Bowed cutting board

[FS7]

Your evaporation differential is too much as it is with only one side oiled. That, or the side that's swollen was directly on a surface and wouldn't equalize. Slop oil on the unfinished side, and then; put little feet on the bottom--maybe, rubberized--so it won't slide off the counter and will weather equally.

One way to keep one face from soaking in more mineral oil than the other is to place the entire board into a pan that is deep enough to hold the board and oil above and below the board. When you do this, the board will float in the oil, so you need to provide some way to hold down on the top of the board to keep it submerged. Since your board has one face that has soaked in more oil than the other, I would try this method. Let it soak for a couple of days held down so it is completely submerged. The oil should even out on both surfaces which should flatten it out.

This is next. I have since trimmed about 1/16" off all the edges, re-routed, and sanded. It's standing on edge in the gun room, where I put misbehaving lumber to think about what it's done. I have a table top in there that has returned to flat and I've been waiting to get back to that project. Hopefully it will be able to breathe a bit better and might even out some. After that, I will need to buy some more mineral oil and make sure the plastic bin I have can fit the boards.

When I made the board I may have been too aggressive. It's mostly maple and walnut checkerboard, with a middle strip or either bubinga or bloodwood (I don't remember and I can't tell from the end grain). The saw was slightly out of alignment when I ripped, so the checkerboard corners weren't perfect. I was probably being too cute when I did this, but I ripped 1/8" channels along the seams and glued in thin strips of Chakte Viga. I figured this would add some detail and hide the imperfect joints at the same time. It did, but I know now it's definitely moisture since the normal expansion direction of wood is in the long direction of the board (because of the end grain) and I can see that the accent strips are about 1/64" shy of where the rest of the board is. The fact that I did this only the top may have hurt things too.

I will move on to other boards and let this one sit a bit.

[rwe2156]

A just punishment for such misbehavior would be put the panel in cauls & clamps * hopefully it will get its act together.

Sometimes you have to use more radical methods.

By this I mean one of two ways, neither of which are very good options for you, but worth mentioning:

1. Plow a groove (or grooves) down the length almost through to the top, clamp the board slightly overcorrected, and fill the groove with either a spline or epoxy, or both.

2. Rip the panel apart and reglue.

3. Re flatten

That said, how did you store the panel?  If you laid it down on a table, that is what caused the issue.

Also, was the wood totally acclimated?

[FS7]

A just punishment for such misbehavior would be put the panel in cauls & clamps * hopefully it will get its act together.

Sometimes you have to use more radical methods.  

By this I mean one of two ways, neither of which are very good options for you, but worth mentioning:

1. Plow a groove (or grooves) down the length almost through to the top, clamp the board slightly overcorrected, and fill the groove with either a spline or epoxy, or both.

2. Rip the panel apart and reglue.

3. Re flatten

That said, how did you store the panel?  If you laid it down on a table, that is what caused the issue.

Also, was the wood totally acclimated?

The wood should have been acclimated. It was bought dried, planed, and sat in the shop for a while prior to use. After final dimensioning, I had it oiled (unevenly, apparently) sitting on painter's pyramids in the shop. There wasn't really any good reason that airflow wouldn't have been good on both sides, but I am pretty sure one side had a lot more oil than the other.

When I set it out in the grass the sun caused it to cup. That has since been mostly corrected. The bow, however (long dimension) is very slow to move. It's hard to tell if it's moving at all.

What might actually be nice would be to add splines in the short dimension that are slightly oversized. If I could do what you say and clamp it flat, I could possibly route 1/8" channels along the checkerboard seams, clamp it past flat, and glue in something like 17/64" strips to push it towards flat. That would actually go well with the existing design I had. The hard part here would be getting it flat enough to route or dado with the saw.

[Alan S]

... I ripped 1/8" channels along the seams and glued in thin strips of Chakte Viga.... the normal expansion direction of wood is in the long direction of the board (because of the end grain) and I can see that the accent strips are about 1/64" shy of where the rest of the board is. The fact that I did this only the top may have hurt things too.

I think you have identified the problem.  Are these strips on the concave side?  They should have a bigger effect than the mineral oil.

If these accent strips have grain that runs along the surface of what is otherwise an endgrain board, they are very likely to cause warping by limiting the expansion and contraction on that side of the board.  Shrinkage would put them on the convex side if the board is drier than when they were glued in, and expansion onto the concave side when it's moister. 

If the grain of the strips were parallel to the other grain of the board, this would not apply.  Crossgrain strips are a problem.

[FS7]

I think you have identified the problem.  Are these strips on the concave side?  They should have a bigger effect than the mineral oil.

If these accent strips have grain that runs along the surface of what is otherwise an endgrain board, they are very likely to cause warping by limiting the expansion and contraction on that side of the board.  Shrinkage would put them on the convex side if the board is drier than when they were glued in, and expansion onto the concave side when it's moister. 

If the grain of the strips were parallel to the other grain of the board, this would not apply.  Crossgrain strips are a problem.

This makes sense. I could rip them out and let the board equalize again, assuming that without that limiting movement and stressing the wood it should flatten out. That would leave gaps to fill, though. I could try to fill them with endgrain pieces, but that's probably a fair amount of work on the bandsaw. I could essentially recreate the design, just with the proper grain orientation. 

I might also just plane it and lose that 3/16" or 1/8" off the board's thickness. Wouldn't be the end of the world.

I think it makes sense to rip the accent strips out and see if the bowing fixes itself. If not, no reason to lose any more of the board.

[daddo]

Frankly I wouldn't have a problem cutting on a slightly bowed cutting board. Most meats and veggies aren't naturally flat anyway.

[FS7]

Frankly I wouldn't have a problem cutting on a slightly bowed cutting board. Most meats and veggies aren't naturally flat anyway.

You're right and I accept a little bit of warp on most of my boards. I use rubber feet with stainless screws and I use neoprene washers under the feet when there is some wobble. What you're cutting usually isn't flat, and lots of countertops and tabletops aren't dead flat either. Take a board and move it around to different "flat" surfaces in your house and you'll find that a lot of them aren't actually flat and level.

In any case, this was a bit more than I wanted to accept, especially since it can be one of my nicer pieces.

I ripped out some channels (about 1/4" deep, 3/8" wide for the six middle ones and 1/2" wide on the outside) and the stress relieved almost immediately. I put some water on the concave side and it's now almost perfectly flat after all of 10 minutes. It might be tedious, but I can now take 3/8" and 1/2" hardwood, cut it into small strips, and glue it into those channels so the grain matches what's already there. Even better, I can do some creative designs with different woods. It's wildly impractical to put this much effort into a cutting board, so I'll almost certainly keep this for myself.

I'm a little upset that I made such an obvious mistake after all these years.