After playing with the locations of the motors and gears I roughly sketched an assembly diagram with the location of the motors and shafts to allow me to estimate various part sizes.
My gears were described as “27 mm Diameter Plastic Cog Wheels for 4mm Motor Shaft, 40 Tooth Gears”. So I needed to work out how far apart the centres would be when the gears were meshed together. Too far apart and the teeth won’t meet, too close together and the gears won’t fit. As an experiment I placed the gears next to each other and used a pencil to mark some paper, I measured the distance between these as 25mm.
Following the details on Roy Beardmore’s gear calculation page I concluded that the Pitch Circle Diameter of my gears was 25.7mm and due to the gears being the same that also is the separation between each of the gear pairs. This is only slightly more than my approximated value.
Now I can accurately draw up the positions of the motors and shafts and start building the clock framework.