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98 WORKING WITH PLASTIC

APPLYING HOUSEHOLD ADHESIVE
Solvent cements work well when bonding together similar types of plastics, but they do little
or nothing when trying to glue plastic to wood, metal, and other materials.
For these, you can try a household adhesive. As noted in Table 9-1, contact cement works
well when bonding plastic pieces to metal or wood. You can get contact cement at the home
improvement store. Two- part epoxy (you mix liquid from two tubes) is used for the same
things, and is good when you need a very strong bond.
If you are joining pieces whose edges you cannot make flush, apply a thicker type of
glue— contact cement, epoxy, and household glue are good contenders. You may find that
you can achieve a better bond by first roughing up the joints to be mated. You can use coarse
sandpaper or a file for this purpose.

Some plastics don’t like to be glued. You can just about forget bonding nylon and high- density
G polyethylene (HDPE), unless you use an industrial cement that you can’t get anyway because
they’re expensive and require special applicators. Instead, use mechanical fasteners to hold
these pieces together.

Using Hot Glue with Plastics

Perhaps the fastest way to glue plastic pieces together is with hot glue. You heat up the glue
in a glue gun, and when the glue is all melty, squeeze the trigger to spread it out over the area
to be bonded.
Hot- melt glue and glue guns are available at most hardware, craft, and hobby stores in
several different sizes. The glue is available in a “normal” and a low- temperature form.
Low- temperature glue is generally better with most plastics because it avoids the “sagging” or
softening of the plastic sometimes caused by the heat of the glue.

How to Paint Plastics

Sheet plastic is available in transparent or opaque colors, and this is the best way to add color
to your robot projects. The colors are impregnated in the plastic and can’t be scraped or
sanded off. But you can also add a coat of paint to the plastic to add color or to make it
opaque. Most all plastics accept brush or spray painting.
Spray painting is the preferred method for all jobs that don’t require extra- fine detail. Care-
fully select the paint before you use it, and always apply a small amount to a scrap piece of
plastic before painting the entire project. Some paints contain solvents that may soften and
ruin the plastic.
Among the best all- around paints for plastics are the model and hobby spray cans made by
Tamiya. These are specially formulated for styrene model plastic, but work with many other
plastics, too. You can purchase this paint in a variety of colors.

Household Plastics for Bot Constructions

You need not purchase all the plastic for your robot at a hardware or specialty store. With a
bit of digging, you might find some of the plastic you really need right in your own home.
Here are a few good places to look:

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