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How a 3D printer saved my stove

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When he couldn’t get a replacement part for his cooker, Open Knowledge correspondent James Tulloch turned to 3D printing.

Allianz-My broken cooker control knob with the shaft pin controlling the gas supply exposed

Judging by the news, the 3D printing revolution is poised to transform the way we make everything from chocolates to cars, from bionic arms to jewellery. 3D printers translate digital design files into physical, three-dimensional objects. In China, 3D printers are building houses in a matter of hours. In Europe, scientists are 3D printing human tissues that could be used for organ transplants.


I had a more modest goal: I wanted a new control knob for my gas cooker.You see, I had broken three of these plastic knobs, leaving me twisting exposed metal shaft pins to turn the gas on and off (see image right). This made me very nervous.


Superglue didn’t work. I couldn’t find replacements online. So I contacted the manufacturer. “The control knob for your appliance is actually obsolete,” customer services said. “We don't make the part anymore.”


Planned obsolescence, I thought, our disposable culture in a nutshell. It dawned on me that I might have to buy a new cooker for want of a plastic knob! Unless I could make it. Could the 3D printing revolution help? Forget upgrading, hang obsolescence, I could take control of the means of production! Let’s put this tech to the test. I got back online.

Allianz-A computer-generated image of the first design of the cooker knob showing the clasp for the shaft pin

The Edinburgh Hacklab sounded just the ticket. “This is just the kind of thing we see 3D printing being useful for,” Gareth Edwards, one of the lab directors, told me. “If you go to India you see guys in tiny workshops fixing things, making parts. They don’t throw things away. We have lost that, but I think this can bring it back.”

Just what I wanted to hear, this was looking promising. Gareth introduced me to another enthusiast, Laura van Weegen, who was taking a 6-month sabbatical from work as a business architect to hone her 3D printing skills. She was to be my designer.    

“There are three ways we could do this,” Laura explained. “The first is by measuring the dimensions of the knob and feeding them into 3D printing design software. The second is by using a 3D scanner. The third is by using a phone app which takes multiple photos to build a 3D image.”

Given that my control knob was splintered into two pieces, we didn’t have a 3D scanner to hand, and taking photos from every possible angle seemed rather laborious, we opted for method one.

Laura got to work with a set of electronic measuring callipers. I went home and measured the diameter of the shaft pin the control knob had to fit onto. “Will it be right the first time? Probably not,” Laura cautioned, “but I think we can do it.” Excellent!

We reconvened a few days later. Laura had fed all the measurements into the Rhino 3D software program and created a draft design. Onscreen it looked worryingly complex. The trickiest part was the cylindrical clasp which dropped down from the inside of the knob cavity and fit onto the shaft pin that controlled the gas (see image right). This needed support scaffolding so that it would not collapse during printing. Laura downloaded the design file onto an SD card.

Allianz-Coating the 3D printer plate with glue before printing. Rolls of PLA material for the printer are seen on the left.

We were ready to print. We were using the entry-level Ultimaker 2, a model that builds objects from the bottom up using a printer nozzle which “extrudes” layers of material (or “filament”) onto a glass plate. The nozzle heats to 200 degrees Celsius so it can melt the PLA thermoplastic material which it builds with. We started with white PLA because it was already loaded into the nozzle.

The nozzle moves horizontally left and right, forward and back, controlled by two belt pulley systems. When printing starts, the glass plate moves up from the base of the printer to meet the nozzle and gradually moves downwards as more layers are added. But first an insider’s preparation: smear glue onto the glass plate. “It helps stop the PLA from sticking to the glass,” Laura explained, before inserting the SD card and setting the printer in motion.

Allianz-A view of the 3D printing process showing supports below and within the cooker knob

It was mesmerising. The nozzle darted back and forth tracing the design with imperceptibly thin layers, starting with the supports, which looked just like scaffolding in miniature. Gradually the shape emerged, as if surfacing in ultra-slow motion (see image right). About two hours later the knob was ready, we stripped away the scaffolding and I hurried home, absurdly excited.

Allianz-Success! Version four of my 3D printed control knob in action.

I was to be disappointed. The clasp was too loose to properly grip the pin shaft and turn the gas on. It was also completely flush with the hob surface. Our measurements must have been wrong.

So Laura went back to the design, trimming the clasp diameter. Version two fit the shaft pin better and controlled the gas, but it soon started slipping, which made me even more nervous about whether the gas was on or off. And it was now too high off the hob surface. We had overcompensated.

So Laura further reduced the clasp diameter and moved the clasp further up into the body of the knob. More confident now, we switched to black PLA. Prototype three started promisingly but ended badly, with a hole in the top above the clasp position. “I have no idea how that happened,” was Laura’s perplexed response. Still, we were getting closer, the new knob was a better fit, survived a long weekend’s cooking, and Laura promised version four would close up the hole.

She was good to her word, the final design was the best yet and for the first time in several weeks I could cook without fear! And the total cost for 3D printing time and materials: about 14 euros.

The final stage is to take the design and make it in a stronger, more durable material, and so I ordered the design reprinted by a commercial 3D printing firm. I’m sorely tempted to inform the cooker manufacturer that the control knob for my appliance is no longer obsolete.