I have assembled the top and bottom frames. So far, I have left out the holes for the set screws. They require a complicated interior cut to hold the trapped nut. I can’t think of any way to do that with the tools I’ve got.
What I eventually decided to do was get a tap tool and put threads in the wood itself. I stripped a couple of these threads because I wasn’t careful.
To make the threads I started by drilling a 4.2 mm pilot hole through to the 8.4 mm holes that hold the rods. Then, I took the tapping tool and tapped the threads for an M5 screw. I turned the tool forward until I was about a centimeter from the end. Then, I backed off a half turn to clear some chips. I worked the tool forward until I was clear through the end of the hole. Then I backed it out slowly.
At this point, I inserted the set screw. Since it is easy to strip the thread I pre-set the screw close to the final position. I used a 8 mm rod to test the hole to see if the set screw wasn’t blocking it. If it was still clear, I turned the set screw one more time and tested again. Repeated until the hole was blocked. Then, I backed the set screw off just until I could get the rod through. When I did the final assembly, I only turned the set screw a half turn forward from this position, which holds well without striping the thread.
I found that the best way to assemble the xy-frames was to do the top one first and then line the bottom one up with it. I started with 4 pieces of scrap (all the same height) under each corner. Three corners have a corner bracket while the last one has the top corner (the one with the smaller holes). I set up the 4 xy rods and the x-stage. I locked down all the rods at their correct position except for one end of one of the y-rods. I then made sure the x-stage moves freely in the y direction before locking down the last set screw.
I then stacked the corners of the bottom frame on top of the corners of the top frame. I put a piece of 1/4 inch plywood scrap between the “top” corner block and the z-motor-bracket so that the 4 corners lined up. I inserted some rods down the corners to line up the blocks. Once its all set, I inserted the x and y rods and locked them into position.
