drawing large arcs(tools)

[junkdog]

Hello
im new to your forum great info

i was wondering if you guys know of a place that sells these arc blending tools
that i see at lee valley that are butyrate plastic stacked on top of each other they sell ones that up to 36 inches long
but i need ones that are closer to 10-12 feet long we build skateparks and use radiuses up 100 feet
thanks Bryant

[P.I. Stazzer-Newt]

Secondhand fishing rods? - available in a variety of lengths and tapers...

[outofthenorm]

Home depot in the trim racks. I like solid pine quarter round or similar for anything longer than 10 or 12 feet.

[kenjamin]

For the 16' radius arc of my birdwing mast template,

http://ford.physics.fsu.edu/Xena062.jpg

I used one side of a heavy 3" door hinge attached to a board screwed to the wall of my garage. The other side of the door hinge was attached to a double thickness of 2" x 6" x16' white pine. Screwing the two thicknesses of 2" x 6"'s together made for a very straight beam that had one end of it hinged to the side of my garage. I used a router at the other end of the hinged beam to machine the profile of my mast and also used it to machine the internal halyard tunnels of each half of my birdwing mast.

[David G]

I've swung arcs with radii as big as 150' mechanically. Set up in a parking lot. Used braided monofilament attached to an awl at the pivot end. A board with a pencil wedged into it at the other end to mark the arc.


"Equations are just the boring part of mathematics. I attempt to see things in terms of geometry" -- Stephen Hawking

[Captain Blight]

I use braided Spectra fishing line. Very very low stretch, low cost (compared to tuba sixes) and you could, if you so wished and had the room, tie several together and strike an arc several miles in diameter.

I do have a couple battens I've ripped from some very high ring count Douglas fir porch flooring. This comes in lengths to 12 feet, and is dimensioned at 3-1/2"x11/16". Pick your planks for grain straightness and runout and store them well supported off the floor. They're an invaluable tool and should be treated with respect.

[patrick.blanchard]

for lofting, I use an electrician's fishing tape, only the fiberglass one piece round will work. The others have humps and hollows.

[TerryLL]

Bryant,
I have one of those arc bending tools you mentioned, and it's next to impossible to get either a fair curve or a perfect arc using it. Great for drawing random curves and not much else.

For a mathematically perfect arc with a radius of 100', your best bet is to use a piece of no-stretch line 100' long. Nail one end down, stretch it tight and swing your arc with the free end. If it's a fair curve your after, which is simply a curve without any dips, lumps, or other imperfections, then any sort of spline that bends fair will do the trick, but your result will probably not be a true arc, just a very smooth curve of unknown radius.

There are other mechanical and mathematical methods to develop an arc section, but the tight-line method is certainly the simplest.

[htom]

You could use a Long Compass. (http://gicl.cs.drexel.edu/people/sevy/luthierie/compass/Long_compass.html) I first ran into these in a theatre shop.

[P.I. Stazzer-Newt]

These - Blending Curves (http://www.leevalley.com/wood/page.aspx?c=1&p=51161&cat=1,42936,42958) are designed to create what the roadbuilders call "Transition Curves" - curves where the bend radius changes from one value (infinite in the case of a straight line) to another - smoothly.

You can do this on a small scale with a tapered spline batten (dinghy sail battens work well at drawing board size) - the only tight line method I know that works is to use a section of an ellipse developed using the Loop-and-two-pins method and , frankly, freehanding it with a hosepipe and a mark one eyeball usually works better.

[merlinron]

or use "total station".......

[dmg]

Aside from most of the above methods, which I also have used, the EASIEST way is to find a buddy or an independent draftsman/architect. Have him punch in your numbers, and run the patterns on a plotter. Transfer as soon as possible to thin plywood, scarfed as required, for multiple uses. 100 ft. radius is pretty flat curve.

The curves I use over 16-18' doors is maybe 25-30'r.

Dave

[junkdog]

those are a lot of cool ideas i have drawn large radiuses in the parking lot as well

but i am just really interested to find a supplier of longer blending curves that could be used with a measure stick that they use in bending steel
say a 48 inch stick that you apply as a chord across your arc and measure the hieght of the cord to determine the radius then do the math to find the radius or as most bending shops they have a chart based upon the same length stick

my biggest problem is space and ease of settup i would like to use these blending curves on jobsite
i have a radius cutter in my shop skilsaw on steel bar that is 30 feet long fine for shop terrible for fieldwork as a parking lot isn't always available and more often than not ground is not very flat

thanks for all your responses thats awsome

any west coast boat builder guys (vancouver )
i happen to have an old shipsaw pickles ransome ithink
i am interested to perhaps cut some pcs
intersted to find out more about that saw as well