Help needed with understanding accuracy in measuring tools. I want to go straight :-)

[Boyan Silyavski]

Thanks guys,
so it seems clear to me that i will pull the trigger at the straight edge. A sort of investment.

The 2 angle finders from aliexpress will wait for the moment. My idea was to use them like this:

Look at the gantry picture bellow. Using the straight edge or epoxy , like for the long rails, i could flatten the upper side/1/
But then how to flatten the opposite side? I don't have a fixed gravity epoxy formed horizontal surface at home. If it was my proper house, i would have done it long ago. So just flipping sides and pouring epoxy would be simple. So i thought of connecting the 2 angle finders un U like shape so i can measure distance and parallelism bots sides. So using the epoxy leveled top or bottom as a reference i could file , sand and so on, the other side. if they were on one plane , it would be easier, but damned overhang...i don't like it.

Anyways, i bought 2 packs of 1kg west system epoxy kit 105/209. After pouring some where necessary, the rest i will use to form a flat table surface and fix some short adjusting legs. As i have a very precise inclinometer / ~0.5mm per 3m, or so i calculated it when i bought it, don't remember but was the most precise on ebay/ i can fix me a portable level base precision surface for similar projects. I need a bigger garage:-)

Another thing is that just now i found how to make precision straight edge at home. 3 edges in fact. very interesting read. Now i am contemplating how to make it in reality. will need some polishing paste. maybe vibrate the edge for quicker removal. or slowly, like making a katana, while watching movies at night at home...

PS. i want to be as most as precise as possible, cause i know that even if you try, you are not. So if you don't try, its even worse