How to cut cornice with mitre saw?

Cutting cornice with a mitre saw allows for precise, professional-looking joints, ensuring your decorative trim fits perfectly against walls and ceilings. The key is accurate measurement and proper material support.

Essential Tools and Safety for Cornice Cutting

Before you begin, gather the necessary tools and prioritize safety:

• Mitre Saw: A compound mitre saw is ideal, as it can cut both bevel and mitre angles simultaneously.
• Measuring Tape: For accurate length measurements.
• Pencil: For marking cut lines.
• Bevel Protractor / Angle Finder: Crucial for measuring existing wall corner angles quickly.
• Safety Glasses: To protect your eyes from flying debris.
• Dust Mask: To avoid inhaling sawdust.
• Cornice Material: The actual trim you'll be cutting.
• Scrap Wood: For test cuts.
• Trimming Attachment and Adjustable Stop (Mitre Saw Accessories): These are vital for evenly supporting the cornice during sawing.

Understanding Cornice Angles and Positioning

Cornice mouldings are designed to sit at an angle between the wall and the ceiling, not flat. This unique positioning requires specific techniques when cutting.

For precise cuts, using a bevel protractor or angle finder is essential to measure the actual corner angles of your room quickly. This tool allows you to determine the exact angle, enabling you to cut the profiles along the line bisecting the corner angle, ensuring a seamless joint. "Bisecting the corner angle" means dividing the measured corner angle by two; this resulting value is the angle you'll set on your mitre saw for each piece of cornice. For example, a standard 90-degree corner requires each piece to be cut at 45 degrees.

Setting Up Your Mitre Saw for Cornice

Proper support is paramount for clean, accurate cuts. When sawing a cornice on a mitre, ensure that it is evenly supported. A trimming attachment and an adjustable stop are typically needed for this purpose. These accessories prevent the cornice from shifting during the cut, leading to a much more accurate result.

The most common method for positioning cornice on a mitre saw involves cutting it "upside down and backward." This means:

• The edge of the cornice that will touch the ceiling (the top) rests against the fence of the saw.
• The edge that will touch the wall (the bottom) rests against the saw's base.
• This method allows you to cut the moulding flat on the saw, using only the mitre angle, provided your saw has enough depth.

Step-by-Step Cornice Cutting Guide

Follow these steps for accurate cornice cuts:

1. Measure Your Corners

• Use your bevel protractor to find the exact angle of the wall corner you are working on. Wall corners are rarely perfectly 90 degrees.
• Divide the measured angle by two. This is the mitre angle you will set on your saw for each piece of cornice.

2. Position the Cornice on the Saw

• Place the cornice moulding on the saw using the "upside down and backward" method described above. Ensure it's firmly seated against both the fence and the base, simulating its installed position.
• Hold the material securely against the fence and base, or use clamps if available, especially when working with long pieces.

3. Set the Saw Angle

• Adjust your mitre saw to the calculated angle (half of your measured wall angle).
• The direction of the angle (left or right) will depend on whether you are cutting an inside or outside corner and which side of the corner piece you are cutting.

4. Make Test Cuts

• Always make a test cut on a scrap piece of cornice first. This allows you to verify your saw settings and positioning without wasting your actual material.
• Fit the test pieces together to ensure a tight, seamless joint. Adjust your saw settings slightly if needed.

5. Cut Your Cornice

• Once satisfied with your test cuts, carefully position your actual cornice piece.
• Hold the material firmly and make the cut slowly and steadily. Allow the blade to come to a complete stop before raising it.

Specific Corner Types

Understanding how to set your saw for inside versus outside corners is critical. The following table provides general guidance for common 90-degree wall corners:

Note: These are for standard 90-degree wall corners. For non-90-degree corners, always measure the exact angle and divide it by two.

Inside Corners

For an inside corner (where two walls meet inward), the cuts on the cornice pieces will meet to form a point that recesses into the corner.

• Left piece of cornice: Position the cornice (upside down and backward). Angle your mitre saw blade to the right (e.g., 45 degrees for a 90-degree wall corner). The longest point of the cut will be at the bottom (wall side) of the moulding.
• Right piece of cornice: Position the cornice. Angle your mitre saw blade to the left (e.g., 45 degrees). The longest point of the cut will also be at the bottom (wall side) of the moulding.

Outside Corners

For an outside corner (where two walls project outward), the cuts on the cornice pieces will meet to form a point that extends out from the wall.

• Left piece of cornice: Position the cornice (upside down and backward). Angle your mitre saw blade to the left (e.g., 45 degrees). The longest point of the cut will be at the top (ceiling side) of the moulding.
• Right piece of cornice: Position the cornice. Angle your mitre saw blade to the right (e.g., 45 degrees). The longest point of the cut will also be at the top (ceiling side) of the moulding.

Troubleshooting Common Issues

• Gaps in Joints: This usually indicates inaccurate angle measurements or incorrect saw settings. Re-measure the corner and make new test cuts. Small gaps can sometimes be filled with caulk.
• Splintering: Use a sharp blade designed for fine cuts. Lowering the blade slowly and supporting the material well can also help.
• Incorrect Lengths: Always measure twice and cut once. Account for the length of the angle cuts when measuring the overall piece length.

By following these guidelines and paying close attention to detail, you can achieve professional-quality cornice installation using your mitre saw.