I don't remember the final numbers on mine but made a template to use as a reference and drill jig in case I ever want to make another. In practical terms an even pin count/ratio wasn't really important or necessary because you could just plug the ratio into the software and it got calculated in auto-magically.
To figure the diameter I just gave it a close estimate then turned a disk out of thin, like 14ga, steel and brought it down in .005" increments until things lined up for 35 pins.
Then went to 10ga for the jig and ultimately the two outside halves of the sprocket.
Made one for .325 and one for 3/8ths that also works for 3/8lp
Keep in mind for pin placement that your 28 pin sprocket is being driven by the chain rather than the 7 pin that's driving the chain (so opposite wear surfaces), unless maybe your going to use design specific (expensive) drive chain...
To figure the diameter I just gave it a close estimate then turned a disk out of thin, like 14ga, steel and brought it down in .005" increments until things lined up for 35 pins.
Then went to 10ga for the jig and ultimately the two outside halves of the sprocket.
Made one for .325 and one for 3/8ths that also works for 3/8lp
Keep in mind for pin placement that your 28 pin sprocket is being driven by the chain rather than the 7 pin that's driving the chain (so opposite wear surfaces), unless maybe your going to use design specific (expensive) drive chain...