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Explaining runout is pretty easy if you have piece of wood that is perhaps a 2X4, but explaining what happens when light hits the two halves a perfectly book matched thin thin piece like a top is not so easy. Today I was driving through our rural landscape - Kent County MD, called the best agricultural land in the state - and I ran across something.

Thinking of the fibers of wood as straws, the perfect top is one that is both vertical grained AND the straws run full length without poking out of the surface anywhere - harder to do with thin wood

1) Here is last year's corn harvest and the remaining short stalks are tipped the direction the harvester was driving. Think of these as the fibers/straws that are inside the wood

2) Stepping back, we can see light and dark areas where the sun hits the flat side of the corn stalk or the end of each hollow tube

3) In the center you can see the color difference as a line where the harvester was going opposite directions

Just like the top where the light is hitting the face or the ends of the fibers

Yeah pretty much!

I took this pic of a tree to use as a prop for explaining how you get runout from cutting boards off a log.

That's definitely a "twister". With a little practice it's relatively easy to spot twisted trees by just looking at the bark.

I have noticed them on the sides of steep hills and in areas of constant wind - Point Reyes CA, sticking out into the ocean with a northwest exposure, has an amazing array of these things.

Ed

Years ago we spent several summers in the Bitterroot Mts. of northern Idaho searching for straight Engelmann Spruce trees on forestry land. The straight ones were few and far between to say the least. On top of that the tree had to have a problem of some sort like lightning strike, leaning, etc. before the Forestry Service would let us cut it (ostensibly for fire wood). It was hot, exhausting work when we found one we could cut. We frequently had to hike several hundred yards with billets strapped to our back packs to put them in the truck. Once we were back to our camp we melted paraffin over the camp fire (dangerous, I know) and waxed the billet ends. We had an unbelievable supply of straight Engelmann spruce billets but I decided I didn't like Engelmann for our guitars and we sold almost all of it to violin and cello makers. The folly of youth! But it was fun in a strange way. Sadly, most of the forest we were scouting burned in forest fires a couple years after we quit harvesting wood.

i read that the tree actually twisted/turned to try to grab as much sunlight as it could. true?


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As to the original post, had the harvester approached the corn from the same direction each pass, the corn stalks would all be bent in the same direction and you wouldn't notice the "runout". This would be similar to doing a "slip match" - the runout is still there, but you don't see it as a change of reflectance.
If you have a top with straight uniform grain from top to bottom you can open the book and then flip one half so the opposite face is up. As long as there are no "markers" to indicate that half of the top has been flipped a casual observer won't notice it. This can effectively hide the runout as it will then be running in the same direction on both halves.
Is this ethical to do? Considering how a small amount of runout can show up under finish on a perfectly fine top and should only be considered a cosmetic flaw it might be. However this technique might also be used to hide a large degree of runout which can be a structural flaw (poor bridge holding), and then it might not be. YMMV
I would be curious to know what others thoughts on this might be?

That sounds like a pretty cool job though. But it does amaze me that with all that hard back breaking work I can still get good quality Engleman tops for $50 bucks.

Shhhh!

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Hutch

Get the heck off the couch and go build a guitar!!!!

As long as you don't call it bookmatched or mastergrade, I don't see why it would be unethical. If you're worried about bridge holding, just make sure you point the runout so the back edge of the bridge isn't peeling at the fibers. People build successfully with curly redwood, and that's about as bad as you can get for a bridge gluing surface.

Sometimes guitars built out of "junk" wood sound better than the expensive stuff

"But it does amaze me that with all that hard back breaking work I can still get good quality Engleman tops for $50 bucks."

What is even more surprising is that you can get decent quality ("A" grade) Sitka or Lutz tops from our sponsors for $5 -$10 each when you buy in quantity. I have bought Engelmann tops at similar pricing from other vendors. Often by cutting around defects or doing a "burst" you can "upgrade" these tops to eliminate what are essentially cosmetic flaws. A few may not cut the mustard, but other uses can be found for them.
If you go this route and you sell instruments you have to have a clientele that plays the instruments rather than "collects" them.

cleanheadsteve asked:
"i read that the tree actually twisted/turned to try to grab as much sunlight as it could. "

That's a pretty common myth. Supposedly tropical trees show regular changes in run out, seen as 'stripe' figure on quartered faces, because the sun is alternately to the north and the south, and the tree is twisting to follow it. Trees, of course, are not sunflowers; they don't twist around as a whole to get the branches into better positions to catch the sun. I could accept that the leaves might turn to track the sun, but it might be trickier than it seems to demonstrate that.

One model I've seen suggests that twist is a response to bending stress on the trunk. Trees that lean or have unbalanced branch loads, due, say, to sun on one side, might thus be more prone to develop twist. This would certainly fit with twist correlating with wind loads. In the case of a tropical tree, then, it would be logical that it would have more leaves on the north or south side, depending on where the sun is, and that would alter the bending load on the trunk, which could change the twist angle.

Myself, I'd have to consider it on a case by case basis, since runout can have a big effect on stiffness. My .02

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formerly known around here as burbank
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http://www.patfosterguitars.com

I still do not understand how they get the dramatic contrasts like a plaid fabric on mowed golf fairways. I know it has to do with the direction of the mowing, but why so contrasted?

One explanation I've read for spiral growth is that it provides for distribution of nutrients from the roots to all sides of a tree as you go up the trunk. If a tree is growing in rocky ground in the mountains, the roots on one side of the tree may have a much poorer supply of nutrients than the roots extending out on the other side. In a tree with straight growth, all the limbs on the same side of the tree would be supplied from the roots on that side of the tree, which could result in poor growth occurring all the way up the side that has a poor nutrient source. With spiral growth, there would at least be healthy limbs on all sides of the tree. I don't know if that has been demonstrated to be a true explanation, but it at least seems like a plausible one.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I think I heard the explanation that makes the most sense to me from Ervin Somogyi. He said that as the sun goes overhead from east to west during the day, the tree naturally wants to follow the sun. Magically the sun disappears on the west horizon and reappears the next day on the east. So the natural tendency for plants in the northern hemisphere is to turn clockwise.

And that paragraph in Somogyi’s books was the last straw for me and I sold them shortly after. The only lutherie books I’ve every sold on.

No, that explanation is complete hogwash - obviously Ervin made little effort to research the literature on spiral grain (or any other of the “science” he wrote about). Awesome artist - lousy scientist.

Spiral stem growth is under moderate to strong genetic control, like most wood quality traits. Some species tend to have left spiral, others right, a few have little if any grain angle. But within any species, there are exceptions.




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Relative to the other recent post on runout for a custom guitar for a customer that asked for a top without runout, would the above explain when Engelmann Spruce tends to show runout regardless of its processing?

If the billet splits with a flat surface, the top processor isn’t much concerned by the grain angle, as he/she can still cut parallel with the axis of the fibres, to yield material with little runout across the face. The difficulty is when the split surface is not flat, because the grain angle changes as the tree grows.

Remembering that there is a lot of genetic variation in grain-angle development, spruces are known generally to grow from the pith with left-hand spiral, going through a transition becoming straighter, then becoming more right-hand spiral and more consistent angle toward the bark. The top processor needs to find section where the grain angle is consistent, in order to have a flat split surface, so needs to avoid the transition areas toward the centre of the tree and may have to deal with the idiosyncratic grain angle development of a given tree. Starting with a big-diameter log helps, but that’s more of a problem with Englemann than with old growth Sitka, red or even Norway, just because they’re generally smaller.


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It's from the way the surface absorbs or reflects the light. Refraction or Reflection.

Having been full time soundboard producer for over 24 yrs, I can address a lot about hows trees grow. how different characteristics are either determined by genetics or physical environmental conditions and how we deal with the various attributes and fiber types nature throws our way. Regarding the slope of fiber in a tree. In can vary a lot. We see trees that have what we call a rind twist. Where the outside 2-4 inches is very twisted. But inside that the fiber relatively straight. This sometimes happens after some major "event" in the forest around our tree, that is evidenced by an extreme change in growth pattern. Abrupt changes of slow to fast growth, and usually has a pitchy growth line too, that would look like a glue seam in a VG cut board. That's just one thing.. About dissecting block into soundboards. Different processors do different things. As stated in another post. Most trees have "some twist". We can deal with twist from Larger trees much better than smaller ones. Lets cut a round of a 40" diameter log. We split it half on the heart check. Then we pattern out the face as we look for knot indicators around the outside or in the heart. we pattern into field of yield.. For us, we often rip the heart out to get inside information about location of those inside knots, from when our tree was but a wee lad.. Then we dissect the round into blocks which are oversize trapezoid shaped block when viewed by the end grain. On the average of some of the nicest material there is maybe 3/4" rock corner to corner of a split face block 23" long x 10" wide. Some sawyers will go for the most yield and trim off the wings following the grain slope of the inside [heart side] of the block. Some sawyers with split the difference and follow the slope of the middle of the block. What we do at Alaska Specialty Woods is determine by the color and texture what will be the highest grade bookset based on those characters and crowd the grain-slope at that side so that the presumed joining edges will have no apparent grain slope, and therefore will not have the "flash" associated with that slope. 2 reasons. You want the fiber running the length of the board in the middle where most strength is needed for string tension etc. and of coarse as already mentioned, No Flash. The extremities of the instrument are glued to sides. This is just a touch for the subject.

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.

Alan, i believe the longitudinal infiber striping you see in spruce is what we refer to as eade. I am not sure of the spelling. but it looks like a long tunnel curl. Where this is located in a tree that has it, is right at the butt, within a few feet [2-12’, depending on the tree and it’s size]of the roots/stump. The fiber is all funky near where it starts into the root system. It tends to be extremely more dense and hard there, and sometimes more pitch pockets and inclusions. When splitting block of this type of fiber with a froe, the split edge will be straight where the froe/knife edge is driven into the block and as the length splits, the face of the becomes very scolloped. We actually have a sort on the shelf we have labeled tunnel curl. In UK it’s called Rowing. It makes sense you see it in red spruce. Those trees are so much smaller than Sitka, often under 30” DBH.

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.

The striped ribbon we often see on quarter-sawn tropical woods is interlocking grain arising from a seasonal change in grain angle. The sunny side of the tree doesn’t shift north-south with the season — in fact there is much less seasonal change in sun angle than at higher latitudes — but the seasons are typically associated with changes in rainfall, sometimes dramatically so. The rainy season in the tropics can vary a lot from year-to-year, and so to the regularity of the ribbon figure in tropical hardwoods. (“I bless the rains down in Africa!”)
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. As you would expect, reaction wood is more common in the stump and butt log of the tree, as these areas are under the greatest fluctuation in stress, and also near and around knots. Wherever you find it, reaction wood is generally undesirable from a mechanical properties POV.


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