Simple and Easy Box Joint Jig

This is my box joint jig based off Woodfather's design which is used with a single rip blade. It has a pin that matches your blade's kerf and a set of spacers in a 1:1 ratio to the fingers of the box joint. You can easily change the size and spacing of the box joints by changing the width of the spacers. Want 3/8" fingers? Use 3/8" spacers. Want 8 mm fingers ... you know the drill. For simplicity I used 1/4" plywood for my spacers which lets me cut each finger in two passes using my 1/8" blade.

Mine follows the original plan closely with a couple of minor modifications. I added a tab to the back of the fence so it clips over the jig and stays in place on it's own. The tape acts as a spacer allowing the fence to slide freely.

I added edge banding to the fence where it rides along the jig. The mating face of the jig also has edge banding and both are waxed. The fence travels smoothly left and right.

The pin (pic above) is a screw 3.17 mm in diameter with the head removed. The kerf of my Freud rip blade is 3.19 mm. The resulting joints are snug but allow room for glue.

The block on the far right is glued in place and never changes. I used cyanoacrylate in case I ever need to remove it. Below you can see the edge banding along the top of the jig.

The spacers are held in place by a scrap of wood approximately the right length, then a small wedge is inserted to keep everything snug.

Mine is a wee bit taller and the sides come farther back. This allowed me to attach a handle. I tried first without a handle but my left hand kept searching for a hold. I find it more comfortable with a handle.

The strip of ply along the front of the fence (red arrow below) is only 3/4", not sure what I was thinking, but it will have to be replaced with a deeper version that will accommodate more than a couple pieces.

An unplanned change which didn't work out, are the runners being short in front (see above). The wood took a funny bow and were binding so I had to cut them down but now the jig wants to tip forward. Definitely leave them long in front. Adding the handle stopped the tipping so I'm not sure if I will bother replacing the runners.

Dovetail Ratios

Dovetail Angles

Playing around with dovetail ratios. Three are common, plus phi (1:1.618) and pi (1:314) which I've never heard of anyone using but thought I would toss them in for fun.

If you are interested in the relative strength between dovetail angles, search the web for:  THE RELATIONSHIP BETWEEN DOVETAIL ANGLE AND JOINT STRENGTH - Notes from The Forest Products Research Laboratory tests (KS Walker) reported in Woodworker Magazine, January 1958.

To save you some reading I'll summarize the conclusions. In glued dovetail joints the angle made no significant difference. In unglued dovetails wider angles were stronger. The article claims that unglued dovetails were stronger because the joints could slip whereas glued dovetails the wood fibers separated. They tested hardwood and softwood, each from the same board. The softwood failed sooner in unglued joints because it more easily compressed and slipped free.