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I’m remodeling a couple of rooms and coping the baseboard joints. For the most it’s going well, especially after getting new blades for the coping saw! The problem is the fireplace walls are not set at 90 degree angles, they are 122 degrees. So, if I am going to cope the joint, how I calculate which angle to make the miter cut? Is it as simple as 61 degrees, half of 122?

After a miter cut is made, what is angle for back cut with coping saw? For example, a 90 degree corner would be a 45 degree miter and then a back cut of just more than 90 degrees from the face of baseboard. What would it be for at 122 degrees?

Imager
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With mitre cuts you're nearly always going to bisect the angles*, so with 122° corners you will be aiming to mitre at 61°.

But you're going to have to do some test cuts anyway to ensure the saw is giving you exactly what you need once set to 61° — that setting on the saw is not a guarantee you'll get an angle that exactly matches the one measured by another tool!

Re. the coping cuts, you don't have to sweat a specific angle. Since you have to do this by hand and eye anyway just saw for a tight fit at the leading edge, that's all that is required.

*Occasionally for specific jobs you'll cut the two angles unevenly, but they will still sum to the same total.

Graphus
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