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5 tube balancing argument

Hiranya Roychowdhury hroychow at NMSU.EDU
Fri Oct 11 09:58:09 EST 1996

At 01:52 PM 10/10/96 -0700, Lou Cantolupo wrote:

>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

It is true that ultraspeed machines need to be balanced far more precisely
than the regular tabletop microfuges or even the superspeed machines. The
simple reason is the rcf achieved in the ultra. However, balancing can not
be ignored even in the smallest of the clinical low speed machines. The
origininal issue was about balancing and not its precision. Correct me if
I'm wrong, but I think the rotors designed for ultras only carry
even-numbered slots/buckets. So, the odd-numbered balancing dilemma is a
non-issue for such rotors. I suspect that the designers and manufacturers of
the ultracentrifuges avoid the possibility of a disaster by not making
available any rotors that might accomodate odd number of tubes. But, were
such rotors available, I'm sure one could do the balancing trick with 3 or 5
or... tubes as long as the tubes were perfectly balanced. For example, with
a three tube combination, the operator has to make sure that all the three
tubes weigh exactly the same. (I use a pan balance to balance my ultra
tubes, anyway)

Dr. Hiranya Sankar Roychowdhury
Plant Genetic Engineering Lab.
New Mexico State University
Las Cruces, NM 88003
Ph. (505) 646-5785
hroychow at nmsu.edu

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