Stress or something else?

[Raym]

Take a look at these and help me understand if this is stress in the log or should I have done something different. I took a few 1" boards after each face cut before I started cutting my 8/4 boards. They will still be usable as they are for an order of turning stock. The wood is poplar and the logs were decent but a little off center pith.



 

The cant was rotated 180 degrees and got the same thing....



 

[black]

I cut a lot of Poplar (Populus Alba), the one with the diamond pattern in the bark.
My experience with it is that it has lots of stress, but if you stack it with heavy weight on top for a period it dries straight. If the logs come from a dry area they are much better than those from wet moist areas.
We cut mostly beams for roofs and use the centre section and cut boards from the outside, but also don't mind cutting boards from the complete log. Stack them quick and keep them from the sun. The also need to be sealed or cut soon after felled or the ends will crack.

[GeneWengert-WoodDoc]

This wood is yellow poplar, also called tulip poplar, Liriodendron tulipifera.  The tree, especially around 16" diameter, often has a great deal of stress, called growth stress.  There is compression in the core and tension in the shell.  So, this warp is indeed common.  This species is,not related to aspen, people, cottonwood, or other species in the Populus genus.

There was an article in Sawmill & Woodlot magazine in the past month or two about this, with discussion on a sawing and drying technique to handle this.

[black]

[black]

This is when I cut Poplar with a Lucas mill.
When coming back on the vertical cut it starts to curl out if you try to split it.
I know its not the way to cut but I put the picture up to show the stress.
I don't know the Yellow Poplar but am shear all cotton wood will react the same.

[GAB]

To date I have sawed one poplar that did not show signs of stress.
I've sawed some that had a lot more stress than what you are showing.
Glad to see that I am not the only one seeing stress in pople.
Gerald

[beenthere]

Pople (popple) often refers to aspen, not yellow poplar. just sayin....

[woodmills1]

Try a small white oak.

[fishfighter]

In the short time I been sawing, I been very lucky as far as logs with stress. Had two oaks so far that I couldn't use as lumber. Could of used them to make recurve bows. :D

[GDinMaine]

I have sawed poplar that was behaving quite well, but also seen it do the same thing you have in the pictures. One of my customers pulled the plug on a log, that was producing boards that bent 2-3 inches sideways by the time I finished the cut.

[GeneWengert-WoodDoc]

Keep in mind that the species called "poplar" in Virginia (the original poster's location) and in the Southern U.S., is totally different and is not a relative of the wood called poplar in the northern U.S., Canada, Rocky Mountains, Plain States, Europe, South Africa, Australia, and maybe elsewhere.

On the other hand, growth stresses are found in many species of wood.  With such stress, logs are often sawn with two saws at the same time (Skragg mill, twin band mill, etc.) or the log is turned 180 degrees often when using one saw.  The logs are live sawn (through and through sawn), and not grade sawn.  Then the unedged lumber pieces (sometimes called unedged flitches) are not edged at the sawmill, but first are dried, and then after drying the flitches are edged or ripped to get the desired lumber pieces.  This is done in order to minimize warp in the final product.  This is sometimes called SDR manufacturing (Saw, Dry, Rip).  It is pretty effective.

[wolf nemeth]

Gene,  if I  let a log lay for 6=12 months  before milling, will I get lumber less prone to warp?

[GeneWengert-WoodDoc]

Unfortunately, very little growth stress disappears with time.  People have looked at presteaming as well, and a few other techniques including high temperature drying.  Nothing seems to be overwhelming.  Note that in North America we have very little growth stress, compared to countries with eucalyptus.  So, we look to their efforts and experiences for guidance.

Funny comment:  if you store for 6 to 12 months without really good sprinkling with cool water, you actually will get less lumber with stress because you will get less lumber overall.

:D smiley_clapping smiley_clapping smiley_tom_dizzy02

[mesquite buckeye]

 

 

Here is an American wood with a bit of stress. ;D

Slippery elm, I believe.

[DRB]

Off center heart means the tree leaned.  That means one side of the tree was always in compression the other always in tension.  The greater the lean the greater the stress built up in the log and the greater the heart is off center.   You start cutting and one side will curl one way the other the other way.  No way to stop it the log is not going to saw nice straight lumber and if it is very far off center it would be better to make it into firewood.  That is why a log buyer will downgrade logs with off center hearts and why limbs are not worth sawing. An old rule of thumb is a tree that leans more then 10 degrees is a cull.  Not always true some that lean more then that may still be usable but something to think about when buying standing timber. When buying logs always pay less for off center heart the more off center the less usable. 

[longtime lurker]

I've cut the odd stressed log. And the even ones too!!! :D

Log stress is a fact of life in what I mill most of the time and dealing with it is just part of my regular day at the office. It's not so much a matter of if what I mill is going to move - more a matter of how much.
There's really only a couple of things you can do about it:
1. cut shorter lengths so the bend isn't so apparent
or
2. oversaw and straighten.
or
3. play in market segments where its not such an issue. No-one really cares if a pallet board has 1/4"of deflection.

Having said thats heres a couple of thoughts I've got. Some I can back up with evidence but a lot are just opinions based on experience.

I'm not a believer in centering the pith. Doing so in stressed logs will give you 1 straight board - the one with the pith in it. That is if when you've dropped tension the log hsnt pulled itself around and moved the heart off center anyway. My opinion and the way I saw everyday is to cut to taper and try and hold parallel to the sap from four sides, leaving short, tapered, low value pith boards and increasing my recovery of high value outer heartwood boards. My best boards always come off just under the sap and I want them long. Conversly if you cut to heart you get shorts, then longs with sap one end and none the other. They still move like that.

I tend to run a backsawn pattern in springy logs. The object being to produce boards with bow rather then boards with spring. Bow I can weight out in a pack, or a builder can pull back with a clamp - spring has to be ripped out or the board is virtually unsaleable. Or I'll run a through and through pattern in smaller logs so I get backsawn off the top and bottom then quartersawn out of the middle portion of the log.

I accept that I'm going to get lower recovery. Nothing for it but to bite the bullet there - I've experience with everything from a quad canter with chipper reducers down to a lucas mill and there's not one of them that can deal with springy logs better then another.  Faster yes... easier yes.... but the end result in terms of log recovery is pretty much the same.
Probably the best #1 for small springy logs I've seen is a McKee twin, which is an outsized overhead end dogging scragg configuration that can handle full sized logs rather then what a scragg normally gets fed. But even its not a panacea, and you're back to heart centered sawing with high value shorts again. And I've seen one of them bogged down when the log sprung and both blades were pinched that tight they stopped sawing...

I tried SDR. We still do it in one high shrinkage species, but other then that I am of the opinion that when I factored in the costs of (a) double handling flitches back to the benches and (b) kilning timber I then discarded and (c) general nuisance because bent boards are a pain to put into a stack I was better off just oversawing and ripping them back to straight boards in the first place. I think SDR is a good thing and it does work to some degree but I remain unconvinced that its cost effective.

For quarter cutting saw oversize flitches, straighten them, and then cut boards. It's far faster to put two cuts on a flitch to make it straight then break it into boards then it is to break the flitch into bent boards than need to straighten every one. maybe if you had a good twin edger with a linebar infeed that might change but I've never had one to play with to know.
For backsawn that may or not be necessary, depending on how thick you're cutting and how much its bowing. It's not hard to weight out bow in 1 to 2"thick boards... any bigger then that and you're going to need to oversaw and facecut your flitches that way as well.

Downturn and facecut becomes second nature. Either that or you learn to ride the linebar by advancing and receding your headblocks as the log passes the saw. Even then you're still going to need to facecut, but less often. Thats why 4 or more headblocks are so popular in Australia... the closer you can ride that linebar the more consistant the thickness of your bowed flitches shall be.

Handle your logs better. End seal immediately after felling and keep the bark as intact as possible in species where you expect them to spring. The object being to hold as much moisture in the log as possible. Then saw them as soon as you can. I've got nothing beyond gut feel and eyeball evidence to support it but I know this makes a difference in dense timber like eucalypts. The wetter they are when I saw then the less spring they have. Sapwood is designed to carry water and when you fell the tree it starts doing just that... carrying water straight out the tree, and at a far faster rate then heartwood does. By not holding that moisture in you've created a whole of log moisture gradient in just the way you dont want it to go. Sapwood being porous also dries faster... dry wood shrinks... and that also pulls it in the direction we least want it to go. My gut tells me I get significant increase in recovery cutting logs that are wringing wet against those that have been handled less carefully, just because I don't have to require so much oversaw allowance. It may or may not give me an extra board but I get less movement in what I do get. Less bow to weight out in the stack is never a bad thing. In Australia its pretty common to see sprinklers running on the log piles trying to hold moisture in them.

I always wanted to cut from a log pond... shame that eucalypts sink.

[GeneWengert-WoodDoc]

A leaning softwood tree does get an off center heart (or pith), plus it is likely (almost 100%) that compression wood is present.  Compression wood, which actually causes the wider ring spacing and the oval shape, also causes immediate warp when sawing, plus more warp when drying, plus large weakness in the lumber to the point that compression wood is not allowed.  Note that softwoods also have spiral grain, especially with the first 25 growth rings that causes warp.  Spiral grain is present with centered or uncentered pith.

The presence of lean as an indicator of high stress is generally not true for many hardwoods.  That is,  many hardwoods develop troublesome stress even when the heart is close to centered.

Note that 10 degrees is a lot of deviation...10 degrees means that tree is leaning over 2 feet in 16'.    I would be tempted to be very concerned with trees with half that amount.

[Magicman]

As longtime lurker pointed out above, off center pith on Pine logs are just a way of life, and the tree did not necessarily have to be a leaner on a hillside.  It could have been an "edge" tree or had competition from another tree on one side.


 
Whatever the cause does not matter.  What matters is how you set the log up for the first face opening. 

Below is an illustration of sawing an off center pith SYP log into 2X4's.


 
Initial setup.  (The red crayon lines are for illustration purposes.)


 
First face opened and flitches sawed.


 
Second face opening and flitches taken down to the cut line.


 
Third face opening.  Flitches removed and the cant split for 2X4's.


 
Forth face opening and saw through.  The above off center pith log produced a nice whack of stable 2X4's.

[Dad2FourWI]

Nice pics Magicman!!  ;D

You sure make it look easy!!!! (never feels that easy when I am making the calls!!  :D :D )

-Dad2FourWI

[Magicman]

You've gotta work with what the customer has.  He expects you to turn out good lumber from not so good logs.

[samandothers]

This is a very timely thread.

Gene your reply #2 helped put some questions and frustration I had this weekend at ease.... a bit.  I too was sawing poplar in SW Va. this weekend and fought stress the entire time.  I did not expect the amount I experienced in most every log. I expected some as the trees were off a hillside and several had off centered pith.

I was attempting to create 2x4's.  I will use these to hold up board and batten siding on a pole barn.  I would attempt to saw a thickness of 1 5/8's.  The ends were fine but the middle of a 12' board would be almost 2 inches as the cant would raise.  I also experienced a great deal of warp and bow.  These to issues are not bad since I can still mount on my poles and use to support the board and batten.  The thickness issue though I may have to treat with a planer.

[Raym]

much thanks to all.....