slab flattening jig

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Project by Jay20650 posted 07-11-2012 12:46 AM 6752 views 2 times favorited 13 comments Add to Favorites Watch

These pictures show the new torsion box table I made with an upgrade capability…rails on the side and a router jig turn it into one very large slab flattening jig. Pictured is an 8ft piece of walnut that is destined for a dining room table top. It has a matching piece for the other side to end up with a live edge table. The torsion box is the size of a full sheet of plywood, it has become an indispensable fixture.

-- Jay,

13 comments so far

View ic3ss's profile


391 posts in 3226 days

#1 posted 07-11-2012 12:58 AM

Nice idea. It would be even better if the slab stayed flat after milling it. I hope it works well.

-- "I am endeavoring, ma'am, to construct a mnemonic memory circuit using stone knives and bear skins."

View Arthouse's profile


250 posts in 3099 days

#2 posted 07-11-2012 02:35 AM

Nice idea but a lot of work. I have taken 4 foot wide slabs to a C N router . It does the same thing and only cost 50 bucks . Nice ingenuity I hope it is dry.

-- "The hand is the cutting edge of the mind but the wind and sun are the healing factors of the heart

View HalDougherty's profile


1820 posts in 3686 days

#3 posted 07-11-2012 02:36 AM

They never stay completely flat… A good router sled beats hours of belt sanding, hand planing, card scraping, etc.

-- Hal, Tennessee

View a1Jim's profile


117688 posts in 4026 days

#4 posted 07-11-2012 04:39 AM

Good idea well done.

View SergeantSawDust's profile


173 posts in 2631 days

#5 posted 07-11-2012 06:48 AM

I think it’s a great idea! Definitely a labor and time saver! Also this reminds me of Marc Spagnuolo’s (thewoodwhisperer) made his torsion box assembly, and how he flattened his roubo bench. If he thought it was a good idea then that’s the way to go! Great job!

-- Woodworking for the hobbyist woodworker.

View Monte Pittman's profile

Monte Pittman

30407 posts in 2787 days

#6 posted 07-11-2012 10:03 AM

So is this a router planer or are you bending the slabs?

-- Nature created it, I just assemble it.

View woodworkerscott's profile


361 posts in 3263 days

#7 posted 07-11-2012 04:26 PM

Been meaning make one these for awhile now. You’ve inspired me. Thanks for posting.

-- " 'woodworker''s a good word, an honest word." - Sam Maloof

View Pete Tevonian's profile

Pete Tevonian

78 posts in 3367 days

#8 posted 07-11-2012 05:23 PM

I made one of these about a year ago—6’ x 4’—to flatten some giant Siberian Elm cross-sections and slabs. Works really well and is a lot less work than people might imagine. It takes time, but it’s basically foolproof and predictable. The key is a powerful router and a couple good flat-bottom bits. And taking wood from alternating sides to balance out the movement. I also learned the basic lesson of take some wood off, and then let the piece react, and then take more to flatten it again.

The biggest problem I have with the torsion box and router jig is where to store it!

-- Pete in Wilmette, IL

View Jay20650's profile


42 posts in 3140 days

#9 posted 07-11-2012 05:48 PM

Pete, you are on the money. I take a bit off both sides, take the slab back inside to sit for a week or so, take some more off etc…I ordered a pretty inexpensive 2” flat bottom router bit and it seems to do the trick.

As for where to store it, that is an issue, mine ended up on a corner of my deck with a canopy over it! It’s a temporary home, but I have to say I really enjoy having it outdoors. The canopy has adjustable legs, so I can lower it to completely cover the table when not in use. Slabbing makes an enormous amount of wood chips and dust, and even though I wear a reperator while slabbing, it is nice that I can set up a fan to blow the dust away from me while working. A nice feature on this that you can’t see in the pictures is that I routed slots in the rails, epoxied screw inserts into the torsion box sides, cut some all-thread, epoxied on wood handles, and the rails are a cinch to adjust and clamp in place. I do add parallel bar clamps to the rails before flattning just to be sure.

SawDust, the torsion box idea was definetley inspired by Marc, though I assembled it slightly differently. It is really flat as well, I was pretty surprised how well it came out.

-- Jay,

View Milo's profile


869 posts in 3768 days

#10 posted 07-11-2012 06:36 PM

I just did this on my workbench, and I love the results. I did take the belt sander and a hand plan to it after I was done with the router, but the router probably did 99% of the real work.

-- Beer, Beer, Thank God for Beer. It's my way of keeping my mind fresh and clear...

View sam20650's profile


30 posts in 3051 days

#11 posted 07-16-2012 02:46 PM

Now if I could just have my canopy back so I can take it to shows (which is what it was bought for) :)

Actually other than moving out of the traffic pattern on the deck I actually really like having out there. We have used it for a table/bar during parties, for picking crabs, and the cat really enjoys it as a woodchip covered bed. Oh yeah and we use it for flattening slabs and coins and as an assembly table…

-- "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." -Abraham Maslow

View Pete Tevonian's profile

Pete Tevonian

78 posts in 3367 days

#12 posted 07-16-2012 03:04 PM

Did you see Nick Offerman’s cover article in Fine Woodworking a few issues back about his slab-flattening router setup? Same basic principle, but his can be disassembled. He has a trough that he moves along the slab, and the router slides back and forth in the trough, on a router-table insert. My setup uses a long beam that spans the table rails, with the router fixed in the middle, and I just slide the whole beam back and forth. My setup takes a lot more room, because you need space on either side of the table for the extra beam length, but Offerman’s way requires him to almost be up on top of the table to push and pull the router across the width of the slab. I see pros and cons both ways. But the ability to disassemble the slab support beams would be nice. But again, he has a dead-flat assembly table that he uses as the reference surface for the beams and ultimately the whole jig. Not having that, the torsion box was a necessary intermediate step for me.

Did you use MDF for the top/bottom of the torsion box? Does it stand up okay to being outside all the time? Or did you seal it in some way?

-- Pete in Wilmette, IL

View Jay20650's profile


42 posts in 3140 days

#13 posted 07-16-2012 03:17 PM

I did see the article, Idecided to go in a different direction, instead of the sled being adjustable I made the rails adjustable. The router slides on this one so I could route most of the 4ft width without a really long sled. It was finished with a mix of BLO, poly, mineral spirits, all sides. Seems to be holding up…

I also have a sled the router fixes to for other projects I have worked on, so far I like this set up better, granted I haven’t had to route all the way across yet!

-- Jay,

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