I'm not sure how to cut crown molding using a manual miter box. I'm trying the butt/cope method and getting a poor result. With the piece nested upside down (wall edge to the fence and ceiling edge on the table) and the angle set at 45, the resulting angle is nowhere near mating.

Everything I've been able to find says to set the angle at 45. I could see how that would work for a picture frame but not compound work. It must be that the spring angle of the molding is 38, but, how do I find the correct cut angle? I know it's closer to 33 but I haven't done enough trial and error to dial it in yet.

Is there some classic text from an old timer that would teach me the old way to do jobs like these? Is it time to relearn High School Trig?

Any help would be greatly appreciated. Thanks.