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THIS project is making a router jig and and using it to make a template for both a 15 foot and 28 foot radius. The template will be used to sand curved braces for guitars or ukes, and eventually to make radius dishes. The following is confusing, so I will make every effort to answer questions in the comments.

USING the three point method to scribe the arc with a pencil was easy (see LJ "Tooch" Large Radius Arc Jig), but the difficulty was cutting the radius on the band saw and trying to sand to the line. With a base line 30 inches long, and a rise in the curve of only 3/8 inches, staying in the thickness of a pencil line can leave flat spots on the curve of ~6 inches. It took a while to come up with the idea of making a jig for the router to scribe the arc.

THE ROUTER jig is two sided for making a template with both a 15 foot and 28 foot radius. Each channel in the bottom of the jig has two offset straight lines using the three points defining the base line and the center rise of each radius. The jig and template are both 1/2" MDF.

THE TEMPLATE has five "blind" holes for removable dowel pins that serve the same purpose as the nails in the Tooch project. The center pin is common for both radii, and two holes on each side define the end points of each radius. Only two dowel pins are used for any cut - one in the center and one at the end point of the cut. The router depth was set at 3/8" to not cut all the way through the template. The cut in the template was then completed with the band saw, and the edges cleaned up with a flush trim bit on the router table.

THIS PROJECT was very rewarding, but there was a lot of "trial by error" and sleepless nights of consternation. The result met my best expectations for smooth and uniform curves, but keeping track of two curves on both jig and template, which is up and which is down, and which is convex or concave was mind boggling. Now I can get back to work on the two uke's on my workbench.

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I love the smell of math in the morning, and dont! Sometimes making the jig for a project is more interesting (sleepless nights) than the project its required for.
 

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Funny, I just asked a question on this post about how he made the arch on the headboard.


I made a jig to cut rockers for a bassinet but they were a lot smaller.

I love the smell of math in the morning, and dont! Sometimes making the jig for a project is more interesting (sleepless nights) than the project its required for.

- wildwoodbybrianjohns
+1 I am often more proud of the jig than the project, especially when the jig is pretty. :)
 

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Very interesting! I find your concept intriguing; having radiused braces myself, I can definitely see the time it would save you. Thanks for sharing!
 

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Hi.
Really interesting stuff, but could you explain a little bit more how this is done? I just dont think I'm smart enough to get this right
 

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hstr,

Thank you for your interest in the long radius jig. This method is only useful for very long radiuses where close tolerances are important. The link below shows the old carpenter method for drawing arcs. I don't know if you are familiar with this, but it is the basis of my method.

At one time I tried to do a video of the long radus jig, but it got too complicated so I abandoned the idea. Then I tried to do a blog with the same end result. I may try again and will let you know if I have any success.

 

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Thanks for your reply, HankLP.
I'm familiar with the old arc drawing method, and have been doing some 15' and 40' radius templates, but it's just not smooth and correct enough.
I was more curious about how you were setting up and moving your router to get it right.
 

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Thanks for your reply, HankLP.
I'm familiar with the old arc drawing method, and have been doing some 15' and 40' radius templates, but it's just not smooth and correct enough.
I was more curious about how you were setting up and moving your router to get it right.
 

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I hope this additional information further clarifies how the long radius arc jig functions. Message me if there are questions. This jig was designed to cut two different arcs on opposite sides of the jig. The discussion below addresses only a single arc.

1…...........2…...........3

4…...........................5

...................R

ROUTER JIG Holes 4, 2 and 3 above correspond to the nail locations for the crossed sticks layout used in the "old arc drawing method." On the bottom of the JIG, the holes are connected by a 3/8" groove, 3/8" deep. The center hole "R" locates the router bit, and must fall on the line that bisects the angle defined by holes 4, 2 and 3. It is also critical that the break in the top edge of the template falls on this line.

[NOTE: It is easiest to locate "R" first and proceed with the layout from there]

TEMPLATE holes are 4, 2 and 5. These are the holes (i.e. nails) on the radius. They are blind holes that do not go through the blank, and are meant to hold 3/8" dowel pins. The left and right segments of the arc are routed separately, using holes dowel pins in holes 4 and 2 for the left segment and 2 and 5 for the right segment.
DO NOT glue the pins in the dowel holes.
 
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