In every lab I've seen, people are quite meticulous about cleaning parts that are to be used in ultrahigh vacuum, as well as the components of the chamber itself. The parts may be put in an ultrasonic acetone bath and wiped down with isopropanol or methanol. Gloves are worn and special lint-free tissue used for the cleaning. This sometimes even extends to using a new tissue for each side of the flange knife-edges, so as not to spread dirt from one side to the other.
Analysis with a residual gas analyser usually reveals the pressure of the evacuated system to be dominated by water, and then after a good bakeout, by hydrogen. Bakeout seems to be so good at getting rid of everything but hydrogen, that I'm wondering, what's the actual effect of doing all that cleaning first?
Has anyone ever constructed an ultra-high vacuum system with half-assed, or no cleaning of parts? How'd it turn out?