Archive for the Category ◊ Wood ◊

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• Sunday, March 17th, 2019
honeycomb lumber defect

As much as we love wood, it can hit us with some awful surprises. Honeycomb, a drying defect, is among the worst. Here I will recount my sad tale of 8/4 quartersawn white oak, hoping you will be spared the same fate. 

First, let’s briefly review a simplified version of the drying process

The outer part of the board – the shell – loses it bound water and shrinks earlier than the inner part of the board – the core. The shell is in tension because it wants to get smaller but is limited by the still moist and swollen core, which is thus in compression. If this happens too fast, surface checks may result, which later may close and go unnoticed.

The shell sets in size. Now, as the core loses its moisture, it wants to shrink but is limited by the surrounding shell. Thus, the core is now in tension and the shell in compression, a condition known as case-hardening

The kiln operator modifies the moisture content at the end of the drying process, and ideally, there would be no remaining stress. However, the irremediable state of reverse case-hardening must be avoided, so a bit of case-hardening is acceptable in the final state of most kiln-dried lumber, demonstrated by a slight inward curve of the tines of a test fork sawn from a cross-section sample of the board (below).

lumber test forks

Note that this is not a matter of a moisture gradient across the thickness of the board; it is physical stress. If you resaw lumber, you’ve certainly encountered this.

But what if the core dries too fast? Hygroscopic wood movement is a powerful force, stronger than the wood itself. Therefore, the core of the wood, desperately trying to shrink within the restricting frame of the shell, simply breaks. Honeycomb! (top photo)

Worst of all, this is not visible from anywhere on the outside of the board. The only clue you might get, which is inconsistent at best, is to note the board is oddly concave across its width on both sides. The cracks, revealed only when you crosscut the board, occur perpendicular to the annual rings in both flatsawn and quartersawn lumber.

So, what happened in this white oak board? Probably several factors conspired. 8/4 is, of course, much slower to dry than 4/4, white oak is a relatively difficult species to dry well, and quartered lumber is a bit slower to dry.  My guess is that this board was not sufficiently air dried before going to the kiln. Further, since 8/4 white oak is less common, this board was probably lumped together in the kiln with thinner lumber and/or faster drying species for which a faster kiln schedule would work. In other words, it was rushed to market. 

case-hardening test

What about using the parts of the board without honeycomb? Nope, best not. Even sections distant from the frank honeycomb were severely case hardened, as demonstrated by these test forks (above). Whether a lot or a little of the interior core was removed, the tines are bent over each other. It was amazing how forcefully they bent inward against each other before I halved their widths so they could cross over each other. Again, to be clear, there was no moisture content gradient across the thickness of the lumber.

case-hardening stress

Severe stress like this wreaks havoc in the building process. I tried to salvage the expensive board but as I would incrementally remove thickness, attempt to resaw, or shape the wood, it persistently distorted. I was constantly and futilely chasing true surfaces. Enough.  

Woodworker, beware.

Category: Wood  | 5 Comments
Author:
• Monday, October 29th, 2018

dark red meranti

Dark red meranti, pictured above, is a generally uninspiring reddish brown, rather uniform looking wood that does not therefore find its way much into fine woodworking. If you have not come across it as solid wood, you likely have seen it as the skin of middling quality plywood, where it is referred to as lauan or Philippine mahogany. It is about the same density as khaya and genuine mahogany, but a bit softer. It has several cousins in the Shorea genus, including the softer and even more forgettable light red meranti. Any claim of these woods as “mahogany” is untenable.

There is, however, one more wood that does have a strong claim as a mahogany substitute: utile, also known as sipo. Entandrophragma utile is in the same genus but not as hard as sapele, and easier to work. It is a generally consistent but not boring wood that can look quite nice, especially flatsawn, where you otherwise might have used genuine mahogany. Its darker ray lines sometimes also add interest. I’ve also seen some wild ribbon striped quartersawn utile.

The volumetric shrinkage of utile is 11.8%. That’s pretty good but no match for genuine mahogany’s freakish 7.5%. Still, with a nice T/R of 1.4%, you can expect utile to behave quite well.

Unfortunately, dear readers, I do not have any utile in my shop at this time, so I cannot offer you a photo. However, this is a good time to refer you to the magnificent resources created by Eric Meier. His huge website is a treasure trove of well-organized information, including beautiful and useful photos. As good as the website is, I highly recommend also buying his book, Wood!, which I think is the best book on wood available, and one of the best books in the entire woodworking field. [As always, my recommendation is unsolicited and uncompensated.]

If you are contemplating using any of the woods discussed in this series of posts – “genuine” mahogany (Swietenia macrophylla), African mahogany/khaya (Khaya spp.), sapele (Entandrophragma cylindricum), or utile/sipo (Entandrophragma utile), I offer these suggestions:

  • Consider each on its own merits rather than trying to imitate some other wood, namely “genuine” mahogany.
  • Pay close attention to the particulars of each board, including color, density, figure, and, of course, the orientation of cut from the log. There is much variation within each species.
  • Watch out for defects, especially compression failures. For this reason, and the point above, consider buying these woods planed or at least hit-or-miss planed if you can.
  • Scraping is a good way to tame the interlocked grain on quartered surfaces.

Enjoy building!

Category: Wood  | Tags:  | One Comment
Author:
• Sunday, September 30th, 2018

sapele

Sapele, Entandrophragma cylindricum, stands out as significantly darker, redder, heavier, and harder than the others in this bunch. Though it would often work in the same context as genuine mahogany, I suggest not thinking of it as a substitute for the venerable old boy, but rather as a wonderful wood in its own right.

The species offers some spectacularly figured wood. Most common is the neat ribbon stripe in quartersawn boards. The striping is finer and bolder than that of khaya, and can be obtained quite reliably. The pieces pictured above are unfinished, fairly middling stuff, but the ribbon figure will pop pretty well with oil-varnish mix, and the color will deepen considerably.

Also, consider ribbon-stripe face veneer plywood, which can be found reasonably priced in a variety of thicknesses, as a nice backing for a cabinet or for drawer bottoms. You know a wood has reached all-star status when you see it as fake veneer in an elevator in a fancy downtown building.

Sapele can also produce spectacular curly figure and pommele figure. The latter is similar to blister maple, sometimes in a finer pattern. The wood is popular with instrument makers.

On the other hand, flatsawn sapele, without special figure, is a decent wood but not something that really excites me on its own. Still, it may fit the bill as a predictable, diffuse-porous, reddish wood that can finish fairly dark and will darken further with time.

No pushover like genuine mahogany, sapele is about as hard as white oak and sugar maple, and nearly as dense. It machines pretty well as long as you take precautions to avoid planer tearout on the quartered rowed surfaces and burning from ripping on the table saw. For smoothing to a finished surface, I suggest skip the handplane and go with scraping and sanding.

Sapele is about as stable as black walnut, with a volumetric shrinkage of 12.8%. The T/R is a nice 1.5, but that offers little advantage when using quarted boards for the ribbon stripe.

Shopping at different dealers, I’ve had good luck with the sapele being fairly consistent, and it has seemed safe to buy in the rough. (However, check the comment in the first post in this series – compression failures may lurk.) I’ve also found it more expensive than khaya or utile but still significantly less than genuine mahogany. It is a popular wood.

How do you pronounce it? I’d been saying sa – ‘pay – lay (like the legendary soccer player), but most often I hear sa – ‘pee – lee, and sometimes, sa – ‘pell – lee.

There’s one more post coming up in this series.

Category: Wood  | Tags:  | 7 Comments
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• Sunday, September 23rd, 2018

Khaya

Next up is khaya. The wood available to us may be any of four species in the Khaya genus: K. ivorensis, K. grandifoliola, K. anthotheca, and, less so, K. senegalensis. Ask the guy at your lumber yard what species he’s selling and he’ll probably look at you the same way we look at an 88° try square, even if the importer had kept the species distinct. In fact, you’ll probably create confusion by asking for the “khaya” bin because it is more commonly referred to as African mahogany.

And so, this is the only wood comparable to genuine/true mahogany (Swietenia) that generally bears the “mahogany” name. Botanically, it is in the same family (the next major grouping above genus), Meliaceæ, as Swietenia. It comes to us from West African countries.

Just like true mahogany, when African mahogany/khaya is good, it is indeed a very good wood. The problem is that I have had just as much frustration with inconsistency in density and color in khaya as with true mahogany. There is variation among species, but also with the geographic source of the tree, and the local conditions in which it grew. Therefore, as a practical matter, I suggest that you not be too concerned with the provenance of the wood, but evaluate each board on its own merits. Khaya is about half the cost of true mahogany, and there is some great stuff available.

Some khaya is less dense, and quite light in color – an uninspiring pale pink hue. The flatsawn wood looks particularly anemic. When quartersawn, these boards often have a hairy surface that can be difficult to finish. They come off the planer with hairy rows that are hard to tame with planing, scraping, or even sanding.

I try to avoid these boards and instead look for darker, denser boards. Many quartersawn khaya boards exhibit a fairly coarse, beautiful ribbon stripe. The boards in the photo at top are a good example of dark khaya with great ribbon stripe. Look how nice it finishes:

African mahogany

More quartered African mahogany:

Khaya

The color below is a bit more red but also very nice:

African mahogany

Good flatsawn khaya is also very worthwhile. In some case, it is difficult to distinguish from high quality true mahogany. In general though, I’ve found that true mahogany’s legendary chatoyance is harder to find in khaya.

Unfortunately, khaya seems to be quite susceptible to the dreaded compression failures that I discussed in reference to mahogany in the previous post. With the possibility of these defects, as well as the great variation in the other properties of khaya, I suggest buying your boards S2S planed or hit-or-miss planed, if possible. Look them over carefully.

Coming up: sapele and others.

Category: Wood  | Tags:  | 2 Comments
Author:
• Saturday, September 15th, 2018

mahogany

Fasten your seatbelt as we ride through the world of mahogany! Our tour will be mostly about woods that are similar to mahogany, and sometimes referred to as “substitutes” for it, but are better considered on their own merits.

We start our journey with “genuine mahogany,” aka Swietenia macrophylla, big-leaf mahogany, Honduran mahogany, Central/South American mahogany, or if you want to live and buy dangerously, just call it “mahogany.” Just the name sounds, you know, classy. People, including people who buy furniture (such as you might build) but know nothing about wood, are almost always impressed by “mahogany.”

Note that in the rear-view mirror is Swietenia mahogani, aka Cuban mahogany, the best of them all, once used for building ships and furniture, but long since essentially unavailable. You might find a bit of it for sale that was rescued from the occasional tree downed in a storm in south Florida, and there is a plantation operation on a South Pacific island. I once read that it works like “cold butter,” and having had a tiny piece of the stuff some years ago, I can confirm that description.

But back to S. macrophylla. When it’s good, it has a lot going for it. Boards with good density and color are a pleasure to use in your projects. It usually planes easily on the flatsawn surface, while the quartersawn surface often exhibits attractive “ribbon-stripe” figure due to interlocked grain. This is difficult to plane but quite manageable with scraping and sanding. The wood is soft enough to saw and chisel easily but firm enough to hold detail.

The stability of mahogany is legendary. Radial shrinkage is 2.9%, tangential 4.3%, yielding an excellent T/R of 1.5, and paltry volumetric shrinkage of 7.5%.

Then there’s the chatoyance – that wonderful shimmery gleam, lovely but not overpowering – that mahogany does so well. You know, classy. A shellac and wax finish looks great.

Unfortunately, big-leaf mahogany is a big pain in the neck. Why? First, because it is expensive. I cannot find even the drabbest mahogany for less than $10 per board foot. Yet it is extremely variable in quality. Some boards in the bin will have that nice density and color, while others are junk wood – light in color and density, or often with defects. In fact, I suggest avoid buying mahogany in the rough; look for S2S or hit-or-miss planed stock.

In the photo at top, all three boards are genuine mahogany. Yup, the real thing. The top one resembles sapele (more on that in an upcoming post), the middle board is what I consider nice flatsawn mahog, and the bottom one is genuinely trash wood, as far as I’m concerned.

The most notorious defects are compression failures, sometimes called “windshakes.” These are jagged cracks across the grain, usually through the full thickness but not the full width of the board. The fibers are broken, rendering that part of the wood useless. It occurs in the tree from severe wind forces, snow loads, or, what I suspect is mostly the case with mahogany, when the tree is felled. Beware: this defect is very difficult to notice in rough boards, where it lurks to disappoint you when you bring the wood home and plane it.

compression failures

See the defect in the board below? No? Neither did I before I took it home.

hidden compression failures

Here is the other side of the board, with the compression failure clearly visible after I skimmed it on the jointer. The defect goes through the full thickness of the board.

compression failure

S. macrophylla is listed in CITES Appendix II, and on the IUCN Red List as Vulnerable. We are probably encountering mostly plantation grown wood, and the quality is uneven at best.

And so, regrettably, mahogany is nearly off my list of good options for wood. Next, we’ll look at a common alternative, Khaya, aka African mahogany. There’s that word again.

Category: Wood  | Tags:  | 3 Comments