The Incra I-Box Jig: Simple and Accurate Box Joints

John Featherman, Retired Woodcraft of Harrisburg Employee Posted on
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The Incra I-Box Jig is an advanced jig which makes cutting box and finger joints simple and accurate. There is a little bit of a learning curve, but once I got the hang of it, I really like the ease and simplicity. The jig can be used on a table saw or a router table, and consists of a miter bar, support table, fence, blade guards, backer boards, and adjustable pins. The replaceable backer boards are used to help prevent tear out. The pins are the heart of the jig and are used to space the cuts to the proper width and distance.
theincraiboxjigsimpleandaccurateboxjoints_harrisburg-york

The Incra I-Box Jig on a SawStop table saw
After assembling the jig, it is placed in the miter slot and final adjustments are made to square the whole jig to the cutter. Then using what Incra calls “kiss,” the pins are moved until they just touch the cutter and then are backed off at least one-eighth of an inch. A BIG warning– failure to do this could result in damage to the pins and/ or cutter and if being used on a SawStop will fire the brake cartridge.
Next, using a scrap piece of the same wood as the finished box, the cutter height is adjusted and the front guard distance is set from the fence. A test cut is then used to adjust the pins to the exact width of the cutter. After setting and locking the pins in place, begin cutting the joints. Prior to starting, I like to mark the bottom of each box side so I can properly orient them in the jig. The left/ right or front/ back are cut first as a pair and then used as a guide to properly space the initial cuts on the remaining two sides.
theincraiboxjigsimpleandaccurateboxjoints_harrisburg-york

The author’s finished tool storage box
If I’m using my table saw, I like to use my dado set to cut my joints. Freud and Forrest both make a specialized box cut set which will cut either quarter inch or three-eights inch by simply reversing the two blades. Forrest also has a three-sixteenths and five-sixteenths set, or a four piece set which has all of the different widths.
Incra provides a very good video which walks through assembly and use, plus tips on making things like splined box joints. Overall, I’m quite pleased with the I-Box Jig. Again, it had a learning period, but the simplicity and accuracy of making repetitive cuts is definitely worth the investment.

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