I think some of the terminoligy used when talking about soundboards may be confusing to people who are just getting into dealing with soundboard woods. Also when talking about a "visual" flaw vs a "structural" flaw, I think it is hard to distinguish. I know some of these things were a bit mysterious to me when I started dealing with these woods. Maybe a few explanations would help.
Straight Grain- Pretty straight forward, visually the grain lines run straight along the face. The importance comes from a couple concepts. One, wood is generally about 5 times stronger along the grain as opposed to across the grain. Two shrinkage along the grain is extreamly low when compaired to shrinkage in the tangential or radial orientation. To visualize, a straight grain board will shrink or expand very little along its length with much more shrinkage in its thickness and width. If a board had straight grain along half its length then took a hard turn, you would see a significant increase in shrinkage or expansion along it length, and that shrinkage or expansion would be greater the farther off straight the grain ran(in a non linear fasion).
Radial and tangential- Radial shrinkage is generally much lower than the tangential(generally 1/2, but in some woods may be as high as 1/4). A soundboard that is quartersawn with straight grain, will change the most in thickness, and less in width than thickness per. each unit of volume. Obviously the thickness of a soundboard is small compaired to its width, so the change in dimension will remain small(not much wood expanding and contracting), and the width is the second greatest dimension on the board so having the a lesser value of change is desirable, with the longest dimension being length it makes sense to have that orientation be the one with the smallest change of all(not to mention strength factors as mentioned above).
Quarter sawn- grain lines run perpendicular to the face.
Flat or Plain sawn- grain lines run parallel to the face.
There may be some advantage in terms of strength between the two orientations, but generally it is small. Dimensional stability(most significant), and potentially issues with repairs due to a crack forming are also considerations. It is important to remember trees do not grow square, and the concept is to optimise stability. A slight descrepancy should not tell you this wood is junk(that is silly). When large trees are cut it is easier to hold closer to perfectly on quarter, but some species are more difficult to find in these large diameters(say red spruce) and a little off quarter is not going to significantly hurt the stability of the wood.
Fibers- Wood is fiberous, and length of fibers will vary in different species. Fibers sometimes grow fairly straight, sometimes twist around each other(interlocked).
Twist- again simply what is says. The tree grew in a twisting fashion and the grain is oriented as such. A wild card structurally and in terms of stability. Not good.
Side grain- grain or fibers that runs with the surface or face. More reflective than end grain.
End grain-grain or fibers that ends at a surface or face. End grain exposes the vascular structure of the wood and transfers moisture much more readily. This is why special attension is paid to sealing endgrain during drying, and also when finishing. Less reflective than side grain.
Short Grain. Sometimes you will hear this term to describe wood that has had the length of most of its fibers cut, leaving little full length fiber. If the fibers run at an angle to a surface of a board that is fairly thin(relative to the typical fiber length), this term may apply (also described as severe runnout). It is important to remember what is is doing to strength, as well as the stability of the wood. Remeber wood is about 1/5th as strong across the grain as with the grain, and stability- this orients the grain less than ideal as described above.
Runnout- grains or fibers run at an angle to a surface or face exposing end grain. Same concept as short grain although the degree of runnout may be slight to extream(short grain describing extream runnout). In general, 2 degrees(about 3/4" of rise over 24") or less has little effect on strength at common soundboard thicknesses. Buy cutting split billets close to the split face this can be minimised and kept well under 2%(less is better). Since runnout exposes end grain, you will be able to detect this by a change in reflection(especially when bookmatched sets are placed side by side) as one side will appear darker than the other. It is hard to quantify the degree of runnout with only visual clues though. Some common sense would tell you to watch out for strong changes in appearance, and be less concerned if you see slight differences.
Reaction wood- Wood that compensated for stresses impossed on the tree when growing. Areas that need to become stronger to resist the force become harder and denser (compression wood), on the opposite side of the stress you will have lighter less dense wood(transition wood). The biggest issue here is than the difference in density and strength effects stability due to changes in moisture as well as varies the strength of the wood in these areas(which may focus stress).
Pin knot, knot- Simply where a limb grew. Pin knots are very small limbs or branches. Knots would generally indicate a more substantial limb. It is important to remember a larger limb may impose a good deal of stress as it is loaded(snow, wind or what have you). This can lead to Reaction wood forming. A small limb is not going to impose much stress on the tree so the reaction wood that may be developed would be less notable. The limb itself will change the direction of the fibers also. This will lead to potential areas with various degrees of runnout(when cut this will appear as curls or knot shadows). Often a small pin knot runs through a soundboard leaving a small deflection in the fibers(not much impact). If the pin knot runs across, parallel to the face, the deflection of fibers around it could be significant.
Curly, flamed figure- The grain grows in a rolling pattern. The figure displayed is due to runnout in the face, and the difference in reflection between end and side grain. Very tight strong curls may result in heavy short grain presence. Curly figure will alway decrease the stiffness in the longtitudinal direction as the wood is not running straight, and this leads to drastic reduction of strength in what normally would be the strongest orientation. I have found it increases the cross grain stiffness due to the change in orientation.
Pitch Pocket- Just what it sounds like. A large pocket may lead to a significant void and weak spot in the board. Small pockets have little effect, and are more of a visual annoyance.
Early Wood- the inner lighter colored wood between the darker lines that make up growth rings. This grows faster(usually spring), is more vascular, lower density wood, softer.
Late Wood- the darker colored wood that makes up the growth rings. This is slower growing wood that formed in the dryer summer. Denser, less vascular, harder wood.
Ring Shake- Seperation or cracks that seperate the rings.
Heart Shake, Heart Checking, Cracks, Checks and so forth- All cracking and checking most of the time due to drying stress.
All these types of damage can occur for different reasons. Drying stress is generally only a problem when you have to cut away too much wood to remove the damage. Sometime this can be rooted in damage to the wood during growth and these can be harder to detect(weaker structure or microfractures), and become problematic down the road. Some damage is said to occur from hard freezing and rapid thawing, wind, fire, bacterial damage weakening the structure, and so forth. If you notice wood splits abnormally easy, develops seperation between rings, cracks easily when flexed(reasonably). It is a good idea to play it safe an use different wood. Just be sure you don't toss wood that may only have a simple drying defect if it is good solid wood.
Natural coloration- Just that, this is a visual grading variable depending on personal taste.
Staining- This can be from different sources. Mineral staining is usually viewed as a visual defect, but has no structural issue. Mold, or bacterial staining, this can be as simple as a bit of minor coloration from slow drying to significant rot. Both are generally considered defects, especially when the structure may be in question.
Medullary Rays- Cells that extend from the center of the tree, and have a different appearance from the surrounding wood. The size and coloration will vary from species to species. The strong even visual presence is a good indicator as to how close the wood is to quarter and its natural split(at least this is what I have found). A freshly split bit of bracewood will show medullary rays very well on the quartered face, were as they do not appear on the flat side face. Have a look at a freshly split bit.
There are many other terms I am not thinking of at the moment, so maybe others could fill in the blanks. To me the structural issues absolutely weigh heaviest in grading. If the wood little issue in the area of structural flaws you will have a good soundboard, and it generally is pretty stiff for the species. Some of the strictly visual elements have little significance structurally and are often the ones most focused on. This is why the 2A soundboard is often the best value, and may even be structurally equal or better.
My 3 big considerations;
1. Orientation
2. Minimal runnout (no matter what caused the runnout)
*Usually Medullary rays follow if #1 & #2 are looking good.
3. No major structural issues(large pitch pockets, knots, heavy reaction wood, rot, non-drying related cracking, checks, shake)
Secondary but structural variables;
4. ring counts or more accurately ratio of early and late wood.
5. Cross grain stiffness(looking to make sure it is not notably weak)
Visual stuff positives;
6. Nice even natural coloration
7. unique coloration, or figure(bearclaw, not curly)
Visual negatives;
8. Staining
9. uneven hard natural coloration
10. small pin knots(I mean very small)
11. small pitch pockets (non structural issue)
I always consider location when I look at these things. If there is a pitch pocket that falls up and under where the neck will set it is not an issue(even visually). If there is a pitch pocket in the area most likely to be where a soundhole will be cut, it is an issue(if someone has an offset or non-standard soundhole) so that area counts visually. If something falls well outside the usable pattern area, and has no effect on the wood that will be used. It is not an issue.
These are the things I weigh when evaluating stock. I place the highest concern on #1-#3.(that gets you to paint grade), #4-#5 have to be good to get 2A or better. #6-#11 usually set the grade 2A or better. I get very nervous about calling something 4A because visual grading is so subjective, I don't even mess with a 5A or "master". I figure there are so few that could be potentially be called that(shoot 4A is rare enough), and even if they really had nothing that could be a downer, it's not worth thinking about to increase the value of a couple set by a few dollars. I have been frustrated in the past when I recieved what was supposed to be "master" and had structural downers, although it was reasonably pretty.
Curly woods, are a different animal. As it is a given this wood will not be stiff longtitudinally. So I don't think about grading these, although I try to make sure the grain is fairly straight(the waves are straight?
) and the wood is close to quartersawn.
There is my 2 cents(a lot of typing for a couple coins),and what I have come to understand, hopefully some of the verterans can correct anything I may be mistaken about
, or fill in gaps I overlooked
. FWIW
Rich
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