3D knitting could make solid but soft furniture

If the art of knitting wasn’t mind-boggling enough, researchers have designed a prototype machine that can knit in 3 dimensions.

They’ve called the new fabrication technique “solid knitting” and have the aim of one day producing a machine capable of knitting furniture.

The technique works by building up knitted layer by knitted layer in a similar way to 3D printing. But rather than being held together by melted plastic, each knit layer is stitched to the previous one.

The team behind the research, from the Robotics Institute at Carnegie Mellon University in the US, presented its research paper and prototype machine this week at SIGGRAPH 2024 – the annual Conference on Computer Graphics and Interactive Techniques in Denver, Colorado.

“[Solid knitting] can easily be unravelled and re-knit, unlike other 3D printing methods which require finished objects to be laboriously melted down and re-extruded into filament in order to be recycled,” first author Yuichi Hirose said in a SIGGRAPH blog post about the project.

“To automate solid knitting, we built a working prototype, solid knitting machine, and a design tool to help program the machine.”

The machine can produce dense, firm, triangular or rectangular prisms of varying lengths. It uses elastic cord as the yarn, as the machine needs to stretch the yarn loops quite significantly.

The technique can also be applied to hand-knitting to produce larger, more intricate shapes, such as a pair of sandals. A tutorial for the hand-knitting technique, as well as the software for creating machine-knittable 3D patterns, is freely available online.

“Solid knitting is sort of a fusion of knitting and 3D printing, but the dense yarn volumes which solid knitting creates have very different material properties than you can get from either traditional technique,” co-author Mark Gillespie said in the SIGGRAPH blog post.

“Knitting is great for making hats and socks, because it creates soft surfaces into which you can put your head and feet. But because knitting just produces this hollow surface, knit objects don’t hold their shape independently — after you take your socks off, they just become floppy tubes rather than retaining the shape of your feet.

“At the other extreme, 3D printing creates rigid objects that are really good at retaining their shape but lack flexibility and softness — I would not want to walk around in 3D printed shoes or relax on a 3D printed sofa.

“Solid knitting offers a middle ground, producing results which feel very different from both traditional knitting and 3D printing. Solid-knit objects have enough internal structure to hold their shape but are still much softer and more flexible than rigid 3D prints.

“In this paper we only had time to scratch the surface of the kinds of objects and material properties that you can obtain via solid knitting, and I’m excited to see where this new fabrication technique goes.”