Mini Cannon

Mini Cannon!  Here is a quick lathe project that provides a lot of bang for the buck, ha ha.   Oh my…

First, a note about safety.  A cannon of this size may not look hazardous but it packs quite a punch.  The barrel is very short and I drilled it large enough to provide ample clearance between cannon ball (Daisy BB) and barrel bore.  I expected this feature would reduce the effect to something closer to that of throwing the BB vs. shooting it.  That didn’t turn out to be the case.  I haven’t tried to measure the velocity but I would guess it approaches air rifle speeds based on the dent left in my workshop door.

This design is super simple.  I started with a short piece of 5/8″ steel round stock and turned down approximately 1/2″ from one end to a 1/2″ diameter.  This wasn’t necessary but provided a smaller end for aesthetics.  A BB measures 0.177″ diameter so I picked a 3/16″ drill bit for the bore (always center drill first!).  This leaves a little over 0.010/2 = 0.005″ clearance around the BB.  The drill bit takes a bit more than its diameter so I figured there was at least an extra 2 thou in there for safety.  The bore was made ~3/8″ deep using the tail stock and jacob’s chuck.  Next I drilled a 1/8″ hole roughly 1/4″ deeper.  I figured this would allow for a bit of powder and fuse while the BB would be held at the 3/8″ depth.  Finally I drilled a 1/16″ fuse hole perpendicular to the stock and back far enough to intersect with the 1/8″ hole.  Here is a quick sketch I made for reference during machining:

For powder and a fuse, I dug out some leftover fireworks.  Those little Saturn rockets you find for $0.25 around here have some surprisingly powerful mini cannon black powder!  The fuses slip right out and are long enough to cut for multiple shots.  Using a pair of pliers, I crushed the solid rocket fuel and poured it onto a folded piece of paper.  Next, I placed the fuse and poured a little powder into the barrel.  The photo below shows the BB simply dropped in.  Later on I discovered that nesting the BB in a tiny piece of paper towel helps to keep it from rolling out and acts as a soft seal for more powerful bangs.  For testing purposes, I used a machinist vice to hold everything for the first few shots.  The scrap paper seen here was to ensure the BB was not just rolling out.  I lost a lot of BB’s during these first few firings.

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Lastly, I laser cut some 1/8″ baltic birch and hot glued it to the barrel as shown below.  The mini cannon project made for a perfect Christmas gift for my father and was one of the more rewarding projects vs. time spent.  Also, it was perfectly sized for the Taig lathe.  Happy machining!