Mike is right about the usefulness of the center adapters. Guessing just does not cut it. Even the trick of putting a bolt in the hole and using the hex head and surfaces is not always accurate as most bolts have some tolerance on the edges and straightness. The bolt trick is however a good one in many cases.
There are a lot of challenges for machinists to measure things accurately. Cabinet makers working with hardwoods can have some challenges as well but not quite as bad.
As far as calculating things goes, I have a binder filled with exhaustively calculated measurements for things I expect to do in my shop, in both metric and imperial sizes. A computer and usually a spreadsheet did all the tedious calculations.? I just open the binder and look at a chart for most anything I cannot do quickly in my head or simple calculator. I have spreadsheets set up for more complex things where I just enter a couple or few numbers and it shows the answer. Been adding to this for 40 years so I do less and less math over time.? If I run into anything outside of this, I just look up a calculator on-line.
Am I lazy? Maybe. But it took some time to collect this info. I would rather spend my time now making or fixing something rather than sitting with a sheet of paper grinding out math problems.
