Plastics can suffer from stress due to the heat from machining or the application of force by tightening bolts or fixtures. If the plastic is melting as you drill or cut it you are adding a lot of stress to the plastic that will weaken it and may cause it to break later on. Sometimes it will crack from thermal shock, like pouring cold water on it on a hot day if it has internal stress (I won't go into how I know this :cry
. I have never tried to thermally stress releave it like heat treating steel.
The stress can be observed with a polarizer if the plastic is clear or tinted. Similar appearance to looking at car windshields with polarized sunglasses. Easily observed around the bolts in a plastic motorcycle windshield as they are over tightened.
I try to limit how much I tighten mechanical fasteners used in plastic parts. I make the holes a bit oversized, use rubber washers or gaskets when I can. If the plastic is clear I watch for stress lines as I tighten things down and back off when stress lines appear. I try to remember dimensions will change with temperature.
Just my experiences working with plastics (mostly Plexiglass ) over the years.
Bob
. I have never tried to thermally stress releave it like heat treating steel. The stress can be observed with a polarizer if the plastic is clear or tinted. Similar appearance to looking at car windshields with polarized sunglasses. Easily observed around the bolts in a plastic motorcycle windshield as they are over tightened.
I try to limit how much I tighten mechanical fasteners used in plastic parts. I make the holes a bit oversized, use rubber washers or gaskets when I can. If the plastic is clear I watch for stress lines as I tighten things down and back off when stress lines appear. I try to remember dimensions will change with temperature.
Just my experiences working with plastics (mostly Plexiglass ) over the years.
Bob
