Alternatively I could not fix the larger gear to the axle, but fix the weapon to the gear. This is could drill and fix with bolts or I'd need to get welded. ( Wish I'd bought that welder at Lidl a few weeks ago). The prior option has two failure points and unless I drill a hole in the axle I am not sure this is really that strong. The latter option seems to me stronger but if the weapon failed it would mean a new gear.
This is how I built the axe on Kaizen. A CIM motor drives a Mod 1 16T gear which in turn drives a 48T gear on a dead axle with the axe directly bolted onto the gear, giving it a 3:1 reduction.