Re: I would like to build a simple, mechanical digital computer. Suggestions?

Hi Ed

Building a mechanical digital computer is an impossible task.  Digital and
mechanical devices are mutually exclusive.  Mechanical computers are
typically thought of as analog devices.  In mathematics, there were several
theoretical attempts to define such a machine with the most famous probably
being Babbage's engine sometime in the 1700s.  

There were several sucessful mechanical computers built before and during
WW2. The targeting systems used by the Navy during the war were such
devices as well as the infamous Enigma machines developed by the German
cryptographers.  Shortly after the war electronic computers replaced the
old mechanical devices.  

I'm not sure how to advise you to proceed other than to look at some of the
info available online at ther US patent and Trademark site.  

You might consider building Jacquard knitting machine as a first step
toward your goal as these devices are considered the first practical
computer (read numerical control) devices in the world.  Jacquard knits are
very interesting in that the designs are not made by printing technology,
rather they are formed by introducing yarns of different colors at specific
locations across and down the web.  The yarn selection and insertion point
was originally determined by crude punch cards made from wooden shingles. 
The wooden shingles were replaced by paper punch cards, the tapes and
finally by modern computers.

You should be able to locate a multitude of books on Jacquard machines by
visiting your local library and searching under textiles.

Good Luck
Greg