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Flatten twisted table top w/ router w/o losing mill marks?

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Forum topic by InThatNumber posted 03-10-2015 05:07 PM 696 views 0 times favorited 6 replies Add to Favorites Watch
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InThatNumber

6 posts in 1058 days


03-10-2015 05:07 PM

A while back I lost a bet with a friend of mine, and now I have to build her a new dining room table. The friend wants something very simple and rustic to go into her apartment in the French quarter (think exposed brick walls, gas lanterns, etc.) I’m thinking of a trestle design, both because it fits the style and is efficient for a table on the small side (72×36) because there are no legs around the edge to restrict seating positions.

Reclaimed lumber was the starting point, so I picked up a few pieces of old 3”+ thick barge wood off of CL. Two 10’ boards 14” wide and a few scraps that are around 4-5” wide and 40” long. The larger boards will become the top, the scraps will become the legs. The wood has mill marks that almost disappear when sanded but turn much darker than the surrounding wood when they get a little bit of oil, which creates a great look that I don’t want to lose.

Over the weekend I wrestled the larger boards over the table saw and jointer to start getting them ready to join into a 3’ x 6’ top. They’ll be arranged like this: – two 36” x 12” boards sandwiched between12” x 72” boards on the outside with rabbets and dados to give strength to the joint and exposed end grain.

Two of the boards are almost dead flat without being worked at all. The others are twisted – the longer board about 1/2” over 6 feet, the shorter one about 1/4” over 3’. Now, the top doesn’t need to be perfectly flat when all is said and done, but it should be level corner-to-corner and flatter than it is now.

The only method I can come up with is to flatten the bottom of the twisted boards using the router-sled method, i.e., flip the board so that the eventual-top is down, shim diagonal corners so that the board is stable, and router-plane off enough to get the eventual-bottom flat. If I do that, when I flip it back over I’ll have two high corners diagonally opposite one another – at least 1/4” higher than the center on the long board. My concern is that in taking those down I’ll wind up removing the mill marks from the whole board.

Is there another approach I’m not thinking of that will let me more-or-less flatten the boards without taking so much off the top? Perhaps some way to use the sled to just rout in flat spots on the bottom for the legs to attach to without planing down the whole thing, and somehow to get the board to sit more level in the process so that I don’t have to take so much from the top?

Also, given the issues I’m going to have flattening, do I need to rethink the dado-rabbet joint? Maybe dowels or something that doesn’t require perfect alignment across the entire 6’ span?

Thanks in advance for any comments/suggestions!

Alan


6 replies so far

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firefighterontheside

13442 posts in 1316 days


#1 posted 03-10-2015 05:21 PM

Other than saying that the bottom or the top has to be crooked to keep all the mill marks, my only other idea is to have some transition pieces between each plank, maybe 1” wide that you would sculpt to line up with the piece on either side of it. This way you can flatten the bottoms, leave the tops orooked, and make the sides square to the bottoms. Does that make sense?

-- Bill M. "People change, walnut doesn't" by Gene.

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firefighterontheside

13442 posts in 1316 days


#2 posted 03-10-2015 05:25 PM

So you would flatten the bottoms and get them to an average thickness. Place them along side each other with the transitions in between that are fully taller than the top. Then with a pencil scribe each piece. Now with whatever works best(plane, spoke shave, sander) shape them down to the lines.

-- Bill M. "People change, walnut doesn't" by Gene.

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InThatNumber

6 posts in 1058 days


#3 posted 03-10-2015 07:12 PM

Thanks. It’s a good suggestion, but from a design perspective I worry that adding transition pieces (which would have to be from a different species at this point) would take away from the big, blocky, rustic look I’m going for. Something you said got me thinking though…

If I can figure out a way to clamp the boards to where the adjoining surfaces are as flat as possible and let one of the “loose” corners sit high and plane that way I’ll be taking 1/2” off of that corner rather than 1/4” off of two diagonal corners. The board won’t be a consistent thickness, but aesthetically that doesn’t bother me so much and mechanically I can deal with it by routing out flat and parallel surfaces for the legs to join to. Seems like that way I leave as much of the top surface intact as possible.

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patron

13535 posts in 2801 days


#4 posted 03-10-2015 07:37 PM

i have ‘un-twisted’ countertops
by skill sawing parallel kerf’s on the bottoms
deep enough to make the top somewhat flexible
i do a stop cut so the grooves don’t show out the ends
they can be parralel to the sides
or run diagonal somewhat more in line with the twist

how many and how deep
can be done a few at a time
and more added or deepened as the wood needs

by flexing the top this way
it should lay flatter without taking the board thickness down
or twisting the table legs up to the top twist too
which would result in a rocking table

another quick fix is to just make the foot spreader shoes
with the ends different heights on the two diagonal bottoms

if you are talking 1/4” each it shouldn’t be that noticeable

in the rustic look

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

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InThatNumber

6 posts in 1058 days


#5 posted 03-11-2015 11:07 PM

Thanks Patron… the kerf solution is exactly the kind of idea I was looking at (and the reason I love this site). I’m going to experiment with that approach a little bit the next time I’m able to get some shop time.

Cheers.

View bbasiaga's profile

bbasiaga

754 posts in 1455 days


#6 posted 03-22-2015 08:54 PM

can you screw the twisted pieces to a flat backer board that will pull them flat? Screw it on the the bottom, and incorporate it in to the frame of the table where it will be hidden, and it can also serve as the method to hold the table top to the table.

-Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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