Working with Plexiglas<SUP>®</SUP>

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Working with Plexiglas®


If one knows how to work with sheets of plexiglas® (lucite®; acrylic plastic) sheets, one can make many useful items for the laboratory at relatively little expense. This plastic may be bought at home improvement stores such as Home Depot and Lowes. It is also available in many hardware stores.

PRACTICING

This is for those of you who have never worked with plastic before. Prior to doing any of the following procedures, you must gain skill by practicing on pieces of scrap. Do it!

CUTTING

The beauty of working with it is that it can be cut by using both a score-and-crack technique as is used in cutting glass, and with a saw as used on wood. The score and crack method is a fast one, but often the finished cut is not quite strait enough for "welding" it to another piece. Thus sawing must be resorted to - preferably with a table saw fitted with a fence to guide the sheet straight through the blade.

The problem with sawing is that the cut edge is rather rough and not yet ready for welding to the next piece. The edge is made more smooth and flat by holding the sheet vertically and moving it back and forth on a large piece of fine sandpaper that is laid atop the flat table of the table saw. Edges that are not to be welded may be smoothed by "fire polishing"

"WELDING" PIECES TOGETHER

Joining two pieces of plastic together is probably the hardest thing to do with plastic - especially if the joint is to be watertight. Novices tend to reach for the bottle of glue, but this is not usually the best way. If one softens the plastic of both adjoining surfaces and then sticks them together, the two pieces will "weld" or "fuse" together. The use of chemical solvents is called upon. The problem is that many plastic solvents are either too volatile or dissolve the plastic too quickly for the worker's hands to get things together correctly. What is more is that there are fire hazards with many of the most thought of solvents such as acetone, methyl-ethyl ketone or ethyl acetate. A slow solvent that is not flammable is chloroform (CHCl3), which should, like all the other solvents, be used in a well ventilated place - preferably out of doors.

Suppose you wish to make a right-angle joint of two pieces. After sanding the cut edges, as described above, so that they are both quite smooth AND flat, you do a "dry run" by setting up the two pieces in their desired configuration and prepare various braces or supports to hold them in exactly that position - a right angles to one another. Once you have the support system ready, you are ready to weld. Place the two edges of the plastic in long baths of CHCl3. These "baths" are aluminum foil troughs that are folded up at the ends so that the 3 mm or so of CHCl3 won't escape.

The trough is placed level between two supports such a two pieces of wood, and the CHCl3 is poured in. One piece of plastic is set in each trough. (Two pieces of plastic in one trough quickly become just one piece of plastic!) Allow the plastic to sit in the trough for 60 to 90 seconds.)

Immediately lift out the pieces, fling off excess CHCl3, and press the parts together. Wiggle them slightly to mix their softened surfaces together. Then slip into place the braces that you have previously made to hold the two pieces at right angles to one another. Allow the setup to sit for several hours before moving it. (One must wait for the CHCl3 to diffuse out of and evaporate.)

Once the "drying" is completed, turn the joint over and see how much air was trapped in the joint. If you had wiggled and pressed the pieces together sufficiently in the beginning, there should be little trapped air, and a rather transparent joint. If this is your practice piece, test it for water-tightness and for strength.

BENDING

Bending is a very tricky procedure since you have to apply heat but not ignite or burn the plastic. Generally, try at all costs to have designs that don't need bending!

But if you must make a bend, be sure to have a form beforehand against which you will bend your plastic. A wooden form usually works quite well.

It should be obvious to you that if you want to make a sharp bend, that you want to heat the plastic only on a narrow band - and on both sides of the sheet! Application of this heat is problematic as you are not likely to have the controlled heating equipment of a plastics manufacturer. It will take a great deal of practice for you to waft a flame from a plumber's torch back and forth until the plastic softens and can be conformed to the wooden form.

More gradual bends require that large areas be heated - again, just hot enough to bend but not to burn! This author has never done this before and so must leave your task to your own creativity.

FIRE POLISHING EDGES

Prior to welding your pieces together, you will want to fire-polish all the cut edges that will be exposed. (Do not fire-polish AFTER the welding. Thermal expansion strains will craze your plastic.)

Pass a small flame from your plumber's torch along the edge. The trick here is to melt the plastic and not ignite it (which yields a black ugly surface). As you move the flame along the edge, you will see the melting occur and a glassy-smooth edge will appear. PRACTICE on scrap first!


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