy_2006/SideSide.png
http://i100.photobucket.com/albums/m27/GibbsFreeEnergy_2006/Top.png
http://i100.photobucket.com/albums/m27/GibbsFreeEnergy_2006/side.png

The pictures are in png format and I hope they aren't too big. I wish I had a better editing program; these are ren gens.

[Alexires]

Ok, I've tested some thin tubes with both a saturated Borax solution, and a PVA solution.

I used tubes with about the same thickness as the toilet paper rolls.


Method:

Part A:
Borax was mixed with boiling water and then let cool for about 5-10 minutes.
4 cardboard rolls were then partially submerged in the borax solution and rotated to ensure an even soak. At 5 minutes, one roll was removed from the borax solution and placed in a 100*C oven to dry.

The other 3 cardboard rolls were removed from the borax solution when they had been deemed saturated (deemed so by colour change and slight unraveling of the cardboard) and placed in a 100*C oven to dry.

The rolls were removed from the oven, and the bottom was flattened and folded over as to seal one end. Due to the stiffness of the rolls saturated with borax, they could only be flattened then sealed (without folding). They were sealed with clear packing tape.

Part B:
Boiling water was mixed with PVA in a ratio of about 10:1 (Water:PVA).

4 Cardboard rolls were partially submerged in the PVA solution and rotated to ensure even soak. One roll was removed from the solution at 5 minute intervals so that there was a 5 minute soak time seperating each roll (Eg. 5 minute, 10 minute, 15 minute and 20 minute soak time).

As each roll was removed from the solution, it was placed in a 100*C oven to dry.

When the rolls had dried, they were removed from the oven and the bottom was flattened, folded over and sealed with clear packing tape.

Part C:
A Black Powder composition was made using the common method of 75:15:10 - KNO3:C:S.

Each ingredient was ground till they were of the same consistency, then mixed thoroughly.

Roughly 30 g was poured into the previously prepared cardboard rolls (See Part A and Part B). 2 of the saturated borax tubes were disgarded due to lack of black powder.

Results:
Each tube was taken outside and ignited seperately. All, except the saturated borax tube burnt with ease and was reduced to ash. The saturated borax tube was observed to resist burning to some degree before it was consumed.

From this, I would have to agree with NBK and say that a saturated solution of Borax is the way to go. Make sure that thicker tubes are used (such as thick postal tubes) or alternatively, paper could be wrapped around the tube and soaked with the tube.

Maybe a coat of PVA on the outside would improve flame resistance.

A short note, it seems that the PVA solution dissolved the glue that held the tubes together, so anything over 5 minutes had the tubes starting to fall apart.

I only have one thick roll left after previous experimenting, and a little borax, so I'll try that tomorrow and get back to you on it. I'll also try making some rolls out of paper and whatnot.

I hope this helped to some degree.

[Spudgun]

Thanks Alexires. I am going to run a few tests on cardboard tubes soaked in a 50:50 pva:water solution with the smoke filler in them. I will use a 50:50 KN03:sugar mix this time instead of 3:2.... Will a piece of 2mm visco fuse ignite a 50:50 mix easily enough though?

[Spudgun]

The PVA soaked tubes set alight :( but they did not completely burn out to ash like they usually do, these ones only partially burned through. Alexires, what ratio of sodium bicarbonate do you use with the 50-50 smoke mix? Do you add this before you melt the KNO3-Sugar mix?

[c.Tech]

It probably wouldn’t be necessary to mix the sodium bicarbonate in before melting but would make your job easier.

The idea of adding the bicarbonate causes an over all slower burn rate, so as long as its evenly mixed it should be fine.

Because it would probably be a fine powder and the sugar would probably be granules it’s better to mix the consumption just before melting, so the finer particle’s don’t slowly move towards the bottom.

[Spudgun]

Yes. Does the sodium bicarbonate effect the amount of smoke produced?

[c.Tech]

I'm assuming that adding bicarbonate would also lower the temperature at the same time as slowing the burn rate. If this is so there would probably be more smoke.

This is probably why sodium nitrate doesn’t make as much, if any smoke compared to potassium nitrate. IIRC Potassium nitrate burns at a lower temperature.