A friend of mine
makes the most beautiful clocks in the world, completely from wood. Check out the site, and I'm sure you'll be tempted... Whilst he was going through his R&D stage, I knocked up a couple of programs to work out cog ratios and timings - the final result was Cogs3D, an OpenGL program that simulates cog trains and clocks. Windows only I'm afraid, but completely free (and with no warranties whatsoever). A zip file with the executable and some example files is avalable here
. The program's pretty self-evident, but if you have any problems, feel free to contact me.