Thread: Dry the Log out First?

I think you mean sapwood.

EDIT: Beat me to it Ian.

Originally Posted by silentC

I think you mean sapwood.

EDIT: Beat me to it Ian.

Must be a first, Silent!!

And by 3 minutes too. I must be getting slow in my old age..

But your post was more illuminating than mine, which isn't a first

Originally Posted by silentC

And by 3 minutes too. I must be getting slow in my old age..

But your post was more illuminating than mine, which isn't a first

Umm, not sure about that! I've seen you come back quicksmart with some pretty good guff at times - a bit of a dab hand with search engines & a good dose of common sense seems to be your thing.

(And a worthy debater.....)

Guys, it's been my experience, if the board has sapwood on it or not, the board pulls toward the sapwood and more, the closer it was to the sapwood...
okay time to draw pics.... brb

Yeah I understood what you meant, I was just clarifying for the other bloke that you were talking about it pulling towards the sapwood, ie. your 'sap' was short for sapwood.

So here we go... in the pics below, the log is green, therefore there's no effect given by differential moisture content, none of the boards actually have sapwood on them, so any direct effects of sapwood are negated and the direction of spring is straight off the saw...



Diagram A. The board to be cut out will show spring once cut and the spring will be to the left.

Diagram B. The same sized board from a similar position, but to the left will spring to the left.

Diagram C. This board will stay as straight as naturally possible - it will exhibit bow, but bow can easily be accounted for when it is used.

Diagram D-F. This shows the scenario of a 300mm board cut from the log, straight off the saw this board will again be straight, 10 minutes later its ripped into two 150mm boards (no moisture difference at all) and the two resultant boards will pull as shown.

My experience shows that in the above situations, moisture disparities have nothing to do with the 'pull' on the timber; only position/orientation in relation to the sapwood at time of cutting, In Diagram C. The board shown will exhibit bow, but not spring. A similar board taken from the layer below will again have no spring, but will also exhibit less or even no bow.

Given this information, moisture content doesn't significantly change in any of the examples, but the boards do pull in the directions given, so something other than moisture content is the 'force' behind the boards pulling and the only factor which changes is position/orientation of the board when cut, therefore it must be the governing factor...

But there are other factors that give rise to warping - for example reaction wood, which refers to wood generated in part of the trunk when it is under compression or under tension if the tree is leaning or exposed to high wind (presumably it is under compression on the leeward side and tension on the windward side). Not sure if these result in spring or other warp off the saw, but they certainly do come into play during seasoning.

What Sigidi is showing makes sense if you realise that "wood" is laid down from the centre out by adding layers of cells. At first the cells are 'green' - i.e. have thin walls and are part of the tree's active fluid conduction system (sap). They are also under the most tension. As the cells age, the material in the walls thickens & hardens and various compounds may be deposited in the empty cell cases and their walls. This makes them harder and less compressible, and also the tension decreases. We tend to think of "sapwood" as a sharply defined layer, because in many trees we can see a pretty distinct delineation between the younger cells and the older, more lignified & gooped-up (pigmented) cells. This is really a bit artificial, as there is pretty much a steady continuum from the oldest (inner) cells to the youngest (outer) ones.
There is going to be some smidgin of remnant tension, even in the older cells, which increases a bit as you go out, which is probably the main teason for 'spring off the saw'. The cell-walls contain more water in the younger cells, so that a board containing sapwood is going to shrink more as it dries. Linear shrinkage is generally considerd as neglible, but there is always some, and it doesn't take much difference between 2 sides of a 3 metre long board to produce a good-sized woop in it. Which is why it's recommended to remove the 'sap' wood. How much wood you remove is a matter of experience and the species.

There are also other good reasons for removing sapwood - being the active conduction tissue it's full of sugars, & that plus the much more chewable cell walls makes it much more yummy to many of those nasty little wood-munching critters that want to wreck our nice boards, a better sustrate for fungi & so on.

Sorry - the biologist & academic in me comes out at the full moon - apologies to all those grannies I have just told how to suck eggs. I'll go back into my cave now....

Silent you are spot on with that too; if you look at the crosscut of a log and can see the heart is badly displaced to one side, more than likely it has come from a slope and the heart is displaced to hold the tree up straight. These are very hard logs to cut good straight timber from as one side has very tight grain and the opposite side has very loose grain

a log will never dry.

its quite easy to tell what a bi of woods gunna do actualy

hardwood pulls to the outside of the log and softwood pulls to the center.

attached is a pic of what i mean. now this is not an exact science but you can use this to determine how you aproch a log. how mutch boards of a log will bow depend on a lot of things. age, speed of growth, location, species are just a few.

as for teh heart being off center. the west side of trees around here is closer teh the heart than the right as teh west side gets the hot afternoon sun cooking it every day. the western side is also a lot harder to bark.

I'm sorry if you have taken offence - I was having a gentle dig at your pulling due to sap which is also not quite right - I did assume you meant sapwood but couldn't resist.

Originally Posted by weisyboy

hardwood pulls to the outside of the log and softwood pulls to the center.

In general all this information is correct but you do get the odd log which defies known knowledge.

I have had a few red ironbark and one red bloodwood do the total opposite with the board clamping down on the blade moving towards the heart with such force the 30hp engine actually stalled. With the bloodwood we ended up having to take a chainsaw to the log to get the mill out of it.

Had the same doing split posts on a tallowwood. All the billets split perfect except the butt billet which had grain going everywhere. The first post to come off took 30 minutes to split. Chainsaw first, then wedges got clamped and only had the one chainsaw with us at the time.

all the logs had central hearts and looked good quality logs with little defects (sorry i ment features).