What is the best plastic for cnc windows?

Originally Posted by

Al_The_Man's suggestion is certainly the best; tempered laminated glass the same as is used for vehicle windows.

Polycarbonate is the best next choice but it must be plain polycarbonate, also called Lexan or Tuffak.

Polycarbonate is available in a coated version that is much more scratch resistant than plain polycarbonate but it cracks much more readily and with a strong impact will shatter just like acrylic (Plexiglas).

If you have used plain polycarbonate and it has cracked there are a few possible causes:

Some solvents can cause polycarbonate to crack. These are things like trichlorethylene and dichloromethane. I suspect some tapping fluids might cause it to crack but have not done the experiment.

Some thread locking compunds will cause polycarbonate to crack.

Most soluble coolants will not cause it to crack nor will most lube oils.

Drilling holes with a dull drill and/or a drill running too fast will severely heat around the hole and this will cause the polycarbonate to crack away from the hole. Doing this and tightening mounting really tight will make the problem worse.

Cutting the polycarbonate with a dull saw likewise will heat the edge and can cause cracks to start.

Always use sharp tools, drills and saws, with some lubrication. Soapy water is a good lubricant for both drilling and sawing. When drilling use a moderate speed something like you would you for stainless and feed the drill fast. Make sure the polycarbonate is well clamped because it will try to climb the drill and if the drill grabs it you will find how tough it is as it spins around.

Saw cut edges should be deburred with a scraper to take away the sharp edges.

My company makes polycarbonate parts and we have gone through the expense of learning all the above. Sometimes before the parts were shipped sometimes after which was embarassing and expensive.