Warped

[Mike Davis]

More like curled i guess?

When ever I resaw a board it looks fine, I plane it and it's flat, then after about a week it is curled across the grain.

I'm pretty sure it is caused by a difference in moisture from one side to the other. The wood is dry inside and my shop is very damp from all the rain lately.

So, beside building a new shop, heavily insulating the one I have or adding very expensive heat and air conditioning, what can I do to help with this problem?

I can't take all my wood into the house, usually not even the wood I'm working on.

I do have this last project inside now, but it's not much warmer nor drier in here than the shop.

Any ideas or am I doomed to the round side? :rotflm:

 

[Marlin]

What I did to my shop when I bought our house was to seal it up. I did that by caulking all the seams I could find, putting up some R13, painting all the cement bricks near the floor with water blocking paint, and replacing the garage door.

Now you can always get a dehumidifier and run that on low setting to get the mositure content to about what the house has. I say low setting to not work to fast but to also keep any extra water from getting in.

 

[DaveO]

What are you doing with the wood after re-sawing and planing? You are correct there is often a difference in moisture content between the inside and outside of thicker stock. No matter how dry your wood is it will reach equilibrium with the environment it resides in. If your shop has a high RH then very dry wood will take on moisture. Then when you bring it inside the house with a lower RH it will lose moisture. Different rates of moisture movement on opposing sides of stock is what causes warping and cupping.
The only two things that I can suggest is to stack and sticker the re-sawed wood and give it some time to equalize. And run a dehumidifier in your shop to keep its RH level similar to where the wood will finally reside. Another added bonus is the DH will add a little heat in the winter, not such a great thing in the summer.


Dave

 

[Mike Davis]

I soaked the cupped side of each board with a wet rag and it is starting to straighten out.

Once I get it glued in place the dados will keep it in line well enough.

Before I start another project I have to do some serious thinking and probably spend some money on the shop. Or give up trying to do flat work until I can get a better situation.

 

[PeteM]

I first resaw to rough (over-size) dimensions, sticker it and weight or clamp it down flat for a week or so to let it equalize. Then when I go to final thickness I try to take equal amounts off each side. If the boards are going to sit a while before I get back to them I'll either put them back under weight or at least stack them on edge with some room for air flow between them. Seems to help.

pete

 

[jeff...]

dehumidifier

 

[Mike Davis]

Wetting the curled side worked.

 

[sediener]

So we should aim to keep our shops at the average humidity the piece will eventually see? What is that exactly? 50% or so?

How do you guys deal with movement after milling/resawing? DaveO just helped me resaw some boards and after resawing they bowed toward the cut line. How long do you let it acclimate and then if it doesn't straighten out do you rejoint and then let it acclimate again or just joint and build (which is what I did)?

 

[scsmith42]

So we should aim to keep our shops at the average humidity the piece will eventually see? What is that exactly? 50% or so?

Steve, it depends upon the temp inside the shop. Here are some stats:

Note: "EMC" refers to "Equilibrium Moisture Content", ie the MC that the wood will eventually stabilize to.

60 degrees F, 50% RH, EMC = 9.3% MC
60 degrees F, 40% RH, EMC = 7.7% MC
60 degrees F, 30% RH, EMC = 6.3% MC

70 degrees F, 50% RH, EMC = 9.1% MC
70 degrees F, 40% RH, EMC = 7.7% MC
70 degrees F, 30% RH, EMC = 6.0% MC

80 degrees F, 50% RH, EMC = 9.0% MC
80 degrees F, 40% RH, EMC = 7.6% MC
80 degrees F, 30% RH, EMC = 5.9% MC

 

[Glennbear]

Sometimes it is the simple things that we forget. Are you letting BOTH sides of the resawn stock have air circulation ? When I first started planing my stash of recycled heart pine I had a cupping problem until I realized that by leaving it lying on the work bench after planing it I was causing unequal moisture loss. Once I allowed for air circulation on all 4 sides my boards no longer started to resemble salad bowls :gar-La;

 

[Mike Davis]

So, I should resaw, stack and sticker for at least a week, then plane?

 

[Tarhead]

I take the 2 pieces of freshly resawn lumber and put a piece of 3/4 plywood between them (with the fresh cut side of the lumber facing out). Then C-clamp every ~6" around the plywood sandwich and leave it alone for a week. It gives time for things to settle down and all those evil warping spirits to come out. No matter how dry the lumber is it warps/curls every time.

 

[sawduster]

Couldn't help it .....saw " Warped " and Mike Davis and said to myself
" yeah ......so what " ? :rotflm::banana::kermit:

 

[DavidF]

I first resaw to rough (over-size) dimensions, sticker it and weight or clamp it down flat for a week or so to let it equalize. Then when I go to final thickness I try to take equal amounts off each side. If the boards are going to sit a while before I get back to them I'll either put them back under weight or at least stack them on edge with some room for air flow between them. Seems to help.

pete

This is my solution as well, Creep up on the final dims over a period of weeks and then get it glued up as soon as possible. It goes against the way of working to machine everything to the same dims at the same time, but it does prevent the warping problem. I only machine to final dims when I am ready to use it. With the new digital height/angle gauges and digital table saw fence it is easier to return to a known dim. I then tend to bring the assemblies into the house so our hall tends to be filled with wood when a project is underway!

 

[joec]

I had a warp problem on a raised panel door, using a solid wide board for the panel. Recently I was making a wide panel using a 12" board for the center and sawed through the middle of the 12" board and jointed and glued it back together. The grain obviously matches and I was thinking that this should decrease the chance of warpage. So far so good.

 

[DaveO]

I had a warp problem on a raised panel door, using a solid wide board for the panel. Recently I was making a wide panel using a 12" board for the center and sawed through the middle of the 12" board and jointed and glued it back together. The grain obviously matches and I was thinking that this should decrease the chance of warpage. So far so good.

Joe, I'm sorry ripping a wide board in half and gluing it back together will not make it behave like a different board. The only thing that will achieve it to put a glue line in the middle of the board. Unless you have a center cut board and you rip it to remove the center pith, ripping boards to narrower width will not prevent/decrease movement related to moisture exchange.


Dave

 

[DaveO]

So we should aim to keep our shops at the average humidity the piece will eventually see? What is that exactly? 50% or so?

How do you guys deal with movement after milling/resawing? DaveO just helped me resaw some boards and after resawing they bowed toward the cut line. How long do you let it acclimate and then if it doesn't straighten out do you rejoint and then let it acclimate again or just joint and build (which is what I did)?

No it isn't important to keep your shop environment the same as where the piece will reside. That is why furniture is built to accommodate the movement of wood. It is important to understand how and why wood moves and to take measure to keep that movement equalized, minimized, and allowed to move freely.


Those boards that we re-sawed might have had some internal tensions, or could have reacted to the heat created by re-sawing. IIRC the boards that moved the most were the ones with the crotch feather in them (internal stresses). A week or two should be long enough to allow the newly cut surfaces equalize with their new exposure. If the boards don't calm down they probably never will.

I had a neat lesson in acclimation recently. I planed a bunch of 4/4 Red Oak stock, that I know was kiln dried well, down to 5/8". I built the piece and had a little bit of scrap left over for finishing tests. A couple of the pieces of scrap were lying broad face down on my bench. The next day they had cupped upward. I then turned them on their narrow edge and the next day they had flattened out again. I had a different rate of moisture exchange from the opposing board faces. The one against the bench exchanged less moisture than the face that was fully exposed.


Dave

 

[joec]

Joe, I'm sorry ripping a wide board in half and gluing it back together will not make it behave like a different board. The only thing that will achieve it to put a glue line in the middle of the board. Unless you have a center cut board and you rip it to remove the center pith, ripping boards to narrower width will not prevent/decrease movement related to moisture exchange.


Dave

I read a long time ago the degree of warp in a board was related to its width in relation to its thickness. A wider board would warp quicker than a narrower one. By taking a wide board, ripping it in half, gluing it back together again, would make the grain look consistent and also put two smaller boards side by side. This was something I came up with without any knowledge of its effect, but it seemed to make sense. Also, I could take the two boards and they would fit on my 8" jointer, whereas they would not as a 1"X12". Thanks for the heads up.

 

[Rod]

Let me know if you need to borrow a dehumidifier for a while. I will be in W-S next week sometime I'm sure.

 

[Mike Davis]

Rod,

I'm terribly sorry I haven't called. We have a huge project going at work and I have been working on a storage rack for some work related equipment. I even worked a half day today on my vacation.

I'm home the rest of the week, so let's get together.