Wherever I visit, rules-of-thumb are a hot button topic these days. My normal response has been that engineers are expected to do better than use rules-of-thumb. But Fall is here and the Holidays are close-at-hand, so allow me to be a little more responsive this time.
I develop engineering tools and skills to support and guide my engineering interests. For instance, I have developed techniques to analyze the surface figure errors introduced by element mounting techniques. In the spirit of the coming Season, I will give to one and all (yes, even to Tiny Tim) one of my engineering tools:
It tells the engineer the minimum adhesive thickness necessary to limit the thermal distortion of a mounted mirror. It is easier to use than a finite element code and probably more accurate.
I do not, myself, consider the above expression
a rule-of-thumb but rather one of several engineering tools for use in these
kinds of problems. The curious may read my original paper, SPIE: 6665-03,
2007. The expression is formed by substituting equation (6) into equation
(10), both from the subject paper. I hope you find it as useful as I have.
It’s about as close as I get to a rule-of-thumb in my practice.
Now, let us turn to the approaching Season: The Joyous, Tumultuous, Boisterous, Extravagant Holiday Season from All-Hallows Eve to Twelfth-Night.
We can talk about engineering tools, and rules-of-thumb, any old time.
We should Enjoy and take Cheer Now!