garageFab.cc

Milling plywood was relatively easy. Plastic - a bit more difficult. First, I tried cutting shapes out of black 1/8" thick sheet of what turned out to be polyethylene, according to this plastic id table. I used the same high speed cutter as for plywood - Dremel #194, speed setting 4 and 0.03" depth passes at about 9 IPM. There was a lot of plastic swarf. Then I tried milling a 3/8" thick cutting board made from HDPE. The stuff started melting and forming blobs around the bit, even though I used recommended speed setting (4). After  experiments with speed and feedrate, and online research (good plastic milling info), I switched bits. I wanted to cut gears for RepRap extruder out of HDPE, so I got some small diameter bits on eBay to try. This is a used 1/16" tungsten carbide router bit. After I decreased tool speed to setting 2, reduced the pass depth to 0.02" and increased feedrate to about 12 IPM, the melting stopped. Here is a closeup of small 0.5"x0.5" (less tool diameter) cut out. Finish looks pretty good.