Replies

1. 
   Kyle | Nov 03, 2003 09:13pm | #1

   the easiest way that I know of would be to find someone with a cad program and have them draw you a 45 degree ellipse (ISO Circle) with a 8" Diameter. The could then print it out full scale on a piece of legal size paper. You can make a pattern out of this.

   I don't mind doing this for you, but you would have to know someone that has autocad to print it out.

   To make sure that it is accurate... the top of your pattern that is against the ceiling will be the diagonal of a 4" square, and the end of the pattern which will go in the corner will be of coarse 4".

1. 
   deasmhuin | Nov 04, 2003 02:04am | #5

   Not sure I understand your response.  Are you saying that the cut profile when the stock is flat is a section of an ellipse ?.  There are lots of geometrical techniques to draw an ellipse.

   I tried to analyze the situation with a paper model. If my cove element was planar then setting it at 45 deg to wall at a inside 90 corner, the standard formulas give me a mitre angle of 35.25 deg and a bevel angle of 30 deg (can ignore bevel on thin material).  My model checks out these angles. However, curving the paper clearly shows me that a straight line cut  on the flat stock does not give me the correct profile

1. 
   Timuhler | Nov 04, 2003 08:12am | #6

   I was talking about the curve you would have to lay out on a flat peice of metal or paper or drywall, that would give you the inside corner you want when you bend the paper (drywall) to the radius of the 1/4 circle.

2. 
   OneofmanyBobs | Nov 03, 2003 10:11pm | #2

   Back it up with Bondo to make a foot of rigid molding.  Cut on a chop saw just like any crown molding.  Put tape on the cut edge and trim to the miter edge.  Peel off tape.  There's your pattern.  If you do it by calculation, that would assume your molding matches your calculation.  If you do it by cutting, it will match what you actually build.

3. 
   Timuhler | Nov 04, 2003 12:44am | #3

   If I understand you correctly, you need the inside corner.  The outside corners wouldn't be bad to do.

   I built a cove ceiling last spring and I used roughly a 9" radius for the 1/4 circle.  That made the inside pieces 1/4 elliptical.  I did all the framing, but our trim guy did the 1/4 Masonite to finish it.  My suggestion was to staple tar paper up there and cut the corner, the remove the paper and spread it over the masonite and you would have the proper angle.  That worked really well.

   In your case, I'm not sure what to tell you.  Ken Drake knows how to do this.  I can't remember the name of the curve you need when the metal is flat so that when you bend it, it makes that "mitered" inside corner you need.  I think if I read the old archives right, the consensus was that this is a sine wave, but I'm not sure and I don't know how to plot it.

   I don't think the CAD thing would work unless you figured out the cut and then were able to flatten it out.

1. 
   marv | Nov 04, 2003 01:42am | #4

   I built a cove ceiling..

   WOWYou get out of life what you put into it......minus taxes.

   Marv

1. 
   Timuhler | Nov 04, 2003 08:14am | #7

   Thanks for contributing to this thread Marv.  It's nice to see you have so much to add :-) 

1. 
   FastEddie1 | Nov 04, 2003 03:34pm | #8

   What about running one section square to the wall and coping the other to fit?  That would require only one curved cut per corner.  Also, could you buy a section of pvc pipe of the correct dia, or maybe a sonotube, wrap it with tar paper, cut the pipe and unwrap a pattern?

   Do it right, or do it twice.

2. 
   marv | Nov 04, 2003 05:25pm | #9

   I was comenting on your ceiling work but it didn't come out that way.  What a great job.You get out of life what you put into it......minus taxes.

   Marv

1. 
   Timuhler | Nov 05, 2003 03:00am | #10

   Marv,

   I was just playing with you.  That is one thing about the net, you just can't tell what people's inflection would be. 

   I like to think I have a good sense of humor.  I thought for a moment that you might be someone I knew who was playing a joke on me ;-)  Wouldn't be the first time.

2. 
   deasmhuin | Nov 06, 2003 02:21am | #11

   Thanks to the responses received, I have found the answer to my original query.

   My cove is a quarter section of a cylinder. Two cylinders meet at an inside 90 deg corner by using a mitre angle of 45 deg and bevel angle of 0 deg.  I used a short length of 2" plumbing ABS to demonstrate.  Before cutting, I wrapped a sheet of paper around the pipe with one side aligned with the square end of the pipe.  After cutting, unrolling the paper reveals the desired profile. It is the sine curve

                                        y = r sin(x/r)   i.e amplitude r, period 2PIr

   where r = radius of cylinder

             x = axis along cylinder circumference

             y = axis perpendicular to x along cylinder length

   The math description is not neccessary to cut the cove stock. Using the technique described above with a cylinder of the correct radius, a template can be constructed that can then be used to cut a profile on the flat stock. Only 1/4 of the unrolled curve is applicable.  The orientation of the paper relative to the cylinder is important. One useful reference is to mark a a line (or 2 points) where the cylinder touches the table saw surface. Alternatively, the math formula could be used to draw a graph either manually or with a CAD package. As long as the radius matches the template and the corner is 90 deg, the cove should join perfectly.  The same template works equally well on outside 90 degree corners.

3. 
   Turtleneck | Nov 06, 2003 03:06am | #12

    y = r sin(x/r)   i.e amplitude r, period 2PIr

   Wow

   I was goinna say take a empty toilet roll, quarter it with pencil marks, and cut it on the chopsaw. You could cut it open and lay it flat to see what the template should look like. Turtleneck