How to flatten a twisted board

[Michael Furey]

Michael, Where are you located? A local shop with a CNC could solve your problem in a matter of a few minutes.. shim 1/4" on each high corner and run a surfacing program with a flycutter. 3 min per side if that...flip and you get a perfectly parallel slab. I know some people that will say a cnc doesn't fix every problem and I agree but this type of problem is a easy fix for someone with the correct equipment. IMHO

I’m located in southern NJ along the coast. I know of one guy about a little over an hour from me that has a big planer and very large sander, but he said it’ll be a couple hundred bucks probably for me to have him work it for me. I’m not going to lug these heavy slabs on my trailer for him to do and pay that ridiculous amount when I can do it in a couple hours for $20 haha. I’m going to keep looking around me to see if I can find anyone closer and more reasonable though.

[johnny means]

One thing to keep in mind is that milling the faces off a severely stressed board is likely to simply change the orientation of the stress. You're very likely to just end up with a different distortion.

[Mike Cutler]

Michael

I know that you're against ripping the boards lengthwise, but I really think you should reconsider.
Whatever grain and spalting you see now will be gone, or very different by the time you get those boards flat. A 1/2" cup across the face, with a twist along the length, is going to require that a significant amount of material be removed. When you do finally get the material removed, and the board once again flat, it will just start the entire process of achieving equilibrium,and will start to twist and cup again.
I'm not trying to rain on your parade, But ripping those boards on a band saw, then jointing them properly will remove less material. You're still going to have movement, but it will be much less per individual board and easier to deal with.
Any kerf's can be hidden by using alternate decorative measures, i.e. contrasting woods, metals, resins, etc.

[lowell holmes]

He can rip the board in half, flatten the halves and glue them back together. If done properly the rip joint should be almost invisible.

[Mike Cutler]

He can rip the board in half, flatten the halves and glue them back together. If done properly the rip joint should be almost invisible.

I definitely agree. Done right, it could even mirror book matching.
The largest slab I've done was a single piece of flat sawn padauk ,11' long by 36" wide, and 2 " thick. It had maybe a 1/4" cup across the grain. No twist though. It started out about 17' long. I still have the remaining 6'x 32" slab in the garage.

[Michael Weber]

does the bottom of a table have to be flat? To maintain maximum thickness could just the top be flattened and bottom left as is except for sanding to remove roughness? The bottom could then be just milled flat where it attaches to the base. Or, the base adjusted to match the distortion. IDK, just wondering

[Mike Cutler]

does the bottom of a table have to be flat? To maintain maximum thickness could just the top be flattened and bottom left as is except for sanding to remove roughness? The bottom could then be just milled flat where it attaches to the base. Or, the base adjusted to match the distortion. IDK, just wondering

Michael

Yes, this can be definitely be done, and was in fact done for centuries.
If you do it this way the bottom is milled to the base support structure first, and the top is flattened in place, on the base.

[Dan Hahr]

It’s really interesting to see the variety of responses and it makes me realize that some people must not have ever dealt with really “bad” wood. Twisting to me almost always means that there is some internal stress just waiting to be set free. While I’d love to be able to just slide that bad boy over a jointer and then plane it flat, I doubt you could do it without ending up with a 1” board, especially since it has moved significantly recently.

I’d have no qualms about flattening it with a router sled but that may only work temporarily. As much as it is scary to cut that slab down the middle, that’s the only way to find out just how misbehaved it’s going to be. If it survives that and you can joint and plane it flat, you will save at least 1/2 the thickness that would be lost by flattening it all at once. Glued back, it will be strong and much less stressed. If it twisted more after ripping, I’d be very concerned about going through with the project for a customer. If they were ok with it, multiple rips can eliminate most of the stress, it just gets harder to hide the glue lines.

And polyurethane is not going to stop it from doing what it wants to...

Dan

[Andrew Hughes]

I don’t agree with Michael ripping the slabs and gluing them back together. Without a accurate jointer he might end up with a new set of problems.
I also still believe a jointer is the easiest way to flatin rough lumber.

[Michael Furey]

It’s really interesting to see the variety of responses and it makes me realize that some people must not have ever dealt with really “bad” wood. Twisting to me almost always means that there is some internal stress just waiting to be set free. While I’d love to be able to just slide that bad boy over a jointer and then plane it flat, I doubt you could do it without ending up with a 1” board, especially since it has moved significantly recently.

I’d have no qualms about flattening it with a router sled but that may only work temporarily. As much as it is scary to cut that slab down the middle, that’s the only way to find out just how misbehaved it’s going to be. If it survives that and you can joint and plane it flat, you will save at least 1/2 the thickness that would be lost by flattening it all at once. Glued back, it will be strong and much less stressed. If it twisted more after ripping, I’d be very concerned about going through with the project for a customer. If they were ok with it, multiple rips can eliminate most of the stress, it just gets harder to hide the glue lines.

And polyurethane is not going to stop it from doing what it wants to...

Dan

Yea after seeing everyone’s responses and watching some videos, I think my best bet will be to rip them, joint and flatten them and glue them back together. I’ll probably just do that.

I know polyurethane won’t stop the wood from moving in the future, but it’ll definitely minimize it compared to if it was left unsealed.

Thanks for the thoughts!

[Mike Cutler]

Michael

I think you'll be much happier ten years from now with the table.
It kind of sucks to have rip, re-joint, then reconstruct a nice piece of material but the nature of wood is that it will move.
Dan's post is particularly relevant. As you do begin to mill the slab, it will start to move again. Each piece of material will move at it's own rate. It's challenging, but fun.
Good luck.

[Robert Engel]

Any recommendations on what type of router bit to use?

I used Magnate planing bits. If you go with the 3" you need a pretty beefy router don't take more than 1/32 per pass.

Don't take it down to final thickness in one session. I wouldn't take more than 1/8" max off each side & resticker for 1 week.

Twisted boards are twisted because of internal stresses and are hardest to deal with.