FIX THAT BROKEN AXLE!
The axle seems to be the weak point in the older style Big Bang cannons as many have been broken,
apparently by being dropped and landing on the wheels.
Here are most of the tools and materials you will need.
Start with the drag. From the back side, layout to find the axle center.
Center punch the center point.
Drill a small pilot hole through the drag at the punch mark.
Follow with a 5/16" drill (0.3125").
Counter sink the inside to remove the sharp edge and you are done with the drag for now.
The axle will be made from 5/16" diameter steel rod. You can get it at hardware stores.
Sometimes it is plated making it too big to fit through the wheel. You can polish this off with sandpaper for an easy fit.
Cut off a piece about 1-1/2" long.
File one end square and chuck the other in your electric drill. With the drill spinning, use your hacksaw to cut a grove
about 1/16" in from the end. Make the grove wide enough for your cinch ring and the depth should be half the ring wire diameter.
Coat hanger is too big and large paper clip is about as small as you can use. The best is 1/16" diameter copper coated welding rod.
With the cinch ring on the new axle, put the axle through the wheel and drag leaving about 1/16" extra room for the wheel.
Put a 1/4" flat washer (it has a 5/16 hole) over the axle on the inside of the drag and scribe a line on the axle maintaining the 1/16" clearance.
Disassemble and cut of the excess axle at the line. Keep the saw blade on the side of the line away from the grove end.
Square-up and debur your saw cut and place the axle in the washer on a flat steel surface.
Flux and heat with a torch until the joint will take solder. Feed in solder only until the gap is filled all around, you don't want a bead!
Press the axle through the drag. I like to darken the metal with touch-up gun blue.
You can also use black paint, but don't get any in the wheel.
Put the wheel on and close the cinch ring and you are finished! Ta-Da!