Tensioning 3D Prints For Lightweight, Strong Parts

August 6, 2023 by Bryan Cockfield 28 Comments

Desktop 3D printers have come a long way over the past decade. They’re now affordable for almost anyone, capable of printing in many diverse materials, and offer a level of rapid prototyping and development not feasible with other methods. That said, the fact that they are largely limited to printing different formulations of plastic means there are inherent physical limitations to what the machines are capable of, largely because they print almost exclusively in plastic. But augmenting prints with other building techniques, like this method for adding tensioning systems to 3D printed trusses can save weight and make otherwise unremarkable prints incredibly strong.

The build from [Jón Schone] of Proper Printing consists of printed modular sections of truss which can be connected together to make structural components of arbitrary length. To add strength to them without weight, a series of Kevlar threads are strung from one end of the truss to the other on the interior, and then tensioned by twisting the threads at one end. Similar to building with prestressed concrete, this method allows for stronger parts, longer spans, less building material, and lighter weight components. The latter of which is especially important here, because this method is planned for use to eventually build a 3D printer where the components need to be light and strong. In this build it’s being used to make a desk lamp with a hinged joint.

For other innovative 3D printer builds, [Jón] has plenty of interesting designs ranging from this dual extrusion system to this 3D printed wheel for a full-size passenger vehicle. There’s all kinds of interesting stuff going on at that channel and we’ll be on the edge of our seats waiting to see the 3D printer he builds using this tensioned truss system.

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A Good, Hard Look At Pre-Stressed Concrete

September 29, 2020 by Kristina Panos 43 Comments

From the looks of the average driveway or sidewalk, it may seem as though concrete is just destined to crack. But if concrete is so prone to cracking, how are we able to use it in so many high-stress applications like bridges and skyscrapers? This question came about while I was researching 3D-printed thermite for an article. Thermite is often used in welding railroad tracks, and I linked a video of fresh tracks being welded that had concrete ties. I knew I had to find out how concrete could be made to withstand the pressure of freight trains.

On its own, concrete is brittle and has no give to it at all. But that doesn’t mean it isn’t strong. Although concrete has good compression strength, the tensile strength is quite poor. Around the late 1800s, someone thought to fortify spans of concrete with steel reinforcing bars, better known as rebar. Steel can stretch, adding steel bars gives the concrete some tensile strength to go along with its compressive strength. Rebar also allows for thinner slabs and other members.

Rebar Only Goes So Far

Parking blocks are meant to be replaced occasionally. Image via Checkers Safety

Rebar or mesh-enforced concrete is good for things like parking lot blocks and roads, but it still fails before it ought to. In fact, it usually has to crack before the rebar can chip in any of its tensile strength.

In high-stress concrete applications like bridges and skyscrapers, it’s terrifically important to avoid deflection — that’s when a concrete member flexes and bends under load. Deflection can cause the modern glass skins to pop off of skyscrapers, among other problems.

A solid, rigid bridge is much nicer to walk, drive, and bicycle on than a bridge that sways in the breeze. But how do you do make a rigid bridge? One solution is to apply stresses to the concrete before it ever bears the load of cars and trucks or a steady schedule of freight trains.

Pre-stressed concrete is like rebar-enforced concrete, but with the added power of tension baked in. By adding stress to the concrete before it goes into service, deflection will be reduced or perhaps eliminated altogether. With the addition of tensile strength, more of the concrete’s own strength is able to come into play.

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Mechanisms: Cable Ties

March 22, 2018 by Dan Maloney 63 Comments

Zip ties, Ty-Raps, cable ties; call them what you will, but it’s hard to imagine doing without these ubiquitous and useful devices. Along with duct tape and hot glue, they’re part of the triumvirate of fasteners used to solve nasty problems quickly and cheaply. They’re next up on the list of mechanisms we find fascinating, and as it turns out, there’s more to these devices than meets the eye.

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