During my last day in the U.K. last week, we crammed in as much as possible. It was like a hot dog eating contest. But instead of cased meats, we were consuming culture. And instead of a stomach ache, I became consumed by ennui (just kidding, I got Covid).
One of the last stops before Paddington Station was at Robert Young Antiques in London. I’ll make any excuse to stop here. Everything in the store is wonderful. Of course, we were on the lookout for stick chairs. And we found three winners.
In the front room was this Welsh comb-back with unusual arms. Look how far forward the hands are to the seat. That is unusual. The seat is shallow – 12” at most. But you would be surprised how comfortable these shallow chairs can be.
Also of note: the oval side stretchers. These are a fairly Welsh characteristic as far as I can tell. And they are one that I have embraced with my chairs lately.
And, of course, the seat is not saddled.
The second chair was also Welsh and what we call a root-back chair, likely an 18th-century example.
These chairs have a wildness to them that I always love. This chair is twisted to the right – almost like a corner chair. It’s difficult to see it in the photos. Definitely not symmetrical (symmetry can be boring, darling).
As always, I love to see three-leggers out in the wild. And the little “heart” on the arm indicates it’s sold. Awww. Someone else loves it, too.
The third chair is wild. Look at the negative space between the front post and the back sticks. That is nuts. Also, check out the back sticks themselves. They are fanned out dramatically. That’s a bit unusual for a folk chair. But what is even wilder is that the sticks are hexagonal/octagonal. And they carry their shape above the arm.
The whole chair is fascinating. The legs are so diminutive compared to the massive seat. Even after a few days of sitting with this chair, I don’t quite have it figured out.
The following is excerpted from the third edition of “Make a Chair from a Tree,” by Jennie Alexander.
This third edition of Alexander’s “MACFAT” is the culmination of a lifetime’s work on post-and-rung chairs, covering in detail every step of the green-wood chairmaking process – from splitting and riving parts to making graceful cuts with a drawknife and spokeshave, to brace-and-bit boring for the solid joinery, to hickory-bark seat weaving.
With the help of Larry Barrett, one of her devoted students, she worked on this new version of the book until just weeks before her 2018 death. Larry polished Jennie’s final manuscript, then built a chair in Jennie’s shop using her techniques and tools as we took many of the photographs for this book. Nathaniel Krause (another of Jennie’s devoted students), wove the hickory seat for this book. Longtime friend and collaborator Peter Follansbee helped to edit the text into the intensely technical (but easy to understand) and personal (but not maudlin) words that ended up in this third edition.
The simple post-and-rung chair we suggest presents differing structures and aesthetics below and above the seat. The seat divides two worlds. Above the seat, all curves; below, sticks. Beneath we see a structure of horizontal, straight rungs cornered by four straight, vertical posts. The straight-line geometric understructure gets our bottom out of the mud and takes the weight off our feet. Above the seat we find flared and curved back posts and slats of different lengths, inclined in different planes, that embrace the thoracic (top) and lumbar (middle) spine. Over the years I have cooked up some dimensions and shapes for the slats that I find comfortable, and these are described below.
Make the Slats Making slats calls for a combination of craft and patience. Your first attempt may be only practice. If you work the larger top slat first, and something goes wrong, you can salvage it as the smaller bottom slat.
In Chapter 5 you rived two or more rough slat blanks from the log, each slightly pie-shaped in cross section and about 1/2″ thick, by 4-1/2″ to 5″ wide, and 18″ long. They have straight, long fibers with their ray plane running straight down within the blank from top to bottom. Reject any with fiber irregularity. Slats will have a stressful career.
Examine the end of the rough slat. The rays should be easily visible. The thickness of the finished slat must be parallel to the visible rays, or at least as close as possible. Keep this in mind as you begin to reduce the rough blank to final thickness. Use a sharp drawknife to clean up both sides of the riven blank. Working the riven slat blanks down, you can easily remove material from the high spots. The relatively broad surfaces of the slats are an ideal place for a drawknife with a slightly curved, rather than flat blade. Both ends of the drawknife’s blade come up out of the wood, avoiding splitting cuts. As the slat gets thinner, it might flex under the knife. For additional support at the shaving horse, prop a 1″ x 3″ or 1″ x 4″ under the crossbar and set the slat on that.
Initial dressing of the slat with the drawknife.
First, flatten one side of the rough slat so it will not rock on the support. Then drawknife the other side down to about 3/16″ thick. To avoid tear-out, at some point you will likely need to switch from the drawknife to a spokeshave. Spokeshave the slat to exact thickness. Slide the slat up and down between your thumb and forefinger to gauge the thickness. As the blank nears completion, bend it slightly over your knee or flex it under the shaving horse’s crossbar. Thick areas will resist bending and thin areas will bend abruptly. Continue until each slat has a consistent thickness everywhere. Test the final slat thickness by inserting its corners into the slat mortises. Keep the post mortises’ edges fresh and true. You worked carefully to get them. Because you can’t insert the slat blanks completely into the mortises, a slightly too-thick slat is OK at this point.
The seat slats can take a variety of shapes. Over the years, I’ve come to prefer gentle curves on the top and bottom over the straight lines of some earlier examples. (Measurements are approximate.)
Slat Length In Chapter 9 we briefly introduced adjustable test slats made using lengths of flexible plastic, held together with binder clips so that they could be adjusted in length to give a preview of what the chair would look like. Now that the chair is assembled, re-insert and re-adjust these test slats to determine the final length of the actual slats.
Setting test slats in the mortises to check the curve and the actual length.
The slats’ backward curves are one of the chair’s most dramatic and comforting elements. It is tempting to make slats too long and curve back too much. Remember the slats’ first task is to meet and support the curved back. Excessive aesthetics abandon back support. One way to avoid this is to make sure the slats slide easily into their mortises without a “reverse” bend. When the actual slats are inserted into the chair each one must flow smoothly into its mortise. These test slats provide the correct overall length for the actual slats. The height of each test slat equals the mortise height. They can now be used to mark the initial layout lines on the slat blanks.
Drawing the curved line on the slat with drawing bow.
Lay out the top slat first. Align the test slats in line with the slat blank’s long fibers. Shift the test slat on the slat blank to find the most pleasing location. Then lightly trace around the ends of the test slat. Using a pencil, transfer the top and bottom of each slat tenon to the slat blank.
Connect the top and bottom of the two tenons with a straightedge and light pencil lines. Find the mid-point of the slat length and strike a perpendicular line at this midpoint. You are now ready to create a symmetrical slat design extending from the midpoint back to the tenons on each side.
Shaping the slat with a spokeshave. Some shaving horses might open wide enough to hold a slat in this orientation. Otherwise use a vise, a clamp or double bench clamp, as shown here.
Many variations can be found in vernacular chairs. I find smooth curves from one end to the other to be most pleasing, and that is what is described here. At the midpoint, make a mark 1/2″ below the lower parallel line for both the top and bottom slat, and make another mark above the upper parallel line, 7/8″ for the top slat and 5/8″ for the bottom slat.
Bend a flexible batten so that it touches the mortise entry points at each end and touches the marks at the midpoint. Trace the batten onto the slat blank. You may need a third hand to do this.
Lock the slat in a face vise or double bench clamp. Shave it to shape with drawknife and spokeshave. Do not round the top and bottom edges. The slats will enter the mortise with square edges. Then the exposed edges will be rounded after assembly.
When you are done with the top slat, proceed in the same manner with the bottom slat.
Once you’re sure of the slat’s length, trim it. A wooden bench hook helps to hold the slat for this task.
Next, without attempting to bend either slat, insert each slat into the slat mortises, one end at a time. You must be able to insert each slat to its complete depth. Some minor spokeshave work will likely be needed, both in final thickness (thin the back) and in slat height at the point of entry. A thin slat, though flexible, needs considerable bending in order to pop it into the post mortises. There are several ways of getting the slats to bend. The simplest is to put them in the steam box just like you did the back posts. One concern with this method is the slat will absorb enough moisture to swell in thickness and be a difficult fit in the mortises. We’ve used this method, but care must be taken to prevent damage. Forcing a slightly too-thick slat into the mortises can damage or even split the mortised post.
It’s the heat that makes the wood pliable; the steam is just a delivery system for getting the heat into the wood’s fibers. You can try the slats in the kiln until they are hot enough to be pliable. That can be even more perilous than the steaming method. Not hot enough and they won’t bend, too hot and they scorch, or worse, burn.
Pour boiling water over the towel-wrapped slat. Get the whole thing well-soaked.
We struck on a compromise approach. Wrap a towel around the slat, between the tenons. Ladle boiling water over the towel, allowing it to sit a while so the wood absorbs the moisture (and heat). Try to keep the tenons dry. Get the towel wet all over; keep it wet and hot.
Unwrap the slat and limber it by bending it under the crossbar of your shaving horse, or across your knee. If it still feels stiff, repeat the towel and boiling water step.
Working quickly, bend the slat over your knee to get a feel for its flexibility. Watch for any uneven bending signaling a thin or thick spot. Work the whole length of the slat.
Once it’s flexible enough, install it in the chair. All this pushing and shoving and overbending of the slat can cause damage to the slat mortises, particularly because the mortises are close to the flat surface of the post. To prevent splitting the mortise open, apply a clamp to the post at each mortise location before inserting the slats. Straddle the chair backward. Insert one end of the slat all the way into its mortise. Press the middle of the slat outward while pulling the other tenoned end in; you’re over-bending the slat to be able to slip it into place. When you line up the second tenon and its mortise, then pull the middle back toward you to drive the second tenoned end into the mortise. When it goes well, it’s a very exciting moment. Then do the next slat.
Now the second tenon has entered its mortise, and it’s a matter of adjusting the slat by pulling it in.
Once slats are inserted, stand behind the chair and observe the slats carefully. You should see regular, smooth curves that complement each other. Variation in slat thickness will cause slat kinks. Sit in a temporary seat and lean back carefully. Do the slats support your back? While the slats are still warm you will be able to remove them and make adjustments if needed. You might need to re-soak them with the towel to get them out. Then re-heat and re-insert.
Stand behind the chair to check (and admire) the curve of the back slats.
I see no need for glue. Slats are the thinnest parts of the chair, and most subject to abuse. If one breaks, it will be easier to remove and replace if the slats are not glued.
Pegs If you sit in the chair before the slats are pegged, the slats can give way, pop out of the chair, and you will be on the floor. Slats must be pegged to make sure they stay in place. I have used single pegs in the slats, but I think two is best. Two pegs will keep the slat from pivoting as you lean on it.
Mark the peg locations. If yours are different from the specs here, just be sure to stay away from the edges of the slats (vertically in the post) and the ends of the slats (near the inside edge of the post).
The distance between the peg hole and the end of the slat is crucial. I’ve heard it called the “relish.” You need as much relish as possible to avoid splitting the end of the slat. I find locating the pegs as close to the inside edge of the post to work best. This will keep the peg holes as far as possible from the slat’s end. Large pegs are unsightly. I now make pegs that are 3/16″ in diameter and locate them 1/4″ from the inside edge of the post.
Use a cleaver (or hacking knife) to rive pegs. Just like the earlier riving, split in half, and half again and so on.
I make long, very slightly tapered pegs and bore the peg holes completely through the post. Before boring the peg holes, you may want to pull the posts together again with a twisted cord so the tenons do not move while boring the peg holes. Use a 3/16″ brad-point drill bit. When boring all the way through the post, be careful to block up the back of the post to prevent tear-out.
Jam the chair against the bench and bore the peg holes. The tape is the depth stop.
Pegs are not home dowels – rive them from straight-grain hardwood. I use white oak or hickory if I have it. I shave octagonal pegs with the drawknife and shaving horse.
When driving slat pegs in blind holes, back the post up to keep things supported.
Another option is to bore blind holes and make pegs using a dowel plate. Using an eggbeater drill, carefully bore the peg holes. You can add tape to the bit to function as a depth stop. Then drive the rough-split peg stock through a dowel plate to size it to match the drilled hole.
Size the pegs by hammering them through the dowel plate.
To install the pegs, apply a thin coat of glue. For through-pegs, tap cautiously until they fill both entrance and exit holes. For blind holes, listen to the sound as you drive the peg. It will deaden as the peg bottoms out in the hole.
If some glue remains on the post surface, let it dry thoroughly and then flick it off with a knife. Do not attempt to dilute and wipe off. Then carefully trim the pegs with a flush-cutting saw. Do not mar the post. A paring chisel finishes the task. If necessary, finish with a spokeshave or scraper.
Finishing the Slats You have left the exposed top and bottom edges of the slat square until now. Leave the edges square where they exit the post mortises, but spokeshave all edges; front and back, top and bottom, into a comfortable curve. The chair will most often be picked up under one of the slats. These edges will be most comfortable if simply rounded. The front edges of the tops may be very slightly chamfered and then rounded to make the chair appear even lighter and more attractive.
Chamfer the top of the slat with a spokeshave.
During my years of teaching I have found that slats were the most common failure. Usually it was top slats versus slouchers. Often, the rush to finish up contributed. In your shop there is always another day. Rushing to complete invites failure. Beds also have their benefits.
Editor’s note: Our Mind Upon Mind series is a nod to a 1937 Chips from the Chisel column (also featured in “Honest Labour: The Charles H. Hayward Years”), in which Hayward wrote, “The influence of mind upon mind is extraordinary.” The idea being there’s often room for improvement.To that end, we’ve asked you what else you have thought of, tried out and improved upon after building projects from our books.
Send us your own ideas! Email kara@lostartpress.com. You can read more about the submission process here.
Today’s pick is from Todd Touris, in Canadice, New York. Thanks, Todd!
— Kara Gebhart Uhl
I recently pruned back a couple of heartnut (Japanese walnut) trees that were taking over our garden area. After studying the cut logs, which were only about 5” in diameter at their widest, I decided there was enough material for a chair. Because I didn’t want to use a different wood to make the solid seat required for a stick chair, I decided to build a ladderback roughly based on the three-slat design described in Chapter 20 of “Backwoods Chairmakers.”
Carefully riving the parts, I ended up with some interesting pieces that I was able to rough into posts and rungs with a drawknife. I cut several thin slats from the widest portion of the log with a bandsaw. The wood was still very wet and I was able to bend it on the form without steaming.
Because of the irregular shape of the posts and rungs, I had to do a few things to ensure the mortise and tenons would line up when assembled. First, I cut the tenons using the laser method as described in the “The Stick Chair Book.”
Notice the significant bend of the rung.
Next, because I kept the natural curves of the tree for the posts (no steam bending), I had to figure out a way to get the mortises oriented correctly. Precise angles and use of a bevel were not an option.
After getting a back post orientation that looked good, I clamped the posts to the bench and decided on the best point for the rear seat rung. I then drilled the two mortises for the rung using a bit extender.
I then measured down to the bottom back rung and drilled the mortise for that rung. I repeated the process for the front posts. I then made four square and straight dummy rungs to the correct lengths and dry assembled the front and back post assemblies. I cut two scrap boards to a length that would give the desired depth and orientation of the front to back. Because of the curves of the posts, these lengths were not the same and I had to fiddle with them until I got what I wanted.
Finally, I clamped the front and back assemblies together with the board spacers, marked the remaining mortise locations and drilled them using the bit extender method.
Note, I originally intended this to be an arm chair, thus the longer length of the front posts. Unfortunately, my butt wasn’t going to allow that.
After that, the rest of the construction was pretty conventional. I refined the shape of the posts and rungs. I kiln dried the rungs to bone dry. I cut the slat mortises. I shaped and refined the slats. The assembly went smoothly using hide glue.
I would have liked to have harvested hickory bark for the seat, but instead I used rattan splint, which is sustainably harvested, so no trees were killed in the making of this chair.
The chair is finished with blond shellac and a top coat of soft wax.
From the beginning of this project, I thought this chair had a good chance of ending up as firewood. So, I’m quite pleased with the outcome. Using the wood’s natural curves presented both aesthetic and construction challenges. Perhaps some of the techniques I described could help and encourage others to make a ladderback “hedge” chair.
Yes, I do overcut my pins when cutting half-blind dovetails. (An answer to a question I am sometimes asked.)
Just a gentle reminder – or announcement for those of you who are new here – that six Saturdays a year, we hold “Open Wire” hours from 8 a.m.-5 pm. That’s the place to post any and all woodworking questions to get them answered by us and by your fellow readers. I’m afraid we don’t have time to answer questions that come in via other channels – if we did that, it would leave no time for editing and writing, much less woodworking!
So if you send a question via email (to any of my emails…I got woodworking questions at more than one email today!), Facebook, Instagram etc., you’ll get my standard response to please ask at our next Open Wire – and check out past Open Wires for lots of answers to lots of good questions. (And odds are good that if you have a question, someone else has or has had the same question – so the Q&A helps everyone.)
The next Open Wire is on August 9, starting at 8 a.m. Eastern. (Then October 25 and December 13.)
The following is excerpted from “Shaker Inspiration” by Christian Becksvoort.
Not too many woodworkers can claim five decades of business success, but Becksvoort is among them. In “Shaker Inspiration,” he shares not only his woodworking knowledge and some of his best professional techniques for producing top-quality work, but also the business advice that helped him establish and sustain his long career in a one-man shop. Plus, he shares measured drawings for 13 of his own well-known furniture designs and seven Shaker pieces that he’s reproduced.
Before starting any craft or trade, it’s essential to know the material you plan to work with. Most of us know the rudimentary properties of wood: It’s a renewable resource; it can be soft like pine or poplar, or hard like maple and oak; it splits with the grain, but not across it; no two pieces are alike; it can twist, warp and bow. That, however, is just the beginning. To really know your material, you’ve got to become aware of the nuances. I know I’ve covered this in several Fine Woodworking articles, and in “With the Grain: A Craftsman’s Guide to Understanding Wood” (Lost Art Press, 2015), but it definitely demands a re-hash.
So let’s jump right into Wood Technology 101. Don’t roll your eyes if this seems too elementary. Everybody has to start somewhere, so bear with me. I remember the first project I built in high school. We were taught the use of hand tools (and were tested), power tools (tested), basic joinery (tested), safety (tested) and finishing. My first big project was a 2′-square plant table. I built it to withstand anything. It was glued, screwed and tattooed. A Christmas present for my mom, she put it in the window, right over a hot air vent. Within a week the top cracked down the middle. I asked my shop teacher what I’d done wrong, and he said, “You didn’t let the wood move.” Huh? It wasn’t until I took a wood technology course years later that it all made sense. We’ll get to that shortly.
1-1A. Northern white cedar (Thuja occidentalis) cross-section photomicrograph. Coniferous woods (gymnosperms) are older and simpler in structure than angiosperms (hardwoods), and are comprised mostly of tracheids, with no vessels (they are nonporous).1-1B. White pine (Pinus strobus) cross-section photomicrograph showing tracheids and three large resin canals.
Trees are divided into two groupsscientifically: gymnosperms and angiosperms. Gymnosperms are the conifers. They are the older of the two groups, more simple in structure, have uncovered seeds and generally have needles that stay on year-round (except some species, including tamaracks). Commercially, this group is called “softwoods,” although not all conifers have soft wood, yellow pine being a prime example. Conifers have only tracheids and parenchyma cells. However, they have no vessels, so they are called non-porous.
1-2A. Red oak (Quercus rubra) cross-section photomicrograph. Angiosperms (hardwoods) are more complex than gymnosperms, and have vessels. They are referred to as porous woods. The oaks are ring-porous, showing a distinction between early wood and late wood.1-2B. Red maple (Acer rubrum) cross-section photomicrograph. Maple is a diffuse-porous wood, showing little distinction between early and late wood.
Angiosperms made a more recent appearance on the planet, and are structurally more complex, with vessels, tracheids, parenchyma and other specialized cells. They are porous and have enclosed seeds, broad leaves that usually fall in the winter (with exceptions including holly and various tropical woods) and have a greater number of species. Commercially these are the “hardwoods,” although this is misleading, because angiosperms include trees such as poplar, basswood and even balsa. Of the roughly 1,000 native North American woods, only about 30 conifers and roughly 80 deciduous species are used commercially in any quantity. This huge selection of native woods offers a variety of colors, textures, smells, grain patterns and uses. I would strongly urge woodworkers to “go native,” as opposed to importing exotics and hastening the destruction of the rainforest. I mean, how can you beat the purple-brown of freshly cut walnut, the dark red of aged cherry, the smell of sassafras or the lace pattern of quartersawn sycamore? Native woods are often local, more easily obtained, and less expensive.
1-3. Aged black cherry (Prunus serotina). Cherry is extremely photo-reactive, turning from pale pink to rich brown in a matter of weeks.
Let’s take a look at wood anatomy. Figure 1-4 shows the basics. From the outside is the bark, beneath which lies the cambium layer, the layer of lateral growth. It consists of the phloem, which forms the bark toward the outside, and the xylem, which produces a new growth ring of wood each year. The first cells produced each spring are typically larger (best seen in ring-porous woods such as oak and ash), and make up the early wood, while those produced later in the season tend to be smaller and are referred to as late wood. The outer portion of the tree trunk constitutes the sapwood, which is made up mostly of living cells used to transport water and minerals to the leaves and branches, and move sugar from the leaves to the cells and roots. When a sapwood ring dies, it turns into heartwood. This happens every year, but at different stages and on a different time frame for each species. The amount of sapwood also varies greatly in species, from less than five rings in catalpa, black locust and chestnut, to maybe a dozen in cherry and walnut, and to 40-50 in the maples, while it may take close to a century for tupelo and persimmon to form heartwood.
1-4. Typical hardwood end-grain cross section. JOHN HARTMAN ILLUSTRATION.
Heartwood cells are dead, and often a different color than sapwood. This is due to a collection of extractives such as tannins, lignin, gums, fatty acids, waxes and volatile organic compounds deposited in the cells. These give the heartwood its distinctive color, smell and decay-resistance (or lack thereof).
At the center of the tree is the pith, a soft, spongy material formed behind the apical meristem. The apical meristem (not shown) is the “growing point” at the leader at the top of the tree and the ends of branches that give the tree height and the branches length. To put it more simply, the apical meristem grows the tree taller, while the cambium layer grows the tree wider.
Emanating radially from the pith to the cambium are ray cells, used in lateral transport of nutrients. These play a big part in the stability of quartersawn wood.
Wood Movement I don’t want to spend too much time on what’s obvious to many of us: crooks, bows, warp, spalting, figured grain, burls and reaction wood. Check out “With the Grain” if you want to explore any of these terms a bit further. Let’s just jump into what’s really important: wood movement.
Wood movement is a major obstacle for many beginning and even intermediate woodworkers. The reason is that wood is an anisotropic material. That means that wood has different physical properties along different directions. As mentioned previously, it splits easily along its length but not across the grain. It has tremendous loadbearing capacity along its length (with the grain), but dents relatively easily across the grain. Figure 1-5 shows the amount of shrinkage that occurs in a red oak, from green (just less than 30-percent moisture content (MC)) to oven-dry (0-percent MC). Tangential shrinkage (think flat-sawn boards) is 8.6 percent, while radial shrinkage (quartersawn lumber) is about 4 percent, or roughly half. What’s going on to cause such difference? It’s mostly the ray cells (although the difference in early wood and late wood structure also plays a part), emanating from the center of the tree to the outside; the ray cells act like rebar in concrete. They actually hold the wood cells tightly in place and thereby reduce the amount of shrinkage. Now look at the bottom line in Figure 1-5, longitudinal shrinkage. It’s barely visible. Generally speaking, longitudinal shrinkage is about 0.1 percent, and is generally ignored.
1-5. Shrinkage vs. moisture content of red oak. (Hoadley, R. Bruce, “Understanding Wood – A Craftsman’s Guide to Wood Technology.” Newtown, Conn.: The Taunton Press, 1980.)
Let’s put that graph into perspective. Suppose you have a red oak board that’s 12″ wide (30.5cm) and 100″ long (just more than 8′, or 2.5m). If it is perfectly flat-sawn, it will shrink 1.1″ (2.8cm), or just less than 9 percent, in width from the time it is sawn from a green log, until it is dried down to 0-percent MC. That’s quite a sizable amount. If that same red oak board were perfectly quartersawn, it would shrink only a smidgen over 1/2″ (1.3cm), or 4 percent. Either of those boards, flat-sawn or quartersawn, starting at 100″ (2.5m), will shrink only about one-tenth of one inch (.25cm) in length. That’s next to nothing in comparison, and virtually ignorable. So as a wooden rule of thumb, we say that wood moves half as much radially as it does tangentially, and doesn’t change in length.
Think of wood much like an accordion that changes in width, but not in length. That’s because the cell walls act like sponges, absorbing moisture when the humidity is high, and releasing it when the air dries out. It’s obvious that water is at the root of the problem. Eliminate changing moisture and you eliminate wood movement. So you’ve got a few options when working with solid wood. If you live in a museum where the temperature and humidity are constant year-round, movement is not an issue. You can encase the wood in plastic, or a 100-percent impermeable material and prevent moisture exchange. Or you can do what woodworkers have been doing for thousands of years: You can learn to deal with it.
Backtracking just a little, let me say a bit more about moisture content. Green wood can have from 45 percent of its weight as water (white ash, for example), to more than 200 percent of its weight in water (some cedars, sugar pine and redwood). That’s a lot of water. Much of the water is in the cell cavities. This free water doesn’t affect the shrinkage, only the weight. At about 30-percent MC, the free water has evaporated, and what remains is bound water, inside the cell walls. This is the fiber saturation point. Bound water is harder to eliminate, because it is trapped in the cell walls and it takes a fair amount of energy to drive that water out. That energy can come from either sunshine and wind, or gas, oil or electricity when kiln drying. Once bound water begins to leave the cell walls, they start to shrink. Likewise, the entire wood mass begins to shrink. Sort of like a sponge, more water causes the cell walls to expand, while decreasing water causes the walls to shrink.
1 Per 1 percent change in moisture content, based on dimension at 10 percent moisture content and a straight-line relationship between moisture content at which shrinkage starts and total shrinkage. (Shrinkage assumed to start at 30 percent for all species except those indicated by footnote 2.) 2 Shrinkage assumed to start at 22 percent moisture content.
Air drying will usually bring the MC down to the neighborhood of 12 percent, depending on which part of the country or world you are in, while kiln drying aims for about 6-percent MC. Unfortunately, the wood doesn’t stay at those levels, but is at the whim of the weather. Warm summer air holds more moisture so the wood swells, while colder winter air holds much less water so the wood shrinks. Forced hot air heat has even less moisture, and can bring the moisture down to kiln-dried levels. In essence, wood is always play-ing “catch-up” to the current weather conditions, trying to maintain equilibrium with the moisture in the surrounding air.
Don’t panic over the amount of initial shrinkage from green to oven-dry. For a piece of finished furniture inside a home or office, the maximum range of MC is between 6 percent and 14 percent. That cuts the wood movement down considerably, but not enough to ignore. It’s still a major issue when constructing solid-wood furniture, but it’s manageable, and managing wood movement is what separates antiques from landfill fodder.
Let’s take the problem of wood movement head-on. Here is what you’ll need: First, make yourself a copy of Figure 1-6, “Dimensional Change Coefficients,” and keep it in your shop. Laminate it so it will last for years. Alternatively, you can visit the Forest Products lab website (www.fpl.fs.fed.us) and look up the “Wood Handbook: Wood as an Engineering Material.” Lee Valley Tools has a small paper “Wood Movement Reference Guide” that allows you to dial in 75 different woods and check their radial and tangential change coefficients. Highlight the woods you use most often, or memorize their values. Second, you’ll need a moisture meter. This is a must have item for the serious woodworker. I owned one before I had a table saw. You can get a digital pin-style meter at a home supply store for $30 to $40. Top-of-the-line electromagnetic wave meters can run in the neighborhood of $500, but the cheaper ones will work just fine. Finally you’ll need a calculator.
1-7. Dial caliper showing .105 gap over drawer. Use the formula above to determine and measure the ideal expansion gap.
This isn’t rocket science, just a simple calculation. Here is what it consists of: the width of the piece in inches or centimeters, multiplied by the current MC, and the expected change as a whole number (how far from the maximum MC off 14 percent expansion, or the minimum MC of 6 percent for shrinkage), multiplied by the Dimensional Change Coefficient for the species you’re working with, and whether it’s flat-sawn (Ct or tangential) or quartersawn (Cr, radial). Because not all boards are 100-percent flat-sawn or quartersawn, you can pick a number in between these values. A good guess works, although I always try to err on the side of a more conservative value, just to be safe.
For example, I’m making a cherry drawer 6″ (15.24cm) high, in midwinter, with wood that has an MC of 7 percent. It’s mostly flat-sawn. Worst case scenario, it will absorb moisture next year and reach a max of 14 percent. That’s a 7-percent change. Working from Figure 1-6, the coefficient for flat-sawn (tangential) cherry is .0025. On my trusty calculator, I multiply 6 (width) x 7 (change in MC) x .0025, which equals .105″, or just more than 1/10″ (2.7mm). With a dial caliper I don’t even have to convert to a fraction; I just set the dial to .105 (or 2.7mm), and make my drawer front that much smaller than the opening.
1-8. Tool handles of various native hardwoods. Dovetail saw with tiger maple handle, D-8 with apple handle, brace with cherry handle, three awls with lilac, dogwood and plum handles, hornbeam chisel, walnut chisel and live oak and ash mallet.
Fitting that same drawer in midsummer, when the wood has an MC of 10 percent (14 percent max minus 10 percent current equals 4 percent), the equation looks like this: 6 x 4 x .0025 = .06, or <1/16″ (1.5mm). In this case, the drawer can be a mite taller.
Wood movement won’t go away if you ignore it. It’s something I take very seriously. Every time I fit drawers, doors and backs, make tabletops or do any sort of cross-grain construction, I reach for the moisture meter and the calculator. It only takes a few minutes, and will prevent serious future headaches. It keeps you and your customers happy. If you know what you’re doing, knock on wood, and follow these simple calculations, you’ll never have a piece returned for a stuck drawer or split case side.
