the dial indicator seen in the video measures the distance to the fixed jaw of the vise, and how it changes when i move the X axis of the mill table. i've adjusted the vise (with a little hammer) until that distance stopped changing (you can still see it move by about 0.02 mm in the video — you can get closer if you want/need to, but this is enough for what i'm doing)
that means the fixed jaw is now very parallel to the X axis of the mill, and therefore very square to the Y axis of the mill. this means i can put a workpiece in the vise, up against that fixed jaw, and any cuts i make (by moving the table) will be nice and parallel or square to the side of the workpiece. this makes it easier to make precise parts.
basically, machining is just high school geometry that has the ability to remove your fingers
one hole will fit the leadscrew, one hole will fit the knob.
if you didn't know: 'boring' is the process of making a hole with a tool that has a single cutting edge (you can see such a tool in the second picture). it can make more precise holes, it can cope with weird situations better (like holes that intersect each other, which would cause a drill bit to wander) and it can make weird sizes. in this case i did it for the latter reason — i don't have an 11mm or a 12.5mm drill bit, so i drilled to 10mm and bored it out to the required size.
