Expert: William J Perkins - 6/10/2007

Question
This is very basic, but I just can't help my friend who doesn't know why some
clocks have 2 keyholes and some have 3.  And aren't there even clocks with one,
and/or fake keyholes? And is it possible to overwind;we have had conflicting
opinions. Thanks in advance.

Answer
Indeed this is basic, very basic, yet about as important as it can get.  I'll take a whack at it.
Mechanical clock are generally comprised of gears, wheels, shafts etc. sandwiched between two or more plates.  These parts are arranged from a power source, usually a spring or a weight.  Through a set of gears a specific task is performed, keeping time, announcing the hour, playing a melody, usually to announce a quarter hour.  The set of gears keeping time is called the time train, it is a stand alone motor which when activated, put in motion what is termed the motion works.  The motion works are those few pieces that actually turn the hands and release into motion the other trains of the clock.  The striking activity, the motor that gongs the hour and/or halfhours is again, a motor unto itself.  This train is kept in a lock down condition until the movement of the time train causes a lever to lift that releases this motor, causing it to lift and drop a hammer(s) against a chime rod a predetermined number of blows which upon completion of returns to a lock down condition.  In the event the clock chimes as well as strikes, it is the one released by the time train.  When released the chime train sets in motion the chime mechanism which lifts a series of hammers to play a sequence of notes.  When it has completed this task it returns to its locked condition, at the same time it locks, it lifts a lever which releases the strike train to do its thing.  
If a clock simply keeps time it will have one train between the plates, beginning with a great wheel that is powered by either a spring or weight.  The weight can be either chain driven or cable driven.  If spring or cable driven it will have a winding shaft to which a key is applied to apply power.  If the clock has one or more trains a key shaft will be present to apply power.  If the clock is chain driven, the chains are pulled down to lift the weight(s) thereby providing power.  
As stated at the beginning this is a very simple concept but rather difficult to explain succinctly.  I hope this does it for you.  I wish you luck in wading through all this verbiage.  Contact mw if I have missed something.  WJP