# Duplicating archs/curves with a router?



## Thorn495 (Feb 28, 2014)

I'm making some curved trim above a window. Let's say I rough cut the piece with a jig/scroll/band saw. I use a belt sander for the final shaping of one side of the curve to my best ability. I don't want to spend time trying the sand the other side to the right radius and consistent thickness. Is there a way to set up the router to copy the outside curve onto the inside?

Say the piece is roughly 1 3/4" in width and I want it down to 1 1/2", is there a jig that could be used on the well finished side of the curve to smooth out and trim the inner/rough side?

Please post pictures or insert links if you know how to set this up.


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## Justin Huisenga (Apr 2, 2011)

Both inner and outer cuts are easily made with a router and trammel arm. Getting consistent results sanding back to the line after rough cutting is like trying to nail jelly to a tree. 

When I make arch tops I either form bend or segment the blank. If I form bend I just draw the arc and built a form. If I segment I make a template with a router and trammel and route the blank righteous with a large diameter pattern bit. After I fab the blank with either method it gets sent through the moulder.


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## woodnthings (Jan 24, 2009)

*there are 2 ways ....*

The cheap, easy, simple way is to lay the finished side on a 1/2" piece of MDF, route the MDF using a pattern bit with the bearing riding off the finished surface. Flip it over for use on the unfinished side, using the MDF as your template with a bearing bit. You need centerlines and chords to get it exactly the same. Measure first, measure again and cut last.

If you did not already have a finished side, you could make the template first and use it to create both sides symetrically.

The second way is to program a CNC using the finished side as the "master" and flip in digitally to make the opposite side. Not expensive IF you have one.... :frown2:


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## Steve Neul (Sep 2, 2011)

Sanding would be a lot safer. The trouble with routing curved molding is when you are running against the grain it really has a tendency to have blow outs. Going from 1 3/4" to 1 1/2" is too much. The closer you can bandsaw the trim to the finished size the less chance you have for blow out. It's best if you don't trim more than 1/16" at a time and go slow when against the grain.


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## ducbsa (Jul 6, 2014)

Would this accomplish what you want?

http://www.woodworkingtalk.com/members/ducbsa-52816/albums/router-jig/


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## Thorn495 (Feb 28, 2014)

The curved trim was for this puppet stage window. I got the top sanded to my liking and thought there'd be a way to duplicate it to the inside curve without having to copy it to mdf and use a flush trim bit. I ended up just drawing a line under the outside curve to the thickness I wanted, used a scroll saw to cut close to the line and sanded it anyways.


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## firehawkmph (Apr 26, 2008)

There are companies that make flexible trim, all different profiles. I've used it on occasion and it really worked nice. Google it.
Mike Hawkins


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## Thorn495 (Feb 28, 2014)

I got a book from the library, "Popular Science Complete Book of Power Tools" and it had a good idea for future reference:


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