Reinforced Joints

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If the two mating surfaces are the same width or thickness, use a doweling jig to help drill the dowel holes. Dry assemble the adjoining parts (without glue) and mark where you want to drill the dowel holes. Align the jig with these marks, then drill the holes. (See Figures 4-5 through 4-7.)

If the two mating surfaces are a dissimilar size or shape, use dowel centers to align the holes. These centers are small metal buttons with a point on one end. First, lay out and drill dowel holes in one of the adjoining boards. Place dowel centers in these holes and press the boards together. The centers will leave

Joining Wood With Dowels

4-5 To make a dowel joint in two boards of the same size, use a dowel-ing jig to align the holes. Match up the mating surfaces of the adjoining boards. Using a sharp pcncil, draw a line across the joint and mark both boards wherever you want to install a dowel. (Don t use an awl or knife to lay out this particular joint — it will scratch the visible surfaces of the wood.)

4-6 Align the jig with a mark on one of the adjoining boards and clamp it in place. Bore a stopped hole at the mark, using the jig to guide the drill bit. Repeat for all the marks on both adjoining boards. Note: For this jig to work accurately, you must use a drill bit that is the same diameter all along its length, such as a brad-point bit. You cannot use a spade bit or a Forstner bit.

4-7 Dry assemble the joint

(without glue) to check the alignment of the dowel holes. Place dowels into the holes in one board and fit it to the other. If the holes are properly aligned, reassemble the joint with glue.


4-8 Use dowel ecnters to align dowel holes when joining boards of different widths or thicknesses. First, drill stopped holes in just one of the adjoining parts. Place the dowel centers in these holes so the points face outward. Align the adjoining parts and press them together. If the wood is very hard, you may have to rap one part or the other with a mallet to get the dowel centers to leave a visible mark.

4-9 When you take the boards apart, the dowel centers will have made indentations in the surface of the part that hasn't yet been drilled. Drill stopped holes at these marks, check the alignment of the holes, then assemble the joint with dowels and glue.

4-10 To cut glue grooves in dowels, squeeze the stock gently between the jaws of a pair of pliers Be careful not to squeeze so hard that you crush the wood fibers.

marks on the second board, showing where to drill the matching holes. (See Figures 4-8 and 4-9.)

Here are a few additional tips for making dowel joints:

■ Dowels that run perpendicular to the wood grain of the adjoining parts should not be over 3 inches long. Otherwise, they may restrict the wood movement and cause the joint to split.

■ Drill stopped dowel holes about Vie inch deeper than you actually need to. This will give the excess glue inside the hole somewhere to go.

■ When you slide a dowel into place, most of the glue is wiped off the wood surface. To keep the joint from being "starved" for glue, use dowels with grooves cut into their surfaces. These dowels are available commercially, or you can make your own. (See Figure 4-10.)

spline joints

A spline is a small board, usually just l/s to V4 inch thick, that spans the joint between two boards. The spline rests in two matching grooves, one in each of the adjoining boards. (You can also install a spline in matching rabbets or dadoes if needed.) Splines can be made of solid wood or plywood — the grain direction of the adjoining parts dictates which material is best. If you make splines from solid wood, the spline wood grain must run across the joint, tying the two adjoining boards together. (See Figure 4-11.)

Making a spline groove is no different from making an ordinary groove. Use a saw blade, a dado cutter, or a router bit to cut a groove as wide as the spline is thick. Adjust the depth of cut to about V32 inch more than half the splines width. (This allows space for excess glue.) Cut identical grooves in each of the adjoining surfaces. (See Figures 4-12 and 4-13.)

Dry assemble the joint to check the alignment of the grooves and the fit of the spline. Half the spline should fit in one groove and half in the other, with just a little side-to-side "slop." If everything checks out, spread glue on the adjoining surfaces, in the spline grooves, and on the splines. Assemble the parts.

Spline joints are especially useful for reinforcing miter joints. Depending on how a miter joint is oriented, you can run the splines either horizontally

4-11 Make splines for spline joints from solid wood or plywood, depending on the grain direction of the adjoining parts. If the wood grain runs perpendicular to the joint, as shown on the left, use solid wood. Because the wooden spline must run across the joint, its grain will be parallel to that of the adjoining members; all the parts will expand and contract together. If the wood grain runs parallel to the joint, as shown on the right, use plywood. Plywood is relatively stable, as is wood along the grain. If you make this spline from solid wood, the adjoining members will restrict its movement and the joint will soon split.

4-12 Cutting spline grooves is no different than cutting ordinary' grooves, but the grooves must be identical and they must be positioned carefully on the adjoining parts. To make sure they are, clearly mark the sides of the boards so you know which surfaces are the inside and outside, top and bottom, left and right — whichever combination applies. Cut each matching groove with like surfaces facing in the same direction. For example, when attaching edging to a tabletop, mark the top and bottom surfaces of both the tabletop and the edging. Cut a spline groove in the edges of the tabletop, keeping the bottom face turned away from the fence.

Wood Grain Direction JointingJoining Wood

Wood Grain Pérpenpicular to Joint


Wood Grmn Parallhl. td Joint

Solid Wood Spunb or vertically. (See Figures 4-14 and 4-15.) You can also have a choice of whether to cut the spline before or after you assemble the miter joint. Splined miters in which the grooves are cut after the parts have been assembled are sometimes referred to as open spline joints, since both ends of each spline are clearly visible. (See Figures 4-16 and 4-17.) The "Splined Miter Jig" shown on page 56 will hold workpieces at the proper angle to the cutter when making grooves for both open- and regular-splined miter joints.

Miter Joined Table Top Edge

4-13 Cut a matching groove in the inside faces of the edging, keeping the bottom edges turned away from the fence. When the joints are assembled with splines, the top face of the tabletop will be flush with the top edges of the edging.

Mitre Joint Jig

4-14 When making splined miter joints, you can orient the splines either horizontally or vertically. If the parts are to be joined so the faces are flush (as in a picture frame), cut the grooves so the splines will be horizontal. Mount the workpiece in a jig to hold the mitered surface flat on the worktable. Use the fence to guide the jig and workpiece across the cutter.

Spline Degree Flat Side Spline

4-15 If the parts are to be joined so the edges are flush (like the mitered sides of a small box), cut the grooves so the splines will be vertical. Use the miter gauge to guide the workpiece, holding it so the inside face is flat on the worktable. Tilt the blade or cutter 90 degrees from the mitered surface. (If the miter was cut at 45 degrees, tilt the cutter to 45 degrees — 45 + 45 = 90.) Use the fence to position the workpiece in the miter gauge.

Joiningwood Angle

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  • benjamin dreher
    How to joints for plywood?
    9 years ago
  • Francis King
    How to drill accurate holes for dowels?
    7 years ago
  • KYLE
    How to make a splined miter joint?
    7 years ago
  • sabine
    How to make wood splines?
    1 year ago

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