Log tension

talltimbertwo · September 01, 2020, 03:49:22 PM

I have heard people on this forum, talking about log tension.Since I have only sawn one board on my new mill"story for another day " I don't know what it is. Is it dangerous or just effects board quality. Any info would be great

doc henderson · September 01, 2020, 03:57:51 PM

It is when you saw and the sawn part clamps tight or lifts up. releasing tension that in the log was the sum of all the tension. when you slice it, it becomes evident. It is why sawing branches (grow sideways) is tough. they grew trying to overcome gravity. and will have tension.

boards from the first 10 feet of a "tree of heaven".

second 10 feet with lots of branches going everywhere. spring apart as it is sawn "tension"!
not so much dangerous, as may effect the quality of the final boards.

talltimbertwo · September 01, 2020, 04:34:16 PM

Thanks for an excellent example!

Hackeldam Wood Products · September 01, 2020, 06:59:02 PM

That is a small Hemlock that grew leaning. I turned it and ended up with some good 2X6.
Remember good logs make good lumber. You can roll a good log.

Southside · September 01, 2020, 08:20:14 PM

All logs have compression and tension wood as that is what allows the tree to defy gravity and hold itself up. In some logs one side or the other is much greater - say those that grew on a side hill or edge of a field, when sawing that log you are cutting through what was holding everything together and releasing the tension. This will at times result in examples of what you see above. The board may also slip sideways on the log. Sometimes there really isn't anything you can do to overcome the issue, sometimes you can continue to saw that face and work out of the issue, sometimes you have to skim the log, flip it, skim again, and start over. Reading tension in a log will be one of those skills that you acquire with repeated practice.

Last week we ran some 1x6 dry pine back through the edger into 3" strips, those boards didn't look like it but they were full of stress, they would pull apart from each other and "POP" in the last 6" breaking the fiber - turned into bananas. Had to find other stock to fill the order.