Laser Cutting Acrylic at 45 Degrees

I had an optical requirement to cut some acrylic at 45 degrees, as optical people know, total internal reflection can turn light 90 degrees within acrylic. My laser cutter would not do this "off the shelf" so I decided to make a mirror fixture to do this. Now I can make prisms and stuff.

By mounting a mirror at 22.5 degrees below the laser beam I could make the beam bounce at 45 degrees. People in the know said it would probably not work as the light would be focused and burn the mirror or I would get some optical distortion which would ruin the cut. I am pretty bad at taking advice and went ahead and built it anyway. Here is the fixture.


My calculations showed that the power hitting the mirror would be double what the mirror would normally see, so I set the power to 50% and the mirror looks perfect after a few cuts. When I get a spare mirror in stock I will try 100% power. The cut edge looks perfect too, the picture below doesn't do the edge any justice. It has a nice polished look all the way along. The top left of the "cut picture" almost shows the finish. Cutting 5mm acrylic took 50% power at 2% speed for a rough calibration.


On a safety note the laser points to the back of the machine so viewing is "reasonably safe" as the honey comb should eat most of the light, I still stand to the side when cutting as it is good practice. If you try this yourself, be careful and don't blame me if your cat sleeps on your laser cutter and catches on fire like one story I heard.

Now to sort out the registration and focusing for repeatable precision cutting. If you did want one of these I could be persuaded to build one for you. Right now it fits a Universal VLS6.60 laser cutting machine.

Here is what the 3D model looked like.


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