Compound Miter Formulas
Miter Angle: atan( sin(Spring Angle) ÷ tan(Half Corner) ) × 180 ÷ π
Bevel Angle: asin( cos(Spring Angle) × cos(Half Corner) ) × 180 ÷ π
Note: These are standard compound miter formulas for crown moulding. Spring angle is measured from the wall. Always test cuts on scrap material first.
Compound Miter Calculator — Crown Moulding Angles
Crown moulding installation accounts for over $180 million in Australian finishing trades annually (IBISWorld, 2024). The challenge is that crown moulding sits at an angle between wall and ceiling, requiring compound cuts — both a miter and a bevel. Get either angle wrong and gaps appear at the joint.
Common Crown Moulding Angles (90° Wall Corner)
| Spring Angle | Miter Angle | Bevel Angle | Use |
|---|---|---|---|
| 38° | 31.6° | 33.9° | Most common |
| 45° | 35.3° | 30.0° | Easy calculation |
| 52° | 38.6° | 26.0° | Traditional style |
The Compound Miter Formulas
For spring angle S and wall corner angle C:
- Miter Angle = arctan(sin(S) × tan(C/2))
- Bevel Angle = arcsin(cos(S) × sin(C/2))
For 90° corner with 38° spring: Miter = arctan(0.6157 × 1) = 31.6°. Bevel = arcsin(0.788 × 0.707) = 33.9°.
Frequently Asked Questions
What is a compound miter cut?
A compound miter involves two angles simultaneously: a miter (blade rotation) and a bevel (blade tilt). Required when moulding sits at an angle to both wall and ceiling.
What is the spring angle on crown moulding?
The spring angle is the angle between the back of the crown and the wall. Common angles are 38° (most modern), 45°, and 52° (traditional).
Can I cut crown moulding without a bevel?
Yes, using the nested (upside down) method. Place crown against the saw fence at its spring angle, then make a simple miter cut at half the wall corner angle.
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