Black walnut stability question

[YorkshireMartin]

Hi guys,

The stock in question has been acclimitising for 10 months inside the house in preparation for a piece of furniture. Moisture content would have been probably 15% when purchased and it was stored in a temp/humidity controlled warehouse. Highly reputable merchant.

It was 45mm thick and I've resawn it in half (tonight) on the bandsaw due to a design change.

Within an hour, each piece, which came off the bandsaw flat, has started to cup along the length of 1.2m. I have to be honest I've been a bit taken aback as walnut is known to be stable.

This was planed/thicknessed at least 10 months ago and I'd have thought it had ample time to dry gently. I understand resawing would allow the escape of more moisture by surface area, but still, we're talking 2mm off the straight edge in the center. Reminds me more of spruce/larch type stability problems.

Can someone explain what is going on here? I am a bit lost on this one.

Many thanks

 

[marcros]

Its inner tension/stresses have been released.

 

[YorkshireMartin]

Its inner tension/stresses have been released.

and passed on to me, it would seem.

Thanks dude. Something else for me to research

 

[Beau]

If imported from the Staes unlikely it will lose any more moisture as much of what lands on our shore is so dry it will take up moisture in it's home. As for whats going it's hard to say. If it's just a lack of equilibrium in moisture from centre to outside the board may yet settle down. Sometimes boards just do this and nowt one can do other than work with what you have or start again.

 

[Woodmonkey]

As marcros said, sometimes the wood can spring apart or together when cutting it (this is why we have riving knives) regardless of moisture content

 

[woodbrains]

Hello,

When re-sawing, it is best to place the cut boards immediately in stick, with weights on top to keep them flat. They must remain like this until they have equalised, as the inside will be wetter than the outside when newly cut. It usually takes a few days, or a week. Longer if the boards were particularly different in moisture between the insides and outside faces, such as dense exotics. Stability is not the same thing as having tendency to cup when freshly sawn. Walnut has small movement in service, which is what most people mean when they say 'stable' but when cutting thick boards, the same differential in moisture content will cup boards just the same as any species.

Mike.

 

[flh801978]

I would have left it as sawn until I was ready to use it then resawn and plane all in the one go
Black walnut I have resawn has been ok when done like this

Ian

 

[custard]

The great majority of American timbers available in the UK (Cherry, Walnut, Ash, White Oak, Maple, Poplar) are only available crown cut. That's what the market generally wants, it delivers a high yield, so that's how the logs are processed. But for re-sawing you ideally want quarter sawn. You can sometimes get away with resawing crown cut boards, but resawing is always a somewhat risky job, and with crown cut boards the wastage rate will usually shoot up even higher.

The way I tackle this is by searching out the very, very few UK timber yards that import the entire log rather than processed boards. At one level this is hugely wasteful, as it means shipping useless bark, sap, and pith across the Atlantic. The benefit is you get waney edged, consecutive boards with a decent percentage of quarter sawn and near quarter sawn timber. For square edged and PAR boards it might be practical to use very thick boards (although these command a premium price and 100mm is generally the thickest you'll find) and slice off your own 100mm wide quarter sawn boards.

With crown cut, square edged boards I'd always buy the wood strictly according to a cutting list, so that it's just a case of planing and thicknessing down to finished dimensions. Resawing is a last resort as it seldom has a happy ending.

With your already resawn boards you've nothing to lose, you could try spritzing the concave side with water from a plant sprayer then putting the boards in stick and weighting them down. To be honest these kind of desperate measures rarely work, but occasionally they will so you could give it a try.

Good luck!

 

[custard]

To illustrate the point here are three boards of American timber.

The top board is American Poplar/Tulip Wood. It's a PAR board that's crown cut, but because it's so thick if you sawed off slices (with the bandsaw blade passing vertically through this board) you'd have a series of narrow but quarter sawn boards that would be very stable.

The centre board is American Black Walnut. Again it's a "square edged" and "planed all round" board, and it's crown cut, typical of the ABW available in this country. Resawing this crown cut board into two thinner boards would probably require an awful lot of planing to remove the almost inevitable cupping.

The lower board is also American Black Walnut, but it was taken from a waney edged "boulle" or sawn log bought from a specialist timber yard, this particular board is close to being quarter sawn. It would be easy to divide this with a rip cut down the middle and then resaw the two resulting boards into two thinner boards or even into sawn veneers. I would be fairly confident these boards would then remain reasonably flat with minimal cupping and require only a small amount of subsequent planing.

Moral of the story, resawing is often risky, but if you have straight grained, quarter sawn boards you have a far better chance of success. Resawing crown cut boards significantly increases the risk, and because the majority of American timbers you'll find in the UK are crown cut, it makes sense to avoid resawing American timbers.

Good luck!

 

[woodbrains]

Hello,

The thing with quarter sawn black walnut is, it is sooo boring. Useful for frame members, but a nice, re-sawn crown cut board, book matched for a panel looks great. I have always re-sawn such boards and also sawn it into veneers. I have always been patient and fastidiously put the newly sawn boards or veneers in stick. It is difficult to let them be, when you are rearing to go on a project, but trust me, do this and leave well alone for a week. I cannot remember having trouble with boards cupping. A furniture workshop should always have a stack of softwood stickers on hand.

Mike.

 

[Sgian Dubh]

It's not unusual for deep ripping or resawing to result in boards cupping or bowing. The causes might be, as others have suggested, internal stress (case-hardening or reverse case-hardening for example), or a moisture gradient (uneven moisture content across the width, length and thickness). The cause of distortion during resawing may even be a combination of both a moisture gradient and stress induced by improper drying, or natural growth stress, although in the latter case the stressed sawlog is almost always spotted by the sawyer and rejected from the milling process.

However, if a resawing operation is planned by a woodworker, the prong or fork test illustrated briefly below is a good technique for evaluating the likelihood of success. There's additional information on the subject of timber drying faults at this link which will hopefully be useful to some visitors. Slainte.
******************************************************************************
The Fork or Prong Test.
This test indicates if the wood has transverse case-hardening. To conduct the test, move in from the end of the plank by at least 300 mm (12") and cut a full width and thickness section out about 40-50 mm (1-9/16" to 2") long- see below. Turn the end grain of this short length down on to the table of a bandsaw and cut a pair of prongs about 6- 10 mm (1/4" to 3/8") thick by removing the wood in the centre. If the plank is thick, three or four prongs are possible. The forks will soon tell you if the the wood is stress free.


The forks may move instantly, or it might take an hour or so for the forks to move. If they remain parallel to each other, even if they are not straight as in the top image in the above photograph, or at 3, right, then it is fair bet that the wood is unstressed: you can reasonably confidently proceed to undertake that deep ripping operation you had in mind to create a book matched panel. If the forks move towards each other the wood is case-hardened, 4; and at 5, where the forks spring apart, this is an indication of the rare condition of reverse case-hardening.

 

[custard]

The thing with quarter sawn black walnut is, it is sooo boring.

It's interesting that you think so. That's certainly been the general view of woodworkers for the past thirty or forty years, which is why nearly all the ABW available in this country is still crown cut, it's simply been processed in accordance with established market demands, and up until recently "good taste" in furniture design has been based around the repeated patterns of cathedral grain that crown cutting provides.

But attitudes are changing. There's a generation of furniture makers now coming through who are rejecting the crown cut/book matched look, and instead adopting a cleaner, more contemporary design ethos that's often based around quarter sawn timbers. What you might describe as "boring" they'll say is harmonious, uncluttered, and serving to emphasise the structural form of the furniture.

Incidentally, even if you take fashion right out of it, here's a quarter sawn board of American Black Walnut that's anything but boring!

 

[woodbrains]

Hello,

That's cheating, custard!

It is not that all quartered timber is boring, nor is the boring stuff not attractive in its place, it is just some exciting wood is from the crown cut stuff, and not being able to re-saw it would be frustrating. I like to use a mixture of cuts in my work, particularly rift sawn for frame members, legs etc. Where as you say, crown cut timber is disharmonious. But I'd find quartered black walnut for the large expanses of panels as dull as ditchwater. I'd have to question my choice of that timber if I wanted that understated, uniformity in a piece.

Mike.

 

[YorkshireMartin]

I don't know if it's just me, but the merchants I've visited, whilst friendly and co-operative, have looked at me as though I just asked for [arnie voice] "a phased plasma rifle in a 40 watt range" when I mentioned a specific type of cut I wanted on the stock..."hey, just what you see pal".

As usual, the Americans have all the options.

Thank you very much for the information, I did try to get quarter sawn stock, but it's just not around so I have to make do. The piece in question was actually picked up as a PAR offcut very cheaply, but it was 2" thick and very long with only one knot and otherwise very straight grain, ideal for a pair of aprons. So, I'll handle the cupping on this one but definitely take all the advice on board for next time.

 

[Sgian Dubh]

I don't know if it's just me, but the merchants I've visited, whilst friendly and co-operative, have looked at me as though I just asked for [arnie voice] "a phased plasma rifle in a 40 watt range" when I mentioned a specific type of cut I wanted on the stock..."hey, just what you see pal".

As usual, the Americans have all the options.

Not as much as you might think. Having lived and worked there whacking bits of wood into semblances of furniture, the normal choice in most lumber yards is crown cut, aka, tangentially cut, the sawlog being rotated 90º or 180º after a few cuts in one orientation in order to box the heart. Through and through or slash sawing, at least in the 90s and early 2000s was rare, and radial milling even rarer. There are specialist sawmills catering to a limited but appreciative market that do those rarer cuts. Most of them are in the north east or west coast, although these specialists can be found dotted all over the country. Slainte.

 

[Bodgers]

I don't know if it's just me, but the merchants I've visited, whilst friendly and co-operative, have looked at me as though I just asked for [arnie voice] "a phased plasma rifle in a 40 watt range" when I mentioned a specific type of cut I wanted on the stock..."hey, just what you see pal".

As usual, the Americans have all the options.

Thank you very much for the information, I did try to get quarter sawn stock, but it's just not around so I have to make do. The piece in question was actually picked up as a PAR offcut very cheaply, but it was 2" thick and very long with only one knot and otherwise very straight grain, ideal for a pair of aprons. So, I'll handle the cupping on this one but definitely take all the advice on board for next time.

Was your walnut air or kiln dried?

 

[YorkshireMartin]

I don't know if it's just me, but the merchants I've visited, whilst friendly and co-operative, have looked at me as though I just asked for [arnie voice] "a phased plasma rifle in a 40 watt range" when I mentioned a specific type of cut I wanted on the stock..."hey, just what you see pal".

As usual, the Americans have all the options.

Thank you very much for the information, I did try to get quarter sawn stock, but it's just not around so I have to make do. The piece in question was actually picked up as a PAR offcut very cheaply, but it was 2" thick and very long with only one knot and otherwise very straight grain, ideal for a pair of aprons. So, I'll handle the cupping on this one but definitely take all the advice on board for next time.

Was your walnut air or kiln dried?

Good question, need to look into that. I'd think kiln dried if I had to guess.

 

[custard]

Good question, need to look into that. I'd think kiln dried if I had to guess.

It's a banker's bet that it's kilned dried. There are one or two very specialised timber yards in the UK where you might get air dried ABW, but 99.9% of the stuff is sawn and kilned in the US and then shipped over.

 

[memzey]

Interesting. I heard that a lot of the ABW in this country comes from Romania.

 

[John15]

Interesting. I heard that a lot of the ABW in this country comes from Romania.

Probably not American Walnut though

John