Step 5: Hole drilling
Since the plastic has a diameter of 3/4", I chose to drill the slightly smaller diameter of 23/32". This meant that I could machine down the plastic pieces to exactly fit the way I wanted.
It's very crucial that the holes on the top and bottom pieces are exactly aligned. After you choose your hole positions, make sure to cut both of them at the same time per block--don't remove it from the vise in-between. Doing so will add measurement error.
Because the holes are so big, you'll want to drill them progressively. Start with a center drill to make the starter hole. Then, use a smaller diameter drill, and only cut a fraction of an inch at a time before lifting it to remove the chips. Do the same with the final size drill.
The top piece has holes of depth 65 mm (leaving 10 mm above), while the bottom piece has depth 60 mm. I left the larger 15 mm on the bottom because we'll be threading holes, and we want a bit more strength here.