Accurate Cutting and Coping for Crown Moulding
Fine points of cutting crown moulding for installers. June 16, 2010
Question
I can cope well when I’m doing flat bottom millwork like base or shoe molding, but I'm having problems with crown. I cope it the same way that I’ve seen on shows and read about, but the cope always seems to be off when I put it on the wall even though the cope is spot on the mark where I cut it. I think it’s a problem with the walls not being square, the ceiling wandering, or I may be missing the right angle when I cut my reference 45 degree even though I use a stop block to set the angle on the miter saw. Any ideas on how to get over this?
Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor B:
It could be that the angle of the wall to ceiling is not the same as the way you are holding the crown to cut it. I am assuming you hold it upside down and cut it with a miter saw. Maybe the angle that it is sitting on the saw is not the same and the angle that it sits against the wall and the ceiling. I would look at that.
From contributor B:
Make sure you're coping enough material off the back and not getting some interference when assembling it. I always seem to need to cut away extra in some spots after coping.
From contributor G:
Roll your crown until it fits correctly. Don't go by a measured line on the wall. Is it back cut enough so there is no interference?
From the original questioner:
To answer the questions, I do cut it upside down on the saw and have taken to trimming way more off the backside than necessary. I can usually roll it to where it fits well but I can't nail it like that. I can't figure out how to correct the original cut so I can match all pieces the same. I've always tried to keep the flat surfaces on the top and bottom of the trim, flat against the saw and the wall but if the wall angle is off, I can figure out what correction to make to the way I hold it on the saw. I was thinking of snapping a line “x” inches down from the ceiling on the wall and using that same measurement on the saw.
From contributor G:
If the wall you are putting the crown on is out by more than three degrees you may have to compensate for that when you cut the inside miter to get your cope line.
From contributor A:
Another thing to watch out for is the position of the crown when you do your cope cut on the chop saw. Most crown moulding is made to be off a couple of degrees out of square. So make sure the correct edge is sitting flat on the chop saw (typically the fence). Crown stops help with this problem as long as you set them up correctly.
From contributor J:
When you say upside down do you guys mean bottom of the crown against the fence and top of the crown on the saw top? If yes, why don’t you try cutting your crown flat, back on the saw top, on the chop saw? Assuming you have a compound miter saw there should be stops or markings at 31.62 on the table and 33.xx on the compound. That way you’re not trying to keep the crown from moving when you cut it, 1000 times easier and perfect 45 every time. You should also leave the last three feet of the piece you are coping into loose until the coped piece goes up, that way you can roll them both until they are perfect. That sounds like the problem to me. A coped joint will always look good regardless if the walls and or ceilings are not perfectly square, unless you are not back cutting enough.
From contributor R:
Contributor J is way right about cutting crown flat on the saw. If you don't know what we are talking about look at your saw's manual. If you don't have the manual Google until you find a PDF manual and it will explain. I wonder if the coping problem is the horizontal spots in the crown profile? You know how you can have a severe back-cut on all the vertical spots in the profile, but if the horizontals aren't scooped out, it won't lay right? I've shown this to many people learning to cope on-site, but I can't think of how to explain it right now.
From Gary Katz, forum technical advisor:
Before you start cutting on the flat and adding all the hassle of knowing the exact spring angle of the crown, the exact corner, miter and bevel angles, worrying about whether the back of the crown is cupped (it almost always is), having to learn how to keep the measurement mark out when you're making the final measurement cut - figure out why what you're doing isn't working. Cutting in-position, which is what you're doing is the fastest and most accurate way to cut crown as long as the crown isn't too big and your saw can cut it standing up.
A coped crown joint will work even if the corner is out almost three degrees. That may not sound like much, but three degrees in 8 feet is 4 7/8 inches! I bet your corner isn't out that much! If you can take a quick picture or two of what you're doing, that would help solve the problem. Cutting, coping, and installing crown is a gas if it works and if you're not working hard to do it.
From contributor R:
I'm not sure how tweaking the saw angles is that much more difficult on the flat but I would encourage anyone to do whatever they are most comfortable with as long as it's proven productive enough for them. If you are going to continue cutting crown standing (or in position) I would suggest two things:
1. Make a jig or clamp a stop parallel to the fence that holds the crown in the same position each time you cut. Just drawing a line on the deck is rarely accurate enough in my experience, nor is just sighting that the foot of the crown is flat on the fence.
2. Always make sure the foot of the crown is flat against the fence, and don't worry about top of the crown on the deck of the saw.
Crown by design (or by cupping) isn't often square. By this I mean that if you place the foot of the crown on the wall flat, the top of the crown isn't laying flat on the ceiling. Only the leading edge visible from the outside is touching the ceiling.
From Gary Katz, forum technical advisor:
Contributor R is right about getting the crown positioned correctly against your fence, but making sure it stays there is more important that the precise spring angle (the angle along the back of the crown from the fence to the base of your saw - which is the ceiling). In fact, you can change the spring angle a little without impacting the appearance of the crown. I do it all the time when I'm running crown in a kitchen and the ceilings aren't parallel with the tops of the cabinet doors. But you have to make sure that the crown is positioned at exactly the same spring angle for both pieces that fit together in a corner. The best way to ensure that the crown doesn't move while you're cutting it is with a continuous crown stop. Use one of those and you'll have only minor problems fitting your corners.
From contributor B:
When cutting in position, that crown stop should be set exactly the ceiling projection away from the fence. Measure the ceiling projection of your crown with a framing square and set the stop. You can check to make sure the miter cut is correct buy measuring it. With a framing square check the offset from the long point of the miter to the short point. That distance must equal the ceiling projection. Leave the piece you are coping into loose and let the coped piece dictate its position.
