Replies

1. 
   Guest_ | Apr 06, 2000 12:47am | #6

   *
   I do some archways now and then, but normally nothing over the 6ft/8ft range.
   I would like to know if anyone has any short ways of doing the layout, rather than the inch by inch method to play dot to dot on large ones. The one were doing now is 14'6" wide and at its highest point 86" with the outside at just over 6', between two sections of livingroom.Any suggestions would be nice to speed the day up? Thanks ahead of schedule.

1. 
   Guest_ | Mar 18, 2000 01:58pm | #1

   *Chris,what I usually do is this.Rip two pieces of plywood(osb)to 1 1/2" taller than the total arch and cut them to about 1/8" shorter than the rough opening they will go into.Lay them on the floor on top of one another and tack them together.Find the centerline of the piece and snap a line about as long as I think the radius might be running from the center towards where the floor will be once the arch is in place.Mark the total rise of the arch(in your case 14") from the bottom of tthe plywood at the center and put a nail there,also, put a nail at the outer lower corner of the plywood. Hook both nails with seperate taapes and pull your tape measures down the center line crossing them until you come up with the same number at thier intersection, that is your radius.On the biger arches you may want to double check this by pulling the number you come up with back down from the opposite bottom corner that you used to figure your radius.If it doesn"t match on your center line just arc from both corners twith the same number till they do. After it is cut just cut blocks that will go between the two layers of ply to make it the right thickness.This is why you make it 1 1/2" tall that way you can fit a full 2x4 block on edge at the very top of the arch.a little long winded but hope this helps.jim

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   Guest_ | Mar 18, 2000 03:51pm | #2

   *Chris... same technique as Jim.. with a twist..rip the blocking material so the total thickness of the plywood assembly is 3.5 " (or whatever the tickness of your framed wall)...then the rockers can extend their sheetrock /blueboard right past the opening and do a simple trim..another thing is the ARCH.. is typically an ELLIPSE..in which case i go out to the second floor on my shop and look at the diagram i have of how to strike an ellipse with a string line...only do it about once a year or so ... and that is the only place i've found where i don't lose the instructions..one of these days i'll really get organized...Kermit

1. 
   Guest_ | Mar 18, 2000 04:18pm | #3

   *Chris,To find the Radius for any circular arch, 1) Change the rough opening to inches and square it, 14' 6" = 174" 174 X 174 = 30,2762) Double the arch height and then square it, 2 X 14 = 28 28 X 28 = 7843) Add the result of 1) and 2), 30,276 + 784 = 31,0604) the Radius is the result in 3) divided by 8 times the arch height, 8 X 14 = 112 Radius = 31060/112 = 277.32 or 277 5/16" = 23' 1 5/16"This formula works for any situation where a circular arch is involved.

1. 
   Guest_ | Mar 18, 2000 11:29pm | #4

   *Chris,

   The equation R = ((((L/2)2)/H) + H) / 2 will give you the radius of any arch section. L is the length of the chord (or the length of an opening) and H is the maximum height above the chords midpoint.

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2. 
   jim_evers | Apr 05, 2000 07:22pm | #5

   *I'm trying to figure out your formula. Radius is used to construct a circle. How is the R you describe used to construct an ellipse?

3. 
   Guest_ | Apr 06, 2000 12:47am | #7

   *The formula's not for an elipse. It's for a circular segment.