The Bumbo Wheel Chair is very clever adaptation of the Bumbo floor seat into a mobility device. The origins of the design can be found at the blog of Mary Evelyn: What Do You Do, Dear? Bumbo Wheel Chair
Update: I am now using these Strider wheels, which do not use air and weigh about half as much as the pneumatic tires. They come in several colors.
The two axle brackets are 2" wide, 1/8" mild steel flat strap from the local hardware store. Dimensions:
Full Length (before bending): 9-7/8"
Axle center to bend: 1-7/8"
Axle hole: 3/8" diameter
A second hole, 1/8" is needed for the tang of the special washer.
The axle bracket is bent at an 85-degree angle to match the taper of the sides of the Bumbo seat.
The end of the axle bracket is ground to a nice round radius on a bench grinder.
The axles that come with the wheels are very long. So, I threaded the nuts as far to one end as possible and cut 1" off the other end with a Dremel tool.
The decorative axle nuts came from: Porkchop BMX The thread size needed is 3/8 by 26T.
Two L-brackets secure the Bumbo seat to the base. They are located on the two side webs on the underside of the seat. 1/4-20 bolts are used with large area washers.
"Clip nuts" or "U nuts" are used to make assembly of the chair to base easy. They are 1/4-20 thread and can be found at auto parts stores or eBay.
The base is made from a 15" x 20" kitchen cutting board: Wasserstrom Note: the Wasserstrom cutting boards do not have the groove around the perimeter like the one in the pictures. They are also available in several colors.
Base measurements: The seat is placed against the back edge of the base. The axle center line is 8-1/4" from the back edge of the base. That places the axle 1" in front of the center of the seat. This makes sure that the seat rests on its rear casters normally. The radius of the front edge arc is 10-3/4". This was cut using a bandsaw. I mounted the rear casters at a 45-degree angle just for looks and used 1/4-20 countersunk screws so that they sit flush and don't interfere with the seat.
The axle end will push on the seat a little, but it is not necessary to drill a hole in the seat.