What I like about this picture is that it's a soft drink balancing on a balance bike that is balancing by itself. The soft drink can is just to judge size. A balance bike is a small training bike. What makes it different is that it has no pedals. The child straddles it with both legs touching the ground. They propel it with their feet and learn how to balance by lifting both feet for longer and longer duration. So when they are ready to move to an actual bike, they have the balance part down pat. All they need to do is learn the pedaling part. There will be no need for training wheels.
I have designed this bike to be built with 3/8" Baltic plywood and stuff that can to found at the local hardware store. The included PDF has the dimensions of all the parts.
I wanted this small enough that a child as young as 12 months could use it. It has a minimum seat height of 10½" from the ground It also only weighs 8.4 pounds..
Step 1: Wheels
I immediately rejected purchasing a used child's bike and salvaging it for the wheels. (If you are going to buy a small used bike, why not just remove the pedals, sprocket and chain?) I also found the wheels to be rather heavy. With a little research I found these 10" replacement shopping cart wheels. The wheel has a plastic hub and the tire is solid rubber. They are a reasonable price and each weigh about 2¼ pounds.
The axles hole has a 12mm diameter. This is fine if you want to use metric hardware. I am using imperial hardware so, on each wheel, I bored the hole out to ½". I ran the wheel up a down a couple of times to get the holes a bit bigger.
Step 2: Hinge
The frame of the bike is made from two strips of Baltic plywood. They are held together in the front with an 8" strap hinge. The hinge will also serve to the hold the fork in place.
The hinge must be dismantled. The pins are held in place with a couple of indentations. To remove the pins these must be drilled out. After the hinge is totally disassembled it now can be rebuilt with a 5/16" diameter bolt as a pin. Use some 5/16" washers to remove any lateral movement between the two leafs. I found that four washer were a bit too thick so I took a file to remove a bit of the sides of the hinge barrels.
Step 3: Seat Post
Take five ⅜ x 2" x 7½" pieces of the Baltic plywood and glue them together to make a block. Attach the pattern included in the PDF and scroll saw the seat surface. Then mark the hole positions and drill seven 9/32" holes where marked. Sand and break the edges of the side and the bottom. Countersink the holes for appearance.
Step 4: Seat
The seat is a curved 7½" x 4" oval made from 12 pieces ⅜" Baltic plywood. It sort of resembles a big potato chip. Take the pattern for the curved pieces, glue it to the plywood, and cut the pieces with a scroll saw. Now clamp and glue all 12 pieces together. After the glue dries, sand the top and bottom to make them smooth. Glue the oval pattern to the concave side of piece and cut out with a scroll saw. Round edges and sand smooth. Note that I marked the center with an awl.
Step 5: Complete Seat and Post Assembly
Clamp the post upright into a vise. Align the center of the seat to the center of the post. center and then glue and screw into place. Finish sand and apply finish. I am using teak oil meant for wooden ships. The seat assembly is complete.
Step 6: Make Frame Pieces.
The frame consists of two Baltic plywood pieces ⅜" x 3" x 22". On each of these two pieces mark the hole positions as shown in the attached PDF and drill them to the sizes specified. It wouldn't hurt to counter sink the holes. Now cut a 45 degree, ⅞" notchs at the back corners. Finish sand and apply finish.
Step 7: Add Hinge Leafs to Frame Pieces
Back on step 2 you disassembled the strap hinge. Now it is time to connect the separate leafs to the front of the frames pieces. Each frame piece will require; one leaf, four ¼" flat head screw ¾" long, four ¼" washers, and four ¼" hex lock nuts.
For each side, place the frame piece on a flat surface and align the leaf at the front. The leaf is the same width as the frame piece and should be aligned to the piece where the leaf has been notched. Mark, drill, and countersink the four holes. Position the leaf and attach with with the screws, washers, and lock nuts.
Step 8: Assemble the Back Wheel, Frame, and Seat Assembly
To assemble, you will need the following hardware; a ½" bolt 3" long, six ½" fender washers, a ½" hex lock nut insert, two ¼" bolts 2¾" long, four ¼" fender washers, and two ¼" hex lock nuts.
Place the appropriate fender washer on each bolt and insert into one of the frame pieces. On the ½" bolt place two fender washers followed by the wheel followed by two more fender washers. On the other two bolts place the seat assembly. Then place the remaining frame piece in place. Now place the appropriate fender washer and lock nut on the bolts and tighten. The seat assembly so be as tight as you can get it. The wheel bolt should be tighten just enough to not interfere with the wheel spinning.
Now press the front of the two frame pieces together until the hinge leafs interconnect. lock them in place with a 5/16" bolt.
Step 9: Build Legs of the Fork
All the pieces for the fork are made from ⅜" Baltic plywood, 2" wide. Each fork leg has three pieces. Use the included PDF to cut the piece and drill the proper sized holes. Each fork leg has a piece that needs to ne notched. This is easily done with a scroll saw, saber saw, or a dado blade on your table saw. Clamp and glue the pieces flush with the notches.
Step 10: Fork Spacers
Before building the fork you need two spacers to position the legs. These spacers must have holes to allow the fork to connect with the frame. Take some of the 2" stock used in the previous step and glue two pieces together to double its thickness. Then cut two pieces, each with a length of 1-13/16". In the center of each block drill a 5/16" hole.
Step 11: Finish Fork Assembly
Take the spacers and place them between the fork legs. They should align with the leg notches. The glue and screw into place making sure not to screw into the connection holes in the middle of the spacers.
Step 12: Assemble Frame and Fork
Attaching the fork to the frame requires; one 5/16" bolt 5½" long, four 5/16" fender washers, and one 5/16" hex lock nut. By dry fitting I determined that an addition nine 5/16" washers are needed as spacers. (This is in addition to the four washer used in the hinges.) The bolt is feed from the bottom and the pieces are placed in the following order; a fender washer, the bottom fork spacer, a fender washer, four washers, the bottom hinge barrel, two washers, the middle hinge barrel, two washers, the top hinge barrel, five washers, a fender washer, the top fork spacer, a fender washer, and a hex lock nut. Tighten the nut.
Step 13: Connect the Handle Bar
Cut a ⅞" hardwood dowel to a length of 16". Bevel the ends, sand and finish. Place the dowel into the holes and center it. From the top of the fork legs, screw the dowel in place. With no glue this allows it to be removed for replacement or repairs.
Step 14: Install Front Wheel
To install the front wheel you will need; a ½" bolt 3" long, four ½" fender washers, and a ½" locking hex nut. The fender washers go on each side of the fork legs. Tighten to the point that it doesn't interfere with wheel spinning.
Step 15: Your Done!
The bike is now ready to ride. The seat can be raised in ¾" increments. It easily comes apart for shipping. If the seat is only screwed and not glued to the post, then it will fit into a priority mail large flat rate box for shipping. (I would use a unique hole pattern to make it easier for reassembly.)