How to flatten a twisted board

[Michael Furey]

I’m building a table with live edge slabs. It’s going to be 3 slabs wide. They’re white oak about 16” wide each and I cut them down to 6’ long. I had them standing up in my garage for quite about 8 months. Before that they were cut and dried for about 4 years. I have 2’issues I’m trying to solve. One is the boards have started cupping a little. Some spots are bad (about a 1/2” difference). I was thinking of renting a floor sander to flatten these out since I don’t have a commercial planer or drum sander. Any thoughts on that? My biggest issue though is one of the boards is pretty twisted. When on a flat surface, the one corner is raised by about a 1/2”. What’s the best way to fix the twisted slab and get it flat?

[Robert Hazelwood]

That table sounds like it will be pretty wild.

I think your options are to make a router sled, or to use an electric hand planer (or a jack plane) and winding sticks to get it flat then hand planes or a sander to get it smooth. It will be a lot of work to flatten a 16" wide slab that is 1/2" out, but it can be done. Keep in mind that you will be removing about 1" from the max thickness to take all of the twist and cup out (1/2" from each side). So think about if there will be enough material left at the end. If not, one way to reduce the amount you remove is to rip the slabs in half, flatten each half individually, then glue them back together.

Flatsawn slabs are not going to stay flat though. The support structure will need to be designed so that it holds the slabs flat (and it will need to be stout to overcome a thick slab) while still allowing them to expand and contract across their widths.

[Michael Furey]

That table sounds like it will be pretty wild.

I think your options are to make a router sled, or to use an electric hand planer (or a jack plane) and winding sticks to get it flat then hand planes or a sander to get it smooth. It will be a lot of work to flatten a 16" wide slab that is 1/2" out, but it can be done. Keep in mind that you will be removing about 1" from the max thickness to take all of the twist and cup out (1/2" from each side). So think about if there will be enough material left at the end. If not, one way to reduce the amount you remove is to rip the slabs in half, flatten each half individually, then glue them back together.

Flatsawn slabs are not going to stay flat though. The support structure will need to be designed so that it holds the slabs flat (and it will need to be stout to overcome a thick slab) while still allowing them to expand and contract across their widths.

Understood, I don’t know if I want to rip it in half and then flatten them. If I have to I will though. Once I have them flattened, I’m going to polyurethane the top and bottom to try and minimize the amount of moisture changes. The base will be a trestle style base made of of 3x3 oak. I then attach the top to the base along the length with 2x4’s down the length, close to the edges. I drop large holes in them and secure the top with a screw and a fender washer. It’ll hold it down to the base but allow the top to expand and contract.

[Pat Barry]

1/2 inch over 6 ft really isnt all that much. Work down the high spots and let it re-aclimate. It may or may not stay flat. Battens should restrain it. I would recommend getting it flat, clamping it with cauls and see how it goes. No way I would remove a huge amount of material, because, who knows what will happen next.

[Andrew Hughes]

The best way to flatin a twisted plank is a jointer then you send it through your planer to get two parallel sides.
All other methods are second to this.

[Robert Engel]

The best way to flatin a twisted plank is a jointer then you send it through your planer to get two parallel sides.
All other methods are second to this.

Andrew, he would have to have a 16" wide jointer.

Michael -

When did they start cupping? Or did you just notice it. I'll be they have been cupping over the last 8 months.

Slabs can take a very long time to acclimate, up to 10 years depending on thickness. The fact they are cupping may also be the result of uneven drying do to stacking against the wall. I would move them to stickers and stack them horizontally. Keep the convex sides up.

You could use a moisture meter and take monthly measurements, record and see when they stabilize.

IMO, I would not start milling this lumber until its done moving. If you do, you may end up with much thinner slabs than you want!!

But the way to go is a router sled. Check the WoodWhisperer he has a good video on making a plane sled for flattening slabs. I used a Magnate planer bit worked quite well when I flattened a workbench top.

[glenn bradley]

If I read your original post correctly you are in the position of wanting to use this material in a slab format. although ripping, milling and gluing can bring you closer to flat without as much material loss, you lose the look of the slab. In the absence of a large jointer or large planer and sled, I agree with Robert E. that a router sled is your best option.

[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.

[Joe Chritz]

Not sure where you are at but if you look around you can often find shops that will do some machining for you for a reasonable cost. I live in the middle of nowhere and I have one about 7 miles away with a huge jointer and a 43" wide belt. It may be worth looking around.

[Russell Sansom]

With a scrub plane you can take almost any twist down in a few minutes. It does depend some on the grain direction ... you have to be careful not to tear out below the finished level you're hoping for. But with a few preliminary cuts you will know which direction to go and if that's going to rip out counter-grain chunks.


In a pinch you can put a highly-cambered iron into a jack plane; an option that might be cheaper than renting a sander. If you haven't gone this route before, you should be prepared for some pretty deep scallops. Those take a bit of work with a jack plane, then a jointer or #6 or...well...shudder...a belt sander.


I built a table once from an enormous billet of mahogany that a friend had shipped back from Africa ( 50 years ago ). It was 4 inches thick, 40 inches wide and 6 feet long. I let it sit on edge for 5 years. Then I incised a kerf around the perimeter ( 2 " in from the edge ) and for 20 minutes every morning I hand-sawed down the middle with a big one-man pit saw. Three weeks later I had two slabs. 40" X 6' and now 2" thick. I stood them on end, presumably for a few days to let them adjust to my shop's perfect humidity.


To my horror, when I checked them a week later, they had wound into spirals! It's a long story, but the upshot is that my nutty fantasy of ending up with two enormous 2"-thick slabs of mahogany was crushed. I cut them in half lengthways and those 20" boards pretzeled. After cussing some and sleeping on it, I cut them lengthwise again into 10" boards with the yet more mad twisting in the result! I figured my only hope was to release the imps from this timber a bit at a time, in 1/16" steps. It took several months but patience was rewarded with eight one-inch thick boards.

You might not have 5 or 6 years to lead yourself towards a lesson like this. I guess the two points in this are, 1) consider sawing those puppies in half anyway ( they should be glued up in opposition to each other if you're going to finish them with a sander anyway ) and, more importantly, 2) patience is one of the tools you might need for this job. If you can afford a few months, at least trying relieving the stress in small increments with a few days in between. If you take out all that twist all at once, and you keep doing that until it's all flat, you might end up with several sheets of veneer.
Cheers