3D Printed Door Latch has One Moving Part – Itself!

A group at the Hasso-Plattner Institute in Germany explored a curious idea: using 3D printed material not just as a material – but as a machine in itself. What does this mean? The clearest example is the one-piece door handle and latch, 3D printed on an Ultimaker 2 with pink Ninjaflex. It is fully functional but has no moving parts (besides itself) and has no assemblies. In other words, the material itself is also the mechanism.

The video (embedded below) showcases some similar concept pieces: door hinges, a pair of pliers, a pair of walker legs, and a pantograph round out the bunch. Clearly the objects aren’t designed with durability or practicality in mind – the “pliers” in particular seem a little absurd – but they do demonstrate different takes on the idea of using a one-piece item’s material properties as a functional machine in itself.

Other unusual experiments we’ve seen in 3D printing include 3D printed compressed air tanks, or pneumatic muscles instead of motors for small robots. Exploring new directions doesn’t always require bleeding-edge hardware. 3D printing is a natural fit for these experiments because creating any of these things by hand would be a whole lot of work, but to a 3D printer they are almost trivially simple.

[via Gizmodo]

31 thoughts on “3D Printed Door Latch has One Moving Part – Itself!

  1. Really neat idea. I’ve played around with bendy 3D printed parts for simple crawling robots, but getting the limb dimensions right took a lot of trial and error. Their program looks really useful for speeding up the design process!

    1. It’s in the paper. Because everything’s only stretching in the elastic regime, durability/wear isn’t a major concern (their words, not mine). They tested a pair of walker legs over 5000 times with no wear.

      1. Which sounds a little absurd to me: they’re basing this on HOW much torque the user will apply? I do see the value of using structures to effect springs in solid parts, but this just doesn’t seem like a practical application. At best it will feel flimsy to the user because the handle is flexible (you can see that in the simulation in the video), and the user will tend to over-twist because there’s no “stop” to tell him when he’s reached the end of useful travel, and at worst, when it’s jammed for whatever external reason, the user will probably just twist the handle off. Good idea, bad example.

      2. Elastic regime doesn’t really say that much if you look at fatigue diagrams (smith, s-n curves, german: Wöhler-Kurve …). Also 5000 cycles is not the common limit for infinite strength, and you won’t see micro-cracks for quite some time.

    2. There’s a nice video put together by Dan Gelbert where he discusses Flexures.
      The gist of it is as long as the deflection is only single digit %s the effective life span is infinite for all practical purposes. That figure’s for generic metals so you’d have to investigate the various polymers used in 3D printing. There are expensive materials like Nitonal that have much broader deflection ranges.

      1. Further advantage of metal compliant structures: There is also the possibility to make monolithic mechanisms with wire EDM.

        See examples here:

        I don’t see the advantage of 3D printing (because of material choices) and don’t see the advantage of the shear cells compared to single point hinges -even plastic ones are very common see for example tupperware-, if the material can sustain the fatigue strains. The 3D printing shear cell approach result in less linear movement, has no definitive rotational point, most certain has an higher stiffness.

        Even their prototype video is consisting of single point hinges (handle connected to base, handle connected to deadbolt, connection part (below deadbolt right side) connected to base and deadbolt). It would work without further parts, with the downside of less out of plane stiffness. You could mirror the bottom parts and get a comparable mechanism with the same result by mirroring the bottom parts with less material.

        IMHO only for prototyping useful.

        1. The advantage of 3D printing here is that right now it is easier to get funding for your work and get it published if you 3D print it. 3D printing/additive manufacturing has reached buzzword status with the grant agencies. So has meta-materials, so this project, 3D printed metamaterials, is one that was primed to bring in funding and keep the lab running.

  2. By the way, fairly sure I’ve come across one piece nylon injection moulded latches before, usually using a single box leaf spring/detent… but of course it’s the first time for everything when it’s done on a 3D printer.

    Best common example I can think of though of a similar idea though is the one piece “babyproofing” spring latches that fit to cupboards.

  3. You know what though, since there’s a large dependence, in that particular design, on the rigidity of the door, and the number of points it needs to be supported around it’s perimeter….I’d be feeling inclined to quibble that it’s a “one piece” solution, since in yer typical hollow core interior door, you’d need to have a support structure for it, to allow it to function…. I mean compared to conventional solutions where you only require that it may be solid at two points, or in the case of a simple wire hasp and staple, a single point. So it tends to have the smell of “It’s a perfect solution, if we completely re-engineer doors.” … though I’ll allow that there was probably no intent to competently engineer a an actual usable piece of hardware, just demonstrate a principle.

  4. That’s a perfect use for dual material printing. Make the latch bolt, handle and other pieces from a rigid material, while the areas that need to flex are made of (duh) the flexible material. Fully cover the sides of the latch, with a hole for the handle to go through. ‘Course the handle should be round, not square.

  5. I’m confused as to why everyone seems to be getting hung up on the fact that the main demonstration is of a door. Yes, clearly it leaves some attributes to be desired, but the point here is not to 3D print the perfect door hardware, the point is that this is an innovative way of designing 3D prints

  6. I wonder if anybody’s tried laser-cutting these structures? It seems like the kind of (mostly 2D) thing that you could knock out really easily. Combined with some kerf-like structures you could probably do some fun things with relatively rigid materials.

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