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Mitre every corner. We used to cope because we didn’t have compound mitre saws that could cut an inside mitre to within 1/64th of an inch. I’m on the North Shore of Long Island and all of my crown work gets painted. I have more problems with the edges of the crown shrinking and needing to be refilled than the mitres opening up. How much can wood shrink longitudinally as opposed to laterally? I work with crowns that have up to a nine inch face and the edges can really open up. (PS Throw away the “toys”, cut a couple of test pieces, get the saw set up, and start working. It is amazing how much time can be wasted fooling around with technology in a low tech industry.)
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Here in coastal NC we have to contend with high humidity
year round. After about two weeks of heat or AC there is
a good chance that your "big crown" is going to cup or bow
as it dries, which can cause your inside miter to open.
For that reason I always cope my big crown. If my cope is clean and tight my inside corner won't open up. I know that
there is an exception to every rule,but this is my experience.
To speed things up I cope my inside corners with a Bosch
jig saw, after 2 or 3 practice copes you can get pretty good at it. I remove as much wood as posible especially around
tight details. You can use your saw blade like a rasp to
remove any excess wood that might be left in the back of
your cope.
*I spent the better part of last Saturday installing crown molding in a small bedroom, 9' x 12' with an offset. The molding was not particularly wide, (about 4") but the job was a bitch! I tried to cope the joints as I have many times before, using all the woodworking skills I could muster, and wound up with an ill-fitting bunch of joints that will take far too much caulking. I might as well have mitered the joints with my trusty chainsaw. I have done far better work than this. Oh, the room and walls were not square, but isn't that the reason for the cope joint in the first place? I'm not planning on doing any more crown molding in the near future. By the way, about half the crown molding in my house was done by a professional cabinet maker. It is comforting to me to know that he didn't do so good either!!! Comments???
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There is a math solution for every combination of crown spring angle and corner angle, up to the point where it's just plain not practical. The solution for a 90° corner is familiar; that for an 88° corner is just a bit different. If you don't have the miter & bevel angles right (cutting crown on the flat -- if it's propped up you only neeed miter saw) the joint just won't work. The carving you do to MAKE it work is basically an irritating way of working towards the angles that should have been used in the first place. If the corner is irregular (wavy, curved, bumpy), as opposed to out-of-square, there is no satisfying result and the solution is to fix the corner by floating in some mud.
Mad Dog and I use the Bosch electronic angle-finder, which does the trig to provide the bevel/miter. I think it's a good teaching tool -- you can fiddle with it and see how changing the spring or corner angles affects the way the crown is cut.
I have a question: some suggest that wide crown moves so much across its width seasonally that this is the real problem, not whether you cope or miter. Now, I've seen lots of crown open up and break the caulk/pain because of this movement -- but if it were true that seasonal movement was the problem then these joints would open every year, and every round of caulk would be pointless. This isn't what happens, so the problem must instead be initial shrinkage of the framing or high-MC mouldings? Maybe the initial caulking should be skipped? Or does the problem come from elsewhere?
One nice thing about the cope is that it is easy to install under a bit of pressure, so there's a little give if the moulding retracts, and if a gap appears you'd have to near the wall to see it. You can also let the corner "float" a bit because it holds itself together. Not sure how to do this with a bevel.
Just some observations from the head-scratching front.
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Do it any way you want- the painters'll make it look good!
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What do you think of coping as opposed to mitering? I have always coped every corner that was possible to cope, but recently ran into some huge crown that was way easier to miter and shim the top to fit than trying to cope. Is there crown that should not be coped or was I not taking enough out of the back?
*If wood, I prefer to cope. Unless it has a bead that's more than a half-circle, like picture rail molding. Some large moldings can be difficult, if you're experienced in the field and were having trouble I'm sure you made the correct choice.You could get away with only miters if using a urethane-type molding. Some have proprietary adhesives that dissolve then cure/bond the two mitered pieces together. Results in a pretty strong joint.
*Whenever I choose to mitre inside corners of crown, I always precisely measure the inside corners of the walls I will be installing it on with a protractor, and setting my saw accordingly. This insures me of getting a good tight fitting mitre everytime no matter how much the corner may be out of square. MDM.
*Mad Dog should 'fess up that he has a high-tech electronic protractor by Bosch. I bought the same for this crown job, (see this regarding the photo formatting, which was the coolest thing I did with this job) and it IS a "toy" I think it saved me on average one or two trips to the saw for each joint -- the first cut was usually pretty close to the truth once I got used to it. For the open 135° angles I wouldn't have known where to start, 'cause the framing was a little vague. 1° makes a big difference! The Bosch will also accomodate spring angles other than the two common ones covered in the tables 52/38 and 45/45 -- handy it matching the next piece if you mess up and don't seat the crown right against the wall.To visualize the backcut, hold the reveal-cut crown in front of your eye at the spring and miter angle it will intersect the uncut piece -- any wood you see sticking out behind the surface profile has to be removed. Then understanding the backcut is easy. For 135° the backcuts were extraordinary and skinny rounded-over elements were difficult to avoid destroying. Still, I'm glad I coped ... the builder trimmed the rest of the house with miters and they're not aging well.How big is "really big crown"? This 5 1/4" WM-45 is the biggest one-piece around here.
*Andrew is correct. I do own a Bosch electronic protractor; however, I consider mine to be a tool of the trade instead of a "toy". Toys are something kids play with, tools are something I use to help me earn my living. MDM.
*Uh-oh, got the Dog's hackles up... I was being tongue in cheek, though I think the device is a little too high-tech for the task ... stilll, it seemed that a large protractor (2' or so) would have cost about $40, so the difference in cost was not so great. And it has a LEVEL vial in it! :)
*Hey Andrew, I'm going to resolve a conflict without a lawyer or court here. I was merely stating that I seriously use my Bosch Mitre Finder for a variety of jobs that come my way and feel that it has improved the accuracy of my work and has more than payed for itself in the time it has saved me. I'm sure you can admit to that also. As for being too high tech; I don't think it is. It's saving you a lot of calculating by telling what to set the mitre and bevel on your saw, something a large protractor won't do without calculations. And true, it does have a level in it. Just so you know, no offense taken here. MDM.
*Why the heck won't it remember the spring angle from one measurement to the next? I started wishing i had a (paper) table after a while, which I could get from Delta or a spreadsheet... Having a big protractor is handy.
*wood doctor,
Joseph FuscoView Image"Whenever, therefore, people are deceived and form opinions wide of the truth, it is clear that the error has slid into their minds through the medium of certain resemblance's to that truth." Socrates
*Hey Joe, Good to see ya back. What steps do you take to ensure a good fit when walls aren't exactly square? MDM.
*Hey Andrew, Something dosen't sound right here. The spring angle is the angle the moulding is sprung away from the wall. If you are using moulding coming from one supplier why would you have to measure the spring angle each time tou measure a corner? If I have a batch of crown that I have sent out by a supplier I measure the spring angle on a couple of pieces and usually it's pretty consistent for that batch. All you would have to do is in put 38 degrees each time if you were working with a amoulding that had that spring angle. Why would you have to write it down each time? MDM.
*Mitre every corner. We used to cope because we didn't have compound mitre saws that could cut an inside mitre to within 1/64th of an inch. I'm on the North Shore of Long Island and all of my crown work gets painted. I have more problems with the edges of the crown shrinking and needing to be refilled than the mitres opening up. How much can wood shrink longitudinally as opposed to laterally? I work with crowns that have up to a nine inch face and the edges can really open up. (PS Throw away the "toys", cut a couple of test pieces, get the saw set up, and start working. It is amazing how much time can be wasted fooling around with technology in a low tech industry.)
*No, I meant why can't the darn thing "remember" the 38 degrees from mind-numbing joint to joint on the same job. No writing.
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Ha! They don't call the 99¢ stuff "painter's caulk" for nothing!