I learned the hard way that it's a bad idea to do intricate drilling in acrylic with a drill stop on your bit. The nearest I can figure, the plastic spirals being dug out of the cube through the flutes climbed up into the flute space between the bit and the stop, and then bunched up. The next bits of acrylic ejecta to climb the flutes escaped outward from the flutes, below the stop, via centrifugal force, but remained connected at top and bottom, creating a sort of spinneret of warm plastic that bunched up ever more, spiraling around the bit and creating a chamfer between the bit and stop, which acted like a hot plastic cone digging into the acrylic cube. It was really hard to crack the cone of acrylic off the bit here. I had to use pliers. It had melted and refused into shape. This all happened within seconds on the drill press - too fast to notice what was going on.
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