# How are increasingly accurate machines made?

Making extremely accurate machines seems like a chicken and egg problem. How do you make one if you don't already have one?

For example, how was the first indexing head made without an indexing head to make the indexing plate? How was the first lathe made without a lathe to make the spindle? Is it an iterative process where you start with something hand-made, and each machine can make one slightly better than the last? I suppose that geometric constructions are the source of accuracy of some primitive machines. But how do you get from there to something like the precision screw required for an accurate lathe or micrometer?

• It really is as simple as iterative exploitation of physical and mathematical laws. Of course, as you get more and more accurate, it gets harder and harder to devise methods for doing so - I'd love to see an answer that addresses these challenges in the context of the current state of the art.
– Air
Jul 20 '15 at 17:10
• In general, there's a tradeoff between accuracy and effort. Low quality tools + much effort = high quality tools.
– Mark
Jul 25 '15 at 1:49

Before the extremely accurate machines were made, they first had extremely accurate measuring devices.

I'll use the "first lathe" as an example. The bed of the lathe needs to be very flat, as the rest of the machine can be calibrated with it. One way it can be made that way is by putting the not-straight bed up against a much flatter surface plate, and scraping off the high spots on the lathe bed until they meet perfectly.

The flat surface plate must have come from someplace, and from what I recall they make it by taking at least 3 somewhat flat plates and lapping them with each other. Eventually all the plates will end up very flat.

With a flat enough surface you can make make extremely straight measuring instruments, pair it up with a simple surface gauge and you can start producing items with extremely parallel surfaces. Rolling a round bar on the plate can check how straight it is, and the surface gage can detect taper.

Now with the straight round bar you can use that to align the axis of rotation to the bed of the lathe, thus creating the first rudimentary lathe.

The accurate lathe bearings were probably done the babbitt bearings way where you hold the rotating shaft/part in place and cast the bearing from molten lead around the bar, then you forcefully twist the bar creating a virtually zero clearance bearing. Fairly accurate if done properly and it can deal with slight misalignment of the hole drilled in the lathe head and the axis of rotation.

This was an actual thought process that was spoken out loud by Feynman in his famous paper There's plenty of room at the bottom, in 1959.

Here's the related part:

A hundred tiny hands

When I make my first set of slave "hands" at one-fourth scale, I am going to make ten sets. I make ten sets of "hands," and I wire them to my original levers so they each do exactly the same thing at the same time in parallel. Now, when I am making my new devices one-quarter again as small, I let each one manufacture ten copies, so that I would have a hundred "hands" at the 1/16th size.

Where am I going to put the million lathes that I am going to have? Why, there is nothing to it; the volume is much less than that of even one full-scale lathe. For instance, if I made a billion little lathes, each 1/4000 of the scale of a regular lathe, there are plenty of materials and space available because in the billion little ones there is less than 2 percent of the materials in one big lathe.

It doesn't cost anything for materials, you see. So I want to build a billion tiny factories, models of each other, which are manufacturing simultaneously, drilling holes, stamping parts, and so on.

The whole paper is worth digesting completely, as it writes about several potential manufacturing processes, i.e:

• Miniaturization by evaporation
• Rearranging the atoms

For plenty of detail on building accurate machine tools from scratch, read the excellent and detailed "Foundations of Mechanical Accuracy" By Wayne R. Moore. It's an old book and there are plenty of copies around if you use your favourite web search engine.

The basic principles for increasing accuracy are lapping and comparison of surfaces.

From memory some of Moore's key steps are:

• Flat lapping 3 surface plates against each other to form a master surface plate
• Copying straight edges from the master surface plate
• Centreless grinding to make the first cylinders
• Cylindrical lapping to refine cylinders
• Lapping accurate screw threads from rough initial screws

Since many modern tools today are produced using (an earlier copy of) the "same" tools, "How was the first one made?" can be seen as a kind of chicken and egg problem.

One way to bootstrap accurate machines from relatively coarse and crude tools is described in the book "Build Your Own Metal Working Shop From Scrap" by David J. Gingery, part of the Build Your Own Metal Working Shop Series.

Related: Gingery machines and Morgan Demers lathe project and Build Your Own (metalworking) Lathe. More distantly related: Self Assembly.

• Oh, interesting. I've seen references to "Gingery lathes" on YouTube, but it wasn't explained who or what "Gingery" was. Jul 24 '15 at 19:02