Well, I took it upon myself to call the centrifuge experts, Beckman.
In a small, benchtop rotor, this balancing situation is OK considering
that most small centrifuges have a high margin of...hmmm...tolerance for
off balance situations. What you're spinning is small, doesn't weigh a
lot, and is less prone to the forces of our lovely planet earth.
Technically, it is in balance according to vector forces pulling on a
single point (see prior posting by Dima), but not balanced in a proper
sense. Once all the forces have achieved a steady state, all is
HOWEVER. In an ultra centrifuge, where you routinely approach speeds in
excess of 80,000 rpm (as in CsCl grad's), it is imperetive that you fill
all slots with equal weights. In ultra, where the rotor tolerance is
5/10,000 of an inch in the eliptical orbit, equal vector forces prove
not to be so equal unless they are 100% equal. In otherwords, when you
go fast, the rules can't be bent as easily; you have to optimize your
I hope this solves this!
Dept. Molecular Virology
Rockville, MD 20852
CANTOLUPO at GENVEC.COM