Tension in log

[maineshops]

I'm cutting balsam fir . They are about 50 ft tall and im taking 8 ft logs out of them. About the third log on the mill one board will come off the log like a rainbow and the next board will be flat. Any ideas what might be going on. It is usually the first board under the slab. I'm slabbing heavy to use them as firewood to Dan. 

[Gere Flewelling]

I have noticed similar action with pine and hemlock, but probably not as severe.  I think it has something to do with the relationship to the outer sapwood and the inner heartwood.  The stress seems to be in the sapwood.  I usually try to remove all the sapwood as I am sawing by flipping the log and sawing until it is gone and then saw the heartwood around the pith.  This usually works well for me.  I have noticed that butt logs don't seem to be as bad, but the higher you go on the tree, the more pronounced the stress is.  Even more so the smaller the log is.  There  are probably lots of scientific terms to describe this but these are the observations of an sawyer educated by the school of hard knocks. ;) 

[WDH]

That is natural growth stress.  Some species are worse than others and smaller logs are worse than larger logs within a given species.  It is particularly bad in small hackberry and yellow poplar logs in my part of the country.  Like Gere says, flipping the log 180° helps relieve the growth stress when you start to see it in the boards.  

[Magicman]

 

 Ain't skeered....  :D

[Andries]

I'd be skeerd of what comes off next.

[Magicman]

The crazy thing was that I was sawing 2X6's and the entire cant below that rainbow remained flat and showed absolutely no sign of stress whatsoever.  :

Ya just never know and the log is always the boss.

[jpassardi]

MM: Didn't know you also saw for shipbuilders...

[scsmith42]

MM, Home Depot would cut a 2x4 out of that....

[Magicman]

There were two logs in that whack that popped up like that and they both could have come from the same tree.  ??  We have all seen them do this as well as curling upward like a rocking chair and then there are the ones that move to the side.