Crown Moulding - joinery - coping services...
Crown adds height to a room... How good are you at math? Let a local firefighter help out!

Coping or scribing is the woodworking technique of shaping the end of a moulding or frame component to fit the contours of an abutting member.

Coping is commonly used in the fitting of skirting and other mouldings in a room. It allows for clean joints between intersecting members when walls are not square to each other. The other method of fitting these mouldings that is commonly used is the mitre joint but this technique relies upon the walls being at 90° to each other for neat results. Coping is only ever used for internal corners. External corners are always mitred. See the math that is involved...

Angle calculations

The calculation of the angles to cut crown molding is affected by the angle that the plane of the molding makes with the walls. Crown molding is usually sold in either a 45 degree or 38 degree format, so correct angle determination should be made before attempting to cut the molding.

The formula used to calculate the angle to make the cuts in a spreadsheet is:

  • Cell 1 - slope a (in degrees!)
  • Cell 2 - \frac{A_{15}\times\pi}{180}
  • Cell 3 - slope b (in degrees) (note: slopes a and b will be the same when figuring crown molding)
  • Cell 4 - \frac{C_{15}\times\pi}{180}
  • Cell 5 - wall angle (in degrees)
  • Cell 6 - \frac{E_{15}\times\pi}{180}
  • Cell 7 - \arctan\left(\frac{\cos{B_{15}}\times\tan{D_{15}}+\sin{B_{15}}\times\cos{F_{15}}}{\sin{F_{15}}}\right)
  • Cell 8 - \frac{G_{15} \times 180}{\pi} = Miter Angle (in degrees)
  • Cell 9 - \arctan\left(\frac{\cos{D_{15}}\times\tan{B_{15}}+\sin{D_{15}}\times\cos{G_{15}}}{\sin{G_{15}}}\right)
  • Cell 10- 90-\frac{I_{15}\times180}{\pi} Bevel Angle in degrees