How long for lumber to acclimate?

[Rob Luter]

I got a nice Cherry board from my local hardwood guy to make some boxes. I selected a nice 5/4+ board about 7” wide and 108” long, rough sawn. They store their stock in a closed warehouse that’s not climate controlled.

When I got it home I let it sit in my shop for a couple days before I did anything. I cut a couple 12” lengths off and flattened/trued one side with hand planes. I flipped it over and got the other side close, then ran it through my thickness planer.

The next step was to resaw, which went without a hitch. I ran both halves through the thickness planer again to get both to a uniform thickness, then smoothed with my 4 1/2 to eliminate mill marks. The surface was like glass. My confidence was bolstered.

Two days later I was able to get back in the shop. My perfect box sides were warped in both directions. They are unusable.

So….internal stress? Moisture content? Not enough time to acclimate prior to milling? All three? Hoping some Creekers wiser than I (and more experienced in resawing) can share some experience.

[John TenEyck]

Internal stresses and a large moisture imbalance both will cause resawed lumber to bend almost immediately. If your parts were flat after resawing, but then warped during the ensuing two days, my guess is you left the pieces face down on a bench. A small moisture imbalance in the board when you cut it, or a change in your shop's RH, both would cause the pieces to warp.

John

[Cameron Wood]

Leave as much time as you can at each step IMO, mill oversize and sticker the pieces in cooler spot with not too much airflow.

The plank will likely be drier at the ends, and drier on the outside faces (or the reverse, in less common conditions).

I have some wood (mahogany) that thickness that I've salvaged. It was outside under poor cover for years ending in the exceedingly wet winter.

Cleaned it up and did an initial surfacing, stickered the pieces, and now will keep an eye on it to see how much it moves. The earliest I will use it is next winter.

[Lee Schierer]

Internal stresses and a large moisture imbalance both will cause resawed lumber to bend almost immediately. If your parts were flat after resawing, but then warped during the ensuing two days, my guess is you left the pieces face down on a bench. A small moisture imbalance in the board when you cut it, or a change in your shop's RH, both would cause the pieces to warp.

John

A moisture meter is your friend when you are resawing lumber of unknown moisture.

Just to give you an idea of how log it takes for wood to dry inside. I applied some oil based stain to red oak a week ago. Today, I planed one surface that had been stained to remove the stain. Within minutes after planing the edge, some of the stain came out of the pores creating blotches on the surface of the wood. I had only planed off a few thousandths of an inch.

[Bill Dufour]

I see your humidity today is 89%. It will take a long time to dry out at that RH. You do not say if was ever dry. I would store the board on edge for a month or more before doing more then cutting to rough length. In my climate in summer I would let it sit for a week at least if kiln dried.
Bill D

[Richard Coers]

Did you let the cherry sit on benches, or did you sticker it so air could get all around the boards? Air has to get all around stock as you build. You can even mess up a freshly glued panel if there is a big change in humidity and you have it sitting on a bench.

[Rob Luter]

I see your humidity today is 89%. It will take a long time to dry out at that RH. You do not say if was ever dry. I would store the board on edge for a month or more before doing more then cutting to rough length. In my climate in summer I would let it sit for a week at least if kiln dried.
Bill D

It was kiln dried lumber. It was raining yesterday so the air outside was pretty juicy. That said, my shop (basement) hovers around 68° F and 30-35% RH most of the year. I use a dehumidifier if necessary to keep it stable.

Clearly mistakes were made on my part. As @John TenEyck suggested might be the case, the storage after resawing did not allow for optimal release of any moisture imbalance. It was indeed flat on my bench. I've not yet resawn the second piece I flattened and trued, which remains perfectly flay at 1" thick. Prior to doing so I'll make sure I can rack the resawn parts up somehow to assure they dry evenly.

The remainder of the plank is standing on end and will be drying a good long time before I use it. As my hobby evolves I find myself resawing more and more often. I want to get all this figured out. In the past I used lumber that I'd had for years and was plenty stable. I guess I didn't think about. I will next time.

Maybe my next must have gadget is a moisture meter. Any recommendations for one that works well but won't break the bank?

[William Hodge]

I have used Lignomat moisture meters for years.

It helps to use it a lot to get a sense of your conditions. I check my benches and lumber rack a lot to see how my shop is doing. Checking rough cut lumber as I pull stock lets me catch wet wood. Checking the fire wood has helped me to know that what I'm doing works. I get the MC down to 10% in August, it goes back up to 12% in October..

https://www.amazon.com/Lignomat-USA-...07802380&psc=1

[Lee Schierer]

I got a nice Cherry board from my local hardwood guy to make some boxes. I selected a nice 5/4+ board about 7” wide and 108” long, rough sawn. They store their stock in a closed warehouse that’s not climate controlled.

It was kiln dried lumber. It was raining yesterday so the air outside was pretty juicy. That said, my shop (basement) hovers around 68° F and 30-35% RH most of the year. I use a dehumidifier if necessary to keep it stable.

The fact that it was kiln dried could have been negated through storage in an non-controlled storage area depending upon how long it remained in that space. That is why I purchased my Mini Lingo moisture meter.

[Jim Becker]

There are so many different "little things" that can lead to this kind of thing. While we can expect that KD lumber has been "dried", that process doesn't necessarily mean the moisture content is even through the entire piece of lumber. So as we "slice and dice" it, each surface may initially have a different moisture content that needs time to equalize. When we surface the lumber after that, we have to be sure to try and take equal amounts off both sides...and the fun with that is that we can't forget that face jointing plays into this since before we start officially thicknessing, we've already removed material from one face. This is completely separate from internal stresses that might be released when we resaw or surface/thickness. They were "in the wood" as it was originally surfaced (or not surfaced) when we acquired it and changing those surfaces by machining can result in further stress relief.

A couple of years ago I did a big project for a client using clear white pine that I had to source a bunch of. It was KD and very nice. But it still moved after initial surfacing to "see what I got". I ended up stacking and stickering the rough components on that project about three times over two weeks before going for final dimensions because of that continued movement from moisture release and tension release. IE...it required a lot of patience. And flat/straight/true was absolutely necessary for that project because it was for about a dozen tack room locker doors for an equestrian facility.

[John TenEyck]

Moisture meters are only good to a point. A surface pin meter only tells you the MC near the surface and would have been of no help in this case unless you had resawn a small piece to check the middle. Dual depth meters are more helpful in seeing how much gradient in MC there is in a board. I have one that reads at both 1/4" and 3/4", so that gives me a good idea of what's going on, but some extrapolation is still required if I'm working with 8/4 or thicker stock. Of course we all want our lumber to have a constant MC from surface to center, but that's almost never the case. Lumber changes MC as the RH changes, and the surface when open to the air changes pretty quickly as you saw.

Your comment above is strong evidence that there was a substantial gradient in MC. The resawn piece warped while ..."the second piece I flattened and trued ... remains perfectly flat at 1" thick."

If you plan to resaw a lot you'll want/need to have your lumber with as consistent a MC as possible, which means checking the MC and/or letting it acclimate. But there's no benefit in letting wood acclimate if it has the about the same MC as your shop. Use it. Commercial shops certainly do, every day. And for pieces you plan to plane to final thickness it's not nearly as important as long as you remove relatively the same amount from both sides, as Jim discussed above.

All is not necessarily lost when parts with unequal MC warp. Often, they will straighten out again if you just let them acclimate by allowing air to freely circulate. A day of patience often pays rewards.

I recommend you consider raising the RH in your shop to something in the 45 - 50% range. 30 - 35% is far below the average MC for the area where you live, and contributory to the warping you had on the resawn wood. Wood has to be down to about 6% MC to match that RH. That's at the low end of most KD lumber. 45% RH is 8% MC, and probably more like what newly purchased wood will be. A moisture meter will help you learn what the best range is for your shop. I keep mine at 50 - 55%.

John

[Bill Dufour]

I bought one of those self inking date stamps. I date stamp the ends of good lumber I put on the rack to dry. Not a moisture meter but I know if it stays one summer in the shop, in this climate, it is dry if it is not too thick.
Bill D.
https://www.amazon.com/AmazonBasics-...08BM7V6VF?th=1

[Rob Luter]

Update........


I placed the two warped boards on edge for a few days and as was suggested above, the warpage has mostly gone away as the moisture content reached equilibrium. I'll give it another week than true them up if need be.

I'm planning on making a few dedicated stickers or maybe a small drying rack that will allow the boards to be placed on edge to dry.

[John TenEyck]

Glad to hear that, Rob. Your results are a great example of understanding how wood can move and that just waiting for the moisture to equilibrate is often all that's needed to "solve" a warpage problem.

Thanks for the update.

John

[Cameron Wood]

I have four batches of stickers in different spots- two outdoor (milk crate works good), not counting the assortment of cauls for assembly/glue up.

Cedar is good. Also I grabbed a big bunch of Ipe stickers at the lumber yard out of their dumpster. Both relatively non staining & little affected by water.