Fixing Twist in a Slab or Board





Introduction: Fixing Twist in a Slab or Board

About: BongoDrummer is co-founder of Flowering Elbow. He loves to learn about, invent, and make things, particularly from waste materials, and share the whole process with whoever is interested. Check out his youtu...

Solid wood. You can't beat it for aesthetic appeal. It can stimulate all our senses and generally rocks as a material to furnish everyday life. But with that great power comes great potential for warpage! It's one of the reasons mass-market makers who are all about the bottom line shy away from it in favour of 'manufactured boards'. The natural movement in solid timber can require a lot of experience and knowledge to control. This 'able is about learning to deal with that power, by fixing twist.

'Twist' is the most difficult flavour of warpage to deal with, so lets get started. We are going to be using the little talked of 'de-stressing and strategic weakening' method!

Step 1: Establishing Your Twistedness

To check for twist, make yourself some winding sticks. These are as simple and two lengths of equal-sized wood. Contrasting types of wood work well to highlight twist, but you can also use the same wood and paint one a different colour. Their main requirement is that they are flat, straight, and the same thickness, so that holding one in front of the other, the back one completely vanishes from sight.

To get a handle on the extent of twist a board has, place a winding stick either end and look down the length of the slab. If the far stick isn't visible because it is perfectly lined up with with the closest one, congratulations, you don't have twist. If however, as in our example, a portion of it is still in view, your slab is twisted, or 'in-wind' as the old timers like to say.

You can do a similar test with a spirit level, comparing the level at points along the board, but the beauty of the winding sticks, is that you can use them anywhere - even if the whole board is off level.

Step 2: Ripping, Face Removal, Clamping

They sound gruesome, but they're not.

You have a lot of options when it comes to dealing with twist in a board and your choice will depend on the severity of the twist, the type and size of wood you are dealing with, how you're feeling at the time, weather or not you had ice in your drink etc. I'll list the main ones I consider practical:

1. Ripping. This is a good option if you have a wide board that is both twisted and cupped. Essentially this involves ripping it down the middle with a tracksaw, a bandsaw or even a handsaw(!?) to make two or more smaller boards, which, once squared up can be glued back together straight. The upside is that you are removing less material than if you go with option #2, just the width of the saw's blade - its kerf - and whatever you need to plane off to square the edges. The down side is that even with that little removal, you will loose your nice continuous grain pattern, which will be broken by glue lines. Ironically the boards that are worst affected by this, in which the break in grain is most apparent, are the characterful swirly grain boards that are also the most likely to suffer from twist or warp of some kind.

2. Face removal, or removal of material from the face of the board, can be an option if the amount of twist is less than the thickness of the board. This can be done cave-man style using scrub and jack planes, or with power planers (either hand held or the stationary jointer or thicknesser). If the board it too wide to fit through the thicknesser, it can also be done with a diy router sled - see my coffee table instructable here, for example. The advantage of this method is that you can be left with a complete and solid single piece flat slab. The disadvantage is that it can only really correct minor twist without sacrificing a lot of thickness. Furthermore, removing lots of material can often, lead to what I call 'aftershock-warpage', as internal stresses are changed, and moisture lost from the freshly exposed surfaces.

3. Clamping. This is useful when the board is part of a larger assembly. If, for example, you have a strong frame to fix the twisted slab to it is sometimes possible to 'clamp out' most or all of the twist. Here you are relying on the strength of the rest of the assembly to overpower the slab and pull it flat. Obviously this means the frame needs to be stiffer than the slab your trying to bend into shape. If you can get away with using this solution, it can be the best because it mitigates the disadvantages of the previous two options, namely, you can keep more of the thickness (less waste) and keep it one piece. The problem is that if you have a thick slab you need a very sturdy frame or you risk distorting the whole piece of furniture. If the slab is stubborn you also risk causing splits as you introduce the clamping forces. Much of the rest of this instructable deals with this method, and how to pull it off.

4. Ditch the slab and start with a new straight one. Not an attractive option.

5. Combo. There is nothing to stop you using a combination of some or all of these techniques. In my example the slab was ripped down the middle, both pieces being planed flat, then re-glued. Yet when it spent some time in its final destination it still did some twisting due to the dryness of that environment. On site it was preferable to clamp the twist out, but the frame wasn't up to the job, and I would likely cause the slab to crack if I pushed it.. This leads me to the crux of this instructable: de-stressing the slab and strategic weakening!

Step 3: De-stressing a Slab - the Theory

By cutting part-depth channels along the length of a board we can strategically weaken it in places that will make it more amenable to our re-shaping efforts. Check out the pics for example. The trick here is to add relief to places that are in compression, that way when you bend the board, the remaining material has to move less. It is also much easier to bend across its width, so your frame doesn't need to be ridiculously strong.

Obviously the pics are an exaggerated example. What you want to do is remove as little material as possible (fewer and shallower cuts), while making it susceptible to being bent, or un-bent, in the directions you need. Strategic removal is the aim.

Step 4: Strategically Weakening - in Practice

This is only going to work in situations where one face is going to be hidden, unless you want to add inlay, or laminate another piece of timber or veneer over the channels (which is totally acceptable - I've used this method in the past, make a feature out of it why not?). In the example we are working through I am using a plungable tracksaw to cut the channels length-ways along the slab. You could also use a small router bit, or with care, a standard circular saw. What you couldn't/shouldn't use is a tablesaw or sawbench. In fact you shouldn't ever use the tablesaw with a twisted board - it's very likely to bind and kickback (dangerous!).

I'm cutting about 2/3 to 3/4 of the way through this sycamore slab. The depth and number of cuts will depend on just how warped the board is, and how likely it is to crack if you use the frame to pull out the twist. Avoid cutting near defects that look like they might propagate into larger cracks. Remember the buzzword is strategic weakening.

Thankfully the channels I'm cutting shouldn't reduce longitudinal strength much. But it does make it much more willing to be un-twisted when we come to fix it to the frame (rather than it distorting the frame).

Step 5: Clamping Methods (on Holding It Flat)

Hopefully it goes without saying the when you come to fix your slab to a frame, it needs to accommodate future movement of the slab. It will move most across the grain so in the frame you need slots rather than holes for the screws.

Small pilot holes are useful when screwing into a hardwood slab like this. It's good to clamp it in place and check it is indeed now flattened, before drilling through the middle of the frame's slot into the slab. Then screw on up to fix it.

Step 6: Conclusion

Hopefully some of that was useful. This method can be a lifesaver if you can't afford to take any more off the thickness of your board.

Let me know if you have used it / do use it/ have any improvements.

As always thanks for reading and check out my latest tinkerings on facebook or my youtube channel.

May your winding sticks always line up!



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23 Discussions

Another method for the brave: steam and clamp.

If it is a thick slab, drill on the hidden side so the steam penetrates.

Good overview on all methods for removing twist. Will remember this. I do sense some contempt for hand planes, since you call them cave-man style. I challenge you to a dual: you with a router sled, me with a scrub plane and smoother. I'll even let you build the sled first.

4 replies

Haha. I love a good duel to get the blood rushing! I will let you setup and sharpen your hand plane first as well then.

Actually in a twist of fate, just yesterday I dismantled my router sled to make some room and free up some wood. My big bad CNC build is getting close enough that I will soon be using that instead.

Alright, we just need to settle on a day, then :-) We're actually not so far away. I live in Belgium. I'm curious to see your CNC build.

OK then. I will have to rebuild my router sled, or shall we just say the cnc will do? It's nothing but a jumped up router sled after all ;)

Close enough, let me know when you're in the UK and wanna pop in for a visit/duel.

Sure, use the CNC instead. Might even take you longer with programming and all. Will let you know if I'm in the neighbourhood.

Hi Guys, if the slab is thin you can use the water treatment on it. If the slab is cupped, hose some sunny grass and place the raw slab concave or cupped side down over the wet grass. After a while the slab will absorb the moisture and flatten out. It may be best if it cups slight the other way, so that when it settles the slab will probably come back to flat. When you seal the slab at the end of the project you must seal both sides. Of course this is a bit hard in Green Bay in December.

1 reply

8 months ago

Gday Bongodrummer,

Thanks for the info. Especially strategic destressing which is logical.
In dealing with cupping, I have elevated board between a couple of battons with concave facing down. Under which I placed sawdust which has been mist sprayed with water. The humidity trapped in the dry (con)cave swells the wood fibre straightening board.
Could this method (or variation) be used (strategically) in dealing with warpage?
Thanks again.

1 reply

Hi Layleh,

Yep this is a good one for thinner smaller boards that are consistently cupped. Since cupping is a form of warpage, it does indeed work for some kinds of warp. The trick is to re-balance the moisture content without letting it warp again.

It's a bit more complicated with twisted boards (hopefully the video at the beginning makes that clear).

Very informative, good stuff to know. I'm sure I will need to do this at some point in some project, thank you!

4 replies

hahaha, I hope you get a lot more :)

The strategic weakening idea is excellent, and something I'd never considered. It's picking up tricks and tips like this that really makes me love this community :)

I've always just used a hand plane to remove twist...

1 reply

That is 'THE' definitive way to deal with twist. If you can't afford to loose any thickness though it doesn't work.... I have seen beautiful twisted boards binned for that reason. This is one way to save them.

Good information. The strategic weakening method is especially interesting. A cross discipline question here. Has anyone done any steam heating of large slabs followed by clamping during cool down to remove twist? I am interested in boat building, and the experts in that craft routinely induce some truly amazing twists and bends into normally flat wood to fit their needs. I was wondering if anyone had used these techniques to take twist out of a board?

1 reply

Very good question! My only experience of steam bending has been making an ash drum (, which mostly worked. Some of the challenges with such an approach would be to a) make the equipment - mainly a big enough container for the steaming. b) Not adding so much moisture to the wood that it has to do a whole cycle of drying again and c) constraining the workpiece so as to eliminate twist - It couldn't just be clamped flat, as there is always some 'springback', so it would need to be twisted past flat in the other directing, if that makes sense?

All issues that are dealable. It certainly wouldn't be a quick fix unless you were all setup for steam bending and had done a good number of experiments though...

I'm not a woodworker myself but woodworking has always fascinated me. Especially the intelligent and ingenious methods of overcoming issues like these. Awesome instructable!