I dont recall a formula, but there are charts out there that indicate which
angles to use for different crown moldings. Not all crowns fit against the
wall at the same angles, and not all wall corners are perfectly square in
the corners. Corners that are not square change both the cutting angle and
bevel. Most pro's have adopted clamping a temporary fence onto the saw
table that will hold the molding between it and the saws existing fence at
the angle that the molding will be mounted onto the wall. Then you simply
cut a "90" degree bevel at what ever angle you need to fit into or around a
square or non square corner.
I prefer to cut crown mldg. with the wall edge against the fence and
the ceiling edge to the table rather than flat on the table. However,
with the larger mldgs. it is necessary to do it flat on the saw.
Here's a site with a link that has that info ...
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