Duplicating archs/curves with a router? - Woodworking Talk - Woodworkers Forum

 
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post #1 of 8 Old 11-18-2016, 08:08 PM Thread Starter
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Duplicating archs/curves with a router?

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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post #2 of 8 Old 11-18-2016, 08:31 PM
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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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post #3 of 8 Old 11-18-2016, 08:39 PM
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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....

The answer to your question will only be as detailed and specific as the question is detailed and specfic. Good questions also include a sketch or a photo
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post #4 of 8 Old 11-18-2016, 09:27 PM
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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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post #5 of 8 Old 11-19-2016, 06:26 AM
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Would this accomplish what you want?

http://www.woodworkingtalk.com/membe...ms/router-jig/
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post #6 of 8 Old 11-20-2016, 07:11 PM Thread Starter
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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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post #7 of 8 Old 11-20-2016, 08:12 PM
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There are companies that make flexible trim, all different profiles. I've used it on occasion and it really worked nice. Google it.
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post #8 of 8 Old 01-11-2017, 09:57 AM Thread Starter
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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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