The last three chapters were devoted primarily to ABS, because I think it’s the easiest plastic to work with, and it’s less expensive than some alternatives. It has one big drawback, though: transparent ABS is relatively rare.

Transparent Options

Two popular types of transparent plastic are polycarbonate (often known by the brand name Lexan), and acrylic (sold under brand names such as Lucite, Perspex, and Plexiglas).

Some advantages of acrylic plastic:

• ■ Less easily scratched than polycarbonate.
• ■ More resistant to ultraviolet (polycarbonate gradually yellows).
• ■ Excellent clarity, and can be restored by polishing.
• ■ Cheaper than polycarbonate.
• ■ Available in numerous shapes and colors.

Some advantages of polycarbonate:

• ■ Much greater impact resistance—less brittle than acrylic.
• ■ Doesn’t tend to chip while you are working on it.
• ■ Easier to bend than acrylic.

Among the many applications, acrylic plastic is used in helmet visors, helicopter windows, store displays, signage, and underwater windows. Polycarbonate is used for CDs and DVDs, lenses, safety glasses, water bottles, and instrument panels.

Polycarbonate in a Picture Frame

You can buy untinted polycarbonate from a hardware store, where precut pieces are sold as a substitute for window glass. You’ll find that both sides of each piece are covered with adhesive protective film, which you leave in place while you saw or drill the plastic. After these operations, you peel the film away. You also have to remove the film if you’re going to use heat to bend the plastic.

Perhaps you remember the pentagon-shaped frame that I featured in Chapter 5. Back then, I suggested that a piece of polycarbonate could be installed as a substitute for glass. It’s more expensive, but much easier to use and safer to handle. You can just cut it with a saw.

The protective film on polycarbonate is usually transparent, allowing you to look through it while making measurements. I used a fine-point permanent marker to trace the inner boundary of the frame, as in Figure 18-1.

After drawing the outline, you can saw the polycarbonate in exactly the same way as you sawed ABS. See Figure 18-2.

Removing the protective film is easy, as shown in Figure 18-3.

After sanding its edges, I placed the transparent plastic in the back side of the frame, behind the wooden trim that was glued there previously. Peeling off the protective film tends to charge the plastic with static electricity, which attracts workshop dust. Wiping the polycarbonate with a tiny amount of dishwashing liquid helps to remove the charge, leaving a nice clean, reflective surface, as in Figure 18-4.

In case you may have felt that the cartoon that I used previously was disrespectful to people who have pointy heads, I found a picture that may be more appropriate. See Figure 18-5.

A piece of corrugated cardboard is sufficient to go in the back of a frame. I secured it with ½" brads around the edges. That completed this leftover project.

Mixed Media

The solvent that you used in Chapter 16 dissolves polycarbonate as well as ABS. Does that mean you can cement the two types of plastic together? Absolutely!

When someone builds a little electronic circuit, the finished result can be installed in a project box. This is just a little box that can contain the electronics, often along with a 9-volt battery, while switches, buttons, and LEDs can be mounted on the top. Yes, this is another box project—but useful, and a good way to demonstrate that screws, glue, and bending can be combined to simplify a design, while mixing different plastic media.

Project boxes tend to look pretty dull, but they don’t have to. Why not build one that is partially transparent, to reveal the components inside? Figure 18-6 shows what I have in mind. No doubt it can be used for other purposes, too, such as displaying collectibles.

This only takes about an hour to build. You need a piece of polycarbonate 12" x 4", a piece of ABS 12" x 4", four screws, and some solvent cement with an applicator, which I introduced in Chapter 16.

Begin with the ABS. From the strip 4" wide, cut two copies of the shape shown in Figure 18-7. Because these shapes will be on opposite sides of the box, you should flip the pattern left-to-right for the second piece, so that the textured side of each piece can face outward.

Drill the holes and use a countersink on the outside (textured) surface, to prepare the holes for #2 flat-headed screws. Round the two top corners of the ABS by sanding them till you like the look of them.

Now take the piece of polycarbonate and insert it between your heat-protective tiles, leaving just over 4" sticking out. Apply your heat gun to an exposed strip that is slightly wider than ½" because this has to be a gentle curve rather than a sharp bend. Polycarbonate has a higher melting temperature than ABS, but you are using a piece only ¹/₁₆" or ³/₃₂" thick, so it should lose its stiffness after about a minute.

When the polycarbonate is quite limp in the hot area, remove it from the tiles and wrap it around one of the ABS pieces that you prepared, as in Figure 18-8. Make sure the bottom corner of the polycarbonate lines up with the bottom corner of the ABS. Pull the polycarbonate tight around the ABS and wait till it sets. This will probably require both of your hands, but if someone is with you, they can spray the plastic with a little water to expedite the cooling process.

Put the polycarbonate back between the tiles and apply heat about 4¹/₈" further along the strip. Then wrap it around the next corner in the same piece of ABS.

The polycarbonate will extend beyond the bottom edge of the ABS, so you’ll need to mark it and saw off the excess after the bend becomes rigid. The finished polycarbonate should look something like the example in Figure 18-9.

Clamp the polycarbonate around the ABS piece that you have been using, and place it on some clean rags, as in Figure 18-10. You could use screws to assemble these pieces, but I think solvent is a better-looking option, and quicker.

Check Chapter 16 for the procedure and cautions regarding solvent. Please don’t ignore the need to wear gloves and eye protection.

Trickle solvent in around the clamped edges, and surface tension will draw it into the crack. Pick up the assembly in case some solvent has run through and into the rags. Within a minute or two, the joint should be strong enough to be unclamped, as in Figure 18-11.

You should be able to cement the second side in the same way, if your bends in the polycarbonate have been symmetrical.

Reheat the polycarbonate if it really won't fit.

After you have cemented the second side, it’s time to cut one more piece for the base of the box. This will be recessed inside the other pieces. One dimension of the base will be 4", because your pieces of ABS are 4” wide. You can’t be sure of the other dimension, because of small variations that tend to occur during the bending and gluing process. Therefore you should measure the actual distance between the two sides, then cut the base to fit. Make it a fraction bigger than necessary, and sand it till it slips in without forcing.

You will use screws to hold the base in position, because the box won’t be much use if you can’t get inside it. Turn the box on its side, fit the base in, and nudge it along till you see the edge of it through the holes in the side facing you. Use a sharp pencil to mark the edge of the base through the holes, in exactly the same way as when you inserted the sides of the box in Chapter 17 (assuming you built that project).

I guess I have to admit that when I was building my version of this box, I forgot to drill holes in the side pieces when I cut them. You can see the absence of holes in the previous photographs. I could have rebuilt the project and photographed it again, but I decided that it’s useful to demonstrate that everyone makes mistakes. I hope your memory is better than mine, because it’s easier to drill the holes before you start to assemble the pieces than after they have been glued in place.

When you have marked the edge of the base through the screw holes, remove it, clamp it in a vertical position, and drill pilot holes into the edge, as was described in Chapter 17. Then put it back in the box and insert the screws, as in Figure 18-12.

The last step is to turn the box over and mark the opposite edge of the base through the holes on the other side. Remove the first two screws, drop the base out of the box, and once again, drill pilot holes on your pencil marks.

Before you reinsert the base on a permanent basis, you’ll need to clean up your work area and then wipe both sides of the polycarbonate to make it dust-free. The result should look like Figure 18-6.

The dimensions can be changed easily if you want to use the same basic design to build a different size of box. Also, if you have trouble inserting the screws into the edge of ¹/₈" ABS, you can upgrade to a sheet ³/₁₆" or ¼" thick, without changing any of the steps in the fabrication process that I just described. Only the width of the base will be affected, and you’ll be cutting that to fit anyway.

More Shapes

For all of these projects, you’ve been using plastic in sheets. Suppliers also sell various types of plastic in rods, bars, and tubes, for applications ranging from laboratory equipment to store displays.

You can also obtain molded shapes such as discs, squares, cubes, and spheres, especially in the world of acrylic plastic. Some acrylic discs and spheres measuring ⁵/₈" and ⁷/₈" diameter are shown in Figure 18-13. You can find them from many sources on eBay, and may also see them in some crafts stores. Some people use small pieces of molded acrylic, in a rich variety of colors, to make jewelry. You should find quite a few jewelry crafts books if you check online or at your local bookstore.

More Plastics and Applications

Many other types of plastic exist, such as the PVC (polyvinyl chloride) that is often used in water pipes and electrical conduits. You can also get PVC rods just ³/₁₆" in diameter that are used in 3D printers.

I used some of these rods to make the structure in Figure 18-14. The rods are joined in PVC caps intended for ½" plumbing, cheaply available in bulk. I drilled three holes in each cap, inserted the rods in the holes, and applied PVC plumbing cement, wiggling the rods to get the cement into each joint. This is a solvent, but easier to apply than the type you used with ABS, because it is thicker and takes longer to set. Most PVC cements are brightly colored, but I found one that is white when I searched online.

Does this shape look familiar? It’s identical with the geometry of a soccer ball, as shown in Figure 18-15. This came to be known as the Buckminster ball, although Buckminster Fuller did not actually design it. It was introduced for the 1970 soccer World Cup, and was used for several decades.

The rest of my suggestions, below, are just thought experiments. The materials are not included in the buying guide.

Can you think of applications for this kind of plastic structure? Maybe you could wrap it in chickenwire to make a bird cage—although for a parrot, you should substitute a metal frame to prevent the bird from eating its way out.

If you scaled it up, you could use lengths of 1½" PVC pipe and 3" caps to connect them, and you’d be able to build a little greenhouse—although the frame would be stronger if it was based on triangles instead of pentagons and hexagons. Triangles were the basis of the true geodesic-dome geometry that Fuller established many decades ago. You can find a lot of web sites with precise dimensions for dome structures.

PVC is also available in thin sheets, and the cement that works with them will also work with thin vinyl, which you can buy by the yard from fabric stores. This suggests to me that you could make a geodesic a lamp shade using panels of transparent PVC joined with gray vinyl, as in the rendering in Figure 18-16. In this design, gray diamonds would be glued over the edges of white pentagons, to hold everything together and create the star pattern.

Alternatively, Figure 18-17 suggests mitering 12 pentagon-shaped wooden panels, each with a circular hole that could be filled with translucent plastic. The mitering is not quite as challenging as it seems, because you can look up the miter angle in a standard geometry textbook. It is approximately 58¼ degrees on every edge. Maybe you could design a jig to simplify the sawing.

The basic shape in Figures 18-16 and 18-17 is called a dodecahedron, which is one of the five Platonic solids, named after the Greek philosopher Plato. The full set is shown in Figure 18-18. What other concepts do these shapes suggest?

Plastic, with or without wood, opens up all kinds of possibilities. I’ve suggested some, but there are many more. In particular, one topic that I haven’t dealt with is color. I’ll get to that in the next chapter.