Replies

1. 
   matsmat | May 10, 2010 01:13am | #1

   Yes. Nice and simple, and the easiest way to solve it. But if you haven't ordered the LVL and the supplier doesn't have one in stock, i.e., it has to be manufactured you may have to wait a while (1-2 weeks) before it comes in. So, if your walls are 9 or 10' and you need an OSB archway under your garage header right now look in: Fine Homebuilding #204, tips and techniques, page 20. You are not looking for a true section of a perfect circle, you need an ellipse. An old carpenter taught me this trick years ago but this article explains it effortlessly. For simplicity, I include another nail, call it "E" and snap a perfect rectangle on the plywood. Set the skill saw about 3/16" deep to make the cut and pass through it three times... you can actually make a 16" circle with a skill saw if you have to. Would someone help me out and tell me how to seperate paragraphs on this platform?

1. 
   calvin | May 10, 2010 06:15am | #2

   how to seperate paragraphs on this platform?

   Hit the ENTER key.

1. 
   matsmat | May 10, 2010 06:27pm | #4

   ??
   I tried that, lol.

   Test 1,2,3.

   Maybe it will work for me this time, calvin.

1. 
   calvin | May 10, 2010 08:24pm | #6

   Well, did you try it?

   I now will hit ENTER

   and this is what I get..................

   See how easy it is?

   There was a double ENTER.

   Now, I hit the source button. I didn't get a double space here, did I? Nor here neither. I double hit the ENTER bar here. Maybe you're hooked up into the HTML thing-of which I know little about

   except that here I used the backslash p otherslash

2. 
   DanH | May 10, 2010 07:50am | #3

   Note that you either want a cycloid or an elipse.  An elipse you make with the two nails and a loop of string, per the article. 

   A cycloid you make with the same nails and string, only you put the nails in at the ends of the arch and let the string hang down.  Draw the curve of the string against a vertical surface, then flip it 180 degrees

1. 
   matsmat | May 10, 2010 06:29pm | #5

   Hi
   DanH, hello.

   I would be interested in the details of the cycloid. I'm always interested in new tips :)

3. 
   sapwood | May 10, 2010 09:52pm | #7

   Batten down...

   In lieu of the string, you can use a flexible batten to draw a curve. Actually you use the batten to define the curve and use a pencil to do the actual drawing. Employ nails, clamps, chewing gum, the kid next door, etc to hold the batten into position while you pencil the line. 

1. 
   DanH | May 10, 2010 10:00pm | #8

   If you use a batten (or, eg, strip of spring steel) you get a "sine generated curve".  This has the advantage that you can constrain the ends to achieve rounded corners if you wish (if the strip of whatever is springy enough).

4. 
   Silviphile | May 11, 2010 06:24pm | #9

   arcs, ellipses & parabolas

   DanH,

   You are describing an approximation of a parabola. In order to mark it, try just spraying over your string or chain with a paint that contrasts the background.

   But If you just want an approximation -right side up- you can use an old boatbuilders trick for cambering a deck.

   Get two boards that are straight and longer than your span. (1X6X16 would do in this case of a 12' span.) Put a nail at each end and at the apex. Lap both boards at the apex and fasten together. Remove the center nail and use a pencil held there to trace the arc as you slide the rig from one side to the other. 

1. 
   DanH | May 11, 2010 08:25pm | #11

   Well, actually no, I wasn't describing an approximation to a parabola -- if I'd wanted to describe a parabola I'd have described an exact technique, using a string, a square, and a straightedge.  But I confess that I wasn't describing a cycloid either -- I was describing a catenary.  Right concept, wrong term.  The catenary is the ideal shape of an architectural arch.

5. 
   Joe | May 11, 2010 08:15pm | #10

   This might help.

   If you want to layout a big arc: http://www.josephfusco.org/Articles/Big_Arcs/big_arcs.html

   If you want to layout a big ellipse : http://www.josephfusco.org/Tips/Big%20Ellipses.html