III. Chasing Zeroes

It is easy for a maker to fall into the trap of seeking some definition of perfection. If you’re a machinist just starting out on your journey and creating some part on a mill or lathe, your first passes might get you to a tolerance within .01" of your target dimensions for that part. As you gain more experience, dialing in the accuracy of your tools and knowledge, you may arrive at a reliable .001" plus or minus of your target. You may find that you want to keep pushing your boundaries of precision and accuracy - .001" is nice, but how good would it be to hit .0001"?

This is chasing zeroes. As a pursuit in and of itself, this is a fine goal to aspire toward. Precision and accuracy can often be a show of expertise and mastery of a craft or skillset. When it comes to project work, it is important to consider what the acceptable tolerances are to the work at hand rather than what upper bound of precision you are capable of. If you’re framing a house with construction lumber, then 1/8" or even 1/4" is likely an acceptable tolerance for that work. Fine woodworking, maybe 1/16" or 1/32" is good enough.

When thinking about acceptable tolerances, keep in mind the factors of tools, materials, scale, environment, time and cost. Higher precision often amounts to more expensive tools (for both manufacturing and measuring), more stable materials, and more time investment.

Different material compositions have different properties that may cause their dimensions to change depending on different conditions. Different species and cuts of wood (even down to the particular tree it comes from) will expand and contract due to changes in temperature and humidity. A piece of cedar outdoor furniture going through all the seasons is going to behave differently and have different tolerance requirements than a fine walnut credenza that lives year-round in a climate controlled environment.

This doesn’t apply only to wood material. Even different types of metals will expand and contract based on ambient temperature. This is one of the reasons that tool certifications include both a distance as well as a temperature dimension. For instance, a set of gage blocks might have a certification that their accuracy is guaranteed to be within .001" but only at an ambient temperature of 65F.