After looking at the melting point of plastics, I realized that the plastic that I tried to cut, polystyrene, actually melts at temperatures ranging from 70 to 115 degree centigrade. This was very low indeed. No wonder it melted.
From the melting temperatures data, I decided to try to cut a piece of material taken from a plastic container which was previously used to store chemicals. I believed it was polyethylene. Low density polyethylene was supposed to have a melting point about 110 degree centigrade. If it turned out to be high density polyethylene, then the melting point could be up to 130 degree centigrade and if it were polypropylene, the material could be able to stand even up to 160 degree centigrade.
I just needed to test and see.
The milling operation followed the same program as the previous attempts. I had left the pause for cooling feature for additional air cooling of the tool and work piece.
This time the work piece did not melt. And none of the material got stuck on the tool bit. No water cooling was needed.
That was good! It meant I would not have to mess around with water and suffer any of its damaging effects on my machine.
There were some burrs on the cut surfaces of the plastic which I had to remove by some gentle filing. However, these types of burrs always occurred even when I tried to cut it with a hand saw. Other than that, the cut was satisfactory and was accurate.
The cut polyethylene was placed at the center hole of a sample cd and it fitted in position.
The pin point at its exact center was marked with ink and this would serve as the center point for my future engraving works on cd’s.