Mitre curve.


I have to replace the moulding on a door. The door has two quarter lites at the top, and these lites are curved. I am curious how to calculate the angle that the mitre would need to be.
Any ideas? Is there a rule of thumb?
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I am thinking it would still be a 45 degree miter where the curve meets the straight if the 1/4 lites are 1/4 circles. On a 1/4 circle the arc intersects the vertical or horizontal at a right angle.
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I tried that. It did not work.
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Ok then use a protractor to measure the complete angle of both sides where they meet. Cut your miter at 1/2 of that angle for both pieces for the miter to have a uniform fit at the union. Keep in mind however that you must hold the curved piece at the exact angle in relationship to the other piece when cutting.
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Angle finder.
Dave

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Pat When a curve meets a straight it is usually never a 45 degree If there is a formula I never heard of one
Do a simple full scale layout and then use and adustable triangle to get the angles
Good Luck, George

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I will assume that you have taken the joints in question apart. Use a miter gauge to measure the angle on the vertical stile with a try square clamped on the joint. You want the complementary angle [the actual angle of the new piece]. Use the miter gauge to set up your saw for the cuts. Try a piece of scrap & check the right angle before committing to the real operation. Bugs
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Pat wrote:

Think of a curve as being a large number of very short straight lines...
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If you have the old trim pieces you can use them to find the angle.
If you have new trim pieces and don't have the old ones you can hold the pieces on the door where they will be installed and make light pencil marks to find your angle. Hold one of the curved pieces up (where it will be installed) and put a light mark on the wall and jamb along the top and bottom edge of the piece approximately where the intersection will be. Then hold the straight piece (where it will be installed) letting it overlap your marks from the curved piece. Again, make a mark on both sides of the straight piece where it intersects your first set of lines. The intersections of your two lines will be the long and short points of your angle. Hold your pieces up again and transfer your marks (at the intersection) to your piece(s). Take the piece to your table saw or miter saw and find your angle buy using the marks. This will work for finding angles where curved pieces run into straight pieces or where two pieces of different witdths need to intersect.
Mike O.
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On 18 Dec 2005 17:45:47 -0800, with neither quill nor qualm, "Pat"

If you don't know the curvature OR the angles, how are you going to make moulding, Pat?!? Got a picture of it on your website? Are they domed, gothic, circular, or what? Symmetrical or asym?

Yes, the window's total angles have to add up to 360 (or 180, depending upon the formula used.) <bseg>
Perhaps a trip to your local bookstore or library might help. Look for "Circular Work in Carpentry and Joinery" by George Collings.
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Thanks for the book link. No chance of finding it in my book store.
The "windows" are symmetrical. The radius is 12 7/8. The "windows" make up a the top half of the circle. Using a protractor I figure the top angle is 74 degrees and the bottom angle is 85 degrees. I managed to get the wood bent (steamed) and cut but it is not a nice tight job. I would have liked to have done it better.
Thanks for the advice.
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On 20 Dec 2005 22:01:00 -0800, with neither quill nor qualm, "Pat"

Take some 120 grit sandpaper, fold it in half, and hold the mating pieces together to form the joint. A few strokes should mate them better than they were and tighten up the miter.

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