Next, we need to perform a few additional steps to all the pieces. The two pieces that make up the body need to be glued together. We used polyurethane glue but any wood glue will work fine. While the body is drying, you can drill the holes for the remaining parts. Follow the pattern by drilling the appropriate sized holes in the required locations. Note that the clearance holes should allow a dowel to spin freely, and the remaining ones should allow for a press fit. For simplicity, we made all the holes, through holes. If you want, you can make blind holes where appropriate but keep in mind that there will be right and left handed parts - not all of them will be identical. Once the body has dried, you can drill the required holes in it.

The four wheels need small grooves centered in the outer rim as shown in the image on the right. We created these shallow grooves by camping the pieces vertically in a vise and then filing around the perimeter with a square-shaped file; you will have to reposition the wood in the vise several times. A 1/16" (2mm) deep groove works well. There are other ways to create this groove, but this method seems to be the easiest. If you proceed methodically you can create a suitable groove that is used to locate the O-ring which will serve as a tire.