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    Salad Spinner Centrifuge
    By Steve Schuler | January 16th 2014 01:08 PM | Print | E-mail | Track Comments
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    Back in the day, some chemistry sets came with a mechanical centrifuge. They were operated similar to those old-timey pump style tin spinning toy tops. This is the style centrifuge that came with my chemistry set:


    Note: I came up with this story idea long before I was able to find a second-hand salad spinner and now I can’t remember where I found this picture. I am unable to cite its source.

    Here’s another example of a chemistry set centrifuge on Evil Mad Scientist Laboratories’ site:

    Initially I decided to try building an electromechanical centrifuge out of construction toys. This first test is a combination centrifuge/magnetic stirrer built out of K’nex:

    The plastic tubes that hold the centrifuge tubes are from toothbrush cases. There are two sets of neodymium magnets. The two that spin the stir bar are from an old magnetic keychain I took apart. They are held on to the K’nex gear with two neodymium magnets that hold those LED blinky-buttons on your shirt. The stir bar is from a Magnetix knock-off kit that is given away at trade shows.

    This test is a combination centrifuge/magnetic stirrer built out of Erector set parts:

    The stir bar is a sample from Dynalab Corp (dynalon.com).

    K’nex seemed to make a good magnetic stirrer, but I’d have to build a gear box to get it to spin faster for centrifugation. I don’t know how well the K’nex parts will hold together while spinning faster and with a load of two 15 ml conical centrifuge tubes. The erector set version should be sturdy enough to install a gear box and spin two 15 ml tubes, but the problem is as you spin the axle faster it doesn't make a good magnetic stirrer. The stir bar keeps getting caught up in the vortex and swirling around with the liquid in the beaker. Then you have to switch off the stirrer to let the stir bar settle to the bottom and catch on to the magnets. Switch the stirrer on. Stir the liquid. The stir bar gets caught up in the vortex and swirls around with the liquid again. Switch the stirrer off. Repeat.

    One day, I came across this story about two Rice University students who built a centrifuge out of a salad spinner. I thought it was a pretty clever idea. I've seen salad spinners used before and it occurred to me that you can get them to spin up much faster than those old chemistry set mechanical centrifuges. The following pictures are my design for a salad spinner centrifuge built with toothbrush cases, erector set parts, and zip ties.

    Unfortunately I was unable to fit two 15 ml conical centrifuge tubes in the centrifuge, but two round bottom tubes will fit.

    I also found a this story about using a salad spinner for a PCR plate centrifuge. I don’t have any PCR plates, but I did modify my centrifuge to hold two micro-centrifuge tubes by adding two small sample vials with zip ties (micro-centrifuge tubes and sample vials courtesy Dynalab Corp: dynalon.com).