Sometimes square matters. Not in this case, but it is one gauge of accuracy. Here identical length matters more. But things being square is nice too. I don’t have any high precision equipment so I cut stock as close as I can, then I file, and sand it to fit. It is a tedious, and time consuming process. But that’s what it takes.
Have you ever read any books/articles about hand-scraping? With some care, some planning, a scraping tool, and some machinist’s blueing ink, you can form arbitrarily flat or 90 degree surfaces. Oh, and with spending a LOT of time doing it. But it is kind of fun.
@John_Bump
I am familiar with the hand scraping technique. You forgot one essential bit of equipment needed for hand scraping. That is a flat surface. But yeah, someone had to make something flat originally. Machine tools, and instruments did not just fall out of the sky. For making a primary surface you need to follow the rule of three. Which is that two surfaces in contact with each other can be either flat, convex, or concave. But if three surfaces are all mated then they all must be flat. Because no other combination could work out. That’s how we as a species did it.
So you can build your own surface plate, if you wish (although I found a chunk of 6mm thick plate glass to be flatter than my measurement tools.) A couple years ago I read an interesting article about how there is a surface topology that is not flat and can pass the three-surface test, but it is extremely unlikely to be produced (especially if you flip a plate every now and then during surface generation: nobody’s found anything that works with that, to my knowledge.)
@John_Bump
Yes, I would hope whoever checked their flat surfaces would check them from several different orientations.
I don’t have a surface plate. I use either my table saw top, my anvil, or the glass top of my desk. It depends where I’m at. For the kind of work that I do any of that is flat enough.
For any garage engineering I am of the mind that you cannot rely too heavily on accuracy. So I try to design with some built in fudge factor. I can try to get things close, but realistically I can only count on getting things so close.
The holes I drilled for these plates are about five thousandths of an inch within each other. For some odd reason one is way out. Maybe there was a chip in the fixture that I didn’t catch? That’s the way the cookie crumbles.
It still works, because it is all close enough.