If you have one of those dial calipers that readout in fractions…..THROUGH IT OUT! These are a crutch that will keep you from learning how to use decimals in your woodworking.
Fractions are fine for 3rd grade arithmatic, but they don’t work for furniture building. The smallest common fraction that we use is 1/64″. That fraction translates to 0.015625″. This is way too much for furniture joinery. If you try to fit a mortise and tenon or a dovetail joint to a tolerance of plus or minus 1/64″ you are going to end up with a piece of scrap. We must use decimals in our woodworking. A fraction is nothing more than an unfinished arithmatic example, 1/4 = 1 divided by 4 = .25, or 3/16 = 3 divided by 16 = .1875.
So let’s learn decimals. The standard increment in industry and engineering today is one thousandth of an inch. The thousandth is expressrd 0.001″. In industry we commonly work to three decimal places. The first decimal place to the right of the decimal point is hundres of thousandths. Example 0.100 = one hundred thousandths, 0.200 = two hundred thousandths, etc., etc., etc.. The second decimal place to the right of the decimal point is tens of thousandths. Example 0.010 = ten thousandths, 0.020 = twenty thousandths and so on. And of course we already know that the third decimal place to the right of the decimal point is thousandths. Therefore, 1/8 = 1 divided by 8 = 0.125 or one hundred twenty five thousandths, 3/16 = 3 divided by 16 = 0.1875 rounded to 0.188 or one hundred eighty eight thousandths. As you can see it is not difficult. We learned the alphabet, and the multiplication tables we surely can learn the decimal equivilents.
Keep your calculator as close as your measuring tools and use it to finish those unfinished arithmatic examples. Before you start a project go over the drawing and put the decimal equivilents beside the fractions and work with them, not fractions. If you do your own design write your dimensions as decimals. It may be awkward at first, but in time you will be converting most of the fractions to decimals from memory. Lose the fractions and take up their decimal equivilents and you will be a more accurate woodworker.