lumber pallets/skids

[Brad_bb]

In the first book of Yellowhammer ch1 vs1, "Take steps to save steps", so sayeth the sawyer.

[jpassardi]

When you said that in your video I found it interesting, I wouldn't have thought that either.

[YellowHammer]

I've mused it over quite a bit over the years.  I used to take pictures of other's peoples' Stack Bow, but when I told them what I was doing, it would kind of get them mad.  I would just tell them it's nothing personal, I was just trying to figure it out.   

I have a theory and it makes sense to me, but I've never read about it, but it's there and so here's what I think is going on.  I've even run experiments where I put stacks of lumber on flat concrete, put 1/4" shims under the ends of the pack to actually get a negative bow, sunk down in the middle, and before long, all the stacks had stack bow up in the middle in the top layers!  This was one of those things I lost sleep over, what was going on?

So if you have stickered high packs of wood at least partially air drying where it's moved some, sight down them and see what you see.  In all likelihood, you'll see the bottom layers dead flat, and a gradual and smooth bow up on the unweighted top layer, and each layer in between becoming more and more bowed up from bottom to top of the stack.  I've seen 1/2" bow over 8 feet, but most times maybe 1/4" to 1/8" on a really good pack  If you put a flat 8 foot level or straight edge on the top layer, you'll really see it.  It may be subtle, but I bet it's there.  The problem is that when they dry, they all take a set to the bowed up shape so even the previously straight boards and dry bowed.  So as you look down the stacks, count the layers up where the stack bow transitions from "hey that ain't bad" to "Well, crap!" and most times that seems to be for me, 20-24 ish layers.

So here's what I think is happening:  All stacks will have boards that will move, twist, whatever and since they are on a solid surface, the ground, no matter which way they deform, up or down, the only way the entire stack can react is to move up, causing the bow.  It can't move down because the gound isn't going to move.  The more pieces of wood deform while drying, the more the layers above have to more up, each board acting like a mini jack and the cumlative effect getting more and more pronounced on the higher layers, where even the flatter boards on the layers have to "sympathetically" conform to the shape of the displaced layers below.  The layers of wood have to go somewhere, and they have to go up because they can't go down.  Of course, putting weights on top of stacks will help, but there will always be top stacks with no weights, and those will bow up.

Another thing I've noticed is that even on dead stacked unplanned wood, the effect is the same.  So instead of trying to fight it, I just go with it, and limit all my stacks to that high.  That's also why I hit and miss plane our wood very quickly after it comes out of the kiln.   

Look at your stacks and tell me what you think?