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.

[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

[Steve Rozmiarek]

You can design a way of attaching the top that will pull the twist out if the top is relatively thin, like 1" or less.

[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.

[Doug Dawson]

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?

Rip the slab lengthwise, surface each piece flat, and glue them up. (You may have to stop to let the slab pieces acclimate before doing final surfacing, monitoring the pieces with a moisture meter.) The visual deviation from a single slab will probably be slight to unnoticeable, and long-term stability will be improved.

Whether you do that or not, i.e. even if you don't, a scrub plane is your friend (as somebody else mentioned.) It can take care of large stock removal quickly and efficiently, if you stop just before you get to the finished thickness.

[Michael Furey]

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.

I’m not sure exactly when they started cupping, but I noticed it about 4-5 months ago. I know when I bought the slabs they were flat. They were dried horizontally on sticks. Then I took them home and stood them up in my garage against the wall. Mainly because they were 10’ slabs that I had no room for. I cut them down the other day to 6’ and 2 of them don’t really have much of a twist to them, just the cupping. I’m not really too worried about that. They’re 2” thick, if I end up with 1 1/2” slabs, I’d be perfectly fine with that. The 3rd slab is the issue. I took care of a good amount of the twist by cutting it down to 6’, but some still remains. Unfortunately these are for a customer and I don’t have time to restack then and let them straighten. I told the customer about the issues and what could happen. They were ok with that. I’m just going to build a router sled and take all of them down to probably 1 1/2” (the twisted board will probably go down that much, so I’ll plane all of them to match that thickness). Any recommendations on what type of router bit to use?

[Michael Furey]

Rip the slab lengthwise, surface each piece flat, and glue them up. (You may have to stop to let the slab pieces acclimate before doing final surfacing, monitoring the pieces with a moisture meter.) The visual deviation from a single slab will probably be slight to unnoticeable, and long-term stability will be improved.

Whether you do that or not, i.e. even if you don't, a scrub plane is your friend (as somebody else mentioned.) It can take care of large stock removal quickly and efficiently, if you stop just before you get to the finished thickness.

I appreciate the help with resolutions but I’d really rather not rip it down to flatten it. This is going to be the middle piece of the top so I’m going to take a decent amount off the edges to begin with, but there’s a lot of nice looking grain and some really cool spalting that I really don’t want to cut into if I don’t have to. I’m sure it won’t be very noticeable...but I’ll notice it and it’ll drive me crazy! Haha. I’m going to try and do the router sled. If I only end up taking of 1/4” then I’ll be happy. I’ll just polyurethane it or oil it all around, top and bottom to prevent anything more movement from happening.

[Adam Bullington]

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

[Doug Dawson]

I appreciate the help with resolutions but I’d really rather not rip it down to flatten it. This is going to be the middle piece of the top so I’m going to take a decent amount off the edges to begin with, but there’s a lot of nice looking grain and some really cool spalting that I really don’t want to cut into if I don’t have to. I’m sure it won’t be very noticeable...but I’ll notice it and it’ll drive me crazy! Haha. I’m going to try and do the router sled. If I only end up taking of 1/4” then I’ll be happy. I’ll just polyurethane it or oil it all around, top and bottom to prevent anything more movement from happening.

In that case, the scrub plane (along with some winding sticks) is still worth trying, save you some time and aggravation. You may want to look at some Rob Cosman videos about this on Youtube, he crazy, everything but the tricorn hat. :^)