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

[Boyan Silyavski]

If I'm reading you correctly you mean this;



But if you angle the straight edge on the left it will bend and not be straight any more.

Hi,
maybe you misunderstood me because of my English. I meant there are 2 types, beveled/like a knife/ and ones that look like bar. So as far i understood, you said that the beveled is better, cause you can see easier the light, when touching some surface to be measured.
So what i believe, the square could be more useful for me, constructing a cnc, because it has 4 edges versus one of the beveled.



First it can serve as a master guide to straighten the first square shaft supported rail when mounting on the red axis, fig 1 , so its true straight

Then check the straightness on blue axis, fig2 /hence proper tightening on hopefully straight surface or if not-if properly shimmed.

Then check twist/ green axis/ fig 3 and 4.

With a beveled edge i don't see how you can perform and alight twist, as many of the beveled edges i saw are straight only at the knife beveled blade. fig 2 is where the beveled edge shines, but if i simply flip and use one corner, its the same.



PS: edited, axis not showing