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1、or centuries, granite has been quar- ried along the Maine coast. Way back in the woods behind my shop, on a granite outcropping, sit a few leftover slabs 10 in. thick by 2 ft. wide by 12 ft. long. The granite faces show a series of 12-in.holes drilled 12 in. to 18 in. apart. The old- timers would ha
2、ve driven dried wood into these holes, then walked down the row pouring water onto the wood. Eventually, the granite slabs would split apart. When wood cells absorb water, they swell and expand, and not even granite can stop it.So forget about pins, glue, screws, or fancy joinery; wood will move and
3、 break apart your work if you dont follow the rules. The exact amount of wood movement depends on any combination of several factors, including the environment (the de- gree to which humidity fluctuates) and how the lumber has been sawn (see below). The amount of movement also varies among wood spec
4、ies, particularly among the hardwoods. For example, beech, hick- ory, oak, and hard maple move substantial- ly more than cherry, walnut, and butternut. Last, the type of finish you apply to a piece affects wood movement. Because light skin finishes such as wax and oil al- low greater moisture absorp
5、tion, wood that has been coated with either of them moves more than wood that has been fin- ished with deeper-penetrating sealants such as urethane and lacquer. As a professional woodworker, I cant af- ford to cut corners when it comes to wood movement. So I devote my energy to build- ing furniture
6、right the first timewhether its a chest, a case, a bed, or a table.Understanding Wood Movement Proven methods for dealing with expansion and contractionB Y C H R I S T I A N B E C K S V O O R TFGRAIN ORIENTATION DETERMINES THE AMOUNT OF MOVEMENTYou can predict how lumber will behave by looking at th
7、e growth rings. Flatsawn boards revealing long ring sections that are parallel to the pith of the log will move the greatest amount.QUARTERSAWN BOARDA quartersawn board has annual rings running perpendicular to the surface, so the board will experience far less seasonal movement and will be less lik
8、ely to cup.How wood movesFLATSAWN BOARDMost seasonal movement in a board is along the rings. With annual rings nearly parallel to the surface, flatsawn boards exhibit more seasonal movement and are prone to cupping.44F I N E W O O D W O R K I N GPhotos, except where noted: Dennis Griggs; this page:
9、Karen WalesQuartersawn boardPithFlatsawn boardSignificant movementMinimal movementFRAME-AND-PANEL CONSTRUCTION ISOLATES MOVEMENTS E P T E M B E R / O C T O B E R 2 0 0 345Drawings: Vince BabakBLANKET CHESTSYour approach to controlling wood movement will depend a lot on whether the piece is made usin
10、g slab or frame-and-panel construction. Slab construction is typical in chests, table- tops, and headboards and consists of single, wide boards or narrow boards glued up edge to edge. With solid-wood slabs, you have to worry about cross-grain movement, which can be sig- nificant with large widths. F
11、rame-and-panel construction, on the other hand, minimizes the effects of wood movement by isolating large areas (the panel) and restrict- ing movement to relatively small areas (the frame). The panel is set into grooves of the ap- propriate depth, but it is not glued in place. In- stead, this “float
12、ing” panel is free to expand and contract within the frame. SLAB CONSTRUCTION ALLOWS ENTIRE PIECE TO MOVEA blanket chest, in which the grain runs in a band around the entire box, is an ex- ample of slab construction. The depth and width of the chest remain constant, because the wood does not move le
13、ngthwise. But the wood does change in height in response to changes in humidity. The blanket chest gets slightly taller in sum- mer and shorter in winter. Because movement in the top is from front to back, the hasps of the lock dont always fit. The solution is to use quartersawn wood for the top, fi
14、le the hasp parts to increase clearance, and use a good sealing finish.GrooveOverhang varies with seasonal movement.Extra space allows for expansion.Bottom floats in the grooves.BOTTOM FLOATS IN GROOVESGrooves are cut into the four sides of the chest to hold the bottom. The bottom is sized so that t
15、heres enough space in the grooves to allow for seasonal movement.Seasonal expansion and contraction occurs across the grain of a board.Grain directionGrain directionWith the grain running in the same direction all the way around the case, all four sides will move in the same direction.Frame- and-pan
16、el construction allows the panel to move within the stable frame.The width of a frame is relatively stable.The width of a slab can vary greatly with seasonal changes in humidity.46F I N E W O O D W O R K I N GBREADBOARD CONSTRUCTION KEEPS TABLETOPS FLATBreadboard ends are added to tabletops to help prevent the top from warping or cup- ping. But they must be attached so as to al- low the top to expand and contract. The preferred method for making bread- boards is a single tongue
