I had the good fortune almost thirty five years ago to land an apprenticeship to become a machinist. It was the tail end of an era just before everything went digital and cnc. Apprentices spent the first two years doing all the heavy dirty jobs under the watchful eye of an older journeyman, many of them second generation Poles, Slovaks, Jews, or Italians. They’d watch me struggle with something new and finally saunter over and offer me some concoction on a cracker, usually involved a sardine, slice of onion, and some smelly cheese. After chasing it down with a slug of strong coffee the journeyman would show me a trick that was simple, fast, and always left wondering why I hadn’t thought of it.
A micrometer became an extension of my hand as I learned to quickly turn blocks of metal into precision machine parts. I can still rattle off the decimal equivalents to almost any fraction of an inch i.e. 3/16 equals .187”. Years later I worked in an area where we worked routinely with very tight tolerances. Everything measured in millionths of an inch. An operator might say, “it’s 20 heavy on the front,” meaning the parts were 20 millionths off taper.
It’s amazing to look at some of the old rulers that were often relied upon by pre-industrial artisans. Very crude, often homemade or perhaps by the local blacksmith. Many times the divisions only go down to eighths of an inch. Yet they produced furniture of amazing quality that required incredible precision and accuracy. They had two major differences in the way they worked. One is that although their rulers may have been crude, their cutting tools were capable of great precision. A nicely tuned handplane is capable of making controlled cuts beyond what any ruler can accurately measure. Parts weren’t made to specification; they were roughed in with axes and saws and then made to fit with planes, spokeshaves, or chisels. This made the ruler secondary as a part such as a drawer front would be fit to the opening rather than to a numeric dimension.
An even bigger difference is that these workers were more focused on proportions than dimensions. They used their crude rulers to rough in the comfortable height for a tabletop but I’m convinced that the focus was largely on proportioning one element with another.
Specifications and tolerances have value when you need to mechanize and mass produce. Proportions stand apart when the need is to design something aesthetically appealing and works especially well in one off, custom work.
My micrometer doesn’t see much action anymore and the ruler less and less. Instead dividers and my eye guide the work at my bench.