I like baking. I love coffee. But I hate waste! That's why I spent a couple of weeks in the summer taking apart a couple of old kitchen appliances that weren't quite working, but were in far too good a condition to be thrown away - leaving the small task of fixing and reassembling them...
The first appliance I fixed was an old pair of electronic scales. There were two problems with it: firstly, two of its four plastic feet had come loose, and secondly, it wasn't turning on, despite having new batteries.
The first challenge was getting the device apart at all, as there were no visible fixings on the outside whatsoever. It soon became clear that they were buried under the stainless steel plate that covered the top surface of the unit, which was glued tightly to the underlying plastic. After a considerable amount of poking and levering, the plate came off, revealing the plastic body and screws beneath. Undoing the screws allowed the upper part, containing the electronics and load cells, to be removed from the main body.
It was now possible to remove the on/off button, which was simply a cylinder of rubber with a conductive pad on the bottom, revealing a set of contacts - covered in dirty residue from years of baking (mmm...). This residue was preventing the button from making electrical contact, hence why the scales wouldn't turn on. I carefully scraped the dirt off, pushed the button back in, and sure enough, the scales came to life. Although it was still working, I repeated this procedure for the units button for good measure.
It was also now clear that the feet had come loose because the plastic they were made of had degraded so badly that I could crumble it with my fingers. All four feet had suffered to some extent, so I set about reverse-engineering the geometry in Fusion 360 so I could 3D print a new set. This was complicated slightly by the small steel disc that snap-fitted into the top of each foot (presumably to spread the contact force where it touches the load cell), and I also modified the outside profile slightly so it could be printed without supports. To my surprise, the design worked first time - a rare occurrence with any 3D print, especially one that has to fit with existing components.
With both problems fixed, all that was left to do was reassemble the scales, apply a liberal amount of epoxy resin to the top plate and leave it to set - good as new!
With the scales fixed, I moved on to fixing a coffee machine that had sat unused for a number of years. The problem here was quite simply that very little water was coming out of the head. The machine was easier to get inside than the scales, requiring only two screws to be removed, but then came the task of figuring out what each part does and testing each one to see where the problem was.
Now I was able to see inside, it was clear that the pump was working fine, but water was leaking out of the heating chamber and running down the outside. This was made worse by the fact that the head plate was covered with coffee residue, which had dried solid and blocked almost all of the holes in the perforated plate. Removing the plate was simple enough, but unblocking the holes was anything but: initial attempts to break down the residue by soaking the plate in soapy water or vinegar had little effect, so I resorted to the painstaking method of unblocking each hole individually with a needle.
I reinstalled the plate and tested the machine again - more water came out this time, but the pressure was still far too low because the heating chamber was still leaking. Disconnecting all the pipes and electronics from the heating chamber assembly allowed me to remove it from the housing, but I was stopped in my tracks by the four large socket screws that held the chamber itself together, which, exposed to years of heat and damp, were covered in rust and scale that had welded them tightly in place. It soon became obvious that no amount of force would be enough to remove them on its own, as the allen key was starting to round the screw heads. I was about to resort to drilling them out when I realised I might be able to dislodge them by applying some heat. Sure enough, a small blowtorch, combined with a reasonable amount of force, was all it took to help ease them out.
Opening up the heating chamber revealed a thick layer of limescale coating the inside, along with the rubber gasket that sealed the two halves, which was stiff and also covered in scale. This, along with the screws (which were now good for very little) clearly needed replacing. Luckily, these spare parts were still available from a third-party supplier as they were also used on newer models - a great argument for part standardisation, if ever there was one! I placed these on order and then set to work trying to descale the heating chamber.
The usual method of descaling is with an acid such as vinegar, but soaking the heating chamber in it for three days did little more than make the entire room smell of vinegar - it was clearly no match for this amount of build-up. The only alternative was to remove it manually, by scraping away at it with a variety of hard metal implements. This was another painstaking job that took the best part of two days to completely finish. However, the result was worth it, as the machine will hopefully give many years of service before it needs this sort of maintenance again.
The spare parts had now arrived, so I reassembled the machine and plugged it in for a final test. Thankfully, there was no leakage and everything worked as it should, but I thought it best to run a few litres of water through it before making any coffee - if nothing else, to get rid of the taste of vinegar!
In the process of taking the entire machine apart and rebuilding it, I learnt quite a lot about its design, and two things surprised me:
