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Dealing with unhelpful stresses in wood

Measure twice, cut once...
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CelticRambler
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Dealing with unhelpful stresses in wood

#1

Post by CelticRambler »

A purely "academic" question for now, as I don't have a specific piece of wood or a specific project in mind ... but these things pop into one's head uninvited during long drives!

Trying to make a box previously using reclaimed wood, I struggled with persistent warping of the planed timber. Over on the Other Forum, it was explained that every time I skimmed off the offending areas to leave a perfectly flat board, I was also removing the material that had stopped the previously thicker piece from warping any more than it was; but now that they were gone, the remaining slice could continue it's mission to become a perfect cylinder. :x

My wanderings into the world of sawmilling have indicated that there are some cuts that are better than others in this regard, which is fine if ever I go down the route of slicing my own planks; but I still have quite a lot of old floorboards (chestnut and oak, cut about 100-200 years ago, so well dried by now :D ) with lovely colour and grain in them. What technique(s) can I use to get these into nice flat, usable pieces that don't warp further as soon as I turn my back on them?
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The Continental Op
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Re: Dealing with unhelpful stresses in wood

#2

Post by The Continental Op »

In my experience really dry european hardwood timber rarely warps when machined, cut or worked.

However I nearly killed myself ripping down a perfectly straight piece of fake Teak (whatever they use now instead of Teak) when it suddenly twisted and bent violently on the saw bench closing up on the saw blade gripping it and then flying off. Couldn't believe how twisted the wood suddenly became. Dead straight with straight grain one minute then an overlapping banana bend the next.
kadman
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Re: Dealing with unhelpful stresses in wood

#3

Post by kadman »

What you mention Continental is stress being relieved in the wood when you cut it. Teak is notorious for it, and its probably more related to an incorrect kiln drying process, than anything else. This can happen to some degree with all woods, hardwoods probably more so.

Cr.

Two things affect your boards, and their ability to stay straight in a given environment.
1. The type of cut boards you have, or the type of cut you are proposing.
2. And the proposed storage area environment.

If you expect any board you cut and machine to stay straight, then the environment has to remain stable. If you sheds have an ever changing environment, then your boards straightness will be an ever changing amount as well. If you expect to have nice straight finished floor boards, then they need to be dried to the air moisture content of your finished environment, and then machined straight, and kept at that environment.

Thats why you see most hardwood material boards, wrapped in plastic to maintain their dryness level.
If you take one of these boards and leave it out side in a shed, then it will reach an equilibrium point to match its new environment.

If you want to prepare your own boards to remain straight for inside use, then first you have to dry them to that level, machine them, and maintain their environment.

Simples
CelticRambler
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Re: Dealing with unhelpful stresses in wood

#4

Post by CelticRambler »

Hmm. These were boards removed from open, draughty sheds and stored in an open draughty barn until I picked a few of them out to work with. The They were easy enough to plane to from a very rough 15-20mm thickness with a noticeable curve to a consistent 12mm thickness ... and then in literally the time it took me to prepare the next one, they had begun to warp again. I took some of them down to about 8mm (by design) and it was the same.

I can understand some pieces warping over time depending on heat and humidity, and also understand that that's where good jointing technique comes in; but the greatest offender in that previous situation was a board I wanted to use as the base for a jewellery box, and I could not keep it flat long enough to be able to mark it up accurately for the upper structure. :(
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Re: Dealing with unhelpful stresses in wood

#5

Post by kadman »

CelticRambler wrote: Fri Oct 22, 2021 3:50 pm Hmm. These were boards removed from open, draughty sheds and stored in an open draughty barn until I picked a few of them out to work with. The They were easy enough to plane to from a very rough 15-20mm thickness with a noticeable curve to a consistent 12mm thickness ... and then in literally the time it took me to prepare the next one, they had begun to warp again. I took some of them down to about 8mm (by design) and it was the same.

I can understand some pieces warping over time depending on heat and humidity, and also understand that that's where good jointing technique comes in; but the greatest offender in that previous situation was a board I wanted to use as the base for a jewellery box, and I could not keep it flat long enough to be able to mark it up accurately for the upper structure. :(
Well with material that thin, and moving as quick, it all points to the type of material cut, and I suspect it was a through and through cut.
Which means it was the most material in a log cut. Its for quantity out of the log, not quality.
The radial rings in the plank are at a nearer angle to parralel with the face, than with the board edges. To simplify, if you look at the board ends, and all the grain is at 90 degrees to the edge, this is quartersawn and the most stable.
If you see the grain running more from edge to edge, this is through and through, its the most unstable cut.

Material 8mm and less for a jewellery box construction needs either dovetail or combjoint construction to hold the full width of the board straight. Any other box type construction joint will have vary levels of ability to hold the full width, ripple free.
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kadman
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Re: Dealing with unhelpful stresses in wood

#6

Post by kadman »

There are a few methods of flattening the boards for marking out , but it would be helpful to see what we are working with.
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Re: Dealing with unhelpful stresses in wood

#7

Post by The Continental Op »

Which way are they warping?

Are they cupping?

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kadman
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Re: Dealing with unhelpful stresses in wood

#8

Post by kadman »

Radial rings will always try to straighten when drying,
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CelticRambler
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Re: Dealing with unhelpful stresses in wood

#9

Post by CelticRambler »

The Continental Op wrote: Fri Oct 22, 2021 5:39 pm Which way are they warping?

Are they cupping?
Yeah, that was the main problem.
kadman wrote: Fri Oct 22, 2021 4:42 pm Well with material that thin, and moving as quick, it all points to the type of material cut, and I suspect it was a through and through cut.
Which means it was the most material in a log cut. Its for quantity out of the log, not quality.
That'd make sense. These were (for the most part) ceiling/floor boards used for the purposes of tax-avoidance more than quality woodwork (a room with a ceiling height of 1.8m or less isn't counted in the rateable surface area in France). I would imagine they were the cheapest available boards at the time, and several split lengthways when I removed them.
kadman wrote: Fri Oct 22, 2021 4:44 pm There are a few methods of flattening the boards for marking out , but it would be helpful to see what we are working with.
kadman wrote: Fri Oct 22, 2021 4:42 pm Material 8mm and less for a jewellery box construction needs either dovetail or combjoint construction to hold the full width of the board straight. Any other box type construction joint will have vary levels of ability to hold the full width, ripple free.
As I said above, this was a random "thoughts while driving" thing that came into my head (prompted, no doubt, by the sight of all that lovely timber standing by the side of the road, just waiting to be chopped down and sliced up! :lol: )

The remaining boards are stacked in various (relatively dry, well-ventilated) places, waiting to come in useful. At this stage, I'm more interested in learning the theory of "stresses within pieces of wood" so that I don't waste time in the future trying to get a piece to behave in a way that will never happen. Or start to learn/perfect techniques that would help to control the problem in borderline situations.

If the planks were originally cut through-and-through from a single tree (or set of trees), chances are there are some decent pieces in the mix - I'll start to pay more attention to the end-grain in future! ;)
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Re: Dealing with unhelpful stresses in wood

#10

Post by The Continental Op »

Next question is that when you plane up these pieces are you finishing both main faces or just facing up one good side?
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Re: Dealing with unhelpful stresses in wood

#11

Post by CelticRambler »

Definitely two, sometimes all four, faces (some of the boards would be close enough to 30mm thick to start with)
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Re: Dealing with unhelpful stresses in wood

#12

Post by The Continental Op »

Fair enough I did wonder if facing up one side would exacerbate the problem.
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Re: Dealing with unhelpful stresses in wood

#13

Post by CelticRambler »

I've been wondering if it might solve the problem in some situations! I needed a quick-and-dirty base for a Christmas table decoration last year, so picked out some of the "flat-ish" short boards with significant areas of damage; cut the long sides along whatever line would leave me a "good enough" piece of timber, regardless of whether or not two the edges were parallel; planed just enough off the "bad" face to give me a flat area for fixing to the bar that'd hold them all together, and more thoroughly planed the "good" face so that the candles and candle-holders had a stable surface on which to rest.

Needless to say, with minimal quality control and expectations limited to twelve days, the whole assembly has remained absolutely stable since and has every intention of becoming a family heirloom! :lol:
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Re: Dealing with unhelpful stresses in wood

#14

Post by kadman »

Well there you go right there, problem number 1.

Reducing a 30 mm board to less than 1/3rd of its thickness is guaranteed to give you problems.
Less so if they are quartersawn. Its a guaranteed if you take more from one face than the other.
You need to take from both faces equally.

We still dont know, the moisture content, the cut used, so its a how long is a piece of string question.
Not to mention the sheer waste of planing 30mm timber to a plywood thickness. And in all fairness chestnut is not exactly a quality timber for jewellary box type construction. Its more at home for coffin making as its the poor mans oak.

If you must persist with this construction method using 8 mm chestnut, then you had better brush up on your veneering techniques. I suspect you will be using a lot of veneer as a balancing method to stabilise your chestnut.
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Re: Dealing with unhelpful stresses in wood

#15

Post by The Continental Op »

One thing I'd try is planing the faces little bit at a time, leaving them a couple of days then planing a bit more.

Subsequent planing will remove any slight cupping and crowning but doing it little at a time may stop any sudden movement of the wood?
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Re: Dealing with unhelpful stresses in wood

#16

Post by CelticRambler »

kadman wrote: Sat Oct 23, 2021 11:09 am Well there you go right there, problem number 1.

Reducing a 30 mm board to less than 1/3rd of its thickness is guaranteed to give you problems.
Hauld on there a minute - you're jumping to conclusions! The 30mm board was planed down from about 35, for one job. The 8mm boards probably started off at about 12. The jewellery box was made two years ago, and it's only one of about a dozen different projects covered by this enquiry. ;)

Like I said, I'm not asking for a specific solution to a specific construction challenge: I'm trying to understand how every piece of wood in my collection will behave when I start taking millimetres off it ... so that I don't have to waste time or timber making bad choices in the future.

But on the subject of choice, the primary value in any of these projects will be using that particular piece of timber, with the full weight of it's 200-year history (or 400 if we include the time before the tree was felled) to make something useful and/or beautiful. It just so happens that oak and chestnut make up about 90-95% of all the wood within easy reach of my various saws, as that's what's always been grown in this area (at least until one landowner planted a field of cedars 'round the back of me about ten years ago).
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Re: Dealing with unhelpful stresses in wood

#17

Post by kadman »

I can recomend a book on seasoning timber which is what you need.
The fact that the only mention of thickness was 8 mm, then 30 mm a few posts later, leads me to believe you were converting from 30 to 8.
If you want to discuss how timber behaves, then maybe specific questions you want answered, when you supply the specific details of what you are referring to and what you are starting off with.

I am not getting any younger, and might not last until the end of your enquiry. :lol: :lol:
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Re: Dealing with unhelpful stresses in wood

#18

Post by gugleguy »

kadman wrote: Sat Oct 23, 2021 12:38 pm I can recomend a book on seasoning timber which is what you need.
The fact that the only mention of thickness was 8 mm, then 30 mm a few posts later, leads me to believe you were converting from 30 to 8.
If you want to discuss how timber behaves, then maybe specific questions you want answered, when you supply the specific details of what you are referring to and what you are starting off with.

I am not getting any younger, and might not last until the end of your enquiry. :lol: :lol:
:shock:

ah jayz chin up. Don't know from my woodchips to woodwork myself. c'mon!.....
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Re: Dealing with unhelpful stresses in wood

#19

Post by kadman »

gugleguy wrote: Sun Nov 07, 2021 12:14 pm :shock:

ah jayz chin up. Don't know from my woodchips to woodwork myself. c'mon!.....
Its not me that wont hang on....its CR's fault as he takes ages and ages to answer, its like pulling teeth :mrgreen: :mrgreen:
CelticRambler
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Re: Dealing with unhelpful stresses in wood

#20

Post by CelticRambler »

:| Was I supposed to be answering a question? You might have to point it out to me. :?
Besides, I thought we were free of the Twitterbook instant gratification rules here? :P

In any case, woodworking (and most forumming) has been on hold for a bit, while I was exploiting two of my children in the name of other Grand Plans. And then I had to go dancing this weekend in the Vosges ... 500km away. Great group - will try to catch them again in the Jura in a fortnight. 8-)
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Re: Dealing with unhelpful stresses in wood

#21

Post by kadman »

Yeah, the pups are important, go off and spoil them :D

Forget the dancing, I have it on good authority that Mike Murphy was yer dance teacher, and we know what a twinkletoes he is.
500 clicks to go dancing, jaysus I wouldn,t drive that far, for an old VW :D I've driven further for one :mrgreen:
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Re: Dealing with unhelpful stresses in wood

#22

Post by CelticRambler »

kadman wrote: Sun Nov 07, 2021 2:44 pm 500 clicks to go dancing, jaysus I wouldn,t drive that far, for an old VW :D I've driven further for one :mrgreen:
No point having a full-colour Covid Passport and not making maximum use of it! 8-)

Might take it to a dance in Geneva next weekend, though it's very hard to get parking for an oversized vehicle in that part of the world ... and the most sensible route would require buying a year-long motorway pass with only 6 weeks left on it. :(
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