Crown molding on vaulted ceiling - have the formulas, but getting the wrong angles - Car Audio | DiyMobileAudio.com | Car Stereo Forum

 02-13-2017 #1 DIYMA Novice Join Date: Jan 2013 Location: MI Posts: 317 Thanks: 0 Thanked 4 Times in 4 Posts Rep Power: 58 iTrader: (0) Crown molding on vaulted ceiling - have the formulas, but getting the wrong angles I'm trying to replace the cove molding around the hearth. As u can see from the pic, there should be a vertical molding running up the wall, a short horizontal piece running across the brick, and a longer piece running along the vaulted ceiling. I already got the angles for the vertical and short horizontal piece. But I'm having trouble making the correct angle for the short piece to vaulted ceiling corner. I found the formulas below on Rake Crown Moulding Miter Angles . The spring angle of the cove molding is 45°. I calculated the roof pitch angle as such: Height of south wall is 94”. Height of south side of hearth is 108.5”. Distance between them is 115”. So it’s 108.5-94=14.5”. Tangent is defined as opposite divided by adjacent, so that’s tan X = 14.5/115, and X = 7.18° Trigonometric Crown Angle Formulas for Vertical Plane Crown Molding Angles (cathedral/vaulted ceilings/rake gables) Crown Miter Angle = arctan (cos( Spring Angle) ÷ tan((180° - (Roof Pitch Angle * 2)) ÷ 2 )) And, just like math class, here is where I show my work: Crown Miter Angle = arctan (cos( Spring Angle) ÷ tan((180° - (Roof Pitch Angle * 2)) ÷ 2 )) Miter angle = arctan (cos 45°) ÷ tan((180°-(7.2° * 2)) ÷ 2)) Miter angle = arctan (0.70710678118654752440084436210485) ÷ tan((165.6) ÷ 2)) Miter angle = arctan (0.70710678118654752440084436210485) ÷ tan(82.8) Miter angle = arctan (0.70710678118654752440084436210485) ÷ 7.9158150883058268442674417219033 Miter angle = 35.264389682754654315377000330019 ÷ 7.9158150883058268442674417219033 Miter angle = 4.45° Crown Bevel Angle = arcsin (sin( Spring Angle ) * cos((180° - (Roof Pitch Angle * 2)) ÷ 2)) Bevel Angle = arcsin (sin( 45°) * cos((180° - (7.2° * 2)) ÷ 2)) Bevel Angle = arcsin (0.70710678118654752440084436210485) * cos((165.6)) ÷ 2)) Bevel Angle = arcsin (0.70710678118654752440084436210485) * cos(82.8)) Bevel Angle = arcsin (0.70710678118654752440084436210485 * 0.12533323356430424537311875981651) Bevel Angle = 5.08° A couple things I thought of: 1) Am I following the correct order of the parentheses? I went thru it several times and I think I am. 2) Do these formulas assume that the molding is laying flat or pushed up against the fence of the miter saw? Other formulas on the same page assume the molding is laying flat. I also tried pushing it against the fence, but that didn't work either. 3)The angle from the wall to the vaulted ceiling is technically 97.2°. So I tried that rather than 7.2°, but that didn't work either. By experimenting, it looks to me like a miter angle of 25° and a bevel of 30° is pretty close. And that is nowhere near the numbers I've got from any of the things I've tried w/ the formulas.

 02-13-2017 #2 DIYMA Novice Join Date: Jan 2013 Location: MI Posts: 317 Thanks: 0 Thanked 4 Times in 4 Posts Rep Power: 58 iTrader: (0) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle BTW, the original moldings were cut as if the ceiling was flat, and then they just caulked the hell out of them to fill the gap. I'm putting up stained moldings, so I can't get away w/ that!
 02-13-2017 #3 NCSQ Founding Member Join Date: Sep 2008 Location: NC (252) Posts: 2,119 Thanks: 52 Thanked 12 Times in 7 Posts Rep Power: 136 iTrader: (11) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle Could you try mathway to help you solve this problem??? https://www.mathway.com/Trigonometry I'm curious now but I have no helpful answers. I like building stuff. I'm not very good at it but I enjoy it. Last edited by Notloudenuf; 02-13-2017 at 11:32 AM..
 02-13-2017 #4 DIYMA Regular Join Date: Nov 2014 Location: TX Age: 65 Posts: 525 Thanks: 15 Thanked 33 Times in 26 Posts Rep Power: 47 iTrader: (2) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle Have you considered hand-coping rather than miter-saw cut joints? IMHO it's easier to get the angle and profile correct for each joint with a scribe and with minimal practice you'll get much better-fitting joints for the long-haul. Yeah, I'm olde skoole. 2014 Ford Escape ~ OEM SYNC Non-Sony 8" Touchscreen HU DSP & Amps by JBL MS series ~ Midrange & Tweeters by HAT Legatia ~ Midbass & Subs by SI TM/BM click here to download DIYMA JBL MS-8 Andy's Wisdom.pdf < the 'all meat' version of JBL's MS-8 processor!
02-13-2017   #5

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by FordEscape Have you considered hand-coping rather than miter-saw cut joints? IMHO it's easier to get the angle and profile correct for each joint with a scribe and with minimal practice you'll get much better-fitting joints for the long-haul. Yeah, I'm olde skoole.
I have been coping the inside corners for the base moldings, but this is for an outside corner.

02-13-2017   #6

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by Notloudenuf Could you try mathway to help you solve this problem??? https://www.mathway.com/Trigonometry I'm curious now but I have no helpful answers.
Mathway gave me the same answers. So at least it looks like I'm doing the parentheses in the right order. Maybe the formula is just wrong??

 02-13-2017 #7 DIYMA Regular Join Date: Feb 2011 Location: Jayhawk Land!!!! Age: 49 Posts: 795 Thanks: 0 Thanked 1 Time in 1 Post Rep Power: 87 iTrader: (30) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle Scraps, play with the miter until it fits if all else fails. 1994 Ford Thunderbird SC System - Alpine 7909, Helix DSP Pro, ADS MX Amps & ADS Speakers. On Going Build
02-13-2017   #8

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by syc0path Height of south wall is 94”. Height of south side of hearth is 108.5”. Distance between them is 115”. So it’s 108.5-94=14.5”. Tangent is defined as opposite divided by adjacent, so that’s tan X = 14.5/115, and X = 7.18°
Is the distance between the two measured level (parallel to the floor) or is it measured diagonally across the ceiling?

 02-13-2017 #9 DIYMA freshman Join Date: May 2013 Location: texas Posts: 9 Thanks: 0 Thanked 0 Times in 0 Posts Rep Power: 0 iTrader: (3) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle
02-13-2017   #10

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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That's only for flat ceilings, not the sloped cut that the OP has

 02-13-2017 #11 DIYMA freshman Join Date: Jul 2016 Location: NH, USA Posts: 31 Thanks: 0 Thanked 0 Times in 0 Posts Rep Power: 13 iTrader: (0) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle First you have to do a bong hit and it will all come together. Just like my sub box. Create a short piece 12" and another the length of that short return. Just use a normal outside corner 90 degrees-2-45's. With the long side going toward the peak slide until the bottom of the short piece hits the brick. (The ceiling looks like it is straight?) If it looks right redo it with the correct lengths.
02-14-2017   #12

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by BigAl205 Is the distance between the two measured level (parallel to the floor) or is it measured diagonally across the ceiling?
In this case here is the difference.
If its parallel to the floor the angle is the 7.1863 degrees that he came up with
If its measured diagonally (hypotenuse) the angle is 7.2435 degrees

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02-14-2017   #13

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Scraps, play with the miter until it fits if all else fails.
Yeah that's plan. Unfortunately, changing 1 angle also changes the fit of the other. So I can't just make a 90° corner and then change the bevel until I get the 7.2° pitch. Becuz as soon as I change the bevel, the 90° corner isn't 90° anymore. So it takes A LOT of trial and error. It took me about 30 cuts just to get in the ballpark (miter angle of 25° and a bevel of 30°)

Quote:
 Originally Posted by BigAl205 Is the distance between the two measured level (parallel to the floor) or is it measured diagonally across the ceiling?
I measured it parallel to the floor.

02-14-2017   #14

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by nhtunes Create a short piece 12" and another the length of that short return. Just use a normal outside corner 90 degrees-2-45's. With the long side going toward the peak slide until the bottom of the short piece hits the brick. (The ceiling looks like it is straight?) If it looks right redo it with the correct lengths.
Can't get away w/ that becuz the other side of the short piece is an inside 90° w/ the long vertical piece. So if I tilt the short piece up 7.2°, that will screw up the other corner.

 02-14-2017 #15 DIYMA freshman Join Date: Jul 2016 Location: NH, USA Posts: 31 Thanks: 0 Thanked 0 Times in 0 Posts Rep Power: 13 iTrader: (0) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle the other piece that creates the inside corner is a simple 90. you will have to be creative if you are going to cope into the wall and match the molding.
02-16-2017   #16

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by nhtunes the other piece that creates the inside corner is a simple 90. you will have to be creative if you are going to cope into the wall and match the molding.
So I think what u'r saying is that I should make the outside corner as a simple 90. Then I can tilt the short piece by 7° so the long piece will match the pitch of the ceiling.

This creates 2 problems, both of which can be solved:

1) the short piece will have a small gap where it should touch the ceiling (a gap that can be caulked).

2) The inside corner will be wrong, but that can be remade as a cope adjusted to account for the pitch of the ceiling.

In fact, I can set my miter to 7° to cut a scrap piece, and that will provide a good pattern for the cope.

This is a lot faster than the trial and error method!

 02-16-2017 #17 DIYMA freshman Join Date: Jul 2016 Location: NH, USA Posts: 31 Thanks: 0 Thanked 0 Times in 0 Posts Rep Power: 13 iTrader: (0) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle Get the top of the molding to fit the ceiling. The ceiling is the only continuous plane that will work. Ignore the angle of the brick, the molding will slide up to and hit at its bottom (you may have to back cut so it is a good fit) stare at the diagram I posted and it will come to you. I don't write well enough to explain.
 02-17-2017 #18 Shop Ratt Join Date: May 2013 Location: Cumming,GA Age: 51 Posts: 1,084 12V Company: Hybrid Audio/ Audiotec Fischer USA Position: Logistics Manager Thanks: 16 Thanked 6 Times in 6 Posts Rep Power: 62 iTrader: (25) Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle I owned a interior mill work company. Installed mill work work for 25 before retiring and working for Hybrid. Crown molding is stupid easy to cut. On a slide saw, miter box or over head radial arm saw the angles are marked on the bottom left right swing and on the back of the left right tilt. If you have conventional crown, ( home depot builder grade). The back is tilted to the 33.9 ( clearly marked ) and the bottom swing is 31. something I do not remember. The are also indented. These two numbers will turn a square 90 degree corner. For a the inside of a trey ceiling with 22.5 turns, the tilt and swing are 15 degrees . Also clearly marked and indented on the saw. Lay the crown down flat, with the bottom facing you. Do not bed it in the saw up side down and backwards. That is so 1960 to do that. You will not be able to make the transition from the rake of the ceiling to the out side corner. You will have to make a small turn first around the corner, then turn up the ceiling. Like exterior cornice is done. We also installed cornice on high end homes in Metro Atlanta. Example of transition. Below is pictures of what I was doing 10 years ago. We also have more recent pictures from a few years back, but they are really dark stained work and are very hard to see the cuts and angles. That would be the last image in the volley. Denon DCT-1 / Denon DSV-1 Helix DSP PRO MKII Brax MX4 >> Left channel L1ProR2, L3SE, L8SE Brax MX4 >> Right channel L1ProR2, L3SE, L8SE Brax MX2 >> C15SW-D2 Last edited by BlackHHR; 02-17-2017 at 12:12 PM..
02-18-2017   #19

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by BlackHHR I owned a interior mill work company. Installed mill work work for 25 before retiring and working for Hybrid. Crown molding is stupid easy to cut. On a slide saw, miter box or over head radial arm saw the angles are marked on the bottom left right swing and on the back of the left right tilt. If you have conventional crown, ( home depot builder grade). The back is tilted to the 33.9 ( clearly marked ) and the bottom swing is 31. something I do not remember. The are also indented. These two numbers will turn a square 90 degree corner. For a the inside of a trey ceiling with 22.5 turns, the tilt and swing are 15 degrees . Also clearly marked and indented on the saw. Lay the crown down flat, with the bottom facing you. Do not bed it in the saw up side down and backwards. That is so 1960 to do that. You will not be able to make the transition from the rake of the ceiling to the out side corner. You will have to make a small turn first around the corner, then turn up the ceiling. Like exterior cornice is done. We also installed cornice on high end homes in Metro Atlanta. Example of transition. Below is pictures of what I was doing 10 years ago. We also have more recent pictures from a few years back, but they are really dark stained work and are very hard to see the cuts and angles. That would be the last image in the volley.
Nice!

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02-20-2017   #20

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Re: Crown molding on vaulted ceiling - have the formulas, but getting the wrong angle

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 Originally Posted by BlackHHR You will not be able to make the transition from the rake of the ceiling to the out side corner. You will have to make a small turn first around the corner, then turn up the ceiling.
Honestly, I thought adding the transition piece was just a lazy way of doing it, and that if u had the right formula, u could calculate the correct angles to do it in a single joint.

But after your comment and some additional research, I realize it's not that simple. It can be done, but it involves ripping the molding that goes on the flat part of the ceiling to change the spring angle to account for the slope of the ceiling. I don't have the equipment, the skill, or the experience to do that.

So I'll trying coping the inside corner and tilting the short piece that runs along the side of the brick. Given that it's only a 7° angle, the gap at the top of the short molding should be pretty small. If I can't get that to work, I'll do the transition piece.

 02-21-2017 #21 DIYMA freshman Join Date: Aug 2008 Location: Macon, GA Posts: 50 Thanks: 0 Thanked 0 Times in 0 Posts Rep Power: 110 iTrader: (0) That man knows who Randall Brothers is. Also, mostly just grab some scrap, and play around, when I have been doing crown lately, I put little triangles in every so often and 2 where I land my joints.

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