Super Simple Single Blade Box Joint Jig

featured-image-box-joint-jig

Box joints, or finger joints, are really strong joints. And they aren’t too complicated either. They are basically interlocking teeth that, typically, have the same size teeth as they do spacing in between. The depth of the teeth are sized to be about the same as the thickness of the material or slightly more than.

In the back of my head I’ve been wanting to make a box joint jig for a long time but due to the fact that I really didn’t have a project in mind to use box joints I didn’t actively pursue the idea of making one. Fast forward to last week. I stumbled upon Mario Cappellano’s box joint jig video and was instantly impressed by how simple the jig was. I was sold by his video on the jig so I decided to make one myself. For all the specific dimensions you can download Mario’s plans on his website here. I followed the plans but changed a few dimensions to better accommodate a future project that I have in mind.

The first step in any table saw jig is to mill a pair of miter slot runners. I pressed the easy button here and also tested the accuracy of my new CNC mill by cutting a pair of runners out of the last wide chunk of salvaged maple I had in the shop. You do not need a CNC machine to make this jig. To make things easy I just cut three small slots with the space in between measuring .750”. Then I could resaw the slots out on the table saw.

box joint jig (1)

And the slots fit like a glove. I wasn’t able to actually measure the width of the runners because after spending a half hour looking for my digital calipers I ended up finding them bent into a V shape. Luckily they were just a cheap knock off brand and weren’t worth much.

box joint jig (2)

Then the base of the sled can be glued in place. I made mine a bit longer than what Mario’s plans call for. The reason being is that my first project with this jig will use panels that will be cut on their long side as opposed to the short side where box joints are typically cut. I used a square to make sure the front edge of the base was perpendicular to the fence as I glued it down. I let these sit for about 20 minutes.

box joint jig (3)

Just after the glue set up enough to somewhat hold the runners in place I flipped the sled and shot a dozen or so 5/8” brad nails through the runners into the sled base. The nails will continue to hold the runners in place and allow me to finish building the jig while the glue finishes curing.

box joint jig (4)

Next, the front panel of the jig is installed. I think I goofed up and installed it on the front of the base instead of on top of the base but in the end it worked out.

box joint jig (5)

Sometimes being a wood hoarder pays off. These are the odd sized triangular cutoffs from when I made my shopvac cyclone cart. I literally almost threw these away a few days before making this project. I’m glad I didn’t though as they were nearly the perfect shape for bracing the front panel of the jig.

box joint jig (6)

With them trimmed down a little bit at the miter saw I glued and tacked them on with a few 1-1/4” brad nails. The entire jig, minus the template I’m about to show, ended up being built from scrap wood and scrap birch plywood by the way.

box joint jig (7)

Next the template base and blade guard are glued in. I used some pieces of 2×4 that were already milled to 2×2 dimensions. Just make sure you don’t get any nails in the path of the blade. I think I actually used screws here though.

box joint jig (8)

The floating carriage is super simple as well. It’s just a taller piece of ply with a small shelf attached to the back side to slide the carriage along. I used a thinner piece of the same maple scrap from earlier. A few screws and glue secured it in place.

box joint jig (9)

The carriage indexes a tooth template to determine where to cut and where not to cut. Mario used a stack of same thickness material for his templates which worked great for him. I have access to a CNC machine so I used it to cut a perfect template for 3/8” teeth and spacing. Just to clarify, you don’t need a CNC to make a template for this box joint jig. I’ve got one, so I used it. The material I used was some bamboo flooring samples Eric Penewell sent me last week. Thanks again!!

box joint jig (9.1)

You wouldn’t normally need to make a template this long but like I said the project I want to make with this will have the box joints along the long edge of the material so a longer template is needed. This was actually two templates screwed down side by side.

box joint jig (10)

Here you can see a how the jig will work with a single blade. The key is finding a pin that is the exact width of your table saw blade. This finish nail was the first thing I tried. It fit snug into a saw kerf but ended up producing too lose of a joint. After trying several different pins I finally found a 7/64” drill bit that worked great. The carriage slides freely left to right and the pin is a representation of the saw blade. This allows the exact distance between teeth on the template to be cut with the single blade. This is one of those “why didn’t I think of this” concepts. Great thinking Mario!

box joint jig (11)

The final test run with the proper pin resulted in a joint that is easily assembled and adjusted yet tight enough to remain together against gravity.

box joint jig (12)

Mario’s plan also calls for a stop block to be installed just to the left of the blade kerf to act as a reference point to align the material. Note that If you are cutting both sides of the joint at the same time you want to offset one of the pieces by one tooth distance before you cut. I didn’t in my test pieces as it’s just a test piece. I did, however, use a scrap piece of 5mm hardwood plywood as a backer board to prevent tearout.

box joint jig (13)

This is what the back of the jig looks like in action.

box joint jig (14)

And here’s what the glued up test joint loos like. I glued the joint together and really didn’t wait long enough for it to cure before I cleaned it up with a low angle block plane. It cleaned up pretty well especially considering that the glue wasn’t fully cured. What ultimately matters though is that I now have a super easy to use box joint jig that requires no setup time and no blade switching.

box joint jig (15)

Thanks again to Mario for not only designing but also sharing his free plan for this jig. For all the dimensions and specifics be sure to stop by Mario’s website to download his plan. While you’re there be sure to tell him thanks for the idea and plan! If you liked this project and want to see more stuff like it be sure to sign up for one of my email newsletters so you never miss a new article. Take care folks and I’ll see you in a couple days!



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39 Comments

  1. Roy Wrenn

    Looks great Jay. keep up the great work.I am glad for people like you because I suck at making jigs. thanks for doing your best to keep videos like your free for everyone to enjoy and learn from.

  2. Joshua Smith

    Looks like some super sharp and tight-fitting box joints to me. Stop making it such an easy decision to make this jig! Seriously though, I want a Shapeoko so bad it hurts.

  3. Barry

    I just wonder if the carpenters of the day ask a similar question when power tools first started becoming available. Woodworkers have always taken advantage of innovation and hopefully will continue to do so.

    1. Jay Bates

      Most people deny technological advancements at first until they give them a try. The cool thing is that this was originally designed without the use of a CNC machine so it’s no sweat for anyone without one.

  4. Tom

    Hey Jay, Can you do a video of it in operation and lining it all up. Im interested as it looks really useful. :)

    1. Zach Scott

      I don’t think the bed on a cnc would be big enough for most projects and Jay is a woodworker so he would probably use the methods he is use too. I think everyone needs to quit getting so hung up on the cnc it is just a tool like any other.

    2. Jay Bates

      To cut box joints. Due to the diameter of the bit and the angle at which a CNC cuts the bottom of the gaps will have rounded corners which wont work for a box joint. I also think the CNC adds to woodworking and, for me, wont replace certain tasks. It just helps in certain areas.

      1. Dave

        That’s where you stand your pieces on end ( hole in the table Like Izzy is doing) and machine them that way. I’m not trying to tell you what to do, rather open up different ways of thinking how to achieve a goal. My 2 cents anyways. As long as there is not a radius on the cutter edges the joint will have square corners.
        I’m a little confused about “the angle at which a CNC cuts”, isn’t the spindle perfectly perpendicular to the table?
        Cool tool anyway.

          1. Dave

            Btw, how much space is under the spindle?

            Off subject, am I suppose to get notifications when replies are posted?
            I currently have to try to find where ever I made comments to look..

  5. The Woodfather (@TheWoodfather)

    Well now, my original jig looks like a pile of crap next to this!
    That came out fantastic Jay, well done. I think a CNC would be worth the cost just for making those accurate miter slot runners on the first go!

    I like the extended width you can cut the fingers on now as well, I can’t wait to see it in use when you get to building that project.

    And once again, thanks so much for sharing the plans & video, I really, really, appreciate it.

    Cheers,
    Mario

    1. Adrian Amoroso

      Your jig, Mario, is the pretty girl next door to Jay’s super model in CNC Couture.

      I’m also chuffed by the fact that I built it before Jay did – there is not much I can beat him at :)

  6. Herb

    I think the CNC is a nice tool, and the “Wood Father” made a great template using the wood thickness for the “fingers”. It’s simple and effective. I think people are hung up on the CNC thing because they don’t see it as a tool as Zach mentioned above. It still takes a person to have the idea, program it, and make sure things are lined up correctly… similar to using calipers and dials to square up a table saw, etc. Would I love to own a CNC machine? Sure. Do I see a use for it? Sure. Do I have the budget for it at the moment? No.

    Good work from both of you guys, I like it. As soon as I get my table saw from Grizzly (darn weather in SC) this next week I’ll make this jig and see how it works.

  7. Adam Hollermann

    Very cool Jay. I will definitely take a look at Mario’s plans. I have a project in mind that where I want it to have the strength of box joints, so I appreciate you and others sharing how these jigs can be made. Thanks again to you for your time in making this and other information available to others through your website and YouTube channel.

  8. kurt

    you have a very informative channel/site , i learn something every time i visit, nice jig for box joint cutting using a single blade , i have tried a few methods not as good as this one , we can not use stacked blades in the uk on table saws so this is great solution, thanks to you and mario

  9. James Pugh

    Don’t want to come off negative but, I don’t enjoy CNC projects. Many do and that’s great for them but I wish there was a separate channel for that venue

  10. garym53

    Now how about using the same CNC approach for making a dovetail jig? – I have been meaning to try it myself but my CNC is packed up at the moment.

  11. Mr_Rick

    Is there a dimensional relationship to be concerned about between the first guide slot and the last if you want all your fingers to look the same?

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