I have used this design to build wheels for moving my table saw table and now for a road sign that I have to move every month.
I see several things as my contribution to the science of wheels as the following:
1. Unit construction - each set can be used as a unit and only needs to be attached to the item requiring mobility.
2. Sturdiness - dual wheels adds to the sturdiness of this type of construction.
3. Versatility - wheels like this can be used in many different kinds of projects from toys to machinery.
4. Simplicity - the basic components are very simple and require a minimum of know-how to make.
Step 1: Tools and Materials
Router, table saw, jig saw, lathe, coping saw or Rotozip™ (anything that can make a circle out of wood or other sturdy material) - I use the Rotozip™, but am not sure if it is still available. For certain, it is a dangerous tool to use. I happen to like it a lot for making circular cuts.
Drill or drill press
Forstner™ drill bits, or spade bits - I prefer Forstner™ bits because of the clean hole that they can make.
Saw - wood saw, back saw, hack saw, (anything that can cut wood in a straight line)
Miscellaneous - hammer, screwdriver, pliers.
Wood for wheels - preferably a hardwood like oak or maple. I used plywood, but I think that is probably the worst choice because it won't last very long and chips easily.
Wood for the mounting assembly to mount on the object requiring wheels. Again, a hardwood is probably best, I used scrap wood from a wooden pallet.
Dowel rod for the axle
PVC pipe for the bushing
Step 2: Wheels
As you can see in the pictures, there are two wheels for each assembly. In my case, I made them from plywood (not the best choice) and used the Rotozip™ to make the wheels. The diameter of the wheels really depends on how you want to use the wheels. My wheels were about 3 1/2" in diameter. The main thing you need to bear in mind is that they need to be appropriate for the mounting block size, which again, you can size according to your project.
There are a lot of ideas on how to make wooden circles, and I won't go into any of them here. Just use Google to find out how to make wheels.
The important thing is that the center hole in the wheels must be the same diameter as the diameter of the axle. For wood this is an easy task. You just drill the correct diameter hole. For steel or plastic or other material, this can be a daunting task.
Step 3: Mounting Block
The picture shows one of my mounting blocks. The block is showing the location of the hole for the axle. Also shown is the PVC bushing inserted into the block.
Most likely you will mount the mounting block on either of the two sides farthest away from the axle hole.
Step 4: PVC Bushing
The PVC bushing is made from PVC pipe. I used the thick-walled PVC pipe with an outside diameter of 1" and inside diameter of 3/4". I drilled a 1" diameter hole into the wood to hold the bushing and purchased a 3/4" diameter dowel rod for the axle.
Important point: The PVC bushing is slotted because the tolerance is too close for it to slide easily into the hole drilled for it. I cut the slots with a hacksaw. This way, you can squeeze the PVC bushing into the hole and you do not have to apply very much force.
Two more Important points to note. The bushing serves two purposes.
One purpose is simply to provide a slippery surface so the axle rotates easily in it.
The other purpose and most important one is to ensure that the wheel does not rub against the mounting block. Hence, I made the bushing about 1/4" longer than the width of the mounting block. The bushing protrudes 1/8" on each side of the mounting block. Look carefully at the photo with the details. You may have to glue the bushing or otherwise secure it to the wooden mounting block so it does not slide. I did not find that to be necessary.
Step 5: Axle Assembly
The length of the dowel rod is the sum of the width of the bushing, the two wheels and the space needed for the cotter pins.
In my case the total width consisted of the following:
bushing width = 1"
2x wheel width = 2 x 3/8" = 3/4"
2x diameter of hole for the cotter pins = 2 x 1/8" = 1/4"
2x space from ends of dowel rods for cotter pin holes = 2 x 1/4" = 1/2"
Total = 1 + 3/4 + 1/4 + 1/2 = 2 1/2"
I used 2" cotter pins 1/8" in diameter, an 1/8" drill works fine for this. See the photo.
Step 6: Final Assembly
For each set of wheels, you need to do the following:
1. Insert the PVC bushing into the Mounting Block.
2. Insert one cotter pin into one side of the dowel axle.
3. Insert the dowel axle into one wheel.
4. Insert the combination dowel axle and wheel into the PVC bushing.
5. Add the wheel and another cotter pin on the opposite side.
6. Mount the mounting block onto the project (labeled as "Sign" in the photo).