Bike headset failed

I've fabricated one seat but it didn't work out.  Unfortunately while testing the seat I heard a crack and the steering mount failed.  Back to the drawing board.

Pulled the front fork and disassembled the steering mount.  The mounting holes are rounded and there are some cracks in the wood where it has failed!

You can see that the holes are rounded and if you look closely at the top photo you can make out two stress cracks - lower & upper right where the grain is broken.  Examination of the plywood also shows some failure.

I'll have to use a stronger wood for the mount proper & buttress the plywood to take the stress.