Hey guys, I was hoping someone could set me straight on the two main methods of calculating shaft critical speeds. I have a final coming up but I can't seem to get these two to agree. What I know: -Dunkerly underestimates, Rayleigh overestimates -Deflections used in Dunkerly are those caused by each single mass (eg remove all other masses during calculations) -Deflections used in Rayleigh are those calculated with all masses "attached" What I can do: -Dunkerly's method very well. Wrote a VBA program for it. All calculations agree with all example problems I've run across as well as HW vs solution manual verifications What I can't do: -Rayleigh's method. The answers I get from this do overestimate, but are far, far off from that of Dunkerly, when they should be fairly close to one another. I can follow examples very easily and get the correct answers but I'm missing something in practice myself. For example a HW problem I am working pegs Dunkerly speed at 450 rpm, while Rayleigh gets 1050 rpm which is more than x2 Dunkerly Can anyone point out what I am doing wrong here, at least by my thinking method? I'd be happy to post some of my worked out examples to see if I am just messing math up, but I am positive I am not. I appreciate any help, thanks all!