ROK Coffee Press, Replacement Piston

prusaprinters

<p>My favorite ritual every morning, grinding and making coffee with the ROK machines! For years (6/7?) these are our coffee making machines and we love them! They are really well build and are used multiple times a day.</p> <p>The only thing I find could really be better engineered is the piston as it deforms over time and has in my opinion a less then ideal design and quality compare to the rest of these machines. In my opinion the forces are distributed in a less efficient way and materials are to thin to handle these forces. They often start to show strain marks and soon after start leaking air and water.</p> <p>I decided to redesign the piston, not only using more material to make them more solid, but also redesigning the stress distribution. I added a way for the forces to directly go down through the middle, and also added triangles to handle/correct sideway's forces. I also had some fun running simulations on the new design with 15Bar while normal operations goes up to 9 bar max I think. Though this is pure an indication.</p> <p>Update : NGEN Failed and burned my face. After taking offline I put it now back online with correct materials test for over 100 usage now over more then a month. Works perfect now, better then original in my opinion.</p> <h3>Print instructions</h3><p>Warning : If printed with materials not able to handle the heat+forces the print will deform and most likely turn into a supersoaker spraying boiling water in your face!</p> <p>Believe me, I have had it when I thought PET/NGEN with a TG of 85°C would be good enough for short periodes. It started deforming doing 2 cups after eache other, while I was looking from above to see if it all held up. Burning my lips in the process (O.o) and I still think I was lucky. I directly did pull this file offline but having tested it now for over a month with the correct tolerances and materials. Now I feel confident again as it feels and looks better then the original plungers.</p> <p>How to print it safe:<br/> Print only with filaments that have a good mechanical strength above 100°C. Not only will the part need to hold it shape with ~90°C water around it, it also needs to hold its shape while you apply forces on it at the same time. It also needs to be food save of course. I ended up using ColorFabb HT (PET HIGH TEMPERATURE) witch has a TG of over 100°C with good strength. But I would advice others to maybe go with something even stronger like Nylon (often a TG of ~130°C). Also keep in mind of where the water will go if it part failes and don't put your face there ;). The original plungers come with the same warning so I thought I will put it in here too.</p> <p>Disclaimer : This file and/or any information around it is shared as is and can be used at your own risk. Use your own common sense when printing and using this file as incorrect handling can result in burns.</p>