Tension

[trimguy]

 

 

 
Even though the tree is fairly straight, would it be safe to say that the logs would have a lot of tension in them ? With the majority of the branches on one side?

[Southside]

Only one side of that tree is working day and night to keep it from landing in the water, and it's going to win when gravity is removed from the conversation. 

[moodnacreek]

The trees on the edge are the worst. When you open up a white pine log with a sawmill [take a slab off] you will know right away if it is loaded with tension by the color of the fresh cut wood. Darker than it should be is bad.

[Don P]

There is zero tension wood in a softwood
A softwood props the tree from the underside of the lean on compression wood, that darker dead looking grain, filled with lignin, tree glue. If its in more than a streak don't use it for demanding structure, it is weaker but stiffer, it'll fool you.

It's semantics but its physics too, a hardwood throws a strap of tension wood on top of the lean and tries to cable the tree back upright. Those cells have a rubbery layer inside the cell cavity. Good for bows.

One is generally not much better than the other but they both evolved with a different way of dealing with the problem, which is kind of cool.

[moodnacreek]

Very well said, Don.    With the constant springing of hardwood while being sawn sometimes softwood can be worse. Hemlock and red cedar [not double hearted] can shut tight on a circle saw before you reach the spreader. This can cause a bad accident if the log is small and not dogged down tight. The whole log can be thrown at the sawyer.

[trimguy]

I’m just trying to understand why some logs on the sawmill seem to have more tension/compression when they are fairly straight. Thank you everybody. Thank you Don for the detailed explanation.

[moodnacreek]

The ideal saw log is cut from the thick woods in the fall or winter. That tree grows straight and only it's very top sees the sun.  Field or 'wolf' trees are all limbs with one butt log if any. Pasture pine or bull spruce are softwoods growing in the full sun. These mentioned are called open grown. Unless they are walnut they are not valued as commercial saw timber in most cases. Then you have the trees on the edge that get sun on one side and nothing on the other causing an imbalance in the tension that keeps the tree up. When you take that log apart with a saw the long way you relieve this tension. It is like taking the load off a leaf spring.

[Walnut Beast]

How about dead wood down or standing any less tension?

[Walnut Beast]

How about a tree growing at a 45 degree angle then angles up with a full top. That’s the ash I cut down and it didn’t seem to have much tension in it

[Oddman]

How about a tree growing at a 45 degree angle then angles up with a full top. That’s the ash I cut down and it didn’t seem to have much tension in it

I've noticed that ash doesn't seem to have as much tension as a comparably shaped/grown oak. 

[Walnut Beast]

Out of all the down dead and standing walnut none of it had much tension in it except the sap wood and a log that had many knots all the way through it. It really had some tension in it

[Walnut Beast]

This is from Peterson portable sawmills. Flat sawn boards are cut from the log where the growth rings run parallel to the wide faces of the board. Flat sawn lumber is the most commonly produced as it is very quick to cut and creates less waste.
The flat sawing method of cutting boards is great when dealing with high-tensioned logs. With the grain running parallel with the wide faces of the board, the boards will tend to bow upwards. Flat sawn boards have a lot of flex, therefore bowed boards can be straightened through correct fillet stacking and being weighted down during the drying process.

[Don P]

A flatsawn board relieves growth stress as bow where a quartersawn board will crook as it is released. Usually for construction wood I can push and hold bow in place but can't do a thing to help crook. End use determines a lot of it.