Mitering Arched Door Top Casing to Straight Side Casing

For profiled casings, the only way to achieve a perfect fit is with a curved joint. January 25, 2010

I have never mitered an arched piece of casing. Is there any information that could be passed along to me that would help?

Forum Responses
(Architectural Woodworking Forum)
From contributor V:
I believe arched casing on the head of an opening is usually butt joined (90 degrees) to the straight legs.

From the original questioner:
I just drew it on Delta cad and it comes out to be 18 degrees. On the straight that's fine it's on the ends of the arch. There has to be a productive and fool proof way of doing this.

From contributor C:
Place the arch casing up where it goes, then trace inside and outside of the casing putting marks on the wall and jamb about where it meets the straight casing. Then place the straight casing in its position and mark them. Now you know where the two pieces intersect. Put the arc piece back up and mark the intersection points on the casing, then take to saw and align the blade with your marks on the casing, then after you get one side correct do the same for the other. Then cut the straight pieces to fit, and the sand the joint.

From Gary Katz, forum technical advisor:
Ditto contributor C. You'll find that casings with good details on narrow doors will not align perfectly. That's because you can't really miter arched casing perfectly to straight casing, so some carving/fiddling is usually required. To do it perfectly you have to cut a hunting miter.

From contributor A:
Gary's "hunting miter" refers to the numerous detail/profile intersections that occur when the straight flow into the curved section. If you connect the various intersections it is typically a curved intersection not straight a straight line/cut like regular miters. This is shown in really good books on curved mouldings or handrailing. Like Gary said, fudge it and carve the difference.

From contributor H:
Contributor A has this right. A true miter or an arch top (eyebrow) casing to a straight side leg is not a straight cut but rather a curved cut. You can see this for yourself if you draw the profile CAD. Draw the eyebrow piece and the vertical side leg. Intersect them as they would intersect on the wall. To simulate the miter cut connect each high point of the profile at the intersection of the curve and the straight. You will find that this shows you will have a curved cut for the miter joint. For narrow simple profiles the curve does not vary enough from a straight line to make a difference. On wide and complex profiles though there is a significant difference.