# 19' radius arc cut



## jeepme79 (Jun 1, 2007)

I'm making a 4' wide sofa table, with one of the long sides arc'd at a 19'ish radius. the center of the top will be 3/4" ply, with 1x3 maple around the edges. I plan to cut the arches out of a 1x6, but what is the best way to cut an arc that wide? I would like to use the router and some type of circle jig to make it a consistent arc, but I also need the arc in the ply and the arc in the 1x to mate up nicely. I think a circle jig at 19' would be too difficult without having a bit of slop to deal with.

Any suggestions? Attached is a zipped up sketchup of what I am trying to do.


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## TexasTimbers (Oct 17, 2006)

I built a Japanese stlye arch bridge which had to span 32'. Best I can remember it turned out to be the radius of a 181' diameter circle (90.5) feet that had the not-so-steep profile we (customer and me) both liked. We played around with it in her yard until we both said it was not too steep but still steep enough to have the arched effect.

Later I then laid out the 6" x 20" x 18' laminated beams I had built up that week, and in my back yard my son and I fiddled around with a 100' tape and carpenters pencil until the arch landed where I wanted it to within the confines of the beams. 

I believe the miter on the beam ends where they mated was somewhere between 3 and 5. I don't know of another method to replicate the actual laying of it out, and being able to avoid the full scale method like this but I bet there is a way. 

Make sure and post it because the way I did it took about 3 hours just fooling with moving and re-moving until I got it within a 1/4" of even - "everywhere". Unless you have ever tried this you cannot appreciate the "everywhere" part until you do it.


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## Holden McGroin (Mar 28, 2008)

There are several possible methods for cutting a 19" radius circle. The easiest, by far, is to cut it on a bandsaw using a pegged table extension jig. A router can also be used effectively by making a masonite, plywood, or Plexiglass armed jig replacement base for it. If I were going to undertake fitting a breadboard type edge to it, I'd use the bandsaw jig. One can easily cut the inside and outside and the rabbit joint diameters to match perfectly by moving the centering peg. Good luck!


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## pianoman (Jan 16, 2008)

Draw a line with the stick.....then cut to the line with a jig saw.


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## mmwood_1 (Oct 24, 2007)

Holden McGroin said:


> There are several possible methods for cutting a 19" radius circle. The easiest, by far, is to cut it on a bandsaw using a pegged table extension jig. A router can also be used effectively by making a masonite, plywood, or Plexiglass armed jig replacement base for it. If I were going to undertake fitting a breadboard type edge to it, I'd use the bandsaw jig. One can easily cut the inside and outside and the rabbit joint diameters to match perfectly by moving the centering peg. Good luck!


I think you misread. He's trying to cut a 19 FOOT radius arc. Not inches. A little more challenging.


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## TexasTimbers (Oct 17, 2006)

We cut our radius with a circular saw and it was a cinch to follow the line. Admitted ours was larger but I think a 19' radius may still be cut this way. The curve is not going to be real extreme on a 38' diameter circle, and being that your stock is 3/4" you wont have to have half the neighborhood help you flip it over to cut from the other side as we did .....


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## firefighteremt153 (Jan 25, 2008)

This may or may not help you, but in the past if I needed to layout a larger sized radius I would get a couple of friends, and a 4' 1/4" dowel. I'd get my friends to bend the dowel by both of them pushing it towards each other and in the direction I wanted the arch to run, and then I'd trace it out really quick before they let the radius I wanted slip. Just make sure they hold it on the ends of the dowel in the same spot on both sides. Maybe that will help you or someone else in there projects.


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## TexasTimbers (Oct 17, 2006)

That's a good way I guess Jeremy, but if you need a perfect arc I wouldn't trust the dowel or other such wooden item to bend proportionately on both sides of the apex/centerpoint.

If the jeepster would give us a little more input we could probably zero in on the solution a little better because if he needs something like a half-elipse versus a true circle shape (portion of a radius) we are all maybe writing the wrong prescriptions.


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## frankp (Oct 29, 2007)

I'd think the easiest thing to do would be to take a piece of 1/4 inch mdf and make a template out of it. Use a center point and a piece of string 19 feet long to make an arc on the mdf. Cut the mdf using a jig saw and then use the template to transfer the arc to your workpiece. Cut using whatever tool best fits with the materials as you have them at that point. Personally, I'd use a jig saw or a bandsaw if I had a big enough table for it.

FrankP


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## jeepme79 (Jun 1, 2007)

My initial thought is this. Since I will need to make 3 cuts - one on the plywood piece in the center of the table top, and two on the 1x's (inside and outside arch), I will make a jig with a smaller routerbase attachment. To start, I will take a small piece of 1/8" ply a little longer than 4' (the whole table will be 4' wide, with the arch on the wide side). Then, I will bend that to an arch about 6" smaller than I want and trace that onto scrap MDF or ply for a template. I will then cut the template with the jig saw and sand to the line so it is as smooth as I can get it. I will then make an adjustable router base that will ride along the template. From there I can adjust the router base in the increments necessary to make the three cuts. My biggest concern is that I want the seam between the plywood and 1x to be perfect, and just using the jigsaw may not allow for that. Using a router template on the arch would.

I have a very good picture of this in my head, but that doesn't translate into text very well.


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## TexasTimbers (Oct 17, 2006)

frankp said:


> . . Use a center point and a piece of string . . .to make an arc . .


How ya gonna do that? Whatchya gonna use to make the string lay in a perfrect arc? :blink:


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## TexasTimbers (Oct 17, 2006)

man I must have taken a nap while i was typing. 

Jeep you are right I can't picture it. Just post pictures when you're done.


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## frankp (Oct 29, 2007)

TT, I thought about someone making that exact comment after I posted. You use the string as the radius of the arc. IE you tie one end to a center point, and the other end to your marking apparatus. Pull the string tight and then move sideways along the edge of the circle you would create by making a full walk around the center point. This will make an arc with the right radius. I think there's a real name for using a piece of wood as a tool for this and I'm pretty sure it starts with an m but I have no idea what it is right now.

FrankP


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## TexasTimbers (Oct 17, 2006)

Ahhh I remember that now I have seen this in a mag or somewhere. 

Wouldn't the string tend to stretch a bit? A straightedge would work great like that.


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## jeepme79 (Jun 1, 2007)

Turns out I was making this harder than it should have been. To make my template, I bought a 4'x4' piece of 1/4" MDF. First I attached a small scrap block to two of the corners, 1" in from the near edge. Then I attached one more in the center 2" in from the near edge. From there, I nailed a 1/4" strip of pine scrap to all three blocks, with the arch formed by the 1" offset. Last, I clamped a 1x2 to the arch to make it more uniform as the 1/4" strip wasn't that good. To cut it, I put a 1/4" flush trim bit in the router and used the arch as a fenct to cut the arch in the mdf. I'll post pics when I get a chance.


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## cabinetman (Jul 5, 2007)

I'm touching down a little late on this one, but I thought I'd chime in how I'd do it. I have a 20' aluminum extension pool pole that I use like a compass, or a piece of rope will also work. 

I lay out a 90 deg corner with anything that's straight, like furring strips, and the two legs would extend out past the 19'. Then I lay out flat sheet stock, it could be plywood or MDF, or PB at the 90 deg point and all along the swing of the arc. 

I draw the arc on the sheet stock for the outside line for the template, and shorten up the length to whatever dimension for the width of the template, and using the same point draw the second line.

This represents a 1/4 circle, which when scabbed together and cut out, I use that for the other side. IOW, the layout space is only about 10' x 20'.


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## FishMontana (Aug 24, 2010)

You could try this jig:

http://www.m-powertools.com/products/n-compass/n-compass.htm

Or, I created the arc in Microsoft Visio using some smaller scale, e.g., 1 inch = 12 inches. I then scale up the drawing to 1 inch = 1 inch. Then, I have a print place print the drawing on a plotter or large format printer. A little tape later you have a template that you can use to draw a line or make a wood template to use with a router.


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## TS3660 (Mar 4, 2008)

You could calculate it or draw it up. For instance, a 19' radius over 48" has a center point that is 1-17/64"" higher than the ends. So, just take a strip of 1/4" plywood and bend it by hand between three points and draw a line.


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