Crown moulding: Calculating miters

How to calculate the correct mitering angles in crown moulding installation. November 29, 2000

I am trying to cut crown moulding to fit into a 120 degree angle (corner of two walls). The moulding is a 38 degree type (not 45 degrees). How does one calculate the angles to cut the wood at, using a compound miter saw?

Forum Responses
I would place the moulding upside down on the miter saw, so the bottom edge of the moulding is against the fence. Using only the miter angle (no bevel), you can use the same angle as if it were a flat board. Be sure the small flat on the bottom of the moulding is flat against the fence.

If you are coping the joint, you'll use a 60 degree miter, otherwise a 30 degree on both pieces should be close.

It will help to leave the last piece loose for the last 2 or 3 feet so it can be adjusted to match the next piece.

Use the crown moulding software program that is available on this web site. The answer is a 20 degree miter, and 23 degree bevel. This will work on both the inside and outside walls of 120 degrees. Since your walls will not be perfect, you may need to fudge cut a little on the second piece.

Bosch makes a digital angle finder that is around $100 that is money well spent. Corners are rarely perfect and this allows you to place the angle finder in the corner and then gives a reading for both the miter and the bevel for a compound saw. We have one and it works great. Money well spent!