Acrylic is a wonderful plastic that can be used for all sorts of different projects. It comes in both transparent and colored options, and can be machined, laser cut, or heated and bent into almost any shape.
Types of Acrylic
Acrylic comes in two varieties: extruded and cast. While they may look identical, there are reasons you may choose one over the other based on your fabrication plans.
Extruded acrylic has a lower melting temperature than cast acrylic, which makes it ideal for vector cutting on a laser cutter. This same property, however, makes it less ideal than cast acrylic if you are milling or drilling it.
When laser engraving, cast acrylic is preferred, as the resulting engraving will be a frosty white color that contrasts against the rest of the acrylic. Laser engraving extruded acrylic will result in a clear engraving that doesn’t contrast as well.
Working with Acrylic
If the edge of a cut piece of clear acrylic is frosty, and you’d like to make it clearer, it can be flame polished. While it takes some practice to get right, slowly brushing the flame from a propane or MAP gas torch across the edges to melt them slightly can give them a transparent, polished appearance. Just be sure not to polish edges that must be glued, as the resulting joint may not be as strong.
Using a strip heater, acrylic can be heated and bent at different angles. Store-bought strip heaters can be quite expensive, but there are ways to make do without them. If you have a toaster oven, set it to about 200º and leave the door slightly ajar. Place the part of the acrylic to be bent just above the open door, wait for it to soften enough, and then bend it to the angle desired. If you don’t have a toaster oven, you can (carefully!) use a heat gun to heat the acrylic. When using these makeshift methods, bend the acrylic against the edge of a piece of wood or metal for straight, clean corners.
Bending Small Pieces
If you’re bending a small, thin piece of acrylic, you can use the shaft of a soldering iron as a primitive strip-heater. Place the iron handle-first into its holder, plug it in, and then use a set of third hands to hold the strip just above the iron. Make sure you keep an eye on it, as you don’t want the acrylic to droop onto the soldering iron.
For straight cuts in acrylic, a plastic-scoring blade can be used. With a straightedge as a guide, pull the blade toward you, leaving a score mark. Score the acrylic several more times along the same line, then place the acrylic on the edge of the table and use light, quick pressure to snap the piece in two.
You can also cut acrylic with more traditional blade tools such as a jigsaw, band saw, or table saw. High tooth-count plastic-cutting blades are available for these tools, and are recommended.
Acrylic is typically glued using solvent-based glues, such as Weld-On 4. Unlike many other gluing processes, acrylic glue softens the surfaces of the acrylic and welds them together, chemically bonding the two pieces into one.
To glue acrylic with solvent glue, typically a squeeze-bottle applicator with a needle tip is used. Put the acrylic on the edge where you want it, and place the needle of the glue-filled applicator where the two pieces meet. Lightly squeeze the applicator while pulling it toward you. Capillary action will draw the glue into the joint. Hold the pieces in place for several minutes (a jig with clamps works great for this), and then allow the glue to set for 10–15 minutes before moving it. After 24–48 hours, the joint will cure to full strength.
Using solvent-based glues on laser-cut extruded acrylic can cause cracking due to the internal stresses from temperature differences in the acrylic. To guard against cracking, place the acrylic on a flat sheet of glass in a shop oven (not the one in your kitchen!) at about 180ºF (82ºC) for about 1 hour per mm thickness, then let them air cool. This will anneal the acrylic and relieve the built up stress.
If you try to drill a sheet of acrylic with conventional metal or wood drill bits, there’s a chance you’ll end up cracking it. If the sheet is thin, use a step drill bit instead. If you’re working with a thick piece of acrylic, you can use conventional drill bits if you first place a piece of masking tape over the area to be drilled. If the hole is especially thick, spray some WD-40 to act as a lubricant. This will help remove chips and dissipate heat as the hole is drilled.