Compound Miter (Crown Molding)
Saw settings to cut crown molding flat on the table.
Example
You enter
- Spring angle (deg, 38 or 45) 38
- Wall corner angle (deg, 90 square) 90
You get
- Miter angle (saw table) 31.62 deg
- Bevel angle (blade tilt) 33.86 deg
Checked against published worked examples from: Dave Osborne (daveosborne.com).
Details, formula, and sources
ScopeMiter (table) = atan(sin(spring) / tan(corner/2)) and bevel (blade tilt) = asin(cos(spring) x cos(corner/2)) from the molding spring angle (38 or 45 degrees) and the wall corner angle (90 for a square corner) (first-principles trigonometry; reproduces the standard compound-miter chart).
Formula or tableCrown cut flat on the saw: miter (table swing) = atan(sin(spring) / tan(corner/2)); bevel (blade tilt) = asin(cos(spring) x cos(corner/2)). Spring is the molding profile angle (38 or 45 deg), corner is the wall angle (90 deg square).
Source and editionCompound-miter geometry for crown molding cut flat - first-principles trigonometry; public domain. Reproduces the standard published compound-miter chart.
Free accessPure trigonometry, public; the spring angle and wall corner angle are user-supplied.
What governsEstimate. AHJ and licensed professional govern.
API field namesspring_angle_deg, corner_angle_deg, miter_angle_deg, bevel_angle_deg
- Cut flat the molding lies flat on the saw table (not sprung against the fence); the spring angle is the molding's installed angle from the wallcompound-miter geometry