lets see if it works this way:
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Here is rather long story w/pics about a new box joint jig.
Almost three years ago a woodworking friend was designing a box joint finger template for his dovetail jig and was asking for input about finger spacing, bushings, etc. I was never satisfied with various box joint jigs I have made over the years, so that thread started me thinking again. Good box joints rely on the spacing and size of the cutter and indexing parts to match almost perfectly, usually within a few thousandths of an inch- unfortunately that often doesn't happen with DIY and sometimes even with fixed jigs that use precision cut CNC templates. The bushing, position of the bit in the router, or router bit itself can be off, plus you need multiple, often expensive templates. To solve this problem a number of adjustable DIY jigs have appeared in magazines; the best known one by Shopnotes/Woodsmith even transitioned to a commercial product. But, just because they are adjustable doesn’t mean they can be accurately or reliably set. The user must often use calipers and/or make numerous test cuts to set the jig and repeat that process if he changes finger size. Some adjustable DIY jigs require you to count turns of a crank between each cutting pass, and often depend on the cutter size being an exact multiple of 1/16” or 1/32” due to the screw mechanism. Fixed jigs need a separate pin, template, or bushing for each finger size, so the number of possible joints is often limited. As I said, they rely on the blade or the bit being a precise size- guess what?!
I decided to see if I could design and build an adjustable box joint jig, one that could be used on both a tablesaw and router table that would avoid all the problems with and be easier to use than the current crop of jigs. First, however, I spent a lot of time analyzing box joints and jigs. Eventually, for the first time, I truly understood the geometry and how a box jig MUST work. Also, I realized there is more going on than just the obvious, so I dug a little deeper and what followed was an epiphany. I realized I could capitalize on some of the lesser known or at least unappreciated relationships between the jig parts and cutters to make a better jig.
Now to turn concept into reality. After some design work looking at levers, cog belts, gears, etc., I came up with a fairly simple mechanism I hoped would do what was needed. I hastily cobbled together a
VERY PRIMITIVE prototype from shop scraps. Outwardly it looked like the adjustable Shopnotes and similar DIY box joint jigs that allow you to adjust dual guide pin spacing and position by turning knobs mounted on threaded rods. Unlike those, my design relied on just a single knob that turns a single, special leadscrew that works differently- I was able to make all settings on my prototype easily and precisely with just the one knob- additionally no calipers were needed to set anything. The key part is hidden within the wood blocks in the second photo. Like I said, it was primitive! Sorry about the lousy photos.
It was time for the moment of truth. I set my stacked dado blade randomly- truthfully I had no idea what size notch it would cut! I set the position of the miter bar for the left slot on my right tilt saw and performed simple, one-time calibration to set the jig for my particular dado blade. I call it “kiss calibration” – no calipers required. If it worked like I hoped, once calibrated, I could turn a
SINGLE KNOB to set the jig for any finger width/spacing. Again, no calipers required. Just like the production jig, to set the finger size I cut a notch in a scrap board and placed it over the split guide pins. I turned the knob until the split pins separated and were snug against the sides of the notch. While this was happening, both pins moved simultaneously, but by different amounts, away from the blade. It appeared the jig’s unique “positioning engine” had worked its magic, so I grabbed two boards and made a test joint. I assembled the joint- the fingers fit perfectly and so did those on the second, the third, and many other test joints. It required no tweaking; none of the repeated test-adjust-retest, or fine tuning typical of other jigs. Yahooo!!! I was ecstatic!!! While an operator can always find a way to make initial setup errors, the positioning engine will ALWAYS adjust both the spacing of the dual index pins AND the spacing between the pins and the blade to the precise setting needed with the turn of just one knob, every time!
Not bad joints for a slapped together jig.
The initial success of my rough prototype, the encouragement of friends, and the results of a patent search led me to a decision to attempt to market my design, though I had never attempted anything like that before. I still needed to make a few improvements so it would work on left and right tilt saws, router tables, and with the new crop of reversible, two-blade box joint sets. I began building a better demonstrator/prototype from acrylic that incorporated those improvements- it worked even better- then I filed a Provisional Patent Application to protect my design.
In the Spring of 2009 I contacted a half dozen woodworking accessory manufacturers via email, described my design and its attributes in general terms, and offered to license it. All showed interest. Coincidentally, I thought the company that showed the most interest would be most capable of turning my primitive design into a retail jig. A non-disclosure agreement allowed us to discuss details. Some work actually started on a marketable version before a licensing agreement was signed late in the summer of 2009. I built a new, fully functional, prototype from aluminum extrusion purchased on Ebay. It looked really slick, but didn’t work worth a darn because I don’t have much in the way of metalworking skills or machines. I snapped two perfectly good 1/2” spiral carbide router bits and scared the bejesus out of myself trying to use my router table to mill the aluminum!
Serious factory development started in earnest in the summer of 2009. In accordance with the licensing agreement I stayed closely involved. I made only one visit to the plant, but exchanged over nine hundred emails, phone calls, SketchUp drawings, Solid Edge engineering drawings, parts, sub-assemblies, prototypes, etc. with my licensee. Believe me, it can take an incredible amount of work to turn an idea into something that works as intended and that can be manufactured for a reasonable cost. My licensee’s design and fabrication expertise really came through- three special extrusions and a myriad of unique parts. One patent book I read, said between 95% - 99% of all product ideas never make it to market- not because they aren’t great ideas, but because they are too expensive to produce!
Over the following months, a number of small and a few really significant improvements were incorporated into the pre-production unit I received for testing in the fall of 2010.
The pre-production unit worked much better than my prototypes. One improvement was the addition of micro adjustment. My prototypes worked fine without it, but my astute manufacturer thought it desirable. After some serious design work by everyone, I came up with an elegant and simple way to incorporate it. It still took a fair amount of effort to work out the details. The fit of a joint cut with this jig will seldom need to be fine tuned, but if it becomes necessary, the jig can do it in .001” increments or less. The micro adjustment also aids initial calibration, can be used to correct for poor initial calibration, and fortuitously also makes it incredibly simple to set the jig to make box joints that will accept decorative inserts. It turned out to be the most significant improvement to the jig, but like everything the Devil was in the details.
We gave the pre-production prototype a real workout. During my own testing I used a standard kerf Forest WWII blade that was already on my saw to make tiny 1/8” wide fingers in MDF- narrow, brittle fingers- a real challenge!!! The joint fit perfectly as did the 1/8” joints in oak, maple, and pine. Except for the tiny “bat ears” created by the ATB tooth grind of the WWII, the joints looked as good as they fit. I worked my way through the jig’s full range of finger sizes using boards of different thicknesses, widths, and species. Then I duplicated my testing on a router table- yes,
the jig works on a router table too!! (It needs a miter slot)
After you set the jig to make a normally-spaced joint, you can dial in a precise gap that you can fill with strips of contrasting colored wood, metal, plastic, etc. during assembly. The inserts can be a few thousandths of an inch thick like the maple ones in the mahogany joint in the photo above or as thick as the fingers themselves like those in the photos below. The guys at the factory also came up with some unique variations of their own!!
If you have seen my other post or the miter bar and signature color scheme of the pre-production prototype didn’t already give it away, the new jig is a product of Chris Taylor, Perry McDaniel and the great folks at INCRA Tools. If you get a chance to put one through its paces, I hope you will agree that this jig is right at home with the rest of the INCRA line of precision miter gauges, fences systems, and other woodworking accessories. I really want to thank them for trusting in my idea and doing a truly incredible job translating it into a really fantastic jig.
I obviously have a financial stake in this product, but I have attempted to tell the story of its development, rather than make a sales pitch with a lot of details so hope the moderators give me some slack. I am obviously a bit biased, but I believe this jig is easier to use, addresses all the shortcomings of, and far surpasses the performance and capabilities of all other box joint jigs on the market.
It was first introduced to a limited audience at the Woodcraft National Sales Conference and Vendor Trade Show in Nashville, TN back in June, and a sneak peak was provided by Wood Magazine who selected it as one of their “Innov-8” award winners. The INCRA “I-BOX” (intelligent box joint jig), is now in full production, but the instructional video is not done so it won't be available until sometime in January. As with all INCRA products, you can expect it to be extremely well made, backed by INCRA’s outstanding customer support, and come supplied with a well illustrated and detailed manual and a helpful video.
Thanks for your support. I will attempt to monitor this thread and answer any question you might have.
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George
