Crown Molding - Cope w/scarf Joint or Mitre? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 15 Old 11-08-2014, 01:38 PM Thread Starter
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Crown Molding - Cope w/scarf Joint or Mitre?

I know that the cope vs. mitre has been debated endlessly. However I am doing a coffered ceiling and building my own box beams. So I have 9 squares with no outside mitres, which means that in order to cope I either have to do a double cope, or a scarf joint. Neither of which I would look forward to. Plus that is a lot of cuts. I can cope just fine...did my kitchen recently, but there were a bunch of outside miters therefore I didn't have the double cope/scarf issue.

So I was thinking option B would be to mitre and glue the joints with Titebond. The box beams have plywood ribbing overlaid with MDF (see pics), either screwed together or nailed/glued. So I don't think there would be too much seasonal movement to pull the mitres open. There will be no crown joined to any wall sections, and the boxes all have square corners, and it will all be painted. This would also be the easiest/fastest option.

Option C I was thinking would be to do one mitre in an inconspicuous corner and then cope the rest. So a hybrid of A/B.

Looking for some input/advice on these options. What would you do?
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post #2 of 15 Old 11-08-2014, 09:39 PM
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When ever I do coffered ceilings. I build the crown squares on a work bench. You can miter them, glue and pin nail them from the back. Let the glue set up then lift I them into place and nail them to the beams.
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post #3 of 15 Old 11-09-2014, 12:19 AM Thread Starter
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When ever I do coffered ceilings. I build the crown squares on a work bench. You can miter them, glue and pin nail them from the back. Let the glue set up then lift I them into place and nail them to the beams.
Aha option D. Thank you...something else to think about. And now that you mention it I think I saw Gary Katz do this in FHB.

You would have to be pretty exacting in your measurements to do it this way, no? Not much room for error...
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post #4 of 15 Old 11-09-2014, 06:09 AM
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Yeah you have to be pretty accurate, but you can check your pieces before you nail the squares together. I use a bosch laser distance finder to get my inside measurements. I have done a lot of coffered ceilings and this is my preferred method.
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post #5 of 15 Old 11-10-2014, 10:23 PM Thread Starter
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Right...will take more time but I can still dry fit all the cuts, and then number them so I know what order they go together in. I'll try will one of the smaller squares and see how it goes.

Thanks - you have been most helpful.
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post #6 of 15 Old 11-11-2014, 04:59 PM
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Glad I could help, if you have any other questions or problems just ask.
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post #7 of 15 Old 11-12-2014, 07:12 PM
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Its seems like youve made up your mind but...

I fail to see how this is any different than trimming out a normal room. I would advise against trying to accurately build a square on a bench and then install. That seems like waaay more trouble than just measuring piece by piece, and less accurate.

As far as coping vs mitering, Ive never understood the bandwagon for coping. Mitering has always been the easiest and best way to cut trim, if you know how to do it.


Just my humble opinion...
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post #8 of 15 Old 11-12-2014, 08:45 PM
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Quote:
Originally Posted by ecr View Post
Yeah you have to be pretty accurate, but you can check your pieces before you nail the squares together. I use a bosch laser distance finder to get my inside measurements. I have done a lot of coffered ceilings and this is my preferred method.
I would love to see some pics of all the coffered ceilings you have done. I am sure we could all learn from you. PICS?
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post #9 of 15 Old 11-12-2014, 10:28 PM
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Fire65 I will try to find some pics I don't have a lot of trim pics I have more cabinet pics. I build my coffered ceilings with the Gary Katz method. It is simple and fast It consist of building t's you attach to the ceiling. I make these in the shop take them to the job site and install. Then you have the coffered ceiling layed out. Then you install the bottom 1x to the t's. Next you build the boxes on the work table and lift them into place. Then do the crown the same way. You can glue and nail everything from the back. For coffered ceilings this method has worked great for me rather than doing it one piece at a time. Gary has a article on this method it's worth reading just look up Gary Katz coffered ceiling.
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post #10 of 15 Old 11-15-2014, 08:38 AM Thread Starter
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Quote:
Originally Posted by Chamfer View Post
Its seems like youve made up your mind but...

I fail to see how this is any different than trimming out a normal room. I would advise against trying to accurately build a square on a bench and then install. That seems like waaay more trouble than just measuring piece by piece, and less accurate.

As far as coping vs mitering, Ive never understood the bandwagon for coping. Mitering has always been the easiest and best way to cut trim, if you know how to do it.


Just my humble opinion...
Haven't completely made up my mind but thought I would try to preassemble one and see how it goes. I do agree it would probably take more time at first, and I will probably need a helper to get the larger squares in place.

This is for my own house...I've spent a ton of time planning and building this project up to this point (the coffers are integrated into a fireplace mantle/wall of shelves and cabinets). Project has gone great so far so I don't want to mess it up now with a bunch of miters that open up seasonally. The benefit in pre-assembling is to be able to pin the corners from behind.

That said, if pre-asembling proves to be too difficult I may just do as you say and trim/ glue with simple miters. Beams are ply/MDF so seasonal movement shouldn't be too much of an issue. And I have a jig that bisects non-square corners...

Anyway...thanks for all your input guys.
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post #11 of 15 Old 01-17-2015, 06:45 PM
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I'm late to this party but I would strongly recommend preassembling. You can treat it as no different than any other room but beauty of coffered ceilings is that you don't have to.

I build on a table. All miters get glued, clamped with either Ulmia or Collins pinch clamps, and stitched with a pinner. I then straddle the back if the miter with an upholstery stapler kind of like a poor mans corrugated fastener. For obtuse angles I use HiPerf hot melt glue to hold them then pin and staple them when it sets. Frequently there is a panel that gets attached to the crown. This gets glue and stapled on at the bench as well. You have to measure accurately and then deduct 1/16" from your measurements on painted work and 1/32" on stained. The fit is still tight but the unit doesn't fight you at install when you do. Occasionally on stained work with these deductions I have to tune the back of the crown with a grinder and sanding wheel to get it in.

Every piece of moulding in the pictures below was preassembled and installed with the exception of the beam bottoms. On all three different ceilings pictured there were multiple build ups. On the hexagonal ceiling the light rail rimming but below the ceiling was built on the floor as well before install.

I usually install these alone. A cleat to catch one end of the assembly gets clamped onto the bottom edge of the box beam and I pivot it up from the other. On occasion I have used a drywall lift with stretchers clamped onto the arms. If there is a panel attached to the assembly I add large dabs of construction adhesive to the back before installing.

I preassemble any and everything I possibly can. By doing so I bypass many of the wall, ceiling, and drywall conditions that throw off the angles of pieces installed a piece at a time and get joinery that is more durable because it is reinforced with nails and glue with clamping pressure. It is far more efficient to it this way. I have encountered many skeptical carpenters over the years. Everyone will have a different way of doing things. They tend to change their tune when they see the finished product and the time it took to complete.
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post #12 of 15 Old 01-19-2015, 11:25 AM Thread Starter
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Thanks Justin.

As a follow up this is pretty much exactly what I did, after a couple of trial and error attempts.

Initially I had given up on the pee-assembly process. I was using my 18-guage nailer for more holding power, but it was blowing out chunks of mdf from the faces of the crown.

So I attempted one of the more inconspicuous squares with just simple miters/titebond. I got them to fit eventually but it took a long time with tons of back and forth to the saw. You would think that shorter pieces would be easier to fit, but the reverse is true. With longer pieces of mdf crown you can kind of spring them into place, but there is zero play with the shorter pieces so you have to be dead on.

So went back to the pre-assembly idea again. This time I used my 23-guage pinner, bought a set of Collins spring clamps, and invested (they are fairly cheap now - about $60) in a Bosch laser measurer. These three items I think are essential to do this job properly.

You would think that this would take more time but it doesn't in the end. Get the measurements right the 1st time (check each individual piece on the ceiling if you want), glue, clamp, nail, let dry - repeat. I fell into a bit a of a groove with it as I am working mostly in the evenings and I only bought 8 spring clamps (2 for each corner). Measure, cut, assemble - put it aside to dry and then up on the ladder to install the crown square that I had built the evening prior.

I'm a pre-assembly convert now - I think this is the only way to do this task well. The miters look super tight even before caulk/paint. Not that I'll be doing this again in the near future - just posting in case others have the same dilemma.

I'll post so more pics when it is painted. Justin your pics/work looks great.
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post #13 of 15 Old 01-19-2015, 07:46 PM
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The groove you mentioned and the reduction of footsteps are 2 reasons why I like building this way. The fact that you are assembling pre cut parts on a flat surface that is a comfortable height off the floor instead of climbing up and down a ladder doesn't hurt either.

It also decreases the amount of skill required to do the job. Skill is still a requirement, but the chances of error are reduced and as such the amount of rework assuming one can measure accurately. The best skill a carpenter can have is the ability to simplify a job into smaller more basic steps that require less skill and thought.

I'd agree that the pinner and Collins clamps are necessary. I use a distance meter on longer runs but for shorter runs I find slip sticks or measuring over an even number like 30" then measuring back to that mark and adding the 2 together just as fast and a bit more accurate. That being said I'm not sure that I could function solo on most of the jobs I do without a distance meter.

Post some painted pics. I'm interested in seeing it.
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post #14 of 15 Old 01-24-2015, 11:11 PM
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That's about the only situation where I miter inside corners with crown-inside a box. One big difference is we build the boxes on the ground, and then put them up with a couple of sheetrock lifts.

These are made from MDF and PowerGrab, with a few 23 ga. pins here and there, so no nail holes to have to sand, or craters. Bevels on panels are all separate pieces. A coat of primer on the ground, light sanding, and finish sprayed after everything is up.

Dimensions are about a couple of inches smaller than 4' wide the narrow way. Room is 16 x 22 with 10 foot ceiling. Coffers are 3 x 4 to cover the ceiling. It looks a lot better in person, than in the picture.

This was a first prototype that I put in our TV room. Since then, they've gotten a bit fancier. I've even had two architects, and an interior designer tell us they love it.

The MDF coffers were mounted to a plywood backer, which had flanges sticking out the sides, that were screwed to the ceiling joists. These fillers (too late, and too tired to remember what the proper name is) were nailed to strips, and coffers were fitted tight as each went up against the fillers. After this ceiling, we started dadoing, and they actually go up easier, and no handwork overhead before spraying.

No spiders were harmed in taking this picture.
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post #15 of 15 Old 01-28-2015, 10:22 PM
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