WoodSense: CocoboloComments (0)
This article is from Issue 89 of Woodcraft Magazine.
Beauty that might bite
By Ken Burton
Mention cocobolo to a group of luthiers, and you’ll likely get knowing nods and smiles. A renowned tonewood prized by instrument makers worldwide, this dense, tropical lumber is also a beautiful substitute for the rare Brazilian rosewood traditionally used for many guitar bodies. Sometimes called Nicaraguan rosewood, cocobolo is, in fact, a true member of the rosewood family.
Often featuring multicolored stripes, the heartwood ranges in color from yellowish-orange to almost black, while the sharply contrasting sapwood is a pale yellowish tan. Perhaps the only thing that’s not attractive about the wood is that its dust can cause allergic reactions in woodworkers, but more on that in a bit.
Rainbow wood. Cocobolo colors range from orange to purple, sometimes within the same board.
Where the wood comes from
The lumber comes from a few similar trees, but the most common is Dalbergia retusa. Though a tropical wood, cocobolo doesn’t come from the rainforest. Instead, the trees grow in the drier regions along Central America’s Pacific coast, typically reaching a height of 80 feet, and 3 feet in diameter. Given their desirability, cocobolo trees have been heavily exploited and even poached from national park preserves. Sadly, cocobolo is listed on the CITES (Convention on International Trade in Endangered Species) Appendix II and on the IUCN (International Union for Conservation of Nature) Red List of Threatened Species due to a 20% decline in its population over the last 20 years.
History in woodworking
Cocobolo first drew the attention of North American manufacturers in New England with the opening of the Panama Canal early in the 20th century. Before that, shipping the heavy wood around Cape Horn wasn’t practical. This “new” wood resisted repeated water contact, making it well-suited for fine cutlery handle material. Today, you’ll find cocobolo in both stringed and woodwind instruments as well as in pool cues, chess pieces, jewelry boxes, and furniture.
Selecting the best stock
Several online retailers claim that the lumber from Nicaragua has some of the most spectacular color. As when buying any lumber, the best way to get good material is to choose it yourself, but this can be tricky if you don’t have a specialty hardwood dealer nearby. Your next best option may be to buy from an online retailer that posts photos of individual boards. Online prices vary widely but are usually north of $30 per board foot.
Cocobolo dust is a strong sensitizer that can cause severe allergic reactions, so protect your lungs and skin from exposure. Wear a respirator, long sleeves, and perhaps a skin protectant such as North’s #222 Barrier Cream. Also, be sure to vacuum up the dust and blow off your clothing before leaving the shop. Don’t take this wood lightly. As one woodworker I know put it: “There are two types of woodworkers, those who are allergic to cocobolo, and those who will become allergic to cocobolo.”
Cocobolo is hard and heavy, but relatively easy to work using both hand and power tools with sharp blades. The wood turns well and polishes to a glossy luster. But cocobolo’s high oil content can impede glues. Wiping the surfaces with acetone before gluing may help, but even then the oils may compromise aliphatic resin (white or yellow) glue. For best results, wipe your glue surfaces with acetone and use epoxy as an adhesive. Cocobolo holds screws and nails well, but drill pilot holes first.
Cocobolo’s oiliness loads up sandpaper in a hurry. (One of the shops where I work has banned the wood from the drum sander, as a couple of passes render the abrasive useless.) Use a card scraper before sanding, then an open-coat, stearated abrasive such as Klingspor’s “Gold” to polish away the scraper marks. Stearated papers include a lubricant that helps prevent the abrasive from clogging. Cocobolo’s density requires sanding to a fairly high grit (400-600+) to eliminate obvious scratches.
Many wood turners find that cocobolo polishes well with wax-based finishes such as Hut’s High Gloss. Evaporative coatings such as shellac or nitrocellulose lacquer work better than reactive coatings like polyurethane. In fact, poly on cocobolo has a reputation for never drying. If you want the durability of polyurethane, first apply several coats of shellac. This seals the wood’s natural oils under the shellac, allowing the urethane to cure properly.
One other important note: if glued to another species (especially a lighter-colored wood) color can bleed from the cocobolo into the neighboring species, spoiling the sharply delineated contrast.
Cocobolo: Working Notes
Cocobolo’s reputation as a sensitizer had me worried, so I took a number of precautions. First, I added a dust pickup to my lathe to control the sanding dust. I also grabbed a fresh dust mask/respirator (3M #8210), buttoned my shirt sleeves, and made sure to don my high-necked turner’s apron before digging in.
To start, I hand-planed the edges of a few pieces for gluing—I wanted to see if the warnings of cocobolo’s oiliness were true. I glued two pairs of pieces together. The first pair I glued directly from hand planing. (The wood planed well, a pleasant surprise given its density.) I wiped the second pair with acetone before applying the glue. For both pairs, I used Titebond II, my go-to adhesive for just about everything. After leaving the test pieces clamped overnight to cure, I tried breaking them apart by securing them in a vise and smacking them with a hammer. Both pieces held better than I expected but gave up right on the glue line. (The lengths I go to give you good advice...)
As you can see (left), I turned three pieces from the samples I had. Note the color variation. All pieces started out dark brownish-purple, almost black. As soon as I cut through the outer, oxidized layer, truly vibrant Crayola-like colors leaped forth: oranges and yellows and reds along with deep browns and purples. It was easy to see why cocobolo is sometimes called the rainbow wood. It turned beautifully, but I had to resharpen my spindle gouge more frequently than usual. The cut surfaces were burnished and glass smooth. Sanding went well too, though the paper loaded quickly as suspected. And even with 400 grit, the cross-grain scratches were obvious. So, I did my final sanding by hand, going with the grain. This produced a smoother surface.
Drilling the end grain for the shakers was not as difficult as I thought it might be, though I expect to sharpen my Forstner bits soon. But I had problems sanding the blade for the cream cheese spreader. After turning, the piece cut well on the bandsaw, but cleaning up the saw marks with my belt sander made short work of the paper. The vivid colors disappeared while sanding, leaving but a hint of oranges and yellows. I suspect that the oils from the darker areas tend to bleed into the lighter areas. Finishing was pretty straightforward: shellac on the shakers and mineral oil for the spreader. Will I use more cocobolo? Yes, but probably only as an accent here and there. Its dark color suggests a certain formality that doesn’t quite fit my aesthetic, and its price doesn’t quite fit my wallet.
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