Step 1: Start Design on the CAD system
See Woodenbikes' genius "CAD" instructions to create a cardboard cutout of your body, so you can figure out proper positioning of wheels/seat/handlebars/etc. As he says...
"Using a sophisticated 2D CAD system (Cardboard Aided Design) life size cutout of your foot/leg thigh/back and arm, pivoting on brads at the joints, you can design the bike on the ground to explore sizing and clearance issues. My CAD system sometimes has a Gooey interface if I spill something on it while designing :-)
More seriously, like other CAD systems it has a GUI (Graspable User interface).
Make a cardboard cutout of your lower leg (with foot and pedal), thigh, torso, and straight arm (to a distance 2" back from your wrist). Use it to look for good riding position and clearances for knees to bars, heels to wheels etc. Use the CAD system to layout the riding position, cranks, wheels etc with attention for locating your hands, shoulder, seat-back angle, butt, knees and feet.
For detailed instruction on 12 Steps to designing a sweet handling recumbent, visit Bikesmith Design at http://bikesmithdesign.com/Design/12Steps.html
Step 2: Basic Parts (A kid bike and some 4x4 lumber)
Step 3: Disassemble donor bike and start the design layout
* The bottom bracket (BB) is the main crank axle bearing
Step 4: Mark and Drill the Headset Holes
Use a hole saw (cylindrical toothed drill bit) to drill the larger outer hole first that will support the outermost diameter of the HS cup. Drill it to a depth you want to set the cup, preferably just deep enough to surround all of the cup. (If you drill too deep and mount the cups too close together there is excessive leverage of the steerer tube on the two cups.) Repeat for the top HS cup.
Use a smaller diameter hole saw that matches the extended cylinder of the HS (where it was pressed in the metal bike's head tube) to drill the next hole deep enough to allow the HS cup to be pressed firmly into the beam. Repeat for the top HS cup.
Now drill the approximately 1 1/8" steerer tube hole in from the top and in from the bottom until the holes meet in the middle of the beam. It's OK if they don't align perfectly. you can use a rasp to smooth the transition between them. Gently use a chisel to chisel out the remaining cylinders of wood left between the cylindrical holes cut by the hole saws. Be careful to leave a smooth floor of wood to support the flared out floor of the bearing cups.
Now the bearing cups should be able to be fit in the holes and be seated on wood (not floating).
Step 5: Mark and Drill the Crank Bearing (BB) holes
Drill the largest diameter holes first (While you have good solid wood to hold the hole saw's stabilizing center bit). First drill all the holes and then come back to chisel wood out of the cylindrical cuts of the hole-sawed holes. (This leaves maximum wood to support the drilling operation.)
Using a hole saw selected to match the outer cylinder diameter of the bearing cup for a fairly tight fit. On the bike's right side (where the chain ring will be) drill/saw only as deep as needed to set the bearing cup in up to its protruding lip. Stopping at that level maximizes the supporting wood left in place as a "floor" to the hole. That floor helps support the cup.
From the left side of the bike Drill/saw the large hole to a depth that would have the bearing cups' outer protruding lips about 2 7/8" apart. That will about match the donor bike's original BB width (cup face to cup face). e.g. our inset depth was 5/8" below the surface (3 1/2" inch "4x4" minus 2 7/8"). This means the left cup would be about 5/8" inset into the 3.5" thick wood. Or you could slice about 5/8" off of the left face of the beam (so it's 2 7/8" wide) and mount the cup in to its lip depth just like the right side. We chose not to slice, but to drill deeper to preserve structural and artistic integrity (this time).
Drill 3 holes a little bigger than the BB axle (about 5/8") to form a slot in a direction that will accommodate threading the crank through the slot.
Step 6: Shaping the 4x4 into a hexagonal pencil
* Head-set is the main steering bearing in a bike frame that connects the fork to the rest of the frame. The Head-set has bearing cups and cones that thread onto the fork's steerer tube.