I working on a couple of small MXL timing belt drives and looking for suggestions on determining which belt to use. My center to center distance between pulleys is not currently fixed yet and I'm trying to figure/approximate/calculate which belt(s) to use. I know I want to have enough slack to be able to mount or replace the belts and to get over the flanges of the pulleys but not so much that an external idler causes the belt to rub on itself. Drive and driven pulleys will remain stationary so all adjustment will be through the idler. Almost any tooth count is available in increments of 2-4 teeth.
I will figure out what I need through trial and error and some CAD modeling but I was curious what others may have done. I'm thinking primarily working in reverse with standard belt sizes and my known pulley diameters to determine the C-C distance and then going up a size or two to get the needed slack.