What are the angles for cutting crown molding flat?

Cutting crown molding at the proper angles is crucial for getting a clean, professional look. When installing crown molding, you want the bottom edge that meets the wall to be perfectly flat and level. This requires miter cuts at the correct angles. There are a few different angles to take into account depending on the specifics of your project.

What is Crown Molding?

Crown molding is decorative trim that is installed where a wall meets the ceiling. It is placed to cover the seam and transition between the vertical wall and horizontal ceiling. Crown molding adds visual interest, elegance, and style to a room.

Crown molding comes in different shapes and sizes. Some of the most common types include:

– Ogee – An S-shaped curve with one convex and one concave side. Ogee is a very popular traditional style.

– Dentil – Rectangular blocks set in a row, reminiscent of columns. Dentil molding has a classical look.

– Egg and dart – Decorative carved shapes of egg-like ovals and dart points. Adds ornate detail.

The profile refers to the molding’s cross-sectional shape when viewed from the end. The more elaborate the profile, the more complex the angles required for proper installation.

Why Cut Crown Molding Flat?

When installing crown molding, you want the bottom edge that will sit against the wall to be perfectly flat and smooth. This gives a clean finished look and allows the trim to sit flush to the wall.

If the bottom edge is uneven or angled, there will be unsightly gaps between the molding and wall. Molding that is not cut properly can also appear warped or misaligned.

Cutting crown molding flat requires carefully mitering the joints at precise angles. This miters the two pieces together to create a flat bottom edge.

The Angles Needed for Cutting Crown Molding Flat

There are several important angles to calculate when cutting crown molding flat:

Wall Angle

– This is the angle between the walls that the molding will join. Most standard interior walls meet at 90 degree corners. However, there may be exceptions for angled ceilings or other non-square corners.

Ceiling Angle

– The ceiling angle is the angle between the ceiling and the wall that molding is being installed on. In rooms with a flat ceiling, this angle is typically 90 degrees. For vaulted or angled ceilings, the ceiling angle will be something other than 90.

Molding Spring Angle

– The spring angle refers to the degree of curvature or angle on the back of the molding profile. More elaborate crown profiles have a more severe spring angle based on their shape. The spring angle ranges from 0 to 45 degrees typically.

Miter Saw Angle Settings

– With the three angles above figured, you can now determine the proper miter saw settings for cutting the crown molding flat on the bottom. The saw settings are based on simple trigonometry using the three key angles. Don’t worry, there are charts that tell you the ideal saw settings.

How to Determine the Molding Spring Angle

The molding spring angle must be measured to find the correct miter saw settings. Here is how to find the spring angle:

Step 1 – Lay a piece of the crown molding flat on its back side. Be sure it is sitting evenly.

Step 2 – Using an adjustable bevel square, align the stock flush against the bottom flat back side of the molding.

Step 3 – Adjust the blade of the bevel square until it rests cleanly against the angled top side of the molding profile.

Step 4 – Check the angle shown on the bevel square where the blade meets the stock. This is the spring angle of your crown molding.

Sometimes the spring angle is provided on the packaging or by the manufacturer. If not, use the steps above to measure it yourself.

Miter Saw Angle Formulas

Once you know the three key angles of the walls, ceiling, and molding profile, you can calculate the miter saw settings required to cut the molding flat on bottom.

Here are the formulas to determine miter saw angles:

Outside Corner

– Wall Angle + Ceiling Angle = Miter Angle

– Miter Angle – 90° = Bevel Angle

Inside Corner

– Wall Angle – Ceiling Angle = Miter Angle

– Miter Angle + Spring Angle = Bevel Angle

Don’t worry about memorizing these formulas. Charts are readily available to show the correct saw settings based on your three measured angles.

Miter and Bevel Saw Settings

Crown molding requires both miter (side-to-side) and bevel (up-and-down tilt) adjustments on a miter saw to cut the angles accurately.

Miter

The miter angle is the horizontal angle setting on the miter saw. It makes angled cuts to properly join together multiple pieces of trim.

Bevel

The bevel adjustment tilts the blade vertically, cutting an angle to form the top and bottom edges of the molding. Adjusting the bevel correctly is key for getting a flat bottom edge on your cut.

Set your saw to the proper miter and bevel angles according to the calculations above. Always do test cuts on scrap pieces first to dial-in the angles.

Crown Molding Angle Charts

For convenience, there are established crown molding angle charts that provide the precise miter and bevel settings for standard wall and ceiling angles.

Here is an example of a common crown molding angle chart:

Wall Angle	Ceiling Angle	Miter Angle	Bevel Angle
90°	90°	45° miter	33.9° bevel
90°	45° angled	31.6° miter	31.6° bevel
135° corner	90°	67.5° miter	22.5° bevel

These charts provide pre-calculated saw settings for standard ceiling height rooms and common crown profiles. Simply find the row matching your wall angle and ceiling angle.

For non-standard angles or molding profiles, you would need to use the formulas to calculate custom miter and bevel settings.

Tips for Cutting Crown Molding

Follow these best practices when cutting crown molding miters:

– Always do test cuts on scrap pieces first to verify your saw angles.

– Cut the molding upside down with the finished side facing down on the saw table. This allows the blade to cut the proper bevel angle on the backside.

– Use a miter saw with precise angle adjustment capabilities, not a manual miter box. A compound miter saw is ideal.

– Cut 1-2” longer than your measurements to allow for adjustments during installation.

– Use a fine tooth blade designed for trim work to cut cleanly.

– Sand cut edges lightly to remove burrs or rough edges.

Installing Crown Molding

Once the crown molding pieces are cut with proper miters and bevels, you are ready for installation. Follow these tips:

– Use a high quality construction adhesive on all joints. This strengthens the bond and improves alignment.

– Nail the molding at least every 16 inches, and wherever it meets a stud. This prevents sagging.

– Use a nail set to drive nails slightly below the wood surface. Fill holes with wood putty.

– For inside corners, cope the cut rather than mitering for best fit.

– For outside corners, miter the edges so they join at the corner.

– Use scrap piece cutoffs behind joints as shims and for extra nailing surfaces.

– Caulk along the top and bottom edges for a seamless look. Paint to match.

With care and some practice, you can achieve beautifulprofessional looking crown molding installations by cutting the joints flat on the saw. Using the proper crown molding angles is key for clean, tight-fitting joints.

Conclusion

The essential angles needed for cutting crown molding flat on bottom are the wall angle where it will be installed, the ceiling angle it transitions to, and the spring angle of the molding profile itself. By using the proper formulas or looking up the angles on reference charts, you can find the exact miter and bevel saw settings to make precision cuts. Remember to always test angles on scrap first before cutting your final pieces. Follow the rest of the tips provided above for handling, cutting, and installing the crown molding and you will have attractive, seamless results. With the right know-how on calculating the angles, you can gain expertise in flawlessly cutting crown molding flat yourself.