I've seen the discussions on finding angles for cutting crown flat and for cutting it "upside down and backwards," etc.
However, these only take into consideration the walls being 90 degrees or something other than 90. What about when a room has a ceiling that rises/slopes with say, a 2.5 degree angle? Is there a formula that can take that into consideration?
I understand many would say that putting crown around a room like this would be a design error.
(Cabinet and Millwork Installation Forum)
From contributor A:
If I understand your theoretical room correctly, then it is indeed a design error. Not because of personal taste, but rather because you physically cannot make a right angle turn from a sloping crown to a horizontal plane crown. The result of making such a transition is that the horizontal crown needs to be a wider profile version of the slope side version. For example, if a 3 1/2" face crown is traveling down the sloped ceiling, the perpendicular wall with a horizontal crown will end up being in the neighborhood of a 4" face. Just picture trying to make that inside corner joint and you should be able to see this. The top edge of the crown in the horizontal plane will need to be pushed out from the wall further than normal since it has to meet up with the top edge of the sloped crown, which is rising up the wall as it moves away from the corner. Hence, a similar but larger profile is required.
This way it looks like it can be done and with the same size moulding all around.
In essence, it seems that the way to get around the problem of the end profiles being different lengths due to the ceiling slope or vault, is to make a very small third piece that fits in the corner. It comes off the wall with no slope as if the line of the adjoining wall was horizontal too. To make there be no gap at the top on the sloped ceiling, this small piece is cut to a point at the top where it meets the piece on the "normal" wall. Then, from this small piece, it is possible to join to the piece of crown on the sloped/vaulted ceiling.
Doubt I made that clear, but it's what it looks like in the pictures, and there are clearly still some angles to figure out.
Upon closer examination I'm coming to the following conclusion... I'd appreciate anyone who has examined this issue to submit their thoughts as well.
If coming down at an angle such as a roof rake edge and turning back 90 degrees so as to make an outside corner, I'm of the opinion that the profile of the horizontal moulding will be smaller than that of the rake edge moulding.
If coming down the ceiling edge of a vaulted ceiling and turning in o0 degrees so as to make an inside corner, I'm of the opinion that the profile of the horizontal moulding will be larger than that of the rake edge moulding.
We are starting a crown moulding in Bubinga that goes on the top of a compound curve top of a corner cabinet (curves out and up). It will be up to the shop that has sent this piece to us to make to miter the straight wall ceiling crown into the ends of this curved crown which is coming down at an angle much as a cathedral ceiling crown situation. I'm pretty confident that if they want to miter it they will have to make the wall crown a larger profile, or change the profile they want us to cut so that it is about 1/2" smaller.
Any other thoughts on this?
While the slope in this application is very visible when just looking at it in the room, I measure it to only be a couple of degrees. (I haven't tried to determine the slope in terms of rise/run). Therefore, I've imagined that the third piece in the corners for the above solutions would end up being extremely small, which made me wonder how I'd cut it.
Some day, hopefully soon, I'll get around to experimenting with this in my shop before I actually try to do it.
It seems like you'd want to install the angled walls first, cope or miter the horizontal runs as if there were no slopes and fit them to the angled pieces to determine their slightly altered position on the wall.
M is the miter angle
B is the bevel angle
Tan-1 is inverse tangent
M = Tan-1((Tan * (angle of wall) * (Sin * (angle of crown))
B =Tan-1(Sin * M) / (Tan * angle of crown)
Yes, it will work for vaulting areas!
Comment from contributor I:
Contributer H seemed to have a few deceprencies with his notation and a division by two missing. Also, I found the miter equation go be reversed but center about 90 degree wall angle. I believe I have properly corrected these errors. Note: If you do the calculations on a spread sheet, remember to convert to and from radian measure.
Miter: Normally a board is cut at 90 Degrees. The miter angle is the deviation from 90 degrees.
Bevel: Normally the saw blade is vertical when cutting. The bevel angle is the deviation from vertical.
C is the Angle of Crown Moulding leaning away from wall - Degrees
W is the Angle between walls - Degrees
M=ATAN(COT(W/2)*SIN(C)) This gives Miter Angle - Degrees
B=ATAN(SIN(M)/TAN(C)) This gives the Bevel Angle - Degrees
The equations for a Lotus 123 spreadsheet would be as below.
Row - Column
- F - G - H
2 - @PI/180 - Degrees to Radians
3 - C - Input - Angle of Crown Moulding leaning away from wall - Degrees
4 - W - Input - Angle between walls - Degrees
5 - M - @ATAN(@COT(G4*G2/2)*@SIN(G3*G2))/G2
6 - B - @ATAN(@SIN(G5*G2)/@TAN(G3*G2))/G2
Install the above into the spreadsheet at F2. Start with the blank box. Convert the text into equations and remove the "Input" words by inserting numbers.