Q. We couldn’t get enough No.1 common red oak, so we got a little Select grade, for a lot more money. However, our yield did not increase substantially. Can you explain why?

A. Let’s do some grade comparisons.

SELECT vs. No.1 Common
No.1 Common and Select grade lumber both have the same grade, No.1 Common, on the poorer side. The difference between the two grades is that the better side of Select is clearer, so it will grade FAS. So, when cutting lumber from these two grades with lumber pieces of about the same length and width, and looking for both faces of the parts you are cutting being clear (C2F), the yield will be the essentially the same. That is, the poorer side controls yield with C2F. But if you want clear one face (C1F) parts, then Select yields will be somewhat higher.

Now, No.1 Common lumber can be narrower and shorter than Select. This width can increase Select yield if you have short or narrow No.1 Common.

The bottom line is that Select can sometimes be slightly higher yield than No.1 Common when cutting C2F, but the extra cost may not justify higher price. FAS has much higher yield than No.1 Common, with longer and wider parts as well.

FAS vs. No.1 Common
Extra note: FAS 1-Face is a Select grade piece that is a minimum of 6” wide. Like all the grades, FAS is graded as FAS on the poorer side. The better side in all grades has little effect on the grade except in Select grade.

When comparing FAS to No.1 Common, FAS pieces will give higher yield, including longer and wider pieces being cut. Pith, splits, and grain angle are also limited in FAS, but not so severely in No.1 Common. These many benefits of FAS can make it worth the extra price, if they apply to your operation. So, when grading the FAS side of Select, these benefits of FAS on the clearer or better face can increase yield of Select compared to No.1 Common.

Q. I would like a little better understanding about how wood burns.

A. When wood is first heated up to 212 F (boiling point of water), much of the water in the wood is heated, forms a vapor, and is emitted or leaves the wood. Even though the air around the wood can be over, 212 F, the wood temperature stays at 212 F until most of the water is gone. (Maybe you remember that boiling water on the stove in an open pot reaches 212 F and stays there until the water is all boiled away.) Have you ever tried to light some wet wood in your fireplace but had a hard time getting the fire going? The reason is that the wet wood is emitting water vapor as it is first warmed, not flammable gas; there is little to ignite and continue burn.

The second step, perhaps overlapping the boiling water, some wood components themselves, turn to a gas and are emitted from the wood. Pretty amazing to think of solid wood turning to a gas indeed. These gases, including methane, are highly flammable. In fact, if a source of ignition plus  oxygen, are available, these gases, if allowed to accumulate, can ignite with an explosion. This is where we have a lot of injuries, as someone goes into a room on fire filled with these gases and lets in oxygen, so that we have an explosion. Plus, the flames seem to jump 30 feet or more. Limiting oxygen is how we throttle back a wood burning stove.

As a rough rule of thumb, we usually say that wood gases ignite at around 450 F. Smaller particles ignite at lower temperatures.
Some of the gasses  produced in this second step, if not burned, will turn back to a solid material if they are cooled. Different gasses produce different solids. The condensed materials we usually call creosote. Obviously, creosote is flammable, and quite a risk of damage exists in an old chimney when creosote ignites.

Eventually, the burning uses all the hydrogen in the wood, combined with oxygen. However, there is excess carbon, which burns at 1100F or hotter. If we limited the oxygen in step two, the carbon will not burn and so the remaining carbon is called charcoal. To get the carbon to burn and form carbon monoxide in limited oxygen availability, or carbon dioxide with enough oxygen, requires a hot fire. If you use charcoal briquettes in your grill, you know how long and hard it is to get glowing carbon, which makes excellent heat. It is also why in an industrial wood burning boiler, we use excess air to “fan the fire” to get it really hot to create a lot of energy. In fact, many boilers like to use enough air flow to keep the burning wood particles in suspension, rather than on a grate. It is also why a grate often has holes and air injected from underneath.

Having given this simple explanation, you should appreciate that in a large piece of wood, all three steps can be occurring at the same time: Evaporation starts at the surface and goes deeper; step two starts later and follows evaporation deeper into the wood; a charcoal formation follows. As this mixed activity is not very uniform and rapid, we prefer most fires that are burning for heat or energy use uniform particles. That is also why dust on fire is so rapid. This explanation should also help you understand why dry wood burns better than wet, although drying wood in a kiln before burning in a boiler is more expensive than drying it in the boiler. Finally, a boiler tuned for burning dry wood will struggle if a big slug of wet wood is used for fuel, until all the water is evaporated.

Q. As a matter of curiosity, why is spruce so desirable for acoustic musical instruments?

A. Going back to basics, wood is made of cells that look like miniature soda straws. Wood cells in spruce are likely 3mm to 5 mm long. Over 90% of these cells run vertically in the tree. The cells are closed at the ends, but they do have small valves between adjacent cells — an engineering marvel indeed. What we have in spruce are millions of nearly identical hollow tubes that act as sounding chambers; their uniformity tends to give a uniformity and crispness of sound, especially high notes. In contrast, red oak has cells that have a wide range of diameter and length, so sound purity is lost. Further, a dense wood has a lot of glue (technically called lignin) that stiffens the cells and holds them together. But spruce, being light weight has less stiffener. Plus, in spruce, the cells are wide open (hollow) in the middle, compared to white oak and many other species that has the cells plugged.

Added note: There can be stress inside the spruce wood cells, a natural event caused by the cells holding up a heavy tree that is blowing in the breeze. Stress changes the tonal properties. So, to relieve the stress, spruce is often heated over 130 F for months, which allows the stress to relax. To avoid making the wood brittle when heating, humidity is controlled to avoid over-drying.

This is probably more than you need to know, but maybe you can pass it on to your neighbors and associates the next time you get together. They will think you are so interesting and intelligent, maybe.

Q. What can you tell me about allergies to wood dust?

A. Wood allergies are a complex and involved subject. There is no question that some people are allergic to wood, including pollen, wet chips, and dry dust. 

Some species seem to garner more complaints than others. (Another allied subject is the carcinogenic risk of wood dust.)
In general, the few people who are allergic to the dust of a species will have respiratory and nasal symptoms. However, headaches, rashes, and other medical issues can show up, albeit rarely. However, if a reaction is suspected, contact a professional allergist. 
The knowledge this medical person has far surpasses the information one will find after spending a few hours on the Internet. (This statement comes from an ER doctor.)

Prompt treatment can relieve symptoms better than delayed treatment.

So that you have some information, I suggest that you look at the summary in the Wood Data Base: https://www.wood-database.com/wood-articles/wood-allergies-and-toxicity/

Let me add that sometimes the cause of a supposed allergic reaction is really a reaction to mold and mildew growing on the wood and not the wood itself.

Q. We bought some cherry lumber that was graded FAS. However, it has some very small knots and some gum pockets. Is this acceptable in FAS cherry, as our supplier says?

A. Yes, indeed. Small knots of 1/8” diameter or smaller, and gum streaks and spots are allowed in clear areas (called cutting when grading) without penalty in cherry.

Q. We are sanding some soft maple. We use 400 grit. It seems that sometimes we see some fibers poking through the finish. Are we doing something wrong?

A. Sandpaper has sharp particles that cut off the wood fibers (also called wood cells). However, as the sandpaper gets dull (needs to be changed), the particles are no longer as sharp, so they do less cutting and more tearing. Further, with a hand sander, the operator will push a bit harder to get the machine to work hard and cut as fast as when the sandpaper was fresh and sharp. (This is the wrong response to dull sandpaper. Change the paper to get fresh cutting.). 

This added pressure tends to push fibers down into the surface, rather than cut them all off.

With torn fibers and loose ends pushed into the surface, the fibers will tend to pop back up, especially when exposed to moisture.