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 Post subject: Re: Top runout
PostPosted: Sun May 19, 2019 9:13 am 
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Brazilian Rosewood
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Alan Carruth wrote:
I have read one paper that says that at least some twist is due to built-it stress in the tree. An asymmetric load, such as a tree the leans or is shaded on one side, seems to tend to spiral. This might be one way of making sense of the stripe figure in tropical trees. They probably tend to grow leaves on the sunny side, which switches from north to south seasonally. Thus the load is changing, and along with it, the stress. I have noted in ripping brace stock from quartered stripe mahogany that the stripes with run out tend to bend toward the bark side, while the ones where the grain runs straight along the brace (and, presumably, the axis of the tree) stay straighter. You can get the same bending toward the bark on any tree, and it's more pronounced as you go to the outside. I've also noticed that timbers cut from the heart of a tree tend to 'un-twist' as they season. I have king post timbers in my barn roof that make about a quarter turn from bottom to top; about 12 feet.

Once in a while I see Red spruce tops that show some degree of stripe figure, often associated with changes in grain line spacing. One assumes this is due to periodic logging operations overt the life of the tree, which produced clearings that altered the predominant sun orientation. These tend to make nice tops.

Is this what you mean? I had never seen this before till I made this guitar last year. This is a Carpathian top.

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 Post subject: Re: Top runout
PostPosted: Sun May 19, 2019 10:37 am 
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Brazilian Rosewood
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Tim Mullen wrote:
"A tree’s main response to mechanical stress is the formation of reaction wood, usually on the compression side in softwoods, the tension side in hardwoods."

There's a bit more to it than that. See "Growth Stresses and Strains in Trees" Robert R. Archer Springer-Verlag, 1986.

Ever noticed how much easier it can be to cross cut a quartered plank from the heart side than the bark side? Trees tend to put on new growth pre-stressed in tension relative to the wood underneath. The mechanism is interesting, and may be linked to twist in the tree. It also explains why strips ripped along a quartered plank then to bow outward at the ends, and has a bearing on 'brash fracture' in wood from the base of large trees.


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 Post subject: Re: Top runout
PostPosted: Mon May 20, 2019 1:54 pm 
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Yep, That is the curl pattern we here at ASW call tunnel curl or Rowing caused by the eade grain I am referring to. It comes from cutting tops out of the butt of the tree, very near the rootwad. luthiers who use red spruce would most likely see a higher percentage of this pattern since red spruce trees are so much smaller diameter, and diameter is yield of tops. Boards cut from this section of a tree/log tend to be quite a bit more dense than say 10-20-80 feet or more up the tree, away from the stump.


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 Post subject: Re: Top runout
PostPosted: Mon May 20, 2019 2:09 pm 
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Also, what I see in the carpathian[norway spruce] top, is actual runout or grainslope, as evidenced by what I call/black/white syndrome at the glue joint. Where 1 half is reflecting the light and the other half is refracting the light. But you don't see it at the out edges of the boards[top]. That is because the cut has been made true parallel to the fiber in that area of the tree/log/block. Most of the tops produced in Europe, are not cut from short rounds and hand split blocks, But rather quartering logs in length and then resawing those quarters into planks[that are then cut to length and resawn into acoustic guitar sets. Then the wedges cut to length. Then cutting to shorter lengths and resawn into products. The products are of course guitar tops, violin family instruments and last bracewood.


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 Post subject: Re: Top runout
PostPosted: Mon May 20, 2019 5:26 pm 
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OLF Sponsor
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Joined: Fri Aug 28, 2015 5:26 pm
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Location: Craig, Alaska
First name: Brent
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City: Craig
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Country: USofA
Focus: Build
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Alan Carruth wrote:
Brent Cols wrote:
" ...eade....it looks like a long tunnel curl."

I'm not sure that's it: this is not curl, but simply a periodic variation in run out across the top. The fibers in each stripe are straight, but angle in different directions relative to the axis of the tree. It probably would split with a crosswise waves, as the split direction would vary across the balk. A 'tunnel curl' makes me think of 'bear claw', but it's certainly not that, and I don't think that's what you're talking about.


Alan, This is a type of curl as displayed in the fiber, that runs longitudinally, with the growth lines, and quite different that the type of isolated grain slope of another curl pattern that is 90 degrees to the grain. The more commonly seen in Curly redwood tops, to a lesser extent our light curly sitka. https://alaskawoods.com/shop/flat-top-i ... jumbo-gtr/ and referred to curl that creates the wave pattern and visual energy of "depth" that is across the growth lines when cut perfect VG,. Both of these types of curl are broad and are an isolated grain slope. Bearclaw is a name given to another attribute that occurs in softwood, which as one of 2 types of "indented grain". There is another type of indented grain that occurs in hardwoods like oak. Someone was doing a paper on that years ago and asked me what type the sitka was. Regarding the subject of this thread, grain slope, that is well illustrated in the concept of how it appears to the eyes in relation to how light is handled by the photo of the harvested field. Bearclaw[indented grain] is also a very finite specific spot- grain slope, the very finite deflection of grain caused by the "indent". Though I think it is of no consequence structurally. Whereas the tight heavy curl you see in the very beautiful curly redwood tops, that could be structurally or tonally compromising, because that grain slope is going up and down in each of those 1 inch wide lumps in the fiber.


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