SketchUp Can Calculate Crown Miter Angles, Maybe Not Practical
Unless you are using a standard angle crown molding that matches you saw's presets, and you are only doing 45 degrees corners, calculating the correct angles for your crown is no walk in the park. This is why miter finding tools are so handy. But if you are a DIYer, you probably don't want to spend money on a tool you will probably only use once or twice. Good thing for you, with a little bit of work, Google SketchUp can calculate those angles for you. All you have to do is photograph the profile of the crown you will be using, trace it into SketchUp, work a little magic, and Shazam. It can be used to find both the miter angle and the bevel angle. This whole process might sound a bit tricky, but Matt Jackson over at FineHomebuilding has the whole thing documented on video. The video is in five parts, so head on over to FHB for the complete series.
Your other option is to use good old trigonometry. Good Luck. Though in today's world you can probably just find an app for your phone.
- X = arctan(cos(B) * tan(A/2)) for Miter Angle
- Y = arcsin(sin(B) * sin(A/2)) for Bevel Angle