Box Joint

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The box joint is used in the same situations as the dovetail—assembling boxes, assembling drawers, and casework. (I used it on my bit case— see the chapter "Bits.") It has pretty fair mechanical strength, but what it does is generate long-grain-to-long-grain glue area (the son of glue area that yields the strongest bonding).

The box joint is a machine-cut one (as opposed to something like a dovetail, which, although it is easily machinc-cut. is nonetheless regarded generally as a hand-cut joint).

A lot of woodworkers think the only way to cut the slots is on a table saw with a dado cutter. Make a litde jig to attach to the miter gauge, and go to town. Well. I'm here to tell you the table-mounted router does a cleaner job in the same amount of time. You make a little sledlike jig, but once that's done, it is strictly repetitive cutting.

The router bit yields a cut that's not only square but also Oat-bottomed and clean all around. The cuts are fast, too. If your router has enough moxie, you should be able to cut the full depth in one pass.

(You may know this joint as a finger joint. We're using that name for an interlocking edge-to-edge joint that's cut with a special bit. See "Special Joinery Bits" on page 263 for a rundown on the finger-joint bit.)

THE BOX JOINTING JIG

The box-jointing jig is simply an adaptation of the one you'd make and attach to your table saw's miter gauge. It's a specialized miter gauge for your router table, one that's guided by a couple of fences rather than a slot in the table. (It would be easy enough to build it like the sled—see the chapter "Router Table Accessories"—so it would be guided by the edge of the table. But that would eliminate the very fine adjustment that's possible

A dado cutter cuts slots quickly but tends to leave an uneven, ridged bottom. The router-cut slot, on the other hand, is square and clean all around. Which would you prefer for your box joints?

when you use two fences to position and guide the jig, as you'll see.)

The critical element of any box-jointing jig is the key and its position relative to the bit. The jig itself can be any old scrappy thing, so long as the key is properly sized and positioned.

Before making the jig, decide how wide and deep the slots between the fingers will be. The slots and the fingers are the same size, by the way. The router bit establishes the width of the slot, and thus the width of the fingers. The depth should be governed by the thickness of the working stock. If you arc joining >Vinch-thick parts, the slots and fingers need to be Y* inch deep. If it's ^j-inch stock, then the depth is Yi inch.

My advice is to make a separate jig for each different size of finger you make. While you probably can get acceptable results cutting Yi-inch-deep slots on a jig set up for a Winch depth of cut, splintering or "blowout" is likely to occur as the bit exits a cut. The backing has been cut away.

To make the jig, select suitable materials from your scrap pile. I used plywood because it's stable, and because we've always got odd scraps around. The one part that's hardwood is the key. It is subjected to a lot of wear, and if it is too soft, it will wear and throw off the accuracy of your cuts. The joints won't join, in other words. The key should be replaced if it gets worn, dented, or deformed.

1. Cut the pans to the sizes specified by the Cutting List. The handle is reduced in size as it is shaped, but you'll need the extra size to cut the shape.

Poliakoff Peintre

A dado cutter cuts slots quickly but tends to leave an uneven, ridged bottom. The router-cut slot, on the other hand, is square and clean all around. Which would you prefer for your box joints?

Think of this as a square-cut through dovetail.

2. The back ultimately has two slots cut in it, one for the cutter, the other for the key. Cut only the key slot at this time.

Chuck the straight bit you'll be using in the table-mounted router, and set it for the desired cutting height. Set the fence to position the notch, as shown in Box-Jointing Jig. Cut the notch. Stand the back on edge, and back it up with a sled or scrap of two-by stock. Guide both the scrap and its backup along the fence.

3. Next, fashion the key from the hardwood, making it the same width and thickness as the desired slot. Test fit the key stock in the key slot: it should fit snugly. If it rattles or has any play, rip a new key, making it a little fatter. If it's too thick, plane it until it fits properly. Finally, crosscut the key stock into two pieces, each about 5 inches long.

4. Assemble the base, support, and back. Glue the support to the base, then glue the back in place. Drill pilot holes and drive two drywall screws through the base into the back. Be sure you position the screws toward the outer edges, so the bi won't hit them.

5. Make the handle. On the handle blank, scribe two lines, each I inch in from an edge and parallel to it, as shown in Box-Jointing Jig. The lines should be along adjacent sides so that they cross, forming a 1-inch square. Drill a '/a-inch-diametcr hole in the center of that square. This is the pivot hole for routing the arc profile.

Cobble an overarm pivot. (Sec "Overarm Pivot" on page 170.) 1 nailed a scrap of '/2-inch plywood atop a scrap of y^inch plywood so that the top piece would overlap the

Jointing With Router

a simple &ox-jointing jig routing handle arc on tue router table a simple &ox-jointing jig routing handle arc on tue router table

CUTTING LIST

Piece

Number

Thickness

Width

Length

Material

Bast-

1

W

8"

8"

Plywood

Support

1

vr

8"

4VV'

Plywood

Back

1

w

8"

5"

Plywood

Handle*

1

w

6"

6"

Plywood

Key

1

Vi"

10"

Hardwood

Hardware

4 pes. #6 X IY«" drywall screws

•Start with a piecc this sire; cutting the profile reduces its size.

Different Router Cuts Make Box
The typical box-jointingjig is fairly job-specific. The jig at right cuts '/¡-inch slots in Y+inch stock. Using a smaller bit requires a different jig. The one at left cuts dovetails that join boards end to end.

workpicce. I drilled a hole in the Winch plywood and turned a 6-32 machine screw through it into the pivot hole in the workpiece. Clamp the overarm to the tabletop so the pivot is 4K inches from the edge (not the center) of die bit.

To cut the arc, raise the bit about 'A inch. Switch on the router, and swing the workpiece on the pivot, feeding it into the bit. After sweeping forward and back, raise another lA inch or so, and make another sweep. Repeat the process until the bit cuts through the workpiece.

While you could use the same general procedure to rout a hand hole, 1 drilled a series of overlapping holes with a 1-inch Forstner bit. Then I routed the curved handle edge, as well as the hand-hole edges, with a Winch round-over bit.

Finally, cut along the two lines you marked first on the handle blank, reducing it to its final size.

6. Attach the handle to the jig with glue and a couple of drywall screws. Be sure to position the screws where they won't be hit by the bit.

7. To rout the cutting slot, insert the key in its slot in the back. Set the second piece of key stock next to it. For this step, both keys should be long enough to extend beyond the base's front edge.

Now set the jig on the router table, with the keys between the bit and the fence. The idea is to use the loose key as a spacer to establish the thickness of the finger that will be left between the cutting slot and the already-cut key slot. Bring the fence against the edge of the jig, and slowly turn the bit by hand to ensure you are accurately positioning the jig and fence. Clamp the fence.

Use the key to set the height of

Finger Joint Jig Plans

box-joint jig witm interchangeable. backer hoot dovetail slot in back.

box-joint jig witm interchangeable. backer hoot dovetail slot in back.

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  • steffen
    How to make box joints with a router plans?
    7 years ago

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