This was one of the projects that I really wanted to bring in different thicknesses of wood. I stayed true to the commitment of standard 3/4" thick lumber. The hardest part of this entire design was the tread. I was not expecting this because I knew how I was going to make it from the excavator design. I was not expecting to figure out what size worked well. My original plan was to make the tread taller and not as long. It would not work and did not look right. I finally settled on the current size.
The next problem was how it was all going to fit together. I would love to call it pure genius but in reality it was luck with a little bit of planning. At first I was going to recess the wheel pegs into the tread, but leaving them out was a perfect location mechanism. This guaranteed all the wheels the same distance from the ground.
Now the location for the tread front to back I was not so lucky. First one I placed about a 1/4" from the front. I added the pegs in the rail to limit the up and down movement. It limited it too much. So on the second I though I might get just as lucky with the pegs for the rake in the back. So I pushed the tread against the tread in the pegs in the back. The shovel now hits the engine. I do not know if I am ok with this even though it far better than the first. Everything else went together smoothly.