Dammit. Typed all this stuff in, got disconnected, tried to post and lost it. So, I'll start all over again. This is in response to Ree's post about making custom pulleys. You will need a compass, a good ruler, and a drill press.
You will need a chunk of sheet metal slightly thinner (very slightly) than the space between your chain link halves. Take your center punch and make a dot at least 180mm from the nearest edge.
Measure from the center of one link pin on your chain to the next. Just for example, let's say 15mm.
How many teeth do you want? Let's say 28. 28 x 15mm = 420mm. This is the circumference of your pulley. 420mm / pi (3.1416) = about 134mm, minus a hair. Divide by 2 = 67mm. This is the radius. Set your compass at 67mm.
Make a circle around the first punch mark. Reset your compass at 15mm (link length), and mark all the way around the circumference, hopefully the last mark will line up with the first. If you have to make an adjustment, make it to the circle, not to the marks around it. Punch all of the marks.
Drill the marks with a bit just slightly bigger than the rollers in your chain, to allow for tolerances. Cut the pulley out at the circumference, which will fall halfway thru all those holes you just drilled.
Make whatever other holes you need to mount the pulley, using the compass to center them accurately. Drill the center hole last. File the teeth slightly so that the chain will find them more easily.
I've not done this yet (my bike has a belt, not a chain), but I've made parts for many other machines.