John H McDonald mcdonald at
Thu Feb 23 22:11:40 EST 1995

In article <9502231545.aa07644 at>,

>We are sitting here discussing the construction of gel boxes for molecular
>biology labs. We are thinking of building our own for undergrad teaching labs.
>Some questions we came up with:
>1). What glue to use for construction? Apparently regular silicon has acetic
>acid in it. 

The shop where you buy plastic should have the appropriate cement for 
acrylic or polycarbonate plastic.  Some of these cements are just a 
solvent which dissolves the plastic.  The advantages of these are that, 
if you have a good joint, you can assemble the joint, then apply the 
cement to the edge and it will run in by capillary action.  The resulting 
joint can be as strong as the plastic itself.  Other cements are thicker, 
because they contain both the solvent and some dissolved plastic.  These 
cements have to be applied to the joint before it is assembled, but 
because they can fill small gaps, they may be more forgiving.

>2). What are the ideal dimensions?

Whatever seems ideal to you, that's part of the beauty of building your own.

>3). Where do you obtain the platinum wire and what dimension to use?

Scientific supply companies such as VWR and Fisher sell it.  Get the 
thinnest they sell, it will be cheaper, and plenty thick enough to carry 
the small amounts of electricity you'll be using.  You can get the banana 
plugs and sockets at Radio Shack; if your physics department has a 
stockroom, they'll probably have them too.

>4). How do you bend plexiglass?

Remove the protective paper and put it in an oven, on a cookie sheet, at 
300 F (150 C) for a few minutes.  It should be floppy enough to bend it 
over a wooden form.  You can buy a strip heater designed just for this 
purpose, but they're pretty expensive.  I'm told that if you're real 
careful, you can heat the plastic with a propane torch held just the 
right distance away until it is soft enough to bend.  

>5). What is the ideal tool to use for cutting plexiglass? Table saw, coping
>saw, chain saw (just kidding)?

A band saw is best, a table saw will work.  Be sure to wear eye 
protection, little chips will go flying everywhere.

 >6). Are there different plexiglasses?

Plexiglas is one brand of acrylic plastic; I think it's also what's 
called perspex in other countries.  I doubt there's much difference 
between brands that will make a difference for gel boxes.  You might also 
consider polycarbonate plastic, since it's tougher and resists shattering 
better (it's what bulletproof windows are made of).  Make sure you get the 
correct cement, I think a different cement is needed for polycarbonate.  
When you shop around for plastic (most glass shops sell it, as do many 
hardware stores), ask if they sell scraps.  They often have a big pile of 
scraps, big enough to make gel boxes from, that they'll sell for 
cheaper than custom-cut pieces.  For the combs, delrin works well.  You 
may have to call around a bit to find some, though.  

John H. McDonald
Department of Biology
University of Delaware

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