Preparation for Cementing Acrylic Sheet

Preparation

The first step is preparing the area to be cemented. Edges must be cleanly cut and/or properly machined. If a dull blade was used for a saw cut, resulting in a melted or chipped edge, contact between the sawed edge and solvent may result in crazing of the material. Finish all rough edges on a jointer, shaper or edge finisher. If you cannot do so, wet­sand the edges with a flat surface or block.

Do not polish edges which are to be cemented. Polishing will produce a convex edge with rounded corners and will result in an unsightly, weak joint. Also, a flame­polished edge may craze when it contacts solvent cement.

Crazing may also occur if internal stresses from shop fabrication are high. To eliminate such stresses, anneal the piece at 180°F (80 °C). Figure that the heating time and the cooling time in hours should each equal the material thickness in millimeters, up to 6 mm. For example, you would heat a 3mm­thick sheet (0.118") for three hours and allow it to cool gradually for three hours.

For thin sheet, the annealing (heating) time should not be less than two hours. It is not necessary to heat any piece for more than six hours, though it will not be harmful if heating time is extended due to shift schedules, etc. Remember-each hour of heating time requires a corresponding hour of cooling time.

SURFACE PREPARATION BEFORE CEMENTING

1. Clean cut all edges and properly machine. Improper cuts will cause high stress on the joint.
2. Sand rough edges or use a joiner/shaper.
3. Do not polish edges to be cemented, as polishing produces a convex edge with rounded corners and will destroy a square fit which is needed for strong joints. Flame polished edges will craze upon contact with a solvent cement.
4. Apply cement with syringe, cement applicator or eye dropper.

Solvent mixtures with low volatility should be used. Solvent mixtures of this kind reduce air condensing and humidity on the surface which causes whitening of the joint area.

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