Joining Acrylic Sheet

Acrylic sheet can be joined with solvents to form strong, durable, transparent joints.

Abrasion Resistant Acrylic sheet can be cemented on the non-coated sheet surfaces using the same procedure as the cast and extruded GP acrylic sheet. If solvent cementing on or to the coated surface is necessary, the coating must first be removed by wet sanding with 500 grit or finer sandpaper.

The ingredients in most solvent cement are hazardous materials, and extreme care should be observed using proper ventilation and handling techniques as recommended by the manufacturer of these products. Always follow the manufacturer's recommendations and instructions when using these and any other products.

The ultimate strength and appearance of your joints depend on how carefully you make them. Getting excellent joints requires a lot of care and considerable skill. Practice on scrap pieces. The more experience you have, the better your work will be.

Observe some basic precautions when working with acrylic solvents.

• Always work in a well-ventilated area
• Do not smoke-solvents are highly volatile and flammable
• Protect skin from contact with cement
• Do not attempt to cement acrylic sheet in temperatures under 60°F (15°C). Temperatures from 70° to 75°F (21° to 24°C) are ideal.
• Always follow the cement manufacturer's recommendations

Preparation of the joint

All surfaces to be joined should fit together accurately without being forced. Flat, straight surfaces are the easiest to work with. Any area that is part of the original surface of the sheet should be left untouched.

A smooth cut made with a cooled power saw also should be left alone. However, if the area to be joined has a rough saw cut, it should be wet sanded or finished with a router to get a flat, square edge. Do not polish edges that are to be cemented. Polishing leaves a highly stressed, convex edge with rounded corners. It will make an inferior joint. Always remove the masking from around the area to be joined.

Capillary cementing

Capillary cementing is probably the most popular method of joining acrylic sheet. It works because of the ability of low-viscosity solvent-type cement to flow through a joint area by capillary action. Properly done, it yields strong, perfectly transparent joints; however, it won't work at all if the parts do not fit together perfectly.

First, make sure the parts fit together properly. Then hold the pieces together using a jig that will support the pieces firmly but will permit slight movement as the joint dries.

The joint must be kept in a horizontal plane, or the cement will run out of the joint.

Apply it from the inside edge, whenever possible, on a box corner type joint and from both sides, if possible, on flat pieces. A special needle-nozzled applicator bottle can be used for applying the cement.

If the cement does not flow completely into the joint, try tilting the vertical piece slightly (about 1°) towards the outside. This should allow the solvent to flow freely into the entire joint.

Always let the joint dry thoroughly (usually 10-30 min.) before moving the part. Maximum bond strength will not be reached for 24 to 48 hours.

Dip or soak cementing

This method of cementing an acrylic sheet involves dipping the edge of one of the pieces to be joined directly into the solvent. Only the very edge must be dipped. Exposing too much area to the solvent will result in a weak, slow-setting joint.

You'll need a shallow tray to dip the acrylic. The tray can be made of aluminum, stainless steel, galvanized sheet, or glass. Do not use plastic-the solvent may dissolve it.

Place short pieces of wire, pins, or brads into the tray to keep the edge of the acrylic sheet from touching the bottom of the tray. The tray must be level. Pour solvent cement into the tray so that it just covers all the brads and covers them evenly.

Now carefully place the edge to be cemented into the tray, so it rests on the brads. You can hold the piece upright by hand, but it is better to use some support to hold it in place while it soaks. A couple of padded clamps attached to the sheet and resting on the edge of the tray are fine. Heavy pieces of wood placed against each side of the sheet and resting on the edge of the tray are fine. Heavy wood pieces against each side of the sheet will also work. Slotted wooden supports are usually used for production work, but anything that will hold the piece firmly upright is sufficient.

The acrylic sheet should be left in the solvent for 30 seconds to 2 minutes, depending on the thickness of the sheet, the type of solvent used, and the bond strength required. Soaking time should be long enough to allow the edge of the sheet to swell into a "cushion." The piece must be removed as soon as an adequate cushion is formed. Hold it for a few seconds at a slight angle to allow the excess solvent to drain off. Then carefully but quickly, place the soaked edge precisely into place on the other part to be joined. Hold the parts together for about 30 seconds without applying any pressure. This will allow the solvent to work on the surface of the other piece.

After 30 seconds, you can apply pressure to squeeze out air bubbles. But be careful not to squeeze out the cement.

When the pieces are joined, the part should be placed in a jig to maintain firm contact for 10 to 30 minutes. Do not allow the parts to move during this critical time.

Allow the joint to set for another 8 to 24 hours before doing any further work on it.

Viscous cementing

Viscous cement is used to cement joints that can't be easily cemented using the capillary or solvent soak methods-either because they are difficult to reach or because the parts don't fit properly together. Viscous cement is thick. It will fill gaps and make strong, transparent joints where solvent cement can't.

You can make viscous cement by dissolving chips or clear Acrylic sheet in a small amount of solvent. Let the solution stand overnight.
Apply the cement-like glue with a brush, spatula, or directly from the applicator tube.

Remove the masking material from around the joint area, and carefully apply a small bead of cement to one side of the joint. Then gently join the pieces as described under "Soak cementing."

Masking tape may be applied to protect the area around the joint, but it should be removed carefully after about 5 minutes while the cement is still wet. Don't touch the parts for the first critical 3 minutes, or the joint will not hold. The part may be carefully moved after 30 minutes, but don't do additional work for 12 to 24 hours.