Colleagues:

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!

Al H.
10-24-11