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Author Topic: how does stress/tension in standing timber translate to sawlogs?  (Read 2575 times)

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Offline BenTN

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how does stress/tension in standing timber translate to sawlogs?
« on: September 14, 2015, 02:47:54 PM »
i have never sawed a board in my life other than a few freehand chainsaw pieces, so be easy on me. reading the other thread on tension has peaked my curiousity. i have several pitch (Virginia) pines that will be coming down. most of these trees are wind blown and leaning. they have been growing this way for many years now.

so to my question. how would this growth stress come out on a mill if i were to have them sawed? would they be worth the effort? they normally would become full sized landscape timbers around flower beds and garden. i just hate to see a 20-24" log go to waste when i could always use an addition to the woodshed, or other projects around the house.

Thanks,
Ben

Offline Ianab

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #1 on: September 14, 2015, 03:56:13 PM »
First thing you need to look at is how off centre the pith is. That gives you an indication of how much tension is likely to be in the wood.

If a tree is a decent size, and is leant over (storm, ground movement etc) then all the wood that is already laid down in the trunk formed when the tree was straight. It wont change much.  But if it was a sapling and was leant over, and most of the wood was laid down under stress. You will see this because all the growth wings will be oval from the beginning.

Now this doesn't mean the wood is useless, just that it's likely to move. Use a sawing pattern with this in mind, and try and keep the movement as a simply bow. This can be corrected to some degree in the drying stack, and it you cut 1" boards, they have the flex to be forced flat when you nail them up if they are for a non-critical end use like shed siding.
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Offline BenTN

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #2 on: September 14, 2015, 04:52:39 PM »
thanks Ianab, i guess i need to study up on reading log stress and sawing patterns, drop'em and find out how much i learnt. none of my plans for the lumber would be critical, more shed space and some other outdoor projects.

do the stresses increase with the length of log being cut? would a shorter log of a tension loaded tree be less likely to move when milled?

Thanks,
Ben

Offline Magicman

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #3 on: September 14, 2015, 06:19:04 PM »
@WDH should be able to link to the topic about his Pine leaner.
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Offline bkaimwood

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #4 on: September 14, 2015, 06:58:49 PM »
All trees are at risk for stress, in one way or another...I think a general rule of thumb is that if a tree leans more than 10%, expect to deal with some kind of stress...like others said, reading the pith is key to maximizing usefull lumber. In my opinion, these are the logs where precise pith sawing, from end to end, level pith, is most important...the logs as mentioned with offset piths. Precision is key...using this method, I usually get decent boards, and a decent beam out of such logs...sometimes better, sometimes worse...
bk

Offline WDH

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #5 on: September 14, 2015, 08:06:50 PM »
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Offline BenTN

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #6 on: September 14, 2015, 09:04:44 PM »
That was a good and funny thread WDH. I think I understand the "pith" thing a little better now and how important it is in these stressed pines. I am very interested to see ho your lumber turns out WDH.

Thanks,
Ben

Offline samandothers

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #7 on: September 14, 2015, 10:40:02 PM »
I have enjoyed several of the recent stress threads and approach to sawing.  Live and hopefully learn! 

Danny I enjoyed re-reading the thread on the off center pith.

Offline Brucer

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Re: how does stress/tension in standing timber translate to sawlogs?
« Reply #8 on: September 17, 2015, 01:49:08 AM »
Some species move more than others when you saw out the stresses. The worst species I've run into is Western Red Cedar. If I'm making lumber (as opposed to timbers) I will saw off the 4 slabs, then saw and flip after each cut until I'm down to the cant I want. After that I just clamp it securely and saw right down to the deck.

The WoodMizer 2-axis clamp will usually hold the wood flat to the deck even while the stresses are trying to bow up the centre. The older style WoodMizer clamp definitely would not hold it flat.
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