I added a wheel truck to a 15 foot extension ladder so one person can move it easily with one hand to the place where it will be used.
Two 6 inch lawnmower wheels
3/8 inch concrete reinforcement bar
6 hex head bolts 1/2 inch x 2 1/2 inches with hex nuts
2 cotter keys 1 1/2 inch long
4 lockwashers 1/2 inch in diameter
4 squares of steel 3/16 inch thick measuring 1 3/4 inch x 1 3/4 inch
Electric drill and bits
Step 1: Dimensions
My wheel trucks form a triangle. The ladder rungs are 12 inches apart on center. That forms one leg of the triangle. The other legs are 11 inches and 11 3/4 inches center to center. It does not matter much which leg is 11 inches and which is 11 3/4 inches.
Step 2: The Beginning
Cut two pieces of 3/8 inch concrete reinforcement bar a little longer than their respective sides of the triangle mentioned in step 1. Weld them to the sides of one of the hex head bolts as shown. I welded on the wheel side of the bolt, too. Do this fitting and welding again for the other wheel truck. Remember that the wheel trucks will be mirror images of each other so the wheels are on the same axis when finished.
In the photo you see the wheel trucks assembled. When I did the welding, I simply set a hex bolt on a flat surface, head down. I laid the reinforcement bar next to the hex head and welded.
Step 3: Square Pieces
Make four squares of steel at least 3/16 inch thick and 1 3/4 inches x 1 3/4 inches. Drill a 1/2 inch hole in the center of each steel square.
Notice that I welded a short piece of reinforcement bar to one side of each square and welded the reinforcement bar pieces that form the legs of the triangle to the spacers. The spacers are to make a way over any lip on the ladder rails.
Step 4: Attachment Rods
Redi-Bolt (continuously threaded rod) is expensive. I cut the heads from four 2 1/2 inch bolts and welded them to pieces of 3/8 inch concrete reinforcement bar. The total length of each of the two attachment rods is 20 1/2 inches. That means 15 inches of concrete reinforcement bar is needed for each attachment rod.
Before welding I chamfered the ends of the reinforcement bars and the bolts. When finished welding I ground the area of the weld so the ends would fit through the 1/2 inch holes.
Slip the attachment rods through the two welded wheel truck assemblies. I used the third and fourth rungs from the bottom of the ladder. Add nuts and lockwashers. Tighten firmly.
Step 5: Attach the Wheels
I slipped the wheels onto their axle bolts and gently snugged the hex nut up to the wheel bearings. Then I drilled a hole through the nut and the bolt axle for a cotter pin.
Step 6: Use
Just pick up the end of the ladder opposite the wheel trucks and walk while dragging the ladder behind you. Set it up against the building as you normally would.
Step 7: No Interference
The wheel trucks do not interfere with normal use of the ladder.
Step 8: Storage
To store hang the ladder on wall hooks as you normally would. The wheel trucks are really not in anyone's way.