Tuesday, November 29, 2011

Carbide Cannon

my giant carbide cannon

When I was little I used to see ads for Big Bang cannons in the back of Popular Mechanics magazine.  Oh how badly I wanted one.  But it was not to be.  Years later while searching Ray-Vin for some high power rifle equipment, I came across this site.  Giant carbide cannons!  The daydreams of my youth magnified twenty times!  Of course I just had to build one.  And with my daughter's birthday party being held on 4th of July weekend, I had two perfect excuses.

Big-Bang carbide cannon

Carbide cannons are the coolest noisemakers ever.  First the cannons are filled with a little water.  Calcium carbide is added next.  When the carbide mixes with the water it forms flammable acetylene gas.  Add a spark and KABOOM!  A large bang erupts from the barrel.



the business end

I built my cannon based on these plans in June 2010.  I followed the plans pretty closely with only a few minor changes.  The tee is actually a 6" x 6" x 4" tee instead of a 6" x 6" x 6" tee.  It was a little cheaper and the bottom of the tee is hidden anyway so it looks exactly the same.  Instead of pipe and a cap at the breech end, I used a 4" threaded adapter and cleanout plug.  I topped the breech plug with a wooden finial from a curtain rod.  The carriage was made out of wood left over from the mantle project.  The trunnions are made from some old electrical conduit.  The carriage was finished with whatever stain I had on hand and the cannon was painted with a gray hammered finish spray paint to give it the appearance of iron.

ready to fire

fired
I wanted to use a lanyard to fire the cannon rather than a match or touch stick.  So I purchased a Coleman lantern igniter and inserted it through the top.  The igniter strikes a flint and makes a spark when spun.  I attached a wooden wheel with a spring to spin the igniter.  A door stop served as the lock mechanism.  The wheel is rotated about 180 degrees putting it under spring pressure.  The lock is inserted into a hole in the side of the wheel, holding the wheel in place.  When the lanyard is pulled, the lock is removed and the spring spins the wheel creating a spark which ignites the acetylene.  This setup works pretty well and the kids love to pull the lanyard from a safe distance.  However, you have to wait until just the right time to fire.  If you don't wait long enough then not enough acetylene will be generated and you get a pathetic whoomph instead of a BOOM.  Wait too long and there is too much acetylene and not enough oxygen and you get the same result.  Also, if the flint gets wet it won't spark.  That happened on one occasion and I was forced to ignite with a lighter.  The result was a much louder boom.  I think that by using a flame, the cannon won't fire until the breech is filled with acetylene, but long before it is overfilled.

breech view of igniter

I always get the same question.  "How loud is it?"  My friend came over just as I had finished the cannon body and was still working on the carriage.  He asked the proverbial question.  "I don't know", I replied.  "I haven't fired it yet."  With that we set it up on some saw horses in my garage and stuck the barrel outside.  Not knowing what to expect we loaded it, set the firing mechanism, and took refuge around the corner of my house.  I pulled the lanyard and there was an orange flash and a giant KABOOM!  Our jaws dropped in speechless amazement and I could just just barely hear my friend say "I gotta get me one of those" over the ringing in my ears.  My wife opened the window to see which house exploded on our block and just shook her head as I laughed hysterically.  With the right amount of calcium carbide, you can feel the concussion of the blast in your chest.  In short, it's LOUD!!!  Like heart attack for the elderly loud.  Ear protection is a must.  The video doesn't do it justice but check it out to see it in action.


The second question I usually get is "Will it shoot anything?"  Yes it will.  But it will also likely explode in the process sending shards of PVC into your body.  Large diameter PVC cannot hold much pressure.  The acetylene burns so quickly, pressure in the cannon never rises very high.  But if you block the barrel with something, it is very likely that you will exceed the rated pressure of the PVC and the cannon will explode.  DO NOT PUT ANYTHING IN THE BARREL!!!

storage


inside storage

I think this one probably took me a week of evenings to finish.  The carriage took lots of planning, cutting, and gluing.  And despite the use of so many reclaimed items, it was a bit expensive for a such a frivolous item.  Total cost was probably about $100 for all the PVC.  Large PVC fittings are expensive.  But man oh man was it worth it!

small steel carbide cannon
I was so happy with the large cannon that I had to build a smaller portable cannon to take around and show off.  I used a 2" steel plumbing tee for the body.  The breech is a threaded pipe cap.  I drilled through the cap and epoxied in a piezo grill igniter for spark.  I had to solder a length of copper wire from the ground to the electrode.  The other end of the tee has a 2" to 1.5" reducer fitting.  The barrel is a length of 1.5" pipe.  I cobbled the stand together from scrap parts I had lying around.  This one is plenty loud but has a metallic ping to it when it fires.

grill igniter in breech

7 comments:

  1. I just read this blog from cover to cover and thoroughly enjoyed it. To all your stalkers: I can personally attest to the mad skillz and loving care included each of these projects...Greg can make anything!

    I especially enjoyed the part where you "laugh hysterically" at your wife, and I look forward to the "crafts" posts as described in your blog header. Please elaborate on your crafts projects. More crafts please.

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  2. PS: Uncle Bag wants you to make a gatling gun. Then he will be impressed.

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  3. Believe me, a gatling gun is on my list of future projects.

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  4. How much Carbide did you use and how long did you wait until setting it off?

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    1. It depends on the age of the carbide. I probably use about a tablespoon when it is fresh and wait about 30 seconds. Older carbide you need to use more and wait longer. If you use a touch hole instead of the flint, timing doesn't matter as much. The cannon won't fire until the acetylene fills the cannon and starts to exit the touch hole.

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  5. Hi! Very interested in building one of these for a sailing ship, could you give any advice?

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    1. Pretty much everything is in the post. The flint mechanism gave me problems and did not ignite reliably. I just use a long lighter to a touch hole now. It won't ignite until the gas/air ratio is just right so you get a much louder boom.

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