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I have built a couple of kits, recently, that use this clever arrangement of tabs, slots, and a couple bits of cheap hardware to securely butt one panel against another at a right angle. One panel has a pair of rectangular ports with a round hole in between, and the other has a matching pair of tabs with a smaller T-shaped slot between. In use, the ports receive the tabs and a screw passes through the round hole and along the upright of the T to mate with a square nut captured in the arms of the T. There are many possible variations and the technique has lots to recommend it from a manufacturer’s standpoint, especially if you’re using a laser-cutter to make parts.

Now that I’ve noticed it, of course, I see it everywhere. Does anybody else remember the first time they noticed one, and what it was on? Does it have a common name?

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.


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Comments

  1. Charles Pax says:

     At MakerBot we call it a T-slot.

    1. Chris says:

      Around our workshop, we call it a Pettis joint! The first time I saw it was on a Makerbot at a Makerfaire. We have a laser engraver in our shop and from that point on, we started using the joint for a lot of projects. In fact, we added some “Pettis” templates in our CAD software to easily drop in the required outlines for the joint.

      I have no idea if Bre actually came up with the design, but he is the face of Makerbot, so the name stuck!

  2. Jeff Rowberg says:

    Minecraft mate?

    …kidding.

  3. WC says:

    I usually see them leaving some space on the other side of the nut for the end of the bolt.

    http://blog.makezine.com/archive/2008/08/how-to-lasercut-custom-bo.html

    I don’t think I’ve ever seen a name for the technique yet, though.

  4. Anonymous says:

    I saw it at Makerbot first :)

  5. Mark Adams says:

    That technique is called “interlocking T-Bolt construction” originally by Oomlout labs (http://oomlout.com) member Oomlout – see this page on Thingiverse for more information: http://www.instructables.com/id/How-to-Make-Anything-Using-Acrylic-and-Machine-Sc/

    1. Thank, Mark!  I hadn’t seen that page on Instructables.  And that’s pretty much exactly the joint I’m talking about.  I want to say I have seen photos of laser-cut joints like this older than 2009, however.  This fab-at-home Model I, for instance, appears to be using the joint, albeit with very wide tabs and ports:

      http://fabathome.org/wiki/uploads/e/e8/IMG_0110.jpg

      I’m also a bit opposed to “T-bolt” construction because no “T-bolt,” as such, is used.  This is a T-bolt:

      http://images.google.com/search?q=T-bolt&hl=en&safe=off&prmd=imvns&tbm=isch&tbo=u&biw=1366&bih=655

      1. Mark Adams says:

        You are right- there is no T-Bolt involved. I think that the “Bolted Mortise and Tenon” is a more accurate name.  It seems like oomlout popularized the approach which has been extensively re-used for lasercut projects over the last few years.  Perhaps a follow-up MAKE: blog post that details the history and suggests a consistent nomenclature?

    2. Thank, Mark!  I hadn’t seen that page on Instructables.  And that’s pretty much exactly the joint I’m talking about.  I want to say I have seen photos of laser-cut joints like this older than 2009, however.  This fab-at-home Model I, for instance, appears to be using the joint, albeit with very wide tabs and ports:

      http://fabathome.org/wiki/uploads/e/e8/IMG_0110.jpg

      I’m also a bit opposed to “T-bolt” construction because no “T-bolt,” as such, is used.  This is a T-bolt:

      http://images.google.com/search?q=T-bolt&hl=en&safe=off&prmd=imvns&tbm=isch&tbo=u&biw=1366&bih=655

  6. Chic Thomson says:

    a bolted mortise and tenon joint ?

  7. Jeff Hanson says:

    If you take out the round hole in the face piece and the tee shape in the other, you then have a mortise and tenon joint, which is often used in woodworking. This would then be glued, sometimes there would be wedges in the end of the tenon (piece that goes into the mortise (square hole in this example)) to provide extra holding pressure, sometimes the tenon will go through the mortise and a peg put through a hole in the tenon, which would allow for the joint to be taken apart. In this example the hole/t-slot and hardware would allow for this mortise and tenon joint to be secure, yet still be able to take it apart.

  8. Anonymous says:

    I’ve seen something very similar on most of the Ikea furniture I’ve been putting up recently.

    1. Sam Ley says:

      Agreed, while the specific incarnation of it is adapted for laser cutters, it is quite clearly a modified Bed Bolt Joint. I’m always fascinated by the adaptation of traditional joinery to laser and CNC applications. Sometimes an ancient method that is uncommon now in normal furniture because of how labor intensive it is to make with hand tools suddenly becomes easy again with CNC, like butterfly joints.

    2. Sam Ley says:

      Agreed, while the specific incarnation of it is adapted for laser cutters, it is quite clearly a modified Bed Bolt Joint. I’m always fascinated by the adaptation of traditional joinery to laser and CNC applications. Sometimes an ancient method that is uncommon now in normal furniture because of how labor intensive it is to make with hand tools suddenly becomes easy again with CNC, like butterfly joints.

    3. Sam Ley says:

      Agreed, while the specific incarnation of it is adapted for laser cutters, it is quite clearly a modified Bed Bolt Joint. I’m always fascinated by the adaptation of traditional joinery to laser and CNC applications. Sometimes an ancient method that is uncommon now in normal furniture because of how labor intensive it is to make with hand tools suddenly becomes easy again with CNC, like butterfly joints.

  9. Frank Schäfer says:

    i am carpenter. i would call that a bolted mortise and tenon. it uses some basic joinery from woodworking, but is held in place with a bolt instead of glue.

    1. Thanks.  I like “bolted mortise and tenon,” although I feel like maybe a slightly more specific name is needed to distinguish this very particular geometry.  A set of mating tabs and slots is obviously a pretty basic idea, with a very long history.  I guess what I’m trying to do is run down the modern laser-cut variant of the idea, specifically with the T or cross-shaped slot between the tabs.  A person working with conventional woodworking tools, or even a CNC router with a rotating circular cutter, would have no reason that I can see to favor this joint because of the sharp inside 90-degree corners. Traditional woodworking tools could certainly make them, but I don’t think there’d be any compelling reason to because other operations that don’t require sharp inside right angle corners can easily achieve a functionally equivalent result with rather less work, and are arguably better looking. So I feel like it’s only during the laser-cutting era that this particular variant of the bolted mortise and tenon joint is coming into its own.    

      1. James B says:

        I say “bolt drawn double tenon”.  Calling it drawn helps describe how the bolt is oriented, and it is definitely a double tenon.

      2. James B says:

        I say “bolt drawn double tenon”.  Calling it drawn helps describe how the bolt is oriented, and it is definitely a double tenon.

  10. LDM says:

    I’m voting for a bolted Mortise & Tenon Joint.

    My woodworking instructor has a VERY similar joint that he uses (and has used for decades) for stuff he wants to be able to knock-down, like his workbench or bed frames.  The only difference I see is that he just drills a hole for the bolt in the tenon piece and uses a forsner bit to cut a hole for the washer & nut instead of cutting a T-shaped slot.  His version would be more structurally sound as it doesn’t eliminate as much wood.  You can also do it with one large blind-mortise.

  11. Anonymous says:

    The Makerbot Thing-o-matic has about a million of these connections. It’s 90% of its assembly.

    1. Bre Pettis says:

      We call it a “t-slot” but it’s nothing particularly special. We modified the way that fab@home were connecting things.

  12. Bill Griggs says:

    I not sure what the joinery is called but I do know that it helps to tape all the nuts in place prior to construction. That one tip saved at least an hour on the construction time of my Thing – O- Matic.

    Bill

  13. James B says:

    It has elements of a draw bore tenon, double tenon joint,  and knockdown fastening.  If it isn’t glued, I would call it a knockdown double tenon.  If there as adhesive involved, and the joint is permanent, I would call it a bolt drawn double tenon.  I’ve never seen this exact joint, but have built variations of all of those I described for hardwood furniture and cabinetry.

  14. We use them on our machines http://www.phlatboyz.com and have always referred to them as tabs and slots.When we started the business, we were looking for a connection system for our machines and came across a website that said this system was developed in the 60′s by a french designer trying to connect two pieces of plastics at right angles where glue would not work. Soon after there were many machines being designed like this.

  15. This is really two joints… VERY common in some fashion or other on beds… one is the double through-mortise and tenon, and the other is the ubiquitous bed-bolt.  Typically, the bed bolt would just be cleared out where the nut would go, and the hole for the bolt would be drilled to that cavity, rather than having the slot that the bolt goes through, but there it is. 

    rg

  16. I first saw it on a Makerbot, of course.

  17. I found similar joint used on an antique gas stove.  It was used to attach two cast aluminum parts using a cairage bolt head.  I can send you a picture if you like.  Someone needs to make a repository of all of the variants.  This would be a great resource for all of us using laser cutters and FDM too.

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