Whether a watch is made of metal or plastic, there is one area that is susceptible to damage every time the watch is worn. That area is the watch's face, which is usually covered with a clear plastic disk known as the crystal. Professional jewellers can replace the crystal, but usually at a high price, sometimes costing more than the value of the watch itself. Use a few simple tools and techniques to replace the crystal yourself and save money otherwise spent on having a professional do the job.
Measure the diameter of the broken or scratched crystal. Try to remove the crystal intact in order to make an accurate measurement. If the crystal is too damaged to remove as a single piece, measure the diameter of the opening that holds the crystal in place. Make a thin, circular cardboard template slightly larger than the opening. Trace the bottom of a round pill bottle or similar container to make a clean circle. Trim the template to fit with a utility knife or scissors. The finished template should fit tightly into the watch face opening. Most watch faces have a lip on which the crystal sits. The template should rest on this lip, with no gap between the edge of the template and the outer ring, or bezel, of the watch face.
Attach the finished template to the acrylic sheet with double-sided tape. Watch blanks, or crystals, are extremely thin. Therefore, the acrylic should be between 1/16 and 3/32 inch thick, which you can cut with a coping saw. Use double-sided tape to attach a thin piece of scrap wood to the acrylic. This extra thickness keeps the thin acrylic from vibrating as the saw cuts through it. Vibration or "chatter" can crack the thin acrylic.
Cut out the acrylic disk with a coping saw, making the disk 1/32 inch larger than the template. This prevents the acrylic blank from being cut too small. Remove the scrap wood cutting support and the paper template from the acrylic. Leave the protective backing on both sides of the acrylic and sand the edges of the blank until it fits tightly into the watch's lip. Sand the blank by hand with 220-grit sandpaper; the piece is too small for an electric sander or grinder. Back a small piece of sandpaper with something firm, such as a scrap of wood. This puts greater pressure on the edge of the blank as it is sanded, speeding up the process..
Fit the acrylic blank into the watch face. Once you're sure it fits tightly, remove the blank from the watch face and peel the protective backing from both sides of the blank. Wipe the blank down with a 100 per cent cotton cloth to remove any debris before gluing.
Apply a thin line of clear epoxy glue to the watch's lip before inserting the blank. Use a toothpick or similar device to apply the glue. Carefully place the acrylic blank onto the lip. Once the blank is in position, allow 24 hours drying time before using the watch.
You can also make a watch crystal from polycarbonate, which can be cut with scissors. Scissors will not crack polycarbonate because of its molecular structure. Although polycarbonate is more expensive than acrylic, at such a small size the cost will be minimal. Polycarbonate is 250 times more impact-resistant than glass and is a good choice if the watch is exposed to potential damage from high-impact situations.