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cracking partially on glue line2/23
Looking at the end-grain of an edge glued solid wood panel (in this case, a table top), what are the probable causes of a hairline crack which mostly follows the glue line, but then branches off as shown in the attached image? I have seen this more than once through the years and would like to understand the science behind it. Is it cracking from strain caused by climate-related warping which just happens to occur near the glue joint, caused by the homeowner's failure to maintain sufficient indoor humidity? In my example, the crack has appeared months after the product was installed. Always a hairline crack, never running more than an inch along the glue joint face. The panel might have had warping at one time, we don't know.
My guess is that you've got a glue starved joint there due to too much clamp pressure or not enough glue. The top split may have had a better glue joint so the wood failed before the joint.
I guess you didn't build this, or did you since you know what glue was used? Lots of variables, improper jointing before glue up, improper kiln drying, not finishing both surfaces of the top, not allowing for enough seasonal movement, as mentioned by Al poor glueing technique, etc...
The only part of the glue line which was done properly was that top 1/8", so I'm guessing glue starved too.
At first, I thought maybe dull jointer knives burnishing, rather than cleanly cutting, but that tiny bit would probably have been bad too, except there could have already been a weak line there beforehand.
It might help to know if this was a really big top, which might have pushed you past your open window time for getting the clamps on too.
End cracking is text book improper moisture content wood being glued up. The ends dry the fastest, crack first. Older traditional woodworking insists on a sprung glue joint. The middle of the boards would not have touched after jointing and getting ready to glue. Only the ends would touch. Add the glue and clamp. That preloads the joints on the ends of the boards and allows for a little more shrinkage.
Thank you. That helps a lot.