Dovetail joints on a piece of furniture are one of those features that make it say “master carpenter” rather than “IKEA”. Traditional hand-made dovetails require accurate measurements and even more accurate sawing and chiseling, skills that may take years to develop. A slightly less artisanal method is to use a router and a dovetail template; the router makes perfectly straight cuts while the template makes sure it goes only where it needs to go.
If you haven’t got one of those templates yet, check out [Guy Perez]’s design for an adjustable dovetail template that’s easy to produce with a 3D printer. It consists of ten separate pieces mounted on a T-rail, which enables them to slide sideways and thereby generate pins and tails of varying widths. The T-rail is mounted on a wooden body with an integrated clamp to hold the target piece, as well as an endstop to provide a reference for all measurements.
As you can see in the video embedded below, the resulting jig is easy to use and should result in near-perfect dovetails each time. [Guy] made the CAD files available as well as detailed instructions on their design, so you can easily adjust them if you need pieces with a different tail angle or want to use thicker wood.
It’s getting close to the time of year when we need to start carefully vetting projects here at Hackaday. After all, nobody likes to get punked by an early April Fool’s joke. But as silly as this outsized PC fan looks, it sure seems like a legit build, if a bit on the pointless side.
Then again, perhaps pointless is too harsh a word to use. This 500-mm fan is by [Angus] over at Maker’s Muse, and it represents a lot of design work to make it buildable, as well as workable and (mostly) safe. Using both CNC-cut MDF and printed parts, the fan is an embiggened replica of a normal-sized case fan. The fan’s frame had to be printed in four parts, which lock together with clever interlocking joints. Each of the nine blades locks into a central hub with sturdy-looking dovetails.
And sturdy is important, as the fan is powered by a 1,500 Watt brushless DC motor. With a 4:1 reduction thanks to a printed gear train, the fan spins at around 3,300 RPM, which makes a terrifying noise. There’s a little bit of “speed-wobble” evident, but [Angus] managed to survive testing. The fan, however, did not — the 3D-printed gears self-destructed after a full-speed test, but not before the fan did its best wind tunnel imitation. And the RGB LEDs looked great.
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!
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.
Don’t have a tiny dovetail bit on hand, so make that as well.
Of course, do it all without CNC in free-machining style.
Whoops the brass stock is smaller than expected, so find a clever solution.
That birthday? It’s tomorrow, by the way.
The project was a success, and a few small learning experiences presented themselves. One is that the shape of a dovetail plays tricks on the human eye. Geometrically speaking, the two halves are even but it seems as though one side is slightly larger than the other. [mitxela] says that if he were to do it again, he’d make the aluminum side slightly larger to compensate for this visual effect. Also, deburring with a knife edge on such a small piece flattened the edges ever so slightly, causing the fit to appear less precise than it actually is.