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How many cants can I cut from a single tree?

Started by customcutter01, December 31, 2017, 07:40:59 PM

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customcutter01

I'm going to build a log home, I want to get the maximum number of cants from my trees possible.  At first I was going to go with cants 12" deep and 15" wide, cut on 3 sides.  But I'm wondering if that might be wasteful of resources, so I'm thinking of going to 8" deep and maybe 8-10" thick.

Before, I might get 2 or possibly 3 to 4 cants from a tree.  However if I drop down in size, I think I can get possibly as many as 6-7 from a 30" diameter tree.  4 from the first 21 foot section, 2 from the next 21 foot section, and 1-2 from the next 21 foot section.

Any thoughts or suggestion on this approach?  Has anyone tried this?  How will it affect warpage on the bottom 4 cants leaving the heart section out of the cant?

thanks,
Ken

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killamplanes

Speaking of twist, etc. What specie of tree are we talking about??
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Southside

A big factor will be how close to perfect you want those cants to be. Your butt log will have butt swell and I find in SYP a fair bit of hourglass, especially in longer lengths. That's not accounting for stress, splits, hollows, old massive knots, and other defects.
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Ianab

There are 2 ways to cut good "beams" from a log. One is to try and centre the pith in the beam, and that's what you would do with a smaller log. Because the pith is in the middle of the beam, the warping as it's cut and dried should balance out on the different sides, and hopefully it stays straight.

The other is to cut them Free Of Heart, where you keep right away from the pith. Now you don't have the misbehaving  juvenile wood in your beam at all, and again the beam hopefully stays straight.

What you want to avoid is "splitting the pith", where you end up with the pith on the edge or corner of a beam.

So cutting 2 or 4 beams from a log may be a problem, as the pith will wander down the edge or corner of every one.  Cutting 3 or 5+ beams may be OK. The middle one can be heart centred, and the others are completely FOH.

Other option if you just want to make 2 is to leave your "waste" around the pith. Saw that into something else, you will want some 2x4s and other assorted trim and cladding boards at some point during the build anyway.

Of course this depends on the species and quality of the log. Some are just cantankerous  >:(
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customcutter01

Quote from: killamplanes on December 31, 2017, 11:10:19 PM
Speaking of twist, etc. What specie of tree are we talking about??

I wanted to use mature southern yellow pine.  However on this property, there are very few pines on the property, maybe 200 longleaf pine, hopefully more.  That is why I'm thinking of downsizing the cants and getting more from each tree.  There is also white oak (I would hate to use it, because of food value for the deer), hickory, magnolia, and some other species that I haven't identified yet. 

I'm actually considering contacting local loggers or neighboring properties to see about supplementing the pines that are there already. Once we acquire the property.
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customcutter01

Quote from: Southside logger on December 31, 2017, 11:30:31 PM
A big factor will be how close to perfect you want those cants to be. Your butt log will have butt swell and I find in SYP a fair bit of hourglass, especially in longer lengths. That's not accounting for stress, splits, hollows, old massive knots, and other defects.

Thanks, yes I've considered that.  I was thinking I would try to allow to the butt swell by removing it if not needed to get the 3rd 21' log out of the tree.  I've been doing some practice milling at my cousins since I bought the mill and its amazing how much swell is on some logs.  If I can't get the third log then I'll  just mill the but section off on the 4th side as necessary.

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customcutter01

Quote from: Ianab on January 01, 2018, 12:45:46 AM
There are 2 ways to cut good "beams" from a log. One is to try and centre the pith in the beam, and that's what you would do with a smaller log. Because the pith is in the middle of the beam, the warping as it's cut and dried should balance out on the different sides, and hopefully it stays straight.

The other is to cut them Free Of Heart, where you keep right away from the pith. Now you don't have the misbehaving  juvenile wood in your beam at all, and again the beam hopefully stays straight.

What you want to avoid is "splitting the pith", where you end up with the pith on the edge or corner of a beam.

So cutting 2 or 4 beams from a log may be a problem, as the pith will wander down the edge or corner of every one.  Cutting 3 or 5+ beams may be OK. The middle one can be heart centred, and the others are completely FOH.

Other option if you just want to make 2 is to leave your "waste" around the pith. Saw that into something else, you will want some 2x4s and other assorted trim and cladding boards at some point during the build anyway.

Of course this depends on the species and quality of the log. Some are just cantankerous  >:(

Thanks, this is very interesting information.  Yes I plan on cutting so that I have 3 milled edges and 1 normal growth curved edge less the bark.  I would have thought that the heartwood would have been more stable and less likely to curve, but maybe it has more resin, or other factors that cause the warpage. 

Is there a percentage that you figure as being pith, based on diameter.  Is there a percentage of pith that can be left in a beam or cant?   
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Ianab

The "problem" wood is the first few growth rings around the pith. This was laid down when the tree was just a sapling.  It's since been turned into heartwood, but it's not the same as the later growth ( different cell structure). This causes it to shrink in length as it dries, while regular wood doesnt.  So if one side of you beam shrinks, and the other doesnt, its going to bow for sure. Area affected depends on the species and how fast it grew. Maybe a couple of inches from the pith?
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TNWOODBUTCHER

So if I'm picking up what your putting down. You either want the Herat centered in beams or none at all. Free of heart should warp or bow less than timbers with some heart or heart off centered.  I've been working with too small of trees it seems I have been a little limited on developing Good practices. They tapered to quick and i keep fighting trying to get too wide of boards and cants

WDH

Generally, figure the first 8 to 10 years of growth as juvenile wood. 
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Don P

or up to 30 years in a significant number of samples before the microfibril angle in the cell walls begins to straighten up and act mature in plantation loblolly. The change is not abrupt. In a young tree the microfibrils that form the cell walls are laid on in a diagonal bias of up to and sometimes more than a 45 degree angle to the vertical axis of the tree. As that part of the tree matures and puts on more growth rings and the meristem moves up and away the microfibrils in the cell walls begin to stand up and align with the vertical axis of the tree. Shrinkage is moisture bound to those microfibrils leaving and them moving closer together. If the fibers are mature and so aligned mostly vertically the wood shrinks in width. If the fibers are aligned diagonally and then shrink you lose less in width than normal and more in length. If a board or cant has juvenile wood on one edge or face that shrinks in length and mature wood on the other edge or face that does not, you get crook or bow as it dries.

As you can imagine wood that has this type of alignment within the cells is also weaker, it can be half the strength of mature wood. When we started planting "improved" short rotation trees and harvesting them before they had put on much good mature wood we started having trouble in construction. A large percentage of the wood was juvenile.   About 6 or 7 years ago syp was derated in the strength tables I use for joist and rafter spans.

This is a piece of decking where they split the pith, the wood is all juvenile but much more so on the upper face. It shrank in length more than the bottom side and bowed. This tree grew so fast in height to diameter that it had to throw a compression ring, the peanut butter colored ring full of lignin, tree concrete, to stiffen it and hold it upright. Pay attention to some older decking out in the weather. When you see cross grain cracks take a closer look, it is juvenile heart that has shrunk in length but because it was restrained flat on the deck it couldn't pull like this board and so as the juvenile wood shrank it broke across the grain.





This board didn't crack on the face, it broke 4 screws as the juvenile wood shrank and then pulled up. When it gets wet those fibers swell and it lays back down.





Southside

Thanks Don - that makes a lot of sense. But it begs the question - why are the faster growing seedlings being pushed so hard now?  Is the plan to just pulp it all in 30 years?  
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Don P

That gets into opinion for me.

As long as it can be marketed there is no incentive to grow better timber vs growing on as short a rotation as possible. Juvenile and reaction wood also causes paper producers trouble, burst strength is lower and they have to get more lignin out of the pulp. Higher pulping cost, lower yield and lower quality product. There is not a high enough incentive or penalty to change.

But, think about that same improved tree if we let it go for say 80 years. The first 20 or so year old core might be low quality but it is big. If you then start laying on good mature wood over a larger diameter core the return at the end of that longer rotation is going to be more good wood. I'm not convinced the improved tree is the problem, I lean more towards thinking the short rotation is.

What I said about the transition from juvenile to mature MFA's being gradual, when the angle gets down to around 25 degrees the longitudinal shrinkage starts to become pretty tolerable mechanically, when it gets to around 10 degrees it is fully mature. If the mix I get out of a bundle of framing on the jobsite contains all juvenile wood I'm building weak warpy houses, you know the bundles, pith and bark on the same 2x4. If the mix contains a good bit of mature wood the junk can go into cripples and blocking and if something around 5% is below strength spec I'm still good. The problem there is that the average framer doesn't sort or even know how to, they see a board but don't look at the board. If I frame just a little slower the good dense stuff is held for girders and high load places, you can defect out a piece and raise the grade if you cut in the right place instead of just lopping off the closest end. Point being if the rotation is longer my mix might be the same grade but is higher strength and quality. Now I'm wandering into a rant  :D

Ianab

When a tree variety is "improved", the growth rate is just one of the factors that need to be considered. 

The local Radiata pines grow at those sort of growth rates, but have been selectively bred to also reduce the amount of juvenile wood, increase the space between the branches, reduce the size of the branches, and less likelihood of forming double leaders etc. All things that make for better quality wood. 

Another trick with high quality seedlings is that they can be "cloned", basically taking cuttings from a mature tree. Then the seedling is genetically much older than one grown from seed, and so produces less juvenile wood. 

Couple all that with some pretty intensive management (pruning and thinning) you can produce good sawlogs in 25-30 years. The butt log will have a "defect core" of about 6", which contains the juvenile wood, and the trimmed off branch stubs, so that's low grade. The rest of the wood in the log is stable clear grain lumber. The upper logs are more normal, smaller sizes and normal knots, but still good for construction etc, up to a pulp size log at the top. 

The hardest part? Convincing overseas markets that this fast grown pine IS actually strong and stable. If your experience is with fast growing Loblolly, you might be sceptical about Radiata, when in fact it's one of the stronger and more stable varieties of pine. 
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WDH

Quote from: Southside logger on October 04, 2018, 09:38:03 PM
Thanks Don - that makes a lot of sense. But it begs the question - why are the faster growing seedlings being pushed so hard now?  Is the plan to just pulp it all in 30 years?  
It is all about return on investment.  Given the volume and product mix of timber (pulp and sawlogs, pretty much just a size distinction) and the tree age, and the product, you can determine the rotation age that maximizes internal rate of return or net present value.  For Southern Yellow pine, overwhelmingly lobLoLLy, that sweet spot is about 25 to 28 years depending on the site quality.  Economics is driving the companies to grow em fast and shorten the rotation age.  
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rjwoelk

Whatch for spiral grain in the log. If the grain fellows your right hand fingers no to bad 1 inch in 20 .keep it low down and were it can be held tight. If it follows your thumb dont use it.  Will go left or go out or in. Straight is the best. The other thing i am thinking of is cut on 3 sides you could have pull to the outside as it drys or due to stress.
I had one that( 8x10 2 row) twist out 3/4 of a inch dragging the one above it with it as they were screwed to gether with 14 inch log screws. Ended up planning them flat and just need to restain. Lots of power in a log that wants to twist . Second pic we replaced the cheep homedepot door. We also installed a 4x8 buck. This door is much better closes nicely.  

 

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Don P

On my way looking for a picture I had on the computer I found this one I'd saved sometime, I think it is from one of the USFPL's articles.





The S2 layer is the one most responsible for shrinkage and the mechanical properties of the wood. Shrinkage is moisture leaving the S2 layer and those microfibrils moving closer together. Look at S2 on the mature cell vs S2 on the juvenile or reaction wood, they are going to shorten as they dry.

 Even mature usually has some degree of angle. The juvenile shows a right hand twist. What happens if those were left hand, I assume that's our lefty log.

 ml is the middle lamella, high in lignin, sort of the fibered glue between cells. p is the primary layer, the nonwoven, first, shape forming layer of a new cell. S1 is on the bias and reinforces p. S2 is the thickest and the strength, S3 is the inner liner on a bias. This is very simplified, the microfibrils wind around the cell to cell pits on the radial sides (radial shrinks half of tangential, microfibrils wrapping that donut hole is one part of that, rays are another)

The block diagram is showing a horizontal ray on the right side, looks like 3 cells tall, invisible to our eye unlike a 50 cell tall white oak ray. Top and bottom ray cells show pits (valves) shared with the cells they cross. Vertical travel is up the tracheids, horizontal is on the rays, addressable by cell. And we're special :D

In softwoods a tree tries to straighten up by stiffening under a lean with rigid, lignin rich compression wood (aside, compression wood can fool a grading machine that uses stiffness to assign strength, lignin is stiff but fiber is strong).

A hardwood tries to straighten a lean by creating another layer inside called the G, or gelatinous, layer. This is rubbery, hmm I don't know what its made of. Even on my scanner I've seen that ropey layer hanging out of cells in an end grain slice and if you've ever tried to sand serious tension wood you know it is hard to get it smooth. It's those rubber bands hanging out of the cells. A hardwood forms those tension cells on the upper side of the lean. I think of it as cables thrown over the top of the lean trying to pull the topside back upright. Softwoods and hardwoods are using exactly opposite ways to right a lean. Native Americans sought out leaning hardwoods for bows, they wanted that elastic G layer.

WDH

And who says that trees are simple creatures?
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