This was my first build and I must say that these instructions were very well laid out. I worked on Japanese machine tools with manuals translated to English and they were a nightmare (I called it Japish) the translation was terrible. Prusa is a non-English speaking company and their instructions were very well written for us in the USA. The comments section is very helpful there were alot of good tips in there. Couple of things I think should be changed is including that frame alignment fixture that was posted in the comment section for putting the frame together. I had a hard time understanding what the purpose of putting the y-axis frame inside the z-axis frame until I got to that step in assembly. The electronic plug in at the main board was very difficult to visualize with the pictures 180 degs off from were I had to lay the machine down. Overall very nice job from Prusa
On my bed the powder coating has closed up the holes so I used a 3mm (.177) drill to open the holes so the screws moved freely and could engage the threaded hole
Just double check and see if you have two filaments. I didn't check the length and when I was doing the filament for the heat bed I realized I had put in the wrong filament in this operation.
Before you do this step take a M3x18 screw and capture the nuts for the next operation. I also had to open up the screw hole somewhat for the USA build you can use a 1/8 drill. Put the M#3 screw in and draw the nut into position and then put on the power supply on the frame using the M4x10 button head screw
Make sure the idler bearing shaft is fully set in the opening double check to see that the idler bearing is flat against extruter motor pully
when tightening up the screws make sure you snug down the first screw then go on a diagonal to the next screw snug that screw the go straight over to the next screw and snug down, then go diagonal to the last screw and snug. Keep tightening them this way until all the screws are the same tightness. This will keep the motor housings square to the bracket.
if you are having trouble getting the bearing into place take a utility knife and carefully cut a 45 degree chamfer on both ends were the bearings are inserted. Once started and square press down on a solid flat surface. These bearing holes can be printed with a lead in angle making the bearings easier to install
Steps 7 and 8 should be defined better. I am a retired machinist and if these steps were to make the base square I don't know the purpose of using the frame. If this was just to make sure it fit in the frame that should be noted. All so the insertion of the rods did help squaring the frame. That 3d printed frame guide should be put in the kit for it would speed up assembly and remove confusion.
thank you Ted for the heads up on the location of the end stops I was frantically looking for them until I saw your comment