# Convex / concave surface router jig



## Viktor

This is just a variation of a very common router surfacing jig, except instead of flat surface it creates convex or concave one.









The bridge that supports the router has curved beams (R= 194 cm) which I cut using oversized circle cutting jig. The frame is made from Bosch 45mm T-slot aluminum extrusions and brackets that are very handy for building various temporary contraptions. 
The piece in the picture is headboard (50×109 cm) for twin bed. It was glued from two pieces of sapele each 25 cm wide. I glued them at 7 degree angle to best conform to the target curvature. It turned out to be very easy to do with track saw. Set the angle to 3.5 degree and trim the edge matching grain pattern of adjacent boards. After this I proceeded straight to glueup. The edges were so straight and smooth that I can barely find the seam after it's all done.
I attached the work piece to the wooden beams of the frame with small nails. The beams supporting the work piece were bolted to aluminum brackets through elongated slots that allow accurate vertical adjustments of each corner. After surfacing on both sides 20 mm thick board was reduced to 17 mm. If you increase the number of segments thickness loss can be further reduced.

For concave side just flip the router jig (I reattached the router base with screws). 









I found it is much easier to make passes along aluminum extrusions than working across. The bridge has to be twice as long as the width of the work piece (my was too short, so I attached the router off center and worked from the opposite sides).

I used 35 mm diameter surfacing bit. It works fine on the convex surface. On the concave side the router has to be tilted like so:









When tilted, flat bottom bit produces shallow elliptical grove rather than rectangular one. In this case passes must be made along the work piece, not across, to have seamless transition.









Final product:


















If the rail was circular (a large ring around work piece), one could produce spherical (bowl/dome) shape.


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## watermark

Great ingenuity there!!


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## TheCaptain

Boy, do I have a lot to learn!


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## Viktor

P.S. Here is the bed for which the curved board was made http://lumberjocks.com/projects/80522


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## a1Jim

Good thinking. Well done.


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## RogerInColorado

Very cool and very creative. I can see lots of applications for that.


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## gfadvm

Very innovative jig! I always wondered how to route concave/convex profiles. Thanks.


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## bernwood

Beautiful simple jig - love it. Thanks for sharing. I'm sure I'll be using it in the future.


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