I've been reading here and other corners of the web for quite a few weeks and greatly appreciate all the wonderful info and guidance. That being said I've not seen much mentioned with regards to assembly and alignment, procedurally speaking.

Specifically I'm pondering how best to align SBR to frame. For the purposes of this thread I'm looking at a vertical Z column as on a vertical mill, or a vertical plate for a Z axis on a high sided router.

I have means to make a precision plate to within +\- 0.015mm tolerances realistically. .. basically the limits of the machines and standards with which I can make and measure. However when it comes to installing the rails and screw ends onto such a plate I am not finding much in the way of publicly shared info.

So... my thought is basically this example:

100mm wide 200mm tall 25mm thick cold rolled steel plate as a base to mount the rails to. 2 trued and squared edges.
Mill a reference edge or lip by skimming 3mm off the thickness Leaving a 5mm by 200mm lip vertiaclly. Perhaps going so far as to run an additional cut to slot 2mm deeper next to the lip so as to avoid the tool nose cutting edge radius - leaving as perfect of a 90* corner as possible.
Now install (hand drill and tap while rail is clamped here?) a SBR against this edge and "measure" to the next SBR using a gauge block of appropriate distance as a spacer and install the second rail.
ASSuming I can install the rails perfectly with out them budging from the spaced alignment I should have them dead nuts parallel and only need to install the base plate dead nuts plumb and vertical (for which intend to use my imperial 0.0001 dial indicator) to the frame.
At this point I can use the same process on the other rail plates (vert mill example) and use the vertical plate as a reference to square the axii to.

In best case I realistically imagine I can get the initial axis within +\- 0.01 mm, and the same for the other two axii... so when finished I may have upto a cumulative mechanical error or 0.06mm... not very good.
Which leads me to ask, can I really expect to work out that much error with software compensation?

I am in the end only working with part print tolerances of +\- 0.025 mm on a rare occasion once I employ my diy machine, but I'd still like to have the machine as accurate as realistically possible.

What does the community think...?

Thanks as always,

Nick