How do you make a machine that has perfectly flat/plumb/level metal components without the aide of a machine to begin with?
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Carefully created techniques. Eg to create a flat surface you use three plates. Running again each other to smooth them down and using blue dye between them to highlight high and low spots.
Three are needed because with two they’d mirror imperfections into each other. With three they all average out flat.
Wikipedia explains better: https://en.m.wikipedia.org/wiki/Surface_plate
But basically with a lot of care, and careful technique you can create continually improving precision.
Original paper: https://books.google.com/books?id=wL1ZAAAAcAAJ&pg=RA1-PA192#v=onepage&q&f=false
Really, really, really good craftsmen with years of experience spending hundreds of hours working on it.
Need a piece of metal perfectly level/smooth? Pay a man who is really good at what he does to sit there with a handheld level and file and slowly file away at it.
The same thing goes for intricate carvings or massive structures. When you have enough time, money, and manpower, you can get it done.
It was advances in many areas that created the conditions for precision machining and the first assembly lines.
For example, the Springfield Army wanted interchangeable parts for its firearms. Previously, parts were hand crafted and fitted together by an artisan.
The Enlightenment created a surge in many scientific disciplines. Advances in mathematics, metallurgy, gauging, assembly line management, and the creation of tools to make precision tools, all worked together. Once you made your desired prototype, you could craft the machines to mass produce.
The first industrial machines were hand crafted, but the successful ones were refined and replicated over time. It was a decades long process with incremental advances improvements.
There is a rather in depth book called the foundations of Mechanical Accuracy, that covers this in depth. One of my favorites from it is using three plates to guarantee a flat surface.
A mail, string and pencil will get you circles. Intersecting circles makes elaborate designs.
Bootstrapping. It is possible to make a decent stone hammer with a marginal one. Same with a lathe.
there was precision machinery, it was just hand operated. it all starts with making a lapped surface, and from there you can expand outwards to a lathe and then a mill.
First, understand that there is no such thing as perfect. There’s only tighter tolerances.
Not that long ago 50-60years they used build lathes and mills by [scraping ](https://en.m.wikipedia.org/wiki/Hand_scraper) in the ways. On industrial scale not done anymore but plenty of hobbyist do it to this day.
By scraping it flat by hand.
You can create a flat surface by lapping or scraping three plates against each other. Basically, put some ink on one of them, and rub another on it, then remove all the bits that touch, then switch which plates you compare and do it again. repeat until all three agree with each other.
Plumb and level are relative to gravity, not intrinsic geometry, you can get plumb with a string and a weight, and levels can be checked against themselves when rotated 180 degrees. Add some adjustment and you can correct for inaccuracies of manufacture.
Like the level, many other things can be checked against themselves somehow, and if it’s not right, you can slowly remove material to get it into tolerance. Yes, it’s extremely tedious work.
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