Hi everyone,

I have been given some specific radius's for some curves to be cut in some beams. For example, Arch between the dining and living room is 20'-0" radius with a 3/4" notch from the underside.
What I am wondering, is there a simple way to lay this out? The only thing I can think of is to set the timber up on saw horses and use a squared up tramel 20' long (string line?) to mark out the curve. Anyone have a slick quick way better than this?
Much thanks!

Tim

I'd set it up scaled out. If you can draw in SketchUp or CAD, draw the timber, then draw 6" marks across it. Now draw your curve from the center point. Measure the height at each location along the timber. Print to scale, or write down a sequence of numbers. Transfer to the timber. Connect the dots.



Set the grid distance for as accurate as you feel is needed...

A string will stretch, wire? A long board or two screwed together with pins or some such as points at the ends.

I have used another technique, used by boat builders, where you use a much shorter board with 4 pins, one of which is a pencil, to mark the curve, but for the life of me I can't remember how it works. And a quick google search yields this...... I didn't have is exactly right but this is the method I used.

http://books.google.com/books?id=V8L8y1J...p;q&f=false

Trammel is by far the quickest and most accurate method up to about 20'R. I dedicate a long stiff, lightweight board specifically for this use. setting trammels to radius takes only a minute, finding the center takes a couple of minutes, and then you just swing the arc. Dead simple, fast, and perfectly accurate. It really takes two people to hold the trammel arm over about 15', though.

A tape measure can be used as a trammel as well with pretty decent results. Just drive a 16d nail at the center and hook your tape on it, hold the pencil at your radius and swing it. to be honest, that's how I'd do it in this case.


bmike's way is a good alternative if you can use a drafting program.


And if neither of those options are available, here's a tried and true method I've used. You need to be able to calculate the rise of an arc given the radius and the chord length. You can do that with a construction master calculator (the pro version) or alternatively, there are several online circle calculators that will do it. (here's one http://www.handymath.com/cgi-bin/arc18.cgi?submit=Entry )

Let's assume the finished timber is 10' long (and the curve runs all the way to the end and starts at the very edge of the stick. Using 20' as the raduis, find the rise of the arc in that distance. (7 5/8") So at 5' from each end, square up that distance and mark your centerpoint.

Now, measure between the end point and the center point (5' 9 - 15/32" is what i calculate). use that as your new chord length to calculate a new rise in that distance. I come up with 2-17/32". Snap a line through one of the end points and the centerpoint and find the center of this line. at that point, square over your 2-17/32" and mark a new point. repeat until you have enough points to get the accuracy you need. And then lay it all out on the other end of the stick.


Hope this is clear, I'm out of time.

You can also by $2.00 worth of lamp pull chain at the nearest hardware store, and do this:



It's technically not a circle, but a Catenary Arch. But for shallow curves it's almost the same. No fussing around trying to find the center of the circle. Just mark the endpoints and the offset. Tap on the chain to leave little dimples, and connect the dots. CB.

that's a neat way of doing things.

for smaller radiuses on braces, an adze handle has a pleasant curve to trace from.

Thanks for everyone's reply's. I ended up using a tape measure as a trammel. I drilled a hole just big enough for a nail at 1' for the pivot point and another at 21', to make the 20 foot radius. I used 1 sawhorse 90 degrees to the timber with a board clamped to it at the height of the timber. I then set up the timber on sawhorses 20' away and moved it back and forth to find my 2 points where the arc would enter and leave the timber. Once I bulls-eyed these two points I put a pencil in the hole at 21' and drew the arc. The whole process only took me five minutes and I found it to be quite accurate.

that's what I'm talking about! You can't beat geometry when you need simple, quick, and accurate.

Another interesting side effect of using geometry (and other numberless systems such as direct transfer/scribing) is that your brain is less fatigued at the end of the day when you aren't reading and remembering dozens or hundreds of numbers.

You also stand 3/32" taller and feel 2 weeks younger...

LOL, very true Gabel, very true!

Gabel is so very tall now, he must not have used any numbers since 1984.