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Joining cupped or curved boards, keeping the cup or curve.

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Forum topic by jasnyc posted 02-08-2017 02:41 PM 690 views 0 times favorited 9 replies Add to Favorites Watch
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jasnyc

9 posts in 2509 days


02-08-2017 02:41 PM

Topic tags/keywords: jig tip question joining trick cupped wood mortise tenon curved wood

Hey all.

I have a beautiful long piece of cherry (10 feet, 1 foot wide, 1.25 thick) that I want to make into a bench. It has a pretty consistent cup along its whole length. I want to build a bench, keeping the cup shape, because it seems like it would be a great comfortable shape to sit on. I’ll use about 48” from the middle, and then fold about 18” down from either side of that 48”. (Sketch attached if I can figure out how).

The question is: How do I cut the joinery (wedged through tenons) with the board cupped? I assume I need to create some kind of jig that creates a consistent “reference” surface so that the tenons are square to each other and to the mortises in spite of the undulating nature of the boards.

All ideas welcome . . .


9 replies so far

View TungOil's profile

TungOil

740 posts in 328 days


#1 posted 02-09-2017 04:28 AM

Couple ideas come to mind.

one option would be to flatten the bottom of the board only. Then you can use a ‘normal’ mortise & tenon.

If you prefer the curved look top and bottom you could flatten just the area around the mortise and create a housed mortise & tenon.

or, bandsaw the top of your legs to match the bottom of the bench top, then drill some big round plugs into them and create a floating round tenon. some wedges would dress it up nicely. that’s how I’d do it.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View bigblockyeti's profile

bigblockyeti

4690 posts in 1554 days


#2 posted 02-09-2017 05:21 AM

If you have a radial arm saw you could dado just the areas where the legs will lie on the bottom of the bench. You could also flatten the entire bottom of the bench to make a datum from were everything can be mounted but progressive passes through a planer or on a jointer (if you have access to one that wide) would be a lot of handling and could mark up the top of the bench. I made a bench and went the inverse way with the convex side on the top and since the legs were cut from the same plank, I cut the curvature of each intersecting surface on the bandsaw and left quite a bit to be sanded away.

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jasnyc

9 posts in 2509 days


#3 posted 02-09-2017 06:47 PM

Yes! Thanks for the ideas. I think I’ll go with sawing the legs to match the top, clamp them together and either drill a circular hole for a big floating round tenon or maybe drill out most of the waste and chisel a rectangular floating tenon. But either way, with the legs registered to the top and treated as one unit I can make sure the holes are in line.

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bigblockyeti

4690 posts in 1554 days


#4 posted 02-09-2017 07:05 PM

The only reason this turned the way it did for me was due to the fact that I planed the wood flat before it was dry so I had a fairly smooth albeit severely cupped surface with which to work. I kind of wish I could accurately replicate the result as it turned out to be very popular.

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TungOil

740 posts in 328 days


#5 posted 02-09-2017 07:53 PM

my only other add would be to make sure you tie the legs together with a stretcher of some sort to minimize racking- like the base of a trestle table.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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jasnyc

9 posts in 2509 days


#6 posted 02-10-2017 05:54 AM

I was hoping to avoid a stretcher by screwing in some low profile triangular blocks. The client wants a clean open space under the bench (it’s in an entrance foyer). Thoughts?

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iminmyshop

284 posts in 1827 days


#7 posted 02-10-2017 06:07 AM

Stretchers can be made to look as elegant as you choose. I like to use stretchers on benches as they provide stability. But I also like to put curves in them to improve their aesthetics. Having said that, as you’ve noted, joining two curved surfaces presents a major challenge.

http://lumberjocks.com/projects/198074

http://lumberjocks.com/projects/92844

-- http://www.alansfinewoodworking.com/

View TungOil's profile

TungOil

740 posts in 328 days


#8 posted 02-10-2017 02:35 PM

Corner blocks will work also. I made this bench over 30 years ago (also for my foyer) and it uses corner blocks and has held up just fine. That is 8/4 oak for reference, so a bit thicker than the cherry you plan to use.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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jasnyc

9 posts in 2509 days


#9 posted 02-12-2017 05:45 AM

Yes, TungOil. I was thinking about something low profile like that.

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