in a recent thread (
http://www.modelenginemaker.com/index.php/topic,9496.0/all.html) i got a couple good replies about o-ring sizing. they led me to check the dimensions more closely, and all i found was more confusion. i'm building the kozo new shay, and the book includes an appendix focusing on o-rings. as a beginner, i certainly didn't expect to be second guessing what kozo says, but derekwarner is right, kozo's numbers don't agree with other published references.
the attached picture shows some dimensions for all the o-rings this loco uses, and the closest standard as568 o-ring size i find. then i use kozo's squeeze calculation to determine D for 10% squeeze, given the d. (except for the cylinder, where i set the D=16 and calculate the d). these numbers present some problems. for several of them (highlighted yellow), the calculated D is larger than the oring outer diameter. i think this is because kozo's squeeze calculation assumes equal squeeze on the inner and outer diameters. this assumption breaks when i have to pick the closest inner diameter to match the shaft in question and that inner squeeze uses more than 50% of the total squeeze. if you were to allow for o-ring manufacturing tolerances, even more of my cases would not fit as they are just barely working at nominal.
i really don't know how o-rings deform in 3-d so maybe i'm over thinking all this. thanks for any thoughts or direction.
