What am I doing wrong?

[Richardsth]

Evening all,

I have some scraps pieces off 2x4 green Oak and I thought that I'd try and make a small box for someone with them. So, I picked out a piece which has been outside in my wood pile, that was straight and in excellent condition, and preceded to cut it down to size. I managed to get three thin pieces, and after they were planed and sanded, I left them overnight in my shed. The next day, all the pieces are curved and now useless, so what did I do wrong? Were they too thin (approximately 1cn thick)? Was the shed too hot? i have lots more offcuts that I can use, but I don't want to be wasting my time again.

Cheers Rik

 

[johnnyb]

most wood reacts like this on a deep rip. when I rip 9 inch pine I leave at least a 1/4 inch to plane back flat. often it springs when the very last mm is sawn through. so if you want say 15mm then saw in half then allow to dry and move. then plane up.

 

[Richardsth]

So what you’re saying is that after I cut the beams, give them time to dry out and settle, before going on to plane them.

 

[Terry - Somerset]

I bought some 4x2 green oak to make some raised beds to surround the patio as a raised flower bed. I used stainless steel bolts to bolt them together.

They have rapidly warped - not really a problem - I like to think it adds to the charm!

But green oak by definition is not fully seasoned. Leaving it outside in a pile may (possibly some years later) may render it stable in its position in the wood pile.

But cutting into thinner slabs will release any internal tensions. The humidity in your shed may be very different to the wood pile creating more stress.

I suspect the best way to make use of the surplus is (a) leave in in shed for a few months to acclimatise, and (b) accept that it will warp and make appropriate allowance in the sizes you cut.

 

[Old Chippy]

Evening all,

I have some scraps pieces off 2x4 green Oak and I thought that I'd try and make a small box for someone with them. So, I picked out a piece which has been outside in my wood pile, that was straight and in excellent condition, and preceded to cut it down to size. I managed to get three thin pieces, and after they were planed and sanded, I left them overnight in my shed. The next day, all the pieces are curved and now useless, so what did I do wrong? Were they too thin (approximately 1cn thick)? Was the shed too hot? i have lots more offcuts that I can use, but I don't want to be wasting my time again.

Cheers Rik

Hi I am no expert but when planks are cut from a tree, and to get most planks out of a tree the tree is laid down and slices are removed layer by layer. and as each plank dries the wood starts to Cup or warp. Now the best way to stop this happening as much as possible, the tree needs to be quarter sawn, but this is more wasteful of the available timber, which also makes the planks very much more expensive to buy. If you look at the end grain on a plank you can see the trees growth rings as they curve through the plank. that is why you need to alternate each plank if you are joining more than one plank to make say a table top. Quarter sawn planks have the growth rings running almost straight down through the end grain of a plank, and this reduces how much it cups. Quarter sawn planks are cut from the tree like hours on a clock face. As was said by another member you still have to leave the the cut timber to allow any stresses released plus any moisture that may have still been in the wood. It is best to store it in a temperature near as possible to where your project will be used before it is planed to the final thickness required.

 

[ChrisWiduWood]

One other point to mention is to remove an equal amount of material from each side, ie if you start with 20mm and want a finish of 10, you need to remove 5mm from each face.
If you overhand one side and say remove 2mm and get a clean face, then thickness the other face by 8 to get to the 10, then it will almost certainly cup as you are essentially getting more moisture on the deeper side.

Hope that helps

Chris

 

[Old Chippy]

A very good point Chris

 

[Richardsth]

Right then, I’ll have another go. Only this time, I’ll store the wood in a cooler place, and not in my shed on the hottest day of the year!

 

[profchris]

Right then, I’ll have another go. Only this time, I’ll store the wood in a cooler place, and not in my shed on the hottest day of the year!

I think you've misunderstood the problem - it's not about temperature.

Your oak has a high humidity content because it's green. Over time it will lost that extra humidity until it matches its environment. Indoors is generally drier than outdoors (we're talking humidity in the air here, not whether it's raining).

Until your oak has dried to that level it will be unstable - it will shrink, and it won't shrink evenly. Air drying takes around 1 year per inch of thickness, and if the box is to live indoors then it will dry some more (and so move some more) when you take it inside.

So your oak just isn't suitable yet!

You could resaw it thinner so it dries quicker. It will dry more in your workshop than outdoors. But it will also move as it dries, so you need to resaw it thick enough that you'll get flat boards the right size from it once it has dried. This means you need to be able to predict in what directions it is likely to move (will it cup, or twist, or ...).

This thread might help you understand what will happen to it as it dries, and how to make sure it doesn't move too much again when it's in its final location: Humidity and wood movement - the basics

 

[Richardsth]

One other point to mention is to remove an equal amount of material from each side, ie if you start with 20mm and want a finish of 10, you need to remove 5mm from each face.
If you overhand one side and say remove 2mm and get a clean face, then thickness the other face by 8 to get to the 10, then it will almost certainly cup as you are essentially getting more moisture on the deeper side.

Hope that helps

Chris

Now that does make sense. I divided the 4" planks in to 3, and it was only the centre piece thats probably still usable. The outer two I didn't really do much work on them as one side was already planed. So they were dry on one side and damp on the inside.

 

[Richardsth]

I think you've misunderstood the problem - it's not about temperature.

Your oak has a high humidity content because it's green. Over time it will lost that extra humidity until it matches its environment. Indoors is generally drier than outdoors (we're talking humidity in the air here, not whether it's raining).

Until your oak has dried to that level it will be unstable - it will shrink, and it won't shrink evenly. Air drying takes around 1 year per inch of thickness, and if the box is to live indoors then it will dry some more (and so move some more) when you take it inside.

So your oak just isn't suitable yet!

You could resaw it thinner so it dries quicker. It will dry more in your workshop than outdoors. But it will also move as it dries, so you need to resaw it thick enough that you'll get flat boards the right size from it once it has dried. This means you need to be able to predict in what directions it is likely to move (will it cup, or twist, or ...).

This thread might help you understand what will happen to it as it dries, and how to make sure it doesn't move too much again when it's in its final location: Humidity and wood movement - the basics

I think that I'm being ambitious and impetuous in thinking that I could use my green Oak offcuts now. As this was green Oak last year, I reckon that it will take sometime for it to become seasoned and ready to use for internal projects. I did notice that once the 4" were cut, they were cold and slightly damp inside, despite the outer surface being bone dry. I'll take your advice and cut them in to thicker pieces and allow them to dry out and settle down before reworking on them.

Cheers Rik

 

[Sgian Dubh]

I think that I'm being ambitious and impetuous in thinking that I could use my green Oak offcuts now. As this was green Oak last year, I reckon that it will take sometime for it to become seasoned and ready to use for internal projects. I did notice that once the 4" were cut, they were cold and slightly damp inside, despite the outer surface being bone dry. I'll take your advice and cut them in to thicker pieces and allow them to dry out and settle down before reworking on them. Cheers Rik

You've experienced the phenomenon of moisture gradients within the wood, and how wood reacts to it being worked can be influenced by them. In reality, all wood in normal circumstances has a moisture gradient, either wetter at the shell and drier at the core, or visa versa, dependent upon the wood's moisture content at a specific time and the RH circumstances in which it finds itself. In your case, you witnessed wood that was drier at the shell and wetter towards the core, and that was because it was green when you started storing or seasoning it and had partially dried out when you came to cut it. I'd say it's highly likely the core was still very wet, close to its original green MC, whereas the intermediate zone was somewhat drier, and the shell drier again.

So, basically, cutting it as you did exposed those different MC zones to air and introduced additional stresses to those that were still working themselves out within the full thickness and width of the lump of wood prior to it being cut.

As you've discovered wood can be an unpredictable and frustrating material to work with, especially if you're at an early stage of learning about its properties. If you're serious about being a successful woodworker, which I assume is the case, all I can suggest is that you do your best to learn as much as you can about the subject. At least that way you're less likely to have unexpected results or incidents whilst working the wood and frustrating irritating and puzzling failures in your constructions. Slainte.

 

[johnnyb]

I second everything said above. I'll also say even when it's ostensibly dry any machining often upsets it's balance even just a few mm the most stable stuff is old dry tropical wood like sapele(new stuff can move a scary amount) or quebec yellow pine

 

[spanner48]

Why not copy, in smaller scale, what sawmills do? Cut the planks, then immediately stack them horizontally with 'Keeper Bars across every foot or two, with a heavy weight distributed on top. Leave indoors [i.e. in the same humidity as that in which they're due to be used] in a well-ventilated space for some months. Then they should have relaxed into a flat form, at the right humidity.

 

[Jacob]

Bring the wood inside, stack it in a ventilated way - crisscrossed or in a loose pile etc, wait two years and try again.

 

[morqthana]

Genuine question from someone who knows SFA - isn't green oak really best suited to large heavy timbers for structures, rather than thin(ish) boards for furniture?

 

[TRITON]

Oh what's the term, i forget... ahh, reaction timber.
If you think about how a tree grows, how each , what effectively leads to what we see as the tree ring, each seasonal layer isnt laid on straight and true. It goes up and down, but also diagonally, so the the grain is irregular for a small part.
When you saw up timber, it crosses the grain, releasing tensions in the structure that can pull the board this way or that.
You see its not always just down to moisture content, or the drying, and collapse or shortening tightening of the pores.
Tensions in the tree also play a part.

You see it more often when you take a standard board and run it through the saw.(Bench or band) sometimes, especially it the section is thinner, the section bends, it can bend away from the blade or towards it, which in itself can cause a bit of binding and you need to pop in a wedge at the back to force the two apart so it runs thorough more smoothly
If theres a lot of reaction structure in the tree, boards coming off in the mill can be heavily warped.

When you come to use such, you can find that the movement is such that glue or screws can pull the board back into shape. On wide flat its easier, but usually on the wide flat face, the thickness section if bent will require further machining, along a surfacer or such.
This is why it is always beneficial to dimension larger by about `10% of your finished sizes so after your timber has been sawn so you can pick the truer stuff and re-machine that - planer first, then thicknesser and discard anything that has warped or twisted badly.

 

[Sgian Dubh]

I find it rather interesting that in many of these discussions about wood distorting some contributors use the term tension to indicate a reason for a board to warp in one form or another as, for example, described here in the original post. Tension, in relation to materials of which wood or timber is one is, specifically, a stretching or pulling apart force i.e., pulling in opposite directions. An example of this is the tension experienced by the lower convex face of a loaded shelf whereas the upper concave face experiences compression. Another is the effect of cleaving a log for firewood where the tension acts across (perpendicular to) the wood grain. The shafts of a horse drawn carriage in use illustrate tension parallel with the grain.

A better word to use, I suggest, is stress. The word stress is generic and requires clarification to identify the form of stress such as compression, tension, shear and torsion, all of which can cause distortion or failure in a piece of wood, and they frequently act in combination. For example, the cause of cupping (cross-grain warp) normally involves a combination of compression forces towards one face of a board and tension forces towards the other. A board that is cupped may also be bowed, crooked, and in winding and is the result of combined stress factors.

I guess this post is a gentle suggestion for people, when discussing the cause of distortion in wood, or its failure (breakage) in either its board or partially worked form or in use, e.g., a broken chair leg or severely cupped panel, to generally replace the word tension with stress because stress leads to strain which results in things like distortion and failure. Whilst I suspect everyone generally knows what is meant when someone says, "The wood warped or failed in some way because of tension" what they ought to say is that "It failed or distorted because of stress within it." After that they could, if they feel the need, go further and define which form of stress caused the unsatisfactory result. Slainte.

 

[Ttrees]

Depending what the application, it may be worth a shot selecting quartersawn stock.
A reasonable approach for something not so important maybe splitting the timber and sawing the other face, and either use it now, and not be too bothered with any end grain checks,
or just do the former to speed up the drying time for something shorter, like for a small jewelry box.

That would likely take two years or more for something which you would be storing,
so not thin stock, more like at least 2" or more thickness, and unless you done the whole Follansbee thing and selected cut, split and cleaved the timber to start with, likely more so of a gamble as to how the timber will behave after being sliced.

Good luck

Tom