To calculate the dimensions of the cannon pinion -
D.O.C = Distance Of Centres - 23.40mm - The distance of centres is the distance between the minute wheel pivot hole and the centre arbor pivot hole (as the centre arbor sits inside the cannon pinion).
We then need to find the "module" by taking half the tooth count of the minute wheel, half the tooth count of the canon pinion (there is a 1:1 ratio between the minute wheel and cannon pinion and as the minute wheel has 40 teeth then so too will the cannon pinion have 40 teeth), which gives us 40.We take 23.40 divided by 40 and this gives us a module of M=0.585
Daryn knows from previous experience it is best to round down a touch on most clocks apart from old English longcase clocks which like a fraction more play so the module is then rounded up a fraction.
We settle on a module of 0.575 and this is now used to work out the diameter of the missing cannon pinion wheel by multiplying it with the number of teeth on the missing wheel plus 2.71 so 0.575 x 42.71 = 24.55mm.
We now have the missing information we need to get started.
First we find a piece of suitable brass close to the same thickness as the minute wheel to mark out the wheel blank. You can use engineers blue for marking out but a permanent marker does the job well.
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The wheel blank was rougly cut out on a band saw and then we drilled the centre hole so the wheel blank can be fitted to a mandrel for tooth cutting later. We just need to make sure the mandrel isnt bigger than the finished size hole.
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The wheel is now mounted to the mandrel and turned to its finished diameter of 24.55mm.
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Daryn has the luxury of a lathe almost permanently set up for wheel cutting. The wheel blank on its arbor is now transferred to this lathe and the lathe can be set up and the cutter fitted ready to cut the teeth.
I am posting up some pictures of the lathe set up so you can see one method for cutting wheel teeth.
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Daryns lathe is set up with "direct indexing" which just means he can fix different count plates directly to his headstock spindle and as you can see from the first picture there is a brass bar fitted to the back of his lathe with an indexing pin fitted through the top to fit into the holes in the plate.
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This lathe has its own milling head which can also double up as a drive unit. A pully mounted in a drill chuck is fixed into the milling head and this drives the cutter spindle which is mounted to a vertical slide.
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The arbor used for holding the wheel blank for cutting has the end cut to a point. This makes things much easier when centering the cutter. If this is not done correctly you end up with a wheel full of off-centre teeth. We now also colour the outside of the wheel blank with ink, the cutter only forms the gaps between the teeth so we will now be able to see when the cutter has gone deep enough and formed the teeth correctly as there will not be any ink left on the tips of the teeth.
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Here is the wheel after the tooth cutting process is completed -
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After a little clean up -
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In part 2 we will be making the pipe and rivetting the two together.
(oh boy, not again) For my own experiment I will use your measurements and make a cutter to see if it turns out a wheel like the one you made, once again just trying to prove this cutter making process. Cant wait for the rest...great job 
, see yah soon. William
I am kind of replicating it in my own workshop 