Pith

[woodNthings]

This may be a ludicrous question... When sawing beams that will generally be used for fences, bulk heads, pole barns or other types of posts, is it crucial that the pith be centered? Or close to center? or in the beam at all? I have plenty of logs that could be squared up into 12X12 or 16X16, and the be quartered into 6X6's or 8X8's. Some that I've done this with for staging logs on have stayed strait, but I don't want to sell a bad product.
Please educate me... I'm new! ??? :P

[Jay C. White Cloud]

Not ludicrous at all.  It's more a guide line than a mandate.  If you don't pith or heart center a beam, they can warp, (but not always.)  They rule of thumb, (not a mandate) is "heart center" or "free of heart."  Sometimes you want a little camber in your beams, so if the "crown" a bit, that could be to your advantage.  Sometimes, depending on species, you can dry them straight by putting the crowned timbers on the bottom of a stack.  They may also "relax" on there own.  I have even found that it depends on how you take them out of a bolt (log), which can have an effect on the way internal stresses are relieved.

Hope that helped.

[roger 4400]

Hi. I have a very small experience compared to some members here ( they will answer soon)but what I red over here if you want a good beam try to center the pith. What I experienced....never cut the pith because if you do so your board will be like a bow. Always try to center your pith . For example if you centered your pith in a square 4X4 and cut it in two, both 2X4  will bow. If you have a 6X6 with the pith centered and cut it in 3 2X6 the pith will be centered in the middle one and your board should be fairly straight. Good luck. Roger

[drobertson]

Jay pretty much nailed it,  I have quarted and halved with good success, having minimal warping(crowning) while others crowned from small amounts to quite a bit.  Not sure how to distinquish which one will or won't with the exception of logs that have large sweeps in them,these have inherent stresses that crown quite easily.
david

[Ianab]

One of the issues is "Juvenile Wood" This is those first few years of growth around the pith. It tends to be unstable, and actually wants to shrink in length a little, while the more stable majority of the log doesn't.

So if you get that unstable section on one edge or corner of your post, then it's likely to bow as it dries. Not always. maybe it can be controlled, maybe not enough to matter etc, but it's much more likely to misbehave.

By keeping the pith in the centre of the post the forces are more balanced, and the post is much less likely to bow. Or cutting the post completely away from the pith avoids that unstable wood as well.

So there are various patterns you can use to get multiple posts out of a larger log, but they usually involve one central piece, and the rest being completely away from the pith. It may also be and option to cut all the posts free of heart, and just discard that central section as it's the poorest quality part of the log.

Ian

[justallan1]

Nothing ludicrous about asking, plus I find it cheaper to ask how then wait until later and ask why.
With the same question basically, I need to saw forty 8x8's or 10x10's for a guy, should I use the bigger logs or am I alright using the small ones and just making 4 cuts?
Allan

[Ianab]

I need to saw forty 8x8's or 10x10's for a guy, should I use the bigger logs or am I alright using the small ones and just making 4 cuts?

The heart centred is the most common method, and probably what the client is expecting. Free of Heart beams usually come from larger (more expensive) logs, so you can expect to pay more for those. You should be fine just loading up decent 12 - 15" logs and making 4 cuts, although if you have a market for the boards it's often worth cutting a couple of them off on the way to making the beam.

Ian

[Cedarman]

ERC is one species that bows very little if any if you saw through the pith.  When we made 3 1/2 squares for mailbox posts by the 10's of thousands we would make a 3 1/2 x 7  or 7x7 and slice down the center to make 2 or 4 posts.  Once in a while they would bow a small amount, once in a great while they would bow a good bit, say an 1".  We used to split white pine down the pith and they did not bow either.
We are talking 8' in all this.
Just to show there are exceptions to a good rule of thumb.  Center the pith.

[Jay C. White Cloud]

For Those Asking About Pith,

I will share what we do, and Ian, et al, can add to it accordingly. 

Here is my standard operation:

If we are milling for one of our frames we have two choices, 1.) Wade into the pile and just start milling what we need.  If we can get heart centers, then that is what we will do.  If not, then anything that bows will be set to the side to relax, or TBDL for use.  2.) If I have a specific timber frame contract, I may designate trees on the stump.  Seeing a tree growing can often tell you how miss behaved it maybe depending on species.

If you don't have the benefit of hand selecting standing trees, and are milling for a client, let them make the choice of taking the risk.  In other words, if you have a tree that could yield 4 8" x 8" post, without heart (pith) you are taking the risk of them all bowing.  The alternative is 1 heart center, and maybe some joists/rafters plus boards, but let the client assume that responsibility, it their trees.  Plus it's fair, and less headache for you.  I feel like I'm missing something?

Hope that helps.

[justallan1]

Thanks guys, I get all of the logs free so I guess I'll just go with the smaller then.
Allan

[drobertson]

allan, that's how I prefer to do it as well,  center the pith, there should be some quality 1x's come off all center cut, and for the most part folks building will use these somewhere.  Unless the customer specifies, I will make all the 1x's 4" 6" 8" accordingly.  david

[Magicman]

And then you will encounter some logs with the pith so far off center that you will do well just to get it into the cant at all.  That pith may be on the other side of the log on the other end.  Some logs are just bad.

[Jay C. White Cloud]

Some logs are just bad.

:D :D :D how true...

MM, when you see a bolt like that, what does it tell you about the way it was growing?  We use those for certain types of beams.

[KnotBB]

Some of the bowing is a result of a tree growing on a steeper slopes or hill sides.  Lots of internal stress.  Trees that have the heart center way off center are an indication of slope grown trees. 

We've all cut logs that every time you remove a board the log moves. 

[Jay C. White Cloud]

KnotBB,

You got it, now what I have been trying to figure out for years, why is it different from hard to soft wood and from one species to the next.  I often get this back wards, so bare with me.  If it hardwood leaning on a hill, the pith will be offset to the uphill side, if soft, down hill side.  Does anybody know why?  I have read everything I can get my hands on and talked to hundreds of "old timers," about it...still don't have a definitive understanding. In Japan, Chona Beams are made from them.

[Brucer]

I generally saw anything under 5" wide FOHC -- i.e., without the heart. I saw them so the face nearest the pith is at least 1" away. If it's a longer timber, I may saw it an extra 1/2" thick and then resaw it to take out any curvature.

Larger stuff I saw Boxed heart (unless the customer specifies otherwise). I always try to keep the pith within the middle 1/3 of the timber. Usually I can keep it within 1/2" of the centre.

And no matter what I'm sawing, I always remind my customers -- wood moves.

[Ianab]

Jay, this page talks about Reaction wood in hardwood and softwood, and how it's different.
http://www.gov.ns.ca/natr/education/woodlot/modules/module8/Less1.asp

Hardwood - Tension wood forms on the top side
Softwood - Compression wood forms on the lower side

They form differently, but both are weaker and less stable, hence the advice to be cautious with ANY log that has the pith off centre. Different species, and even different logs behave differently, but it's one of those things that you need to watch for, and if it's a critical application, like a beam, you probably don't want to use that log at all. Unless as you say, you expect it to move and form a natural arch shape.

Ian

[Jay C. White Cloud]

Thank's Ian,

That is what I have learned so far.  I'm still trying to learn more about they cellular structuring of why the form the compression wood on different sides depending on species and soft to hard woods.  It is still a mystery to me, and one of those little things I have always pondered.

You will appreciate this little story.  In Japan, they would, (still do in a few areas) groom and thin trees on the sides of mountains to promote the growth of large trees with this reaction wood in the base at the root flair so it forms an angle as close to 90% as they can get.  Closer to 90% the higher the grade.  Then they flatten it on either side, forming a beam that has this perfect turn in it, with live edge on top and bottom.  This forms the "Chona Hari" or Clam Shell bending beam.  Pre-stressed in this fashion they are stronger than a strait beam.

I will stress what you said earlier, unless you have a background in the use of reaction wood, folks should stay as fare away from it as possible.  It is not for the average consumer.  It is fun when I walk a forest with a forester or sawyer and point out trees I am looking for... :D :D :D  I get comments like.  "Which one are you pointing at?"  or "Are you sure? You want the one with the bend in the end?"  I have even shown up at landings, just to find all my 20' plus logs all cut in half with the bends cut off, just because someone just couldn't except that was what I was buying?  :D :D

[beenthere]

I'm still trying to learn more about they cellular structuring of why the form the compression wood on different sides depending on species and soft to hard woods.  It is still a mystery to me, and one of those little things I have always pondered

Is this kind of like "why do softwoods have needles and why do hardwoods have leaves?" 

There are different cell structures, such that tension wood contains gelatinous fibers  and compression wood has a secondary wall thicknes with high fiber angles.  IIRC 

[woodNthings]

How very informative this has been for me!I feel like my question has been answered and I now know what to look for (concerning the pith) when selecting logs. Also, I cant wait to experiment with some of the off center ones for arch applications I have in mind for my own projects.
I have a fair abundance of pine so I think I will utilize smaller logs in order to center the pith, and cut around it when quartering larger ones.