5 tube balancing argument

brett brett at BORCIM.WUSTL.EDU
Wed Oct 9 11:49:03 EST 1996


>At the risk of starting a bandwidth hungry inconsequential argument
>(judging by the amount of time spent in our lab jibbering about this), I
>would like to ask a simple question:-
>
>Some one here was doing 5 minipreps (equal volume) and was loading a 12
>hole microcentrifuge, when he found that the balance tubes had been
>cleared away. He was about to fill another sixth tube to balance 3
>opposite 3, when I said that you can balance five anyway. This started a
>massive debate, which has now come down to three positions. 
>
>I reckoned that if you put three tubes in, in a triangle ie in holes 1,5,9
>these are balanced. Then you can balance the two others opposite each
>other in holes 2 and 8.
>
>One guy maintains that this is not balanced at all, on the grounds that
>you can split the fuge into two halves where one half has two tubes and
>the other has three, therefore it must be unbalanced. I am not convinced. 
>
>Then another guy said that he balances five by putting them in as near a
>pentagonal position as he can ie 1, 3, 5, 8, 10. I dont think this is OK
>because you cannot remove a balanced pair to leave a balanced three,
>although I doubt it does much harm.
>
>Are there any centrifuge balancing experts out there?
>
>Apologies for innapropriate use of the newsgroup, but maybe some of us are
>trashing our fuges and more importantly several pints are resting on this!
>
>-- 
>John Dixon                                        Lab 44 (1223) 334131
>Wellcome/CRC Institute                            Fax 44 (1223) 334134
>Department of Genetics
>Cambridge University    
>United Kingdom                           e-m: jpcd0 at mole.bio.cam.ac.uk

I agree with you. Load the three tubes, and the rotor is now balanced (ie
it is balanced about as well as an empty rotor). So, now add 2 tubes opposite
each other, and it is still balanced. This is as simple as an 8th grade lesson
in vector mathematics. We use 18 hole rotors around here and you can balance
2,3,4,5,6,7,8,9,10,11,12,13,14,15,16, and 18 tubes without using a special
counterbalance tube. Think about it. Enjoy your beers, John.



Brett Lindenbach
    
Program in Immunology                              
Washington University - St Louis                  
brett at borcim.wustl.edu                             

"I own my own pet virus. I get to pet and name her." - Cobain




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