I’ve learned quite a bit over the years, and one of the things I’ve certainly learned is not to look at the Tg (glass transition) temperature of plastics when determining how safe they are to use for structural components, especially those exposed to heat. When looking at the datasheets for materials, you want to look at the 1.8MPa value, as that’s close to what a tightened screw would exert on plastic.
Not included in the information: PLA, which has a heat deflection temperature of 60C. But PLA can achieve heat deflection temperatures up to 160C when mixed with a nucleating agent and then annealed, allowing crystallization. http://www.matweb.com/reference/deflection-temperature.aspx
…assuming a tightened screw creates the highest load on the component being designed. Even if you stay below that temperature, there is still some deflection. An no mention of accelerated creep. I got bit by this at work. The solution was replacement with aluminum, so I was never forced to really understand how to properly select plastics for elevated temperatures. I definitely remember that staying under the deflection temperature wasn’t good enough. The Cast PU parts definitely warped under load.
You can also add washers to both sides of a thru hole to spread the load, it will increase the compression area from the area under the screw head flange, to the area under the washer. Also allows you to cantilever a pulley off of a fastener… within reason of course, as what would have been bearing stress on the thru hole walls, is now compression force under the washer, I’m realizing a picture is worth a thousand words right now.