Any advice - Resawn board curling up

[Scott T Smith]

Good eye, Scott! To be honest I hadn't noticed that there was pith in the board. Would this also explain the bow in the length of the two boards?

James

James, re the bow I would hazard a guess that there was a slight bend in the log at that location. Look closely at the edge grain on the top board above the bow. Notice how the angle of the grain relative to the face of the resaw cut changes just slightly in the vicinity of the bow versus at the left and right sides of the photo? Ill bet that there is a greater presence of cathedral grain where the bow occured, indicating more movement as the center of the board dried after resawing.

[Scott T Smith]

Not to change the subject too much. But when sawing on your mill for flat sawn material. How far away do you stay from the pith? Are you looking for color change? Or is there some kind of ratio in relation to the log diameter? Jay,

James

James, I don't mill much flat sawn, just quarter and rift sawn, and I try to leave at least 2 - 3" between the center of the pith and the edge of all of my lumber. QS boards that are milled too close to the pith tend to crook while drying. Usually I mill at least a 4 x 4 if not a 6 x 6 from the center of every log, and set it aside to use as either cribbing (dunnage) or farm wood.

I also tend to look at the consistency in thickness of the growth rings. If the center of the log has noticibly larger growth rings in it for the first few inches, I'll try to keep that out of my lumber.

[Scott T Smith]

Having said all that - wherever there may be differences between what I say and what Scott says, believe whatever Scott says. He clearly has forgotten more than I will ever know on the topic.

<grin> Larry, you just made my morning! I seriously doubt that I've forgotten more than you know - but thanks anyway for the compliment! I like your approach to resawing and clamping; very practical solution.

[jay gill]

Scott,
Thanks for the great info. Very perceptive on the curl occurring around the pith. It definitely helps me understand what is going on and how to avoid or plan for these potential issues in the future. The lumber has been in my basement shop since last August, admittedly stored standing on end. The original pieces were ~9' and were cut down to ~36 inches each prior to bringing them into the shop, but it does make sense that there has been additional drying on the outsides based on how the board cupped/curled in all directions.

Jim,
The goal of the wide boards as the back of the case was to to book match the catherdral of the grain across the 6' width, so I was hoping to not have to resaw down to ~6-7" pieces if at all possible thus giving fewer joints. Luckily, my design has the final thickness of the boards at 3/8", but could get away with 1/4" and still include a 1/16" dado to provide some mechanical support to the shelves along their length to prevent sagging. I think I might be able still joint and plane them into usable pieces.

I also have a feeling a moisture meter is in my future.

[Danny Hamsley]

James,

The pith is a necessary evil. Some species are worse than others. Oak and cherry have very bad piths that are prone to splitting and cracking. Walnut behaves much better. I just leave it in the wide boards, captured in the center when I am sawing the boards. After drying, when I get ready to use the board, I rip it out. Splitting a board thru the pith leaving the juvenile wood on the pith side will cause the green board to dry with a pronounced side bend. The juvenile wood on the pith side shrinks a little longitudinally while the mature wood on the bark side does not, causing the side bend. That is why I leave the pith in the center of the board until it dries.

[Myk Rian]

Are you sure the mature wood is under the bark?
When a tree grows, the new wood is on the outside. (Sapwood)
The oldest wood is in the center.

[Scott T Smith]

Are you sure the mature wood is under the bark?
When a tree grows, the new wood is on the outside. (Sapwood)
The oldest wood is in the center.

Myk, during the first several years of a trees growth, it produces a type of wood that the forest products industry terms "juvenile wood". During these years the characteristics of the wood produced each year varies widely from growth ring to growth ring. Usually when the tree reaches between 5 - 20 years of age the cellular structure becomes more consistent, as do the boards ultimately produced from it. This later wood is called "mature wood" by the industry.

All trees have juvenile wood, but in older growth forests it does not have as much of an impact due to the close proximity of the early growth rings. Trees harvested from modern forests are more problematic when the boards contain juvenile wood.

Technical differences between juvenile and mature wood include a different cellular structure, lower strength, higher lignin content, more compression wood, higher longitudinal shrinkage, etc. These cellular differences causes it to react differently when sawn or resawn, which contributed to Jay's problem.

By the same token, during each year's growing cycle the tree adds cells that are referred to as "early wood" and "late wood". Late wood cells are more dense than early wood cells, and the ratio of early to late wood makes a difference in the strength of the lumber. The color differences between the two (latewood cells are usually darker than earlywood cells) is what makes the growth rings stand out on on wood.

[Danny Hamsley]

Are you sure the mature wood is under the bark?
When a tree grows, the new wood is on the outside. (Sapwood)
The oldest wood is in the center.

No, that is not how it works. You would think that the oldest wood near the center of the tree would be mature wood, but it is not. Juvenile wood is produced at the apical meristem as the plant grows. This forms the pith. Then, the first ten years or so of growth in the young stem is juvenile wood. As the tree gets older, the wood that is laid down after this juvenile core has different cell wall configurations and contains less lignin. This is mature wood. If you look at the cross-section of a tree, the mature wood is to the outside, and the juvenile wood is associated with the pith.