slabs cracking

xlogger · May 03, 2019, 07:09:58 PM

Here's a picture of some ash slabs I just took out of the kiln a few days ago. I've not taken stack apart yet but was thinking about those finch savers they sell. Had some bad cracks in this. Maybe in the future screwing some steel metal along each one to see if it helps. Any suggestions or how do any of you protect yours from cracking?

boardmaker · May 03, 2019, 08:09:40 PM

Do you split the pith with those 2 slabs? It's hard to tell in the pictures.

GeneWengert-WoodDoc · May 03, 2019, 10:01:21 PM

Any crack at the end over 1/4" wide is due to stresses in the tree. The crack relieves some of the stress which is good for the manufacturer. If you prevent these cracks with mechanical restraint, then when someone rips the dry lumber, the unrelieved stress will cause excessive warp of the rippings.

There is more stress near the center of a log than near the bark. A wider piece has more stress too.

YellowHammer · May 03, 2019, 11:58:45 PM

From what I can see in the picture, and I might be mistaken, it looks like the center cut boards, in the pith zone, all cracked. I don't saw those. The ones near the top of the stack, the first 3, taken in the upper 1/3 of the log, typically behave well, with some cup, but no major cracking. That's why when I'm sawing, I'll only take 3, maybe 4, slabs at most from each log.

Ianab · May 04, 2019, 01:16:48 AM

If the cracked boards are near the pith, then rip out the crack and trim off the sapwood, and you have 2 good quarter sawn boards.

To cut live edge slabs like that with my mill I have to saw 1/2+/- of the log, then flip over and saw the other side. Usually saw though the pith and get clear of it before flipping. I do this if the slab looks like it would be worth the effort. But one ~24" Blackwood Acacia slab we cut the other day looked perfect. We got it off the mill and loaded it on the trailer, as as we were standing there admiring it, there was this faint "c--ccc--cccc-r--rr-ac-c-k-k-k-k" sound. Over about a minute, as we watched, the slab split about 1//3 of the way down. Big wide crack. Like Gene says, it was tension in the wood, and if the tension is more than the splitting strength of the board, it something is going to give.

Bit of a bummer, but will see what it looks like when it's dry. It could be epoxy filled, or it can be ripped into nice quarter sawn boards.

xlogger · May 04, 2019, 05:17:28 AM

In the past I have put bad crack slabs back on mill and saw out the cracked and edges for boards. I do try to center the pith but sometimes miss judge it.

moodnacreek · May 04, 2019, 07:55:19 AM

All of this is to be expected. In most hardwood and some softwood logs you turn the log to saw your planks parallel to the worst crack. This is where a mirror helps in the sawmill. The worst is the twist crack, a straight crack is not so bad. Then there is those K cracks, all from the wind. This is one of the reasons open grown trees are not so good for lumber. Also logs in storage starting to dry at the ends. Logs should be kept on the stump or wet. Even mud is better than the wind and sun. In the end the planks that dry crack free should command top dollar to offset all the broken ones. Always saw more than you need.