Good article about laser marking plastics can be found here.  One thing about laser marking plastic that needs to be said – Be sure you have a way to exhaust the fumes.  For example acrylic can put out a tremendous amount of smoke and toxic fumes that can almost knock you over.  And not just any low-budget fume extractor will work.  You will need an industrial sized one that can evacuate air inside the laser marking machine cavity within a few seconds and recirculate it back out into the environment.  B

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