Stress

[Rhodemont]

This is a follow up to my post in "watcha sawing" of the 20 ft yellow poplar 4 x 10 roof rafters I am sawing.  I had heard that the poplar would have stress and move when sawn.  The logs are as straight as I ever have.  The butt logs have taper which I have been trimming off before taking full cuts and the second logs up actually roll.  Watching Yellow Hammers video on reading the log to minimize stress movement put me on task to try and read the logs.  I have been taking slabs off each side then continue around each face again taking jacket boards to see if one orientation produced more curl that the other.  I would be hard pressed to say that any of the logs have had one face move more than the others.  So the attached pic shows it all. Slab firewood on the lift, jacket boards on the tractor forks and three rafters rolled on side on the bunks.  This one had a bit more movement that the others so far with the centered pit rafter pretty darn straight and curl away from the center on the two side rafters.  Tulip yellow poplar trees/logs look so straight and clear but they consistently have stress away from the center on all faces.

[Magicman]

I can count on one hand and not use all of my fingers the number of times that I have sawn framing lumber from anything other than SYP.

Your example looks very normal and predictable to me.

[SawyerTed]

Coincidentally I've been sawing poplar 2x6 and 2x8 rafters and framing as well.  What you are seeing is similar to what I'm seeing in a few boards.  

I'm stacking with the hump/bow up and putting weight on top of the stack.  

What I'm seeing isn't bad and the bow is easily worked out with sheathing and/or blocking.

[YellowHammer]

I saw a lot of poplar, and reading and adjusting to stress is crucial, because it's one of my "make money" woods.  Smaller poplar is generally much more stressed than larger diameter poplar, and fresh poplar is worse than logs that have been sitting just a few weeks, and allowed to "wilt" for lack of a better term.  Think of a carrot - peel a fresh one and the peels really curl up, let the carrot sit a little while, the peels don't curl nearly as much.  Think of a poplar log as a big carrot.

Yes, poplar is sometimes bad to have stress, however, it is pretty predictable, and as with any hardwood, the sapwood, especially in poplar, maple, cherry and walnut will really pull like a stretched rubber band or like a "carrot peel."
 
I'm not sure of your sawing pattern, but full sapwood on one face and full heartwood on the opposite face will always badly pull toward the sapwood, just as yours are doing.  So if there were thinner 4/4 boards you could have gotten at the sapwood/hardwood interface, then you could have isolated the transition interface, and put the stress in narrower boards with less distance off the stressed fibers away from the neutral plane.  Then you would have been in pure sapwood, or pure heartwood, and the stress would have been greatly reduced.

The way the boards are sawn off center, unbalanced, with the pith towards the tops, I would expect those boards to be highly stressed and move on all faces.  Sapwood/heartwood interface in one plane, and off balanced pith and growth rings in the other plane.  As with any hardwood, balance of growth rings in at least one face will help equalize the stress in that plane, and put the stress in the other plane of the board.  The ideal thing is to get balance in all planes, but that is generally not doable, so once you've identified if there is a driving force of stress in the log, then that will help you determine which faces or edges of the boards need to be balanced to achieve the goal you want.  Furniture lumber you want the stress in the edge or curve direction, and framing lumber you want the stress in the face plane with the edges straight and unstressed.  In the three boards in the picture, there is stress in all planes, heartwood/sapwood interface in one plane, out of balance in the other plane. 

So if you could have modified the pattern so that the three boards were sawn with the pith in the center of the middle board, I bet you would have isolated the stress to only one plane on these three boards, just need to make sure it is out into the plane you want before you cut.

I'm not sure if I'm explaining this in a coherent way, but basically I would have tried to modify the sawing pattern on the three boards in the photo so they would have been fully balanced, and looked like this ((o)) instead of ((*)) for dimensional or framing lumber.   That would have put the stress in only one plane, and not both.

Thanks for watching my videos, I think I will be sawing either cherry or poplar as soon as I get done with this batch of walnut, and I will keep this topic in mind and hopefully will run into a good "explainer" log.

[Magicman]

I have related before about a customer that had one 16' log that would square 12" and wanted four 6X6's.  I explained to him that it would not work, that he could not get them. 

He insisted that he was a carpenter and knew what he wanted.  After the argument, I sawed what he wanted and he got exactly what I had described; a banana peel.

I walked straight to the invoice book and wrote them down as he left with them draped across the tractor forks.

[Wlmedley]

Right after I got my mill a fellow wanted me to saw him 200 10' 2"x4"s out of poplar for a barn he was building. I have plenty of nice straight poplar trees so I told him I'd give it a shot. I really didn't know what I was doing but I got it done after a few weeks.I wasn't proud of the results and told him so but he said they were good enough for his use and that the boring bees don't bother them.Since then I've found poplar makes nice 1" sheeting and pine makes nice 2"x? .That's the plan I try to stay with.Poplar seems to need turned frequently to get good lumber and with a manual mill it gets pretty rough.

[Rhodemont]

MM:  There was a lot of SYP as I drove through Georgia to the project but have not seen one since getting home.  So, working with what I have got.  Well, I do have some eastern white pine but did not think it appropriate (strength and look) for the exposed rafters in this garage/barn.

Sawyer Ted:  As you describe I am stacking three abreast with hump up with a 16 foot oak cant on top as weight.  The cant is probably 1200 lbs.  At 200 lbs the hump flattens out when I stand on them so if weight will help that cant should do it.

Robert:  Yes your explanation makes sense.   I fell the logs in January/February.    I am cutting to length and skidding out now as I saw them since the ground is drier.  This probably has not been enough time for that carrot to set? The butts are  flared up to about 30 inch with the small end around 20 inch and the second log 20 to 18 inch.  Centering the pith dead center has only allowed three rafters each log.  EXCEPT this one in the pic I thought I could get a 4th horizontally off the top which pushed the log center off on the other three rafters.  The 4th did not work out as I did not clear the corners all the way. (it was resawn to boards which was tough because of the bow which I had to stack two of the other rafters on top of to flatten out on the bunks. They are the top boards on the forks.).   I am not going to do that again, stick to the plan as centered as possible and no last second changes.
I am wondering if the flare on the butt adds to issues?  I can cut a few feet off and just shift my 20 footers up the tree still leaving a third log at 10 to 15 feet for boards.

[Don P]

Our Eastern White Pines grow 2-3' per year and throw out a whorl of branches. In modest sized trees it is harder to get a good #2 grade piece of lumber for a joist or rafter. In the same sized poplar, which is stronger to begin with, it is common to have Select Structural coming off the saw. For that reason I use a lot of poplar framing. The numbers, EWP #2, 575 psi. YP SS 1000psi.

In 2x framing I try to take the stress as bow rather than crook but knowing I can have both in abundance plus cup I usually plane and rerip the lumber to final dimension prior to use. With 4x dimensional it can take bar clamps or a jack to get the bow out. In thicker than that tulip poplar tends to check heavily. I suspect that is why you don't see it in the heavy timber tables.

Do remember most grading rules are revolving around trying to limit slope of grain in some way. Sawing parallel to the bark on tapered logs keeps the runout lower than centering on the heart and ending up with lots of cathedral grain at the butt end of your boards.

[Don P]

Whoops!, delete

[Magicman]

Referring back to my Reply #4 above, these 6X6's were for sills beneath an outside building.

He had an 18" top end log.  If he had allowed it, I could have made four "D" 6X6's and one pith centered 6X6.  The "D" timbers would have evenly bowed and he could have used them with the bark side down so that the building weight would have been pressing them flat.

As it was, they bowed diagonally and he got nothing. 

[SawyerTed]

Magicman, I had a customer demand similar sawing in white oak.  He wanted 6x12s to stack for a "log" building.  Most logs would produce one pith centered timber with side lumber.  

He insisted that I cut two or more timbers per log.  On a few I could make 3 with pith centered in the middle one.  Some I was able to saw 1" or 2" boards in the pith and cut two timbers out of the sides.   On several I had to split the pith.   

The result of the pith split logs was just a waste of logs, fuel and time.

[Magicman]

We have to base our decisions and advice on prior experience.  Sure, there may be exceptions but the butt biters will almost always override the exceptions.

That example in Reply #4 happened probably 15 years ago.  In today's world I would simply refuse to do it.

Yesterday I had three logs that made three 2X6 cants with the pith centered and tomorrow I have one more before I finish that job.  I love standing 18" of cants upright for sawing.