Here's a photo of my broken bird's mouth shaft.

It's really not a shaft design problem--it's a blade design/assembly problem, and the crack in the shaft is just a symptom of that.

Where the shaft ends mid-blade, it creates a stress riser in the blade. The blade is in compression and tension. I'll reglue everything and add a stiffening rib to the back of the blade that should alleviate these problems. The glass blade will be in tension, and the rib will be in compression, and it should all work out nicely.

Shawn