Why did this crown moulding not fit?

Question

I'm assuming it's the mitre cut and not the coping. Mitre cut was with a hand saw and mitre box at 45 degrees. I'm also assuming the ceiling is 90 degrees to the walls and the walls are 90 degrees to each other. Why is this cut so way off?

Answer 1

First off it is not the best idea to assume that the walls and ceiling angles are all at 90 degrees. These should be measured so that you can make minor adjustments in the cuts if necessary.

The primary reason that the cut did fit is because the first piece of crown molding was not installed correctly. It was pushed too far flat toward the side wall in the direction shown by the green arrow in the following picture.

Answer 2

It is entirely possible that walls are not square. With dimensional trim like this you need a compound mitre. It's not just cutting flat at a 45 degrees, you also need a tilt, called bevel angle, that corresponds to the dimensional depth of the trim. Crown is one of the more challenging to get the right "tilt" on. Here is a youtube video that might help you understand:

Answer 3

The molding on the right appears to be pushed in at the top. This seems to be confirmed by the fact that the mitre on the left is gapping at the ceiling (indicating that the bottom of the right side is too low because the molding is pushed in at the top).

Answer 4

Michael Karas and others are spot on: the first piece was not installed at the right slope. What's the right slope? Here are some tips to establish that.

• Place a scrap of the crown on your miter saw, upside down, with the vertical and horizontal faces pressed tight to the fence and table. (That's how it would be cut for a cope.) Now trace the edges on your saw's fence and table. This will let you keep the molding in the same position with every cut.

• Measure the distance from the intersection of the saw's fence and table to one of the trace marks and note it somewhere. Transfer that dimension to your wall or ceiling, as is appropriate. However, deduct a bit from the actual dimension. This will allow you to cover your marks with the molding.

• When installing a piece into which a coped end will fit, leave the last few feet loose initially. This allows you to adjust its rotation when you fit your cope. After the coped piece is installed, fasten the first piece completely.

Walls and ceilings are rarely perfectly square. By using this technique and twisting the first piece as needed you can accommodate a substantial amount of imperfection in those surfaces. There's no need to resort to miters, which almost invariably open and look bad.

Answer 5

This is why we use miters for crown. In this case, you needed a test piece that was coped on the right side. You roll the crown moulding up and down with the test piece over it. When there is no gap, nail the right side. This assures the next piece will fit properly. In this case, the right side needed to be rolled upwards toward the ceiling and then nailed.

Answer 6

I've looked at the picture and in the right hand corner the crown is flat where it should be and the rest of the picture appears to represent a foot. You cannot twist flex a foot of this type of material.

I ran into this situation myself just this week. The gap in the top of the crown represents probably an inch. I coped my crown in the same situation where my crown was installed as it should be with no gaps on the ceiling or wall.

And my crown kept coming out like this in at least 1 corner in every room. This is a framer problem in my situation. If you have a corner out of plumb in or out you will get this result every time.

I've had to cut test pieces before coping my final piece to solve the out of plumb walls I was dealing with and even then you will have to use a good filler in the corners.