Wooden Wedge Bike

Step 5 Drill the through holes and chisel them to make a through slot for crank

Practice inserting and removing the crank from the donor bike frame a few times to see the clearances needed to pass the crank. Note that I had to drill my holes aligned perpendicular to the long edge of the beam to maneuver the crank through while the right chain ring is attached and needs space to move in.

Drill 2 or 3 1" holes inside the BB cut and clear through the beam. Chisel them together to make a through slot to pass the crank through. Cut as little wood as possible to leave maximum remaining strength for the beam supporting the BB cups. Do not cut outside the BB cup hole. For the right side cup hole, chisel the wood inside the BB cut down to make a "floor" 1/2 inch below the surface so the BB cup can fit snuggly into it and be supported by the hole's walls and floor.
For the left side, chisel the wood inside the BB cut down to make a "floor" 1-1/8 inch below the surface so the BB cup can fit snuggly into it and be supported by the hole's walls and floor.