What is the best way to mill timbers. Do they all need the pith centrally located or can you cut several 8x8 timbers from a single large log.( and have no pith or center wood within the timber, will it dry without warping or twisting) nate
Not only will it distort as it dries but if the log is not of substantial size to gain the numerous 8x8's from one piece they will come off the saw with a bow in them. I recently re sawed a number of doug fir 4x4's that were free of pith and had pith with in the stick, they were all wanky, due to shrinkage and the sawyer.
Here on the East coast I would box the heart, the West coast has larger trees and thus the possibility of free of heart wood. Do the logs you are looking at have enough size at the top to offer free of heart timber? The timber could have the free of heart feeling on the butt, the top may not be so nice, I would not want to wonder what that timber will look like in time.
This is a very good question and one which I am struggling with right now. It is unlikely that a halved timber will not to some extent relieve itself of its inbuilt stresses when it is cut along the pith. Some timbers are known to react very badly to this practice, for example, I recently discovered that all Greeheart timbers leaving Guyana are shipped in boxed heart form to ensure the straightness and dimensional stability of the baulks. English oak (quercus robur) was oft times halved and used quite sucessfully giving rise to the description of half timber buildings (half being substituted for halved). Its quite possible to work around known likely drying deflection characteristics of wood especially when a frame is to be scribed. The alternative might be to cut, wait and resaw.
interesting... i've been thinking about this with a white pine timber that is presently hewed to 16*20, that I was considering whether to chainsaw mill it in half and half again, or take (less useful) planks off the sides.
my general sense is to hew to the heartwood and then use the timber as it is and see how it would fit into a structure, but in this case it's too big to lift/drag from where it fell. the tree has been down for 3 years now and this timber has been without bark and squared for 2. i wonder how it would move if sawn down the center.
There is a picture I got somewhere that shows what the most likely distortion of lumber from a log will do.
It has been used many times online, and hopefully is not copyright protected.
It shows what would/could happen if a piece lumber was cut out of a log at different location in that log.
And you can see by this that it may distort because of this.
What I have suggested, and done, and witnessed the result of is cutting pieces of lumber from logs in what I call the clock pattern.
That is one piece from the 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock positions in the log.
Here is a shot of three 6x6 timbers:
The one with my left glove on it was from the 9 o'clock position. The one with my right glove was from the 3 o'clock position. The one in the middle was boxed heart.
Here you can see what happened to some timbers after they had dried a bit:
Again these are not the same three pieces viewing from the same end. Note that the 9 o'clock timber bowed and the 3 o'clock timber didn't that much....
I'm not sure how west coast timber would dry, so I can't comment on that.
I can only comment on what I have seen here with my eastern white pine timbers.
Hope this helps you...
Jim Rogers
Last edited by Jim Rogers; 06/29/0902:52 PM. Reason: corrections
Here is the text of the story I wrote about this in 2003
The other day, at the beginning of a timber framing workshop, we needed to get some timbers out of the pile for the frame we’re cutting.
I had cut out all the timber for a frame quite a while ago and had them stacked up on 4x4’s in one tall pile. The 4x4’s were 4’ on center and each row of timbers weighed about 1000 lbs as that’s the limit for my forklift.
When we removed that 2” stock that was on top of the pile of timbers, working as a weight to hold them straight and flat, we found one of these timbers had “taken off”. Shown here, it’s the one on the left in the above photo.
Now you can see the heart/pith of the timber in the center on the end facing us, as it’s marked with a red lumber crayon, as a plus sign (+). But this heart/pith wandered a bit as it traveled down the timber from this end towards the other end. And about where the forks are it came out of the top for about 3” and then went back in. It was centered on the other end. This wandering heart/pith of the tree, I believe is what caused it to not stay straight. The other two next to it were in the same row under the same load and are very straight. The middle one is a hemlock and the right one is an eastern white pine same type as the bowed one on the left.
While doing another job, cutting up some dunnage blocks, for a customer who was going to use them to block up his cottage while they dig out a cellar, I decided to try cutting some 6x6’s in different patterns to see what would happen to them.
That is the photo with my gloves on the timbers.
Well I cut this very large log into nine 6x6’s. Three across and three high, like a tic-tac-toe pattern. These three timbers (pictured shown above) are the ones from the 9, middle, and 3 o’clock positions. The nine o’clock timber has my left glove on it, the three o’clock timber has my right glove on it and the middle one is in the middle. You can see that the 9 o’clock timber has “taken off” and bent quite a bit. (You can see the opening in between the timbers as the ends touch each other). I knew it had because it did as soon as I released it at the mill. It almost sprang off the cant.
The middle one is some what bent also, and the heart/pith doesn’t truly run down the center of the beam. The 3 o’clock one seems to be the straightest of them all.
These bent timbers were not wasted as the customer just needed them 3’ long so they were all cut up and sold. And they were straight enough for him to use.
I’ve set aside the 3 o’clock timber for the next frame and also milled out a boxed heart replacement beam in case it moves before we get to use it.
This was kind of an experiment in milling timbers for a timber frame. And I thought I’d show you what happened. You should always “box heart” your beams as they are the straightest and strongest. Jim
I have, in my yard, 2-42' 7"x9" top plates, they came form the same log, a 9"x14-1/8" timber. The joinery has been cut, they have a bow in them, about 5", I will take it out with a come along when the frame goes up. English tying joint, wall raising, starting at one end and setting the trusses down the building pulling or pushing the wall as needed.
As Ken mentions, scribing can get around some of the issues. In other words they can be used in certain situations. You could but the bow up.
Jim has some extreme examples, nice to see what you could end up with.
Thanks Ken My next Cabana will have sills so everyone can trip over them as they come and go. I knew what sills are for Ken but for the life of me I could not see the application in a cabana or Gazebo.(head shaking) Oh I suppose I could Timber Frame a raised deck for a Gazebo with notched in floor joists and proper sills but it would add a lot to the cost and I don't think people are willing to pay for something they can't see. Maybe I'm wrong but these things are already pricey as it is. Thane Thane
Life is short so put your heart into something that will last a long time.
The pic in Jim's post is from the USFPL, it belongs to us, so no copyright problems, it appears in several of their publications and many others since.
The juvenile core of a tree contains some wonky wood that has several types of problems, we've discussed off axis microfibril angles and compression wood. This wood is weak, and shrinks longitudinally and has erratic extractive deposition. The juvenile core varies but is generally the first 12-25 years of growth. If the juvenile core is boxed within a timber then that low quality wood is in the neutral axis of the timber where stresses tend to be low...think about shear though.
In some of my fast growing white pine and in many SYP trees I've seen, that juvenile core could be on the faces of a large timber. This has been a problem with the "supertrees" but is also a function of cultural practices. There's a couple of ways of looking at it. If a tree puts on a bunch of growth fast and then as it matures it is putting on quality wood over a larger core then the board footage gain in the stand of high quality wood is maximized. Unfortunately we tend to harvest when the trees hit a merchantable size. That has been the case in the US lumber market so we end up with an abnormally high percentage of juvenile wood and we don't wait for the tree to put on that good wood. Hence the "In Grade" process that readjusted design values in the '90's, our resource was changing. If the trees grow slowly then they have a smaller juvenile core but are many more years to harvest. Juvenile wood typically causes bowing towards the heart upon drying.
In nature there are many exceptions, we've discussed ring porous wood being denser and stronger if fast grown. Dense woods as a rule move more too. Wood shrinks, air (relatively speaking) doesn't.
The growth stress that is usually released at or soon after sawing is in large part the tension that keeps a tree standing upright and varies by species and by tree. Locust, hickory and poplar can have amazing growth stress release on the mill. The release of this stress causes bowing away from the heart.
Drying stress; Notice the heart centered cut in the diagram in Jim's post. It is thickest in the middle tapering towards the edges. Radial shrinkage is roughly half of tangential shrinkage. Notice the quartersawn piece at the 9 o'clock position has changed little in width but a good deal more in thickness. Quartersawn flooring is the most stable as far as opening and closing gaps seasonally for this reason but needs to be sawn thicker than normal or you lose pieces to skip dressing when planing it, it loses twice as much thickness during drying compared to flat sawn stock. The difference in radial and tangential shrinkage is what causes drying stress.
Think about what is going on there for a moment. I think most folks understand the vertical transport through cells up and down the axis of the tree. The rays that radiate, radially, from pith to bark are cells running horizontally through and across the vertical cells take care of horizontal transport. They are ported to the vertical cells by "pits", donuts of microfibrils swirl around the pits to form the aperature. These valves between the cells on the radial sides of the cells and the cross grain of the rays are what inhibit shrinkage in the radial direction where on the tangential faces, those facing the heart and bark have microfibrils oriented vertically in mature cells. So the tangential faces are pretty free to shrink where the radial sides are kind of locked up by the pits and the cross grain rays. Make concentric circles of people around a campfire, pass boards under their armpits. They can snug up sloser together shoulder to shoulder but cannot move towards the fire so easily. When the tangential shrinkage exceeds the tensile strength of the wood perp to grain a check forms. This is pretty much a guaranteed condition if the heart is in the piece.
If you can get a tree large enough to not only get you out of the heart but get you out of the juvenile core, If the tree has no reaction wood, If the tree has low growth stress and straight grain, and if you orient the cut well, pay attention to the branches and knot orientation too. THEN, a FOHC timber is a far superior timber to a boxed heart one, it is straighter, stronger and less likely to check. That is a tall order from my forest.
In the end every one is an individual, some are good, some are bad, some have a compact sound heart, some are juvenile all the way through, some are twisted and headed for the fire .
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