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.

dent in 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 asthetics.  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 safey.  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 pliars, 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.

cannon in vise  cannon tests

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!

laser cut parts