Box Joint Jig

I first started making box joints for my workdesk drawers and since I had seen on The Router Workshop, a PBS program, box joints being cut on the router table, I used the router for mine. When I made my workdesk my shop was a very small 9' by 12' room in our house which really did not have room for a dedicated router station, thankfully my BT3000 Ryobi tablesaw had the option to hang a router under it. For my prototype jig I took a small piece of plywood, glued a square stick to it, and drilled a 3/8" hole centered 1/4" away from the wood square. I then clamped this on top of my Ryobi BT3K Accessory table and routed all my box joints. Sometime later we moved to a house where I had a 24' by 24' garage for a shop. I had plenty of room then to install my BT3K wide table kit and built in a router station on the extension. My router fence detailed in a different page shows this router station. About the same time I designed this box joint jig to attach to the wide table router station with the same method as my router fence. Two holes in the table with "T-nuts" epoxied to the underside and a combination of one hole and one arched hole in the jig plate to allow adjustment. This box joint jig is nothing more than a "spacer fence" where the workpiece is guided into the bit with the small square fence sized several thousandth's smaller than the router bit used to cut the joints. Jigs of this type have been available for purchase from several sources. I have always preferred to make my own jigs; it's usually cheaper plus it allows me to get shop time when I don't have all the stock needed for a larger furniture project. Jig making also hones one's woodworking skills.

As you can see in the above picture the jig is pretty simple. It is just a piece of 1/2" Baltic Birch plywood with a stepped stopped dado down the middle, with the narrower step actually milled through the piece. See the next image.

Each fence insert is milled out of any hardwood in my jig but future fences will be made of UHMW-PE which is a better material for this. I have found that some hardwoods are too fragile for this use.

You may have noticed in the first picture that there is a toggle clamp, see above. This clamp is a necessary addition to the jig to hold a spacer for starting exactly half of your joints. More on this little point later.

Here is the order of operations to use your newly made box joint jig of the spacer fence design.

Mill all your box pieces to uniform widths
Chuck up a spiral bit into your router, install the jig over the bit, and raise the bit through the jig by 1/64" above the thickness of your stock (if you are using two different thicknesses of stock you will need to use two different bit height settings; common sense right?)
Set the fence so that the distance from the edge of the router bit to fence is a "frog's hair" (technical term), less than the diameter of your bit
With a push block mill the fingers on two pieces of scrap, indexing each successive cut by indexing the previous one with the fence. Check for fit if your joint is too tight tap the fence slightly closer to the bit; conversely if your joint is too loose tap the fence slightly away from the bit
Take a piece of scrap with one straight edge and at least twice as thick as your fence is high and using the fence as a guide mill a dado down it this piece now formed shall be called your "spacer"
Take your newly formed "spacer" and install it over the fence and clamp it down with your toggle clamp
Pair all your pieces into "ENDS" and "SIDES" and label them as such, mill one end of all your "ENDS", this will allow your edges to be flush when it's time to assemble your "box"
Remove "spacer", you may want to save it for future use as it may help in setting up your jig for cuts of the same six in the future; I usually discard mine to the burn pile
Mill the rest of your fingers
Dry assemble your box
If you are happy with the fit, glue and clamp your box, let the glue dry, and then either sand each joint flush or use a really sharp chisel to pare each joint flush

Picture of setup.

Push block's will help you to mill the fingers with added safety, keep in mind that All woodworking is inherently dangerous! and all you can do is use tools and techniques that lessen the risk of injury but nothing can or will remove all of the risk. Woodworking with power tools should only be attempted by those who are wide awake, sober, and not distracted! Since I have zero control over you, your choice of tools, materials, techniques, and safety habits:I assume no responsibility for your actions in your shop! Use my instruction at your own risk........where was I, Oh yeah push blocks......To make a push block just mill out a piece of wood, yes any will do, as long as it is at least twice as thick as your router bits' projection above the jig. Make sure that you have at least one square corner with the intersecting sides straight and square to the surface. You can drill a hole in the push block and insert a "shaker peg" as a handle. Keep in mind that this push block will get a dado milled into it.

Steps one through four should have been performed by this time. Step five: pictured below.

Step six is to take your spacer and install it over the fence as shown in the following picture.

Step seven, with your "ENDS" labeled mill a notch on one edge, both ends of all "ends" as in the next picture.

To mill the rest of your fingers use the fence to guide the edge of each successive cut by indexing the previous cut over the fence. Make sure you keep the stock tight to the fence on the bit side by placing slight pressure towards the fence or to the right. To mill your "SIDES" just start by guiding one edge along the fence. When you are done you should have all of your "ENDS" with a notch on one edge and all of your "SIDES" with a pin on one edge. Some woodworkers do not cut their stock to final width until after they have milled all of their fingers for the box joint. Waiting to size the width of all pieces makes it easier to produce a joint that is balanced with all of the fingers of equal size. This is up to you. Some woodworkers even assemble the whole box complete with top and bottom and then saw the lid off which is probably the safest way to have a lid with joints that match the box. The following picture shows the pins being cut.

Dry Fit

Finally a picture of the jig with two of the fences, taken form the bottom. Note that the bolt and the slot it sits in on the left: that is to mount the toggle clamp. I fashioned a holder for mine that is adjustable and removable out of two pieces of BLACK WALNUT, yes there are reasons why my site is called Blackwallnutjigs.com. I'm just nuts about walnut! I like everything about this species of wood, the color, smell, taste of the nut, and mostly the great figure and variety from piece to piece. The attachment hole, lower left and arched slot, upper left are made with circle routing jig set to the same radius as the distance between attaching holes in my BT3K wide table router station. You can clearly see the stepped dado in the center of the jig plate. Notice also the hole for the bit: this must be at least 1/8" larger in diameter than your largest bit that you will use for making box joints and centered the distance from the straight edge of your stepped slot for the fence an equal distance of your largest bit's diameter so as to allow some lateral adjustment of the jig.