"off topic" is a matter of perspective here. The thread title is a somewhat leading question in that it assumes that most people are in fact building diy machines capable of precision. My contention is that they are not and that most lack the means to measure it if they were.

The diy world is mostly aluminum t-slot builds or amateur steel tube welds with cheap Chinese spindles and linear motion components. People who think their diy 4' x 8' table is accurate to 0.001" most likely measured it wrong.