Make sure to mark the center lines on the longer length of the frame. Drill holes for the axle bolts 2.27″ from the center, and 2.5″ from the bottom of the frame. This will give you a 0.04″ gap; you'll likely need to fiddle with these as the frame is wood. Next, cut four 3-7/8″ long piece of wood and push them into the ends of the PVC ...