Cupped boards after milling

[Matt Day]

I moved to Ohio about a year ago, which is not as humid as Virginia where I lived for a number of years and more humid than Utah which I lived for one year. I've gotten lumber from 2 different yards, and each one I've had more movement in the wood than I had when I lived in VA and UT. I'm doing the same stock prep, and leaving in the shop for the same amount of time (roughly).

Generally I'll mill the wood after about a week of it being in my basement shop, but I had two 10"+ boards that cupped over 1/4" which is substantial and rendered the boards useless for what I needed. Could it be just these specific boards, or the drying process at the kiln?

I know I should try to joint/plane equal amounts on either side to try to mimimize movement which I do, but I'm wondering if there are any tips or tricks I'm missing or should try. I thought about kind of doing a skip plane/joint, letting it equalize for a week, then doing the final milling, but I'm not sure.

Any thoughts?

TIA

[frank shic]

did you check the moisture content of the wood?

[Alan Schwabacher]

Boards will tend to cup as humidity changes, wide ones noticeably. It may just take longer to reach equilibrium with your shop now, or your shop may not be as stably conditioned as before.

If you dampen the inside of the curve and/or put the outside in direct sun, they may flatten out enough for you to cut joinery. Or for handwork, you can simply clamp them flat as you cut the joinery. Once assembled, the structure should restrict their movement. If that won't work for what you're building, quartersawn stock would be a good choice.

[Al Weber]

Even though you buy the lumber from different yards doesn't mean it was dried by those yards. Many times they all buy from a mill/kiln operation and if the kiln operation isn't done properly you will see this kind of problem. First I would invest in a moisture meter for future purposes. Second, I would try to find a local mill/kiln operation that will allow you to check moisture content and pick your own lumber. They tend to be more user friendly and many times more quality oriented than the ones who sell to other retail sources. I've run into operations where my entire purchase was garbage due to improper drying techniques. Needless to say, I never went back there for purchases.

[joe milana]

I've tried every trick in the book when I come across wood like that, but none ever seem to work. Even If I can get it flat, I let it sit for a few days and it will move.
What kind of wood, and where did you get it? If a local sawmill, take a piece back & show them. See what they say. One or two board doesn't really tell a story, but maybe they'll offer you a couple more boards to try.

[Kevin Bourque]

Did you stack the wood to allow equal airflow over both faces of the boards?

[Matt Day]

I normally don't sticker my lumber once it's home - shouldn't it be dried by the time it gets to me? Do most of you sticker your wood?

Thanks for the advice on the moisture meter. Does any suggestions for a reasonably priced one? I'll do a search on here too, I'm sure this has been talked about ad nauseum.

[Kevin Bourque]

I normally don't sticker my lumber once it's home - shouldn't it be dried by the time it gets to me? Do most of you sticker your wood?

Thanks for the advice on the moisture meter. Does any suggestions for a reasonably priced one? I'll do a search on here too, I'm sure this has been talked about ad nauseum.

Air passing over one side of a board and not the other will cause cupping regardless of moisture content.

[joe milana]

Matt, Some guys sticker their KD'd lumber & some guys don't. I believe if the sawyers chime in here they will tell you it's not necessary once wood is kiln dried. I used to because I thought it would help, and it looked cool. Now I have too much wood on hand, and it would double my storage requirements. Just use some common sense practices, like don't store your wood on a damp concrete floor. If you store it outside, or in an un conditioned space, bring it in for a couple weeks before putting it to use.

As far as moisture meters, I have a really nice ($$$) one. Since I buy only Kild dried wood, it does me little good. I used to check everything, then I found out the information tells me little to nothing. If I came across some reaction wood, I would check the moisture content. Sometimes it was right on, sometimes a bit high, and sometimes a bit low. If I came across some really stable wood, I'd check it too. Same thing...high... low...and sometimes right on. YMMV. If you are going to air dry your own lumber, then a moisture meter will help.

Wood that cups 1/4" across 10" is just "bad wood"

[Jim Andrew]

I had some ash that I thought was dry, have a cheap moisture tester, and planed the boards, and after a few days was going to use them, when I found them no longer flat, cut off a small piece and had it checked by someone with a good tester, and it was about 3% more moist than my tester showed. I just left the boards lay and later they went back to flat after getting dryer.

[Scott T Smith]

Matt, a few questions before I chime in with suggestions....

1 - what species?
2 - what thickness?
3 - what milling pattern (flat sawn, rift, quarter, ??

Did you sticker after joint/planing?

Was the wood recently resawn from a thicker board?

Can you post a photo showing the ends of the boards? I'm interested in seeing not only the cup, but also the milling pattern.

Thx.

Scott

[Matt Day]

Scott,

1. Maple
2. Originally 4/4 rough sawn, jointed/planed down to ~5/8
3. flat sawn

The boards are about 11" wide (and about 60" long) and I have an 8" jointer, so I joint the face with 2" overhanging, then plane the opposing face with a sled & the 2" overhanging. (You know what I mean ;) ) IIRC, these boards were not the flattest/straightest boards to begin with so I lost some material while milling. They were not resawn, and I did not sticker them after miller.

I just realized I really should have flipped the board over in the picture, but take my word for it there is 1/8" gap on either end.

[Scott T Smith]

Scott,

1. Maple
2. Originally 4/4 rough sawn, jointed/planed down to ~5/8
3. flat sawn

The boards are about 11" wide (and about 60" long) and I have an 8" jointer, so I joint the face with 2" overhanging, then plane the opposing face with a sled & the 2" overhanging. (You know what I mean file:///C:\DOCUME~1\Scott\LOCALS~1\Temp\msohtmlclip1\01\cl ip_image001.gif) IIRC, these boards were not the flattest/straightest boards to begin with so I lost some material while milling. They were not resawn, and I did not sticker them after miller.

I just realized I really should have flipped the board over in the picture, but take my word for it there is 1/8" gap on either end.

Matt, in both instances it appears that your lumber cupped towards the bark, which is the normal tendency of wood cells to shrink as they dry. There are a couple of different potential scenarios to what caused your boards to cup.

It is interesting to note that your cup does not appear to be centered over the pith in the boards.

Scenario 1 is that the boards had a higher moisture content in their core versus their shell. If you joint/planed an equal amount from each side, this would be my guess due to the fact that both boards cupped in the same direction - i.e. towards the bark side.

Scenario 2 is that you jointed a minimal amount from the pith side of the board, and then removed the bulk of the material from the bark side of the board. In the photo both boards are situated with the bark side down.

Scenario 3 is that both boards were laid on a flat surface with the bark side exposed on each board, allowing the bark side to be exposed to air while the moisture was trapped on the pith side of the boards.

In the future, if you can remove equal amounts from both sides of the board when joint/planing, and then stack/sticker them afterward, I think that you'll find that the potential for problems is reduced.

You may be able to fix this. One morning where the forecast is for a sunny day, lay the boards out on your yard for 30 min to an hour, with the cupped side down. Leave them there long enough to not only flatten out, but to cup very slightly in the other direction. Then, bring them into your shop, and stack and sticker them. Let they stay that way for a few days.

I have successfully straightened cupped boards this way before, and with your minimal cup you should be able to achieve this.

[Don Jarvie]

A few suggestions. Joint one side so it's flat and if you leave some rough areas that's fine because the goal is flat. Run then through the planer a few times on each side so there around 7/8 and then attack and sticker them and let them sit for a few days. Recheck them and see if they moved. If they did joint and replane.

[Dale Cruea]

I thought about this for a while.
I have found that, wood will normally move for 2 reasons.
1) if the wood moves as soon as it is cut there is stress in the board. This comes from a bad drying schedule somewhere. Wood is no good.
2) If the wood moves after a few hours of milling it is due to moisture. Either getting into the wood or leaving the wood.
Wood should always be stored after it has been milled so equal air can get to both sides.
I have had some luck with bowed stock taking a wet towel and a very hot iron to the concave side. The covering that side with a dry towel for an hour or so until the heat leaves to board.

[Keith Christopher]

I always sticker after milling from the rough. I've had too many wide boards. I am assuming these were rift sawn which is another big problem.

Have you thought about using a thin kerf blade rip them down the lowest part of the cup and biscut them back together ?