I would like to install crown moulding on an inside radius wall that forms a fairly shallow angle. Any tips on how to do this with stock moulding? This job is only paint grade, if that helps.
How tight is the radius? If it is not too tight, you should be able to form poplar crown around the inside. I would suggest that you try to complete the radius with a single piece so as not to interrupt the flow with a splice. The end of or beginning 12" won't conform as smoothly if you splice anywhere within the radius
There are two ways to come up with curved crown out of wood. One is to build up a block that conforms to the curve of the wall and profile the face at the appropriate angle.
The other way is to take existing straight crown and glue a triangular strip on the back of two pieces to create a solid triangular crown moulding (i.e., you are filling the air space behind the installed crown with wood). You then resaw approx 1/4" thick strips out of each blank, alternating the position of the saw kerf to get one complete moulding out of the two. It is very time consuming, and usually needs a lot of glue and nails to pull together during installation. This method has been documented numerous times in publication such as Fine Homebuilding.
Comment from contributor A:
I am a partner in a plantation shutter business where the issue of creating trim for arches and eyebrows on frame has come up constantly. Our solution was to use Flextrim as you describe. One hint is to start the bend around the radius of the arch at the middle of the piece cut. So, you start on one side, tack/adhere the piece to the frame to the end, then start tacking/adhering the piece from the center to the opposite edge. This seems to minimize the issue of compression/tension building up as you bend around the arc.