Don't you hate it when you have to do magnetic separations and are limited to either 8 wide PCR tube holders that cost a fortune or 1.7 mL tube holders that aren't spaced properly for multi-channel use and ALSO cost a fortune? Yea, it sucks.
Honestly, biotech companies. Why do these stupid magnetic racks cost upwards of $500 when really it should be around $5? Well, no longer.
Here I present a modular magnetic rack system which allows you to have any number of tubes in a row! Break out your 12-channel multichannels! Make your own magnet racks for a fraction of the price!
Your PI will thank you. Or yell at you for not having printed this out earlier. You can never win with PIs.
NOTE: Pictured are a slightly older version of the tube racks. The files contain a newer and better version that I did print but did not take a picture of.
I used the following magnets from K&J magnetics. You could probably buy them cheaper in bulk from ebay but honestly they are not that expensive.
Smaller magnets: http://www.kjmagnetics.com/proddetail.asp?prod=B842-N52
These are used for the 1.7 mL tube holders and for the PCR tube holders. Make sure they are magnetized through thickness! I don't think it matters which side is pointing towards your test tube though.
Larger magnets: http://www.kjmagnetics.com/proddetail.asp?prod=BC42
These are jammed in side by side with the smaller magnet to make a continuous 1-1/4" magnet for the PCR tube rack. Jam it in so the poles line up. Yes they will want to spring out but thats why you jam them in really hard so they don't.
I didn't need to use glue to keep the magnets in the PCR racks although they end up being a bit loose in the 1.7 mL racks. If you just put some tape in there or leave a piece of filament to jam them in it works fine.