This Laser-Cut One-Piece Wedge Tenon Locks Wood Joints Tight

December 4, 2023 by Dan Maloney 24 Comments

Woodworkers have always been very clever about making strong and attractive joints — think of the strength of a mortise and tenon, or the artistry of a well-made dovetail. These joints have been around for ages and can be executed with nothing more than chisels and a hand saw, plus a lot of practice, of course. But new tools bring new challenges and new opportunities in joinery, like this interesting “hammer joint” that can be made with a laser cutter.

This interesting joint comes to us from [Jiskar Schmitz], who designed it for quick, solid, joints without the need for glue or fasteners. It’s a variation on a wedged mortise and tenon joint, which strengthens the standard version of the joint by using a wedge to expand the tenon outward to make firm contact with the walls of the tenon.

The hammer joint takes advantage of the thin kerf of a laser cutter and its ability to make blind cuts to produce a tenon with a built-in wedge. The wedge is attached to a slot in the tenon by a couple of thin connectors and stands proud of the top of the tenon. The tenon is inserted into a through-hole mortise, and a firm hammer blow on the wedge breaks it free and drives it into the slot. This expands the tenon and locks it tightly into the mortise, creating a fairly bulletproof joint. The video below tells the tale.

While the hammer joint seems mainly aimed at birch plywood, [Jiskar] mentions testing it in other materials, such as bamboo, MDF, and even acrylic, although wood seems to be the best application. [Jiskar] also mentions a potential improvement: the addition of a ratchet and pawl shape between the wedge and the slot in the tenon, which might serve to lock the wedge down and prevent it from backing out.

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Complex Wood Joints, Thanks To New Software’s Interactive Features

October 23, 2020 by Donald Papp 23 Comments

Artfully-crafted wooden joints that fit together like puzzle pieces and need neither glue nor nails is fascinating stuff, but to call the process of designing and manufacturing them by hand “time-consuming” would be an understatement. To change that, a research team from the University of Tokyo presented Tsugite, a software system for interactively designing and fabricating complex wooden joints. It’s named after the Japanese word for joinery, and aims to make the design and manufacture of glue and fastener-free joints much easier than it otherwise would be.

Three-way joint that requires no glue or fasteners.

~~It looks like the software is so far only a research project and not something that can be downloaded~~ The software is available on GitHub and the approach it takes is interesting. This downloadable PDF explains how the software deals with the problem of how to make such a task interactive and practical.

The clever bit is that the software not only provides design assistance for the joints themselves in a WYSIWYG (what you see is what you get) interface, but also generates real-time feedback based on using a three-axis CNC tool as the manufacturing method. This means that the system understands the constraints that come from the fabrication method, and incorporates that into design feedback.

The two main limitations of using a three-axis CNC are that the cutting tool can only approach the material from above, and that standard milling bits cannot create sharp inner corners; they will have a rounded fillet the same radius as the cutting bit. Design can be done manually, or by selecting joints from a pre-defined gallery. Once the design is complete, the system generates the toolpaths for manufacture.

Currently, Tsugite is limited to single joints meant for frame structures, but there’s no reason it couldn’t expand beyond that scope. A video to accompany the paper is embedded below, it’s short and concise and shows the software in action, so be sure to give it a look.

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Hackaday Podcast 075: 3D Printing Japanese Joinery, Android PHONK, One-Armed Time Bandit, And Whistling Bridges

July 10, 2020 by Mike Szczys No comments

Hackaday editors Mike Szczys and Elliot Williams scoop up a basket of great hacks from the past week. Be amazed by the use of traditional Japanese joinery in a 3D-printed design — you’re going to want to print one of these Shoji lamps. We behold the beautiful sound of a noise generator, and the freaky sound from the Golden Gate. There’s a hack for Android app development using Javascript on an IDE hosted from the phone as a webpage on your LAN. And you’ll like the KiCAD trick that makes enclosure design for existing boards a lot easier.

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (60 MB or so.)

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This Mallet Has Backwards Dovetails… That’s Impossible!

February 22, 2020 by Mike Szczys 14 Comments

Dovetails are a wedge-shaped joint found in woodworking. The wedge makes for strong joinery because a force that tries to pull it apart also increases the friction on the joint. This mallet has dovetails on either side that keep the head from flying off, but there’s also a through tenon in the center. This is an impossible joint as there’s no way to slide the mallet head onto the handle. The two pieces of wood must have grown that way!

As with everything, there’s a trick here, let it scratch your brain for a while before reading on… if you can guess how it’s done it’ll be very satisfying when you confirm your theory. Both the trick of the impossible mallet and the superb hand joinery are shown off in this video from the [Third Coast Craftsman].

The trick comes in the form of internal voids hidden from view once the two pieces of the mallet have been assembled. The through tenon is exactly as you’d expect: a straight tenon slides into a straight mortise in the mallet. The dovetails to either side of the handle and the pockets they mate with in the mallet head are not at all what you’d expect. The edges of the dovetail have been chamfered at 45 degrees so you can’t pull them to the outside of the mallet as you slide them into place. The opposite is the actual trick. Each of the dovetails bends inward until a ramp at the very end of the mallet pocket pushes it back into place.

Underside of mallet head shows “ramp” detail

Tenons clamped during assembly

The impossible mallet isn’t a new concept and stands as a formidable challenge for any accomplished woodworker. The images above are of [Jim Guilford’s] impossible mallet. Here the trick is fully exposed, showing the dovetail tenons of the handle clamped together as it is driven into place. Two things are striking here; the joints cannot be tested and must be perfect before assembly, and there is a real chance the tenons will break or the mallet head will split apart from the force of assembly. This project will test your courage as much as it will your patience.

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Cool Tools: The Pantorouter Turns Tracing On Its Side

October 1, 2018 by Kerry Scharfglass 6 Comments

Not too long ago we wrote about a small CNC tool for automating certain parts of the woodworking process. At the time it seemed unusual in its intentionally limited scope but a few commenters mentioned it reminded them of another device, [Matthias]’s Pantorouter. It didn’t take much investigation to see that the commenters were right! The MatchSticks device does feel a bit like a CNC version of the Pantorouter, and it seemed like it was more than worth of a post by itself. The Pantorouter is a fascinating example of another small manual-but-automated tool for optimized for accelerating and improving certain woodworking operations.

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A CNC Woodworking Tool That Does The Hard Parts

August 28, 2018 by Kerry Scharfglass 26 Comments

Drawn along in the wake of the 3d printing/home shop revolution has been the accessibility of traditional subtractive CNC equipment, especially routers and mills. Speaking of, want a desktop mill? Try a Bantam Tools (née Othermachine) Desktop Milling Machine or a Carvey or a Carbide 3D Nomad. Tiny but many-axis general purpose mill? Maybe a Pocket NC. Router for the shop? Perhaps a Shapeoko, or an X-Carve, or a ShopBot, or a… you get the picture. [Rundong]’s MatchSticks device is a CNC tool for the shop and it might be classified as a milling machine, but it doesn’t quite work the way a more traditional machine tool does. It computer controls the woodworker too.

At a glance MatchSticks probably looks most similar to a Pocket NC with a big Makita router sticking out the side. There’s an obvious X-axis spoilboard with holes for fixturing material, mounted to a gantry for Z-axis travel. Below the big friendly handle on top is the router attached to its own Y-axis carriage. The only oddity might be the tablet bolted to the other side. And come to think of it the surprisingly small size for such an overbuilt machine. What would it be useful for? MatchSticks doesn’t work by processing an entire piece of stock at once (that what you’re for, adaptable human woodworker) it’s really a tool for doing the complex part of the job – joinery – and explaining to the human how to do the rest.

The full MatchSticks creation flow goes like this:

Choose a design to make on the included interface and specify the parameters you want (size, etc).
The MatchSticks tool will suggest what material stocks you need, and then ask you to cut them to size and prepare them using other tools.
For any parts which require CNC work the tool will help guide the user to fixture the stock to its bed, then do the cutting itself.
Once everything is ready for final assembly the MatchSticks will once again provide friendly instructions for where to pound the mallet.

In this way [rundong], [sarah], [jeremy], [ethan], and [eric] were able to build a much smaller machine tool without sacrificing much practical functionality. It’s almost software-like in it’s focus on a singular purpose. Why reinvent what the table saw can do when the user probably already has access to a table saw that will cut stock better? MatchSticks is an entire machine bent around one goal, making the hard stuff easier.

It’s worth noting that MatchSticks was designed as an exploration into computer/human interaction for the ACM Conference on Human Factors in Computing Systems so it’s not a commercial product quite yet (we’re eagerly waiting!). For a much more in depth look at the project and its goals and learnings the full research paper is available here. Their intro video is down after the break.

Thanks [ethan] for the tip!

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Soda Bottles Used As Heat-Shrink For Wood Joinery

March 23, 2017 by Dan Maloney 80 Comments

Nobody is likely to confuse it with the beautiful joinery that makes fine furniture so desirable. But as a practical technique, using plastic bottles as heat-shrink tubing for composite joints is pretty nifty, and the pieces produced are not without their charm.

Undertaken as an art project to show people what can be done with recycled materials, [Micaella Pedros]’ project isn’t a hack per se. She started with bottles collected around London and experimented with ways to use them in furniture. The plastic used in soda and water bottles, polyethylene terephthalate (PET), turns out to shrink quite a bit when heated. Rings cut from bottles act much like large pieces of heat-shrink tubing, but with more longitudinal shrinkage and much more rigidity. That makes for a great structural component, and [Micaella] explored several ways to leverage the material to join wood. Notches and ridges help the plastic grip smoother pieces of wood, and of course the correct size bottle needs to be used. But the joints are remarkably strong – witness the classic leaning-back-in-a-chair test in the video below.

Its aesthetic value aside, this is a good technique to file away for more practical applications. Of course, there are plenty of ways to recycle soda bottles, including turning them into cordage or even using them as light-pipes to brighten a dark room.

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