I'm sure the info is somewhere but - have any of you got a quick way of calculating sprocket cutting. I got a job here that calls for a sprocket aprox 500mm diameter to drive 1/4" pitch chain. Now OK - the teeth gotta be one pitch apart, & the holes gotta be pin dia.+?, but how do I arrive at a pitch circle for the ring of holes? MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.