I've heard about companies that use some sort of oven to make radius casing and jambs from PVC or similar materials. Anyone know about doing this? I'm sure it could be a homemade deal, but I know there's a company out there that specializes in this.
(Architectural Woodworking Forum)
From contributor B:
When they extrude PVC, the melting temperature is about 330 +/-20 depending on application. So if you have a heat gun from Grainger, you can accomplish the radius. Make sure you heat a wide area and not just one spot. You will burn it. Also, try it out on a sample piece first. It will work but takes a little bit of time and patience to do it. If you have a form and clamps, you can heat and slowly bend it into place. The thickness of the PVC will also play an important part in the amount of time it will take.