Coping Wide Inside Angles on Crown Moulding

Advice on how to cope joints for open angles. August 31, 2009

I have a 45 degree corner that is getting crown treatment. I don't want to miter it, and can't figure out the angle for the coping cut and how the flat cut meets the wall. Any takers on this one?

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor L:
Nest it in the miter saw like you would to cut an inside corner. Cut the molding. The profile line that the saw leaves is the line you follow with your coping saw.

From contributor B:
Are you talking about a bay window? Is the angle really 135 degrees? That would be a 22.5 miter with the crown upside down and sitting in its sprung position in the miter saw. The cut you need for the cope is the same as for a mitered corner. The other piece will be like an outside miter so it will fit to the wall.

From Gary Katz, forum technical advisor:
Ditto. That's a 67 1/2 degree miter - 22 1/2 is what it might say on your saw, but it's an obtuse angle and because of that, the cope has to be backcut more than a 90 degree inside corner. David Collins uses a nifty rotating jig for coping those corners - that allows you to turn the crown to the angle of the cope, so the blade on your saw can be held plumb - which is the easiest way to cut a cope without wasting energy on over-backcutting. But even then, you need a really long blade, and a lot of patience. For short runs, I miter them, pre-assemble the corners with nails and glue, and call it a day. And most of the time, those are short runs in octagon ceilings and stuff.

From contributor C:
What is it about this corner that it needs to be coped?

From the original questioner:
Thanks all... Gary, your answer regarding the steepness of the backcut was what I was looking for. On my mockups I was cutting the coped just like a standard inside corner (at 22.5 instead of 45) and coping away and getting really crappy results. Did get around to almost cutting what seemed to be the entire back off to get a good fit, but that just seemed odd to me.

Just wanted to make sure I wasn't missing something or doing something wrong. And without starting the never ending debate about coping v. mitering... I always cope inside corners, always! That's just how I roll... Thanks to all for the time and sharing of knowledge.

From contributor B:
You can also create clearance on the piece you are coping into. Just mark where the cope will fit and jigsaw most of the material away from that line back towards the wall, leaving the very bottom intact.