Help needed on understanding synchronous motors

Hello All,

I need some help to really understand how big sync. motors are built.

The normal (capacitor start) induction motor (the ones with a short circuit
armature .. sorry, don´t recall the english name for this) is not synchronous,
if I understand it correctly. 

These motors run based on the fact, that there is always a difference between
the stator "speed" (giving by the mains frequency) and the rotor (that
actually turns). The more difference between these two "speeds", the higher
the output torque, which is why these motors have a high load starting

Long, long ago, I took apart a sync motor that drove an analog wall clock. If
I remember it correctly, this motor had a set of stator windings and the rotor
was composed of a magnetic core. As the magnet will always follow the changing
magnetic field of the stator coils exactly (i.e: no "speed" difference), I can
see how this motor is synchronous to the mains frequency.

But how are higher powered motors (e.g. 1/2 hp.) built? 

A while ago I read a post on turning non sync motors into sync´d ones, by
milling flats on the armature. How (by what principal) does this work ??

Coiler greets from germany,