Sorry for what! A good question is what makes us think.

I'll tackle one,

This is a good read on growth stress;
http://www.fs.fed.us/ne/newtown_square/publications/technical_reports/pdfs/2004/316papers/Cassens1GTR316.pdf#search='tension%20growth%20stress%20tree%20checking'

These are a couple of short articles on juvenile wood;

http://www.fpl.fs.fed.us/documnts/techline/properties-of-juvenile-wood.pdf
http://www.fpl.fs.fed.us/documnts/rips/fplrip-4701-001-western-juvenile-softwoods.pdf

I'm working on a deck repair, this is one of the old deck boards that I skimmed 1/16" off of. You can see the heart. Juvenile wood shrinks lengthwise far more than normal wood. When it is surrounded by mature wood that does not shrink appreciably lengthwise it often checks crossgrain when the stresses exceed the strength of the wood. Just below the reddish heartwood is a band of what I call "peanut butter" looking grain. It is duller and lifeless looking compared to normal latewood. That's compression wood. Bad microfibril angle and loaded with lignin. It is stiffer than normal but weaker. I've caught myself using it for scaffold planks because it is heavy and stiff, it'll fool ya! It's weaker and breaks short, without warning.

I have some cedar deck boards with the same pattern, right down the pith. Now I know why. Thanks Don P.

Tim

Thanks for reading, I was starting to get lonely there

If unrestrained it would tend to cause the board to bow as it dries and shrinks,

If on an edge it would tend to cause crook. Growth stress on the board above should have made it want to bow away from the bark but the juvenile core made it bow toward the heart.

This is another pair of good articles on growth stress, juvenile wood, checking, etc. One on hardwoods and one on softwoods;
http://www.fpl.fs.fed.us/documnts/pdf1987/maegl87a.pdf
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr129.pdf

A few post back there was a few comments where folks have said they have not seen the pith location effect bow in a timber. I am guessing with larger dimension stock has enough structure to over compensate the juvenile core. On boards there is less surrounding structure and the core has a bigger effect.

Tim

I would agree, that is part of it, in these last few posts I've also been picking southern pine to show the reaction wood because it has the most I've come across and is pretty easily visible. Eastern White Pine by comparison generally just lays there, its generally pretty stable stuff. The growth stresses in poplar can cause it to split right off the saw but I can't recall a juvenile bow in a stick of it. Red oak I've seen go both ways. Nature is complex and full of unique individuals. I have seen several cases of 6x8 and 8x8 milled logs (which are just boxed heart timbers) where the logs have shrunk lengthwise, leaving a gap in a butt joint in a wall of rows of timbers. Several times in "mixed southern pine" and once in western red cedar.

Going back to a comment on my white pines, the juvenile core can be a foot in diameter, so the wood in it would be weaker than one might expect if the juvenile core was small. By contrast if I let them continue to grow and each year they continue to put on 1/4", it will now be putting that 1/4" of mature wood on a larger cylinder... many more bf of mature wood per year. This might be good for boards but for timbers a compact heart might be a better thing to look for.

With boxed heart around the core hopefully the juvenile wood is encased within a healthy shell of mature wood. Then the reaction wood is in the neutral axis of a beam where stresses are low.

Interesting points regarding the juvenile wood in ewp. I cut a frame last fall, and the timbers were quite manageable. The timbers in last weeks workshop, also ewp, were much heavier. I know my trees came from an area that would have encouraged fast growth. I'm thinking that the trees in last weeks workshop must have been much slower growing.

In softwoods density is somewhat independent of rate of growth. This is a picture that shows dougfir labelled with the specific gravity of each piece. The percentage of latewood is a better indicator of density than rate of growth.

Going back to my little stand of pines, I need to go in and take out the supressed trees. These are now in the understory and will have as many rings as the big boys but are a fraction of the diameter. My guess is they will have been starved of light and nutrients so will be slower grown, with a small juvenile core. But I'll bet it will be unusually light with little latewood. I expect it will be fairly stable wood since density is one thing that causes shrinkage, light low density wood doesn't shrink as much in the same species as a denser piece but is weaker.

I came across this description, thought it might help reinforce some of what we've been talking about.

Warp in lumber is any deviation of the face or edge of a board from flatness or any edge that is not at right angles to the adjacent face or edge (squares). It can cause significant volume and grade loss. All warp can be traced to two causes; differences between radial,tangential, and longitudinal shrinkage in the piece as it dries, or growth stresses. Warp is also aggravated by irregular or distorted grain and the presence of abnormal types of wood such as juvenile and reaction wood, Most warp that is caused by shrinkage difference can be minimized by proper stacking procedures (ch. 5). The effects of growth stresses are more difficult to control, but certain sawing techniques are effective and will be described
later.


The five major types of warp are cup, bow, crook, twist, and diamonding (fig. 8-11). Cup is a distortion of a board in which there is a deviation flatwise from a straight line across the width of a board. It begins to appear fairly early in drying and becomes progressively worse as drying continues. Cup is caused by greater shrinkage parallel to than across the growth rings. In general, the greater the difference between tangential and radial shrinkage, the greater the degree of cup. Thinner boards cup less than thicker ones. Because tangential shrinkage is greater than radial shrinkage,flatsawn boards cup toward the face that was closest to the bark (ch. 1, fig. 1-10). A flatsawn board cut near the bark tends to cup less than a similar board cut near the pith because the growth ring curvature is less near the bark. Similarly, flatsawn boards from small-diameter trees are more likely to cup than those from large-diameter trees. Due quartersawn boards do not cup. Cup can cause excessive losses of lumber in machining. The pressure of planer rollers often splits cupped boards. Cup can be reduced by avoiding overdrying. Good stacking is the best way to minimize cup.

Bow is a deviation flatwise from a straight line drawn from end to end of a board. It is associated with longitudinal shrinkage in juvenile wood near the pith of a tree, compression or tension wood that occurs in leaning trees, and crossgrain. The cause is the difference in longitudinal shrinkage on opposite faces of a board. Assuming that there are no major forms of grain distortion on board faces, bow will not occur if the longitudinal shrinkage is the same on opposite faces.

Crook is similar to bow except that the deviation is edgewise rather than flatwise. While good stacking practices also help reduce crook, they are not as effective against this type of warp as they are against cup and bow.

Twist is the turning of the four corners of any face of a board so that they are no longer in the same plane. It occurs in wood containing spiral, wavy, diagonal, distorted,or interlocked grain. Lumber containing these grain characteristics can sometimes be dried reasonably flat by using proper stacking procedures. Twist, bow, and crook have definite allowable limits in the grading rules for softwood dimension lumber, so it is desirable to minimize these defects. Diamonding is a form of warp found in squares or thick lumber. In a square, the cross section assumes a diamond shape during drying. Diamonding is caused by the difference between radial and tangential shrinkage in squares in which the growth rings run diagonally from corner to corner. It can be controlled somewhat by sawing patterns and by air drying or predrying before kiln drying.

Boxed-Heart Splits
A boxed-heart split is shown in figure 8-8. These splits start in the initial stages of drying and become increasingly worse as the wood dries. The difference between tangential and radial shrinkage of the wood surrounding the pith causes such severe stresses in the faces of the piece that the wood is split. It is virtually impossible to prevent this defect.

Great info Don, thanks.....