A Marriage of Cocobolo and Epoxy

THE FUN OF TURNING

in cross-section and precisely By Jim Rinde centered: Alignment is critical for Lidded a balanced design. Turn off the corners of a 1/4" to 1/2" long section as shown below. Goblet This offset will be the distance A marriage between the top of the goblet, pure epoxy resin, and the top of of cocobolo the wood points as shown at left. and epoxy With oily woods such as cocobolo, it’s difficult to get the epoxy to adhere to the surface Marriage: “to unite by some without some surface preparation. close bond of connection.” I give the wood a wipe with xylene and follow this with a ow do you unite wood with second solvent wipe with methyl resin to form something ethyl ketone (MEK), both which Hnew, exciting, and long lasting? are available at paint stores. What if the wood is cocobolo—a wood with a reputation of being oily and difficult to bond? As you will see, this is not a quick-and-easy project, but one that requires 4 to 7 days to complete. However, when you follow these directions, you’ll produce a bubble-free wood and epoxy composite. Finished size: At this point the wood still 1 3 8 ⁄2" x 2 ⁄4". Prepare the wood contains some residual solvent, From a 2"x 2"x12" piece of so put the wood in a vacuum cocobolo, cut the goblet stock to 7" chamber for 30 to 60 minutes to and the lid stock to 5". For best pull out the solvent and remain- results, dry your stock below the ing water moisture. See the equilibrium moisture content for description on page 18 on that wood in the climate in which building a vacuum chamber. you live. My stock was dry when Now, you’re ready to embed the purchased and further dried by wood with epoxy. To make it easy placing it in a 125˚ to 150˚ F oven to find the center hole in the wood for several days. after it is embedded in the epoxy For this goblet design, it is most and cured, fill the hole with paste important that the wood be square wax before casting it.

What are epoxy resins? Safety considerations time, become sensitized to the epoxy. Epoxy resins are a class of liquid Epoxy resin systems are hazardous The curing agents, Part B, are more chemicals that, when mixed with materials. Obtain the product data hazardous because they generally an appropriate curing agent, react sheet and a Materials Safety Data contain amines that are corrosive to form a solid cross-linked resin. Sheets (MSDS) for all materials. materials. For example, lye (sodium There are hundreds of epoxy resin The epoxy resins, Part A, and hydroxide) is a common corrosive systems (part A resin and part B modifiers are relatively safe to handle if material. Some amines are also volatile curing agent). The best system to you wear disposable gloves and materials, so the materials should be use with wood depends on the change them often. I use disposable mixed either where there is good application. Potting (casting) or polyethylene gloves that cost about ventilation or outdoors. Avoid encapsulation described on these one cent each. The main problem with breathing the vapors from the curing pages requires a slow-curing epoxy resins is that some people, over agent. Always wear eye protection. system. An ideal epoxy resin system for wood encapsulation would have these characteristics: 1. Clear when cured Colors, dyes, and fillers Colored epoxy and (no yellow color) A good way of coloring an epoxy light-colored wood 2. Low viscosity: 1000-5000 cps mixture is to use oil-based artist When using an epoxy resin mixture that (centipoise). colors available from art-supply contains a dark-colored dye and a light- 3. Long pot life or gel time: stores. I have used Grunbackers and colored wood, it is necessary to fill the at least 4 hours for a Norton & Westen brands. These surface pores of the wood with 100-grams- mass at 77˚ F. paints contain linseed oil, which is uncolored resin before embedding the 4. Cures to a tough hard resin. compatible with the epoxy resin I wood in the dark resin. This is to prevent The epoxy I used for this lidded use. I haven’t experienced any the dye from migrating into the wood goblet is Jeffco Products Epoxy curing problems when the colors are and discoloring it. Resin 1403 and curing agent 4123 5 percent or more of the mixture. Coat the wood with clear uncolored at a mix ratio of 100/36 by weight. The color may change when mixed epoxy resin, place it in a vacuum For larger castings, this system with the epoxy resin mixture, which chamber, and degas the coated wood. cures too rapidly and has a is due to the amine-curing agent. There may be a lot of foaming because moderately high exotherm. I’ve had good results with Inlace of the air/water entrapped in the wood. A lower exotherm (slower curing dyes, which are intended for Under reduced pressure, the air comes system) is Jeffco 1403/403 mixed polyester resins and contain styrene. out of the wood. When the vacuum is 2:1 by volume. Both systems are When used in small concentrations, turned off and the pressure is allowed to available from: these give good results. During return to atmospheric pressure, the clear Jeffco Products vacuum degassing, most of the epoxy resin will be pushed into the pores jeffcoproducts.com styrene can be removed with of the wood, effectively sealing the 858-576-9900 prolonged degassing. surface of the wood.

What’s an exotherm? of the resin increases, this heat may happens, the project is ruined and When the epoxy resin and curing not dissipate fast enough and the your health is in danger if you breathe agent are mixed, a chemical reaction temperature of the mass will increase. the smoke and fumes, as they are begins. One of the products of this As the temperature increases, the toxic. That is why I work with low reaction is released heat—an reaction rate increases, liberating exotherm, slow-curing epoxy exotherm. In thin cross-sections this more heat. This in turn increases the systems, as they allow the casting of is not a problem—in fact it is temperature more and so on until the thicker sections with little danger of desirable as it speeds up the curing whole system runs away and begins run-away reactions. reaction. However, as the thickness to smoke and may catch fire. If this —Jim Rinde

Continued

The vacuum chamber and other equipment Epoxies are different materials from wood and require different equipment for successful use. In addition to normal woodwork machines you will need: • A scale capable of weighing to 1 gram. I use a digital balance from the kitchen section of a local store that costs about $50. • Vacuum pump, which you may already have as part of your vacuum-chuck system. • Microwave oven (for household harmony, don’t use the one from the kitchen). • You’ll need a vacuum chamber as shown at right. Make your own chamber from thick-walled one-gallon can. of the acrylic and partially fill the any thick-walled cylinder with a (Note: a normal paint can will groove with a bathtub caulking fixed bottom and a clear collapse; mine is .025" thick). material. The inlet for the vacuum removable top. You’ll also need a For the top, use 3/4"-thick clear is the hose barb fitted into a hole hose barb (available in hardware acrylic plastic. For the sealing drilled into the side of the can and stores). I made a chamber from a surface, turn a groove in one side sealed with the caulking material.

The value of vacuum degassing There is nothing worse than 1. Mix the epoxy resin (part A only) moisture are removed. (Boiling can spending hours preparing a wood with all the pigments/fillers that will continue for 15 minutes or more and epoxy composite for turning be used. Heat this mixture in when the materials are very wet). and then finding bubbles in the a microwave oven to about 140˚ 3. Remove the mixture from the epoxy. That’s why vacuum to 180˚ F to reduce its viscosity and vacuum chamber, cool it to room degassing is so important: It to speed up the degassing temperature, and then mix in the prevents bubbles. process. curing agent. The mixture goes To avoid this disappointment, 2. Place this mixture in the vacuum back in the vacuum chamber a spend extra effort in the chamber and reduce the pressure second time to remove the preparation of the wood and the to – 28 inches of Hg. As the air/moisture that was introduced epoxy mixture. The epoxy resin, pressure goes down, the mixture from the mixing process and the curing agent, pigments/colors, and will start foaming and the volume curing agent. If the curing agent wood all contain some amount of may increase 10 to 20 fold. contains a volatile material, limit the dissolved air and absorbed Therefore the container needs to second degassing to prevent loss moisture. Both the air and have a capacity of about 20 times of this material. moisture can be the source of the volume of the initial mixture. 4. After the second degassing, bubbles in the final casting. Here’s At some point, the foam will combine the wood and epoxy in what works for me: collapse and the mixture will simply your mold. boil until all the trapped air and

18 American Woodturner Spring 2005 Copyright 2005, 2016, American Association of Woodturners. All rights reserved. Mix the epoxy and casting give the epoxy a white pearlescent pressure for a few minutes to pull To calculate the amount of epoxy appearance. These materials were the air out of the wood. (This required, determine the volume of heated and vacuum degassed. causes some foaming and is why the mold, and subtract the volume (See Vacuum Degassing at right). the mold is only half full.) of the wood and multiply this by Vacuum degassing will go After the foaming stops, turn the density of the epoxy. An easy faster if the resin is heated to off the vacuum pump and return way of determining the volume of 140˚ to 180˚ F to reduce its the system to atmospheric pres- an irregular-shaped mold is to fill viscosity. After degassing the sure. Then add the rest of the it with water and weigh it. Since epoxy resin and filler and cooling epoxy mixture; repeat the process. water has a density of 1.0 g/cc, the to room temperature, add 144 Set aside the molds to cure weight in grams equals the grams of Jeffco 4123. Mix well and overnight at room temperature. volume in cubic centimeters. The then repeat the vacuum degas The resin should be hard after this density of the epoxy is approxi- steps. The epoxy is now ready time. Note: Curing is time and mately 1.15 g/cc. For this project, I for molding. temperature-dependent. If the used two 16-oz. plastic containers Fill each mold with approxi- resin is soft in the morning, move as molds and embedded the wood mately 150 grams of the epoxy the assembly to a warmer location two inches into the epoxy mixture. mixture and insert the cocobolo and allow it to cure until hard. This required 540 grams of mixed as shown below center. Note: The Finish the curing process by epoxy resin. mixture will cover only the baking the assemblies at 150˚F for Since the plastic containers are bottom 1" of the wood. 2-24 hours. This post-cure used upside-down, make sure Place the two assemblies in the toughens the resin and makes it they are watertight. I sealed them vacuum chamber and reduce the less brittle. with a bathtub sealing compound. Because you’ll insert the turning stock into the liquid epoxy, cut a section from the bottom of each container (slightly larger than the cross-section of the wood). Pour 400 grams of Jeffco 1403 epoxy into a 32-ounce plastic mixing container and add about 5 grams of a pearlescent filler to

An accurate scale (available in kitchen For this project, 16-ounce disposable After the epoxy cures, the cocobolo stores), a 32-ounce mixing container, plastic containers like the ones shown and epoxy are ready to be turned. This and a two-part epoxy are among the above are ideal for casting the goblet casting included a filler to add a white supplies you’ll need for this project. bowl and lid. pearlescent appearance. Continued

Turn the goblet After the resin is fully cured, remove the plastic container and put the square wood end in a four-jaw chuck, using the hole in the epoxy end to achieve an exact centering of the composite in the chuck. As you increase 2 the inside diameter of the goblet bowl, you will move from cutting only wood to cutting wood and epoxy. I’ve had good luck turning the end grain and epoxy resin with 1/2" and 1/4" scrapers. Epoxy resins turn differently than wood—making a shearing cut with a scraper is easy. Center the wood in the chuck. The outside of the molded Start your cut in the center and cut toward the edge and 1epoxy won’t be concentric with the center of the wood. To up toward the rim. The epoxy is harder than most woods and compensate, turn the epoxy round on the goblet and lid. Make will dull your tool faster; it will also cut slower. Removal rates sure the epoxy for the lid is slightly larger than that of the are about one-tenth or less than that possible with wood. goblet. Next, determine the depth of the goblet bowl and drill a Aggressive cuts of 1/16" or greater will generally result in 1/2"-diameter hole to that depth. fractures and chipping.

Keep increasing 3 the diameter until all four corners of the original wood square are visible as sharp points. Stop to review the shape and refine as necessary. Make your final cuts with a freshly ground tool and take light cuts. To sand, begin at 150-grit and proceed in steps to 2000-grit To turn the outside of the bowl, a live center ensures for the epoxy. Finish 4 stability while reducing the wall thickness. After you the epoxy with a plastic polish, Novus reduce the wall thickness to about 4 mm, slow down the #2, Brasso, or red rouge. After polishing, examine the epoxy lathe speed, which will reduce vibrations. When turning the carefully to reveal small scratches, which require further pure resin, you can make cuts in either direction since the resin is isotropic (non-directional).

When finished turning epoxy, switch 5 to a 1/4" bowl gouge to turn the wood at the bottom of the goblet bowl While turning the stem, bring up the tailstock and stabilize and the stem. Sand and polish in the 6 the goblet bowl with live center. Pad the inside of the bowl same steps as the goblet inside. with layers of toilet paper. Sand to 800- or 1000-grit.

20 American Woodturner Spring 2005 Copyright 2005, 2016, American Association of Woodturners. All rights reserved. Turn the lid What else can you Except for a lip, turning the lid is similar to the goblet. This requires create with epoxy? repeated turning trials to check the diameter until obtaining a snug fit. (If I lift the lid quickly it will lift the goblet off the table, but if I lift it slowly The gallery below includes several it will not lift the goblet). Epoxy resins are much less sensitive than wood other recent designs incorporating to changes in diameter due to changes in humidity. wood and epoxy.

“Cosmos,” 6" diameter. Purpleheart After turning the inside, establish with yellow epoxy and clear blue epoxy. 2 the outside shape of the lid. Before hollowing, cut the lip in Matching the outside contours of the 1 the lid. The length of the lip shown lid with the goblet bowl requires several is 1.8 mm. trial fits.

1 “Bull’s eye,” 9 ⁄ 4" diameter. Maple and translucent red epoxy.

Using the procedures described earlier for the goblet, polish the inside 3 and outside of the lid.

To get precise 4 centering and stability to turn the finial, secure the lid in a “vacuum jam chuck” with 0.02"-thick polyethylene foam as gasket material. Photo: Art Waldinger

3 1 “Octa,” 2 ⁄ 4" x 2 ⁄ 2". Cocobolo with yellow epoxy with blue fluorescence. “I was nearly finished with this goblet when I broke the stem. The situation presented a ‘design opportunity.’ ”

Jim Rinde ([email protected]) worked professionally with epoxies before retiring. He’s a member of the Channel Island Woodturners and lives in Camarillo, California.