Wood movement

[transatlantic]

So this is an offcut from a project I am working on. As you can see, it has warped rather substantially. Although the pieces weren't perfectly flat when I glued it up, they were flat enough. However, now it is clearly awful. Each pieces has cupped, with the pieces on the end affected most.

This material was purchased from a local merchant and was advertised as PAR Redwood Premium Joinery.

- Would it have helped if I had used opposing grain patterns? I didn't here because I read it often makes no difference, and in this particular case, the wood looked nicer the way I had it, but now I'm wondering if it was a mistake.

- I don't have a jointer yet, but lets say I did. If I had left the boards to acclimatize for longer (I left them for a week before gluing), and then planed the cup out of them. Why wouldn't it still have cupped even after that? wouldn't I be in the same situation only with thinner boards?

- When I was sanding this pine, I noticed a very strong pine smell, stronger than I am used to (I usually get small bits from Wickes), and the sandpaper seemed to clogged up quicker. Is this a sign that the wood wasn't as dry as it should be? .. or could this just be the wood resin?

- When I glued it up, it was reasonably flat. Should I have immediately applied a flattening mechanism such as bread board ends to keep them flat? Or would that just put the stress elsewhere? This has actually been left a week and there was no flattening mechanism in the design, just 4x 5ft boards glued up.

 

[Steve Maskery]

Those boards have a very pronounced curve to the grain, they are cut from small diameter trees. So when the wood shrinks tangetially, the rings straighten out. That is what has caused the cupping. If you had arranged them alternately heart side up and then heart side down, the cupping would have cancelled each other out. Each would still have shrunk and cupped, but overall the board would have remained flat. Wavy but flat.

The smell is resin, not water. It looks like good quality wood you have bought.

I can understand you wanting to glue up for best appearance, but in this case, with such pronounced rings, I'm afraid it wasn't the best choice

 

[Beau]

It was clearly wet when purchased. Most softwood I have bought from reputable suppliers is around 15%- 17% so needs some more drying before being ready to work. Never sure why softwood is not dried as low as hardwoods though.

 

[Jacob]

...... Never sure why softwood is not dried as low as hardwoods though.

It's supposed to be dried at source to below 20% (or something) to prevent rot but it's up to the stockist and/or user to dry it further. Makes sense as most of it is for external joinery or carpentry use and doesn't need to be furniture dry

 

[ED65]

- Would it have helped if I had used opposing grain patterns?

I think from the scale of the warping it would have helped somewhat, but not enough that you'd have been able to live with the panel as-is.

I didn't here because I read it often makes no difference

The operative word there is often. There are some cases – with wood that has better grain and is dryer that this might have been – when it's still a good a idea to alternate the rings. Some people get away with not doing it, others don't, so in isolation we can't take a firm lesson on this. Just how pronounced the curve of the grain is probably the most important single factor, others are still significant though including the MC, the wood species and workshop conditions.

and in this particular case, the wood looked nicer the way I had it, but now I'm wondering if it was a mistake.

FWIW I think choosing the best face grain should be the ultimate determinant myself. But where there might be, or is likely to be, a problem with warping then appropriate steps must be taken to counteract the tendency, e.g. battens along the underside or fixing the panel well to a strong table substructure.

I don't have a jointer yet, but lets say I did. If I had left the boards to acclimatize for longer (I left them for a week before gluing), and then planed the cup out of them. Why wouldn't it still have cupped even after that? wouldn't I be in the same situation only with thinner boards?

Quite possibly. Wood dries from the surface out, so the thicker the material the more damp the interior can remain relative to the surface (why readings from moisture meters can't be taken at face value).

I'm sure it's happened to many here something I've seen multiple times in build galleries: the wood prior to milling showing some warp, twist or cup, then the pieces are shown dead flat after milling, then the boards or an assembled panel warped again sometime later (occasionally only a few hours later or the next morning).

How long you leave the wood to acclimate plays a part. Even with thin stuff one week isn't enough. Two really isn't. Longer is better. A few months, now we're talking. Obviously the simple fact is that many can't wait anything like that long, but you'll rarely regret waiting longer when you can.

When I was sanding this pine, I noticed a very strong pine smell, stronger than I am used to (I usually get small bits from Wickes), and the sandpaper seemed to clogged up quicker. Is this a sign that the wood wasn't as dry as it should be? .. or could this just be the wood resin?

Redwood is very resinous compared to other common softwoods, it's part of what makes it so much heavier. I think you should always expect it to smell that strongly.

When I glued it up, it was reasonably flat. Should I have immediately applied a flattening mechanism such as bread board ends to keep them flat? Or would that just put the stress elsewhere? This has actually been left a week and there was no flattening mechanism in the design, just 4x 5ft boards glued up.

How was it stored? If it was flat on a surface (any surface) that will often be a problem. Leant against a wall can still be a problem. Flat but up on sticks and weighted heavily on top is better.

Regardless, a 4'x5' panel is quite substantial and unless the wood is carefully chosen for grain (RS or QS, so near-vertical or vertical grain at the ends) and the wood well dried I think you can expect there to be issues with it staying flat on its own.

 

[transatlantic]

But surely for that kind of thickness we would be talking months for it to dry? ..

 

[transatlantic]

Thank you Ed65, I always find your posts informative!

How was it stored? If it was flat on a surface (any surface) that will often be a problem. Leant against a wall can still be a problem. Flat but up on sticks and weighted heavily on top is better.

The offcut was just left flat on a work surface. The tabletop itself (that the offcut came from) is stored flat on a bench on top of stickers. It is also not flat, but not as bad as the offcut. After gluing it up I screwed 3 battons underneath with over sized holes for wood movement (like the picture below, not my work). I suspect these battons may help to keep the top flat overall, but won't keep each individual piece from cupping? I guess it also won't help with twist?

 

[ED65]

I suspect these battons may help to keep the top flat overall

Should do, that's what they're for

The individual boards are now joined into a single unit so they'll react a little more uniformly than they would otherwise, especially with the battens to stabilise it across the width.

I think it is still free to twist if it wants to unless it's attached to something that will resist this.