Crown sits at an angle to the wall, so a corner needs a compound cut. Cut it like flat trim and every joint opens on the outside no matter how carefully you measured.
Spring angle is a property of the profile, not a choice. If the label is gone, set an offcut into a square corner and measure the angle off the wall.
Waste runs higher than most trim because every corner consumes a compound offcut that cannot be used anywhere else.
Flat trim lies in one plane, so a corner is a simple miter. Crown does not — it sits sprung away from the wall, touching wall and ceiling and floating in between.
That means the joint between two pieces is a cut through a piece of wood held at an angle in two directions at once. The saw needs a miter setting and a bevel setting, and neither one is 45 degrees.
Cut it as a simple 45 and the joint opens at the front edge, which is exactly where it shows.
| Spring | Also called | Miter | Bevel |
|---|---|---|---|
| 38° | 52/38 | 31.62° | 33.86° |
| 45° | 45/45 | 35.26° | 30.00° |
Those are for a square corner, cutting flat on the saw table. The 38° profile is by far the most common in North America, which is why 31.6 and 33.9 are the two numbers finish carpenters know by heart.
Nested holds the moulding against the fence at its installed angle, so the cut is a simple miter with no bevel at all. It is faster, harder to get wrong, and only works if the crown fits between fence and table on your saw.
Flat lays the moulding on the table and uses both settings. Necessary for wide crown, and the reason compound saws exist.
Whichever you use, mark which edge goes to the ceiling before every cut. Getting a piece upside down is the most common crown mistake and the offcut is never salvageable.
A mitered inside corner depends on the wall being exactly square. It never is. As the joint moves with humidity it opens, and it opens at the front.
A coped joint has one piece cut square into the corner and the other scribed to its profile. It tolerates an out-of-square wall, it closes rather than opens with seasonal movement, and it is what finish carpenters do on inside corners. Outside corners still get mitered.
Set an offcut into a square corner the way it will be installed and measure the angle between the back of the moulding and the wall. Or measure how far it projects down the wall and out along the ceiling — equal projections mean 45°.
Because every corner produces a compound offcut with two angles on it that fits nowhere else. Twelve percent is a working figure, more in a room with many corners.
Only for flat cutting. Nesting on a plain miter saw works for anything that fits.