A Mostly Math-Free Method for Marking and Cutting Radius Trim

Marking and cutting radius trim can be tricky, and mistakes can be costly. This expert has a super simple method.

Marking parallel lines on template board | Construction Pro Tips
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How to mark and cut radius trim

I’ve never been good at math so when it is time to install eyebrow/radius casing trim, instead of reaching for a calculator, I just make a full- scale layout table. Drawing on a piece of MDF works best for me. Here is how I do it:

Step One: Draw parallel lines

First, I draw a set of parallel lines representing the inside and outside edges of the side casing trim. I space them the same width of my jamb opening plus an additional 1/2-inch to account for the two 1/4-inch reveals.

Marking where the radius trim will hit the casing | Construction Pro Tips
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Step Two: Make a pair of marks

Next, I make a pair of marks from the top edge of the MDF on the inside casing trim guide lines. Depending on the opening width anything from 6 to 12 inches will work.

Tracing the arc of the radius trim | Construction Pro Tips
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Step Three: Place curved trim onto layout

I place the curved trim molding on my layout with the inside edge hitting both marks that were just made. Then I draw a line where the inside and outside edges of the trim molding intersect the straight lines that represent the side casing.

Connecting the intersecting points with a straightedge | Construction Pro Tips
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Step Four: Draw a line with a straightedge

After moving the radius trim out of the way, I use a straight edge to draw a line through the intersecting points, and that becomes the cut line.

Transfer the cut line onto the radius trim | Construction Pro Tips
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Step Five: Transfer the cut line to the radius trim

From there I put the trim back on my layout table and transfer the cut line to the radius trim.

Trace the cut line onto the casing | Construction Pro Tips
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Step Six: Transfer the cut line to the side casing

This layout also allows me to transfer the cut lines to the side casing as well. Or I could transfer those angles with a sliding bevel gauge.

Checking the fit between the casing and the radius | Construction Pro Tips
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Step Seven: Check the miters

I always check the miters by laying the pieces back on the layout table. I run the side casing long until I’ve fine-tuned the miters and then cut the bottom ends to achieve the final length.

Watch the video below to see Gary explain this entire process.

 

Click here to learn more about installing window trim.

Author Biography

Gary Striegler

Gary began working with his father as a trim carpenter in 1972 at the age of 14. As the president of Craftsman Builders, Gary is still a hands-on builder. About half of his time is still spent on the job site creating the high end interiors that have become his trademark.

He is a frequent contributor to Fine Home Building Magazine and The Journal of Light Construction. Gary also enjoys teaching on subjects relating to home building. He has made presentations for The Woodworking Show, JLC Live Shows, Woodmaster Tools, Kreg Tools, DEWALT Tools, Grex Tools, and White River.