What are the recommended power settings for engraving plastic sheet?

Keep power settings as low as possible to avoid melting, warping, and distortion of the plastic sheet. Using too much power is the most common fault most laser operators have with engraving plastic sheet materials. The cap layer of the plastic is thin and often just 3-4 thousandths of an inch thick, so not much power is required to ablate this layer. Adjust power and speed settings so engraving just barely reveals the base layer, then add 5-8% more power. One indicator of using too much power is a lip that is formed around the outside of the engraved area. Laser engraved plastic sheet should have clean, crisp edges, and should cleanly remove the cap to reveal the base color. 

   —Coherent