Egg mill - egg shell grinder
by QC
Posted on Sun, May 03, 2020 - 03:56:41 PM
3D print mill grinder compost worm box Wurmkiste
Motivation
A while ago we've started an indoor compost in our flat. This so called 'worm box' is filled with earthworms and other helpful organisms. Those break down our leftover vegetables and give us ultra healthy humus and fertilizer for our plants. Every now and then the box need some minerals for the worms to grow big and strong and to avoid flies to grow. This mineral mix can be bought, but also home made out of dried egg shells. The shells accumulate almost on their own, just grinding them down with mortar and pestle is quite a time consuming task. A couple of days ago we've gotten our hands on a broken coffee machine with integrated grinder and the solution was born.
All project parts and additional photos are on github.
Photo of our worm box
Grinder donor
 The coffee maker had some repair done and after trying to fix it one last time just decided to die. Before throwing it away though, the grinder was saved, still in mint condition. It is driven by a 230VDC (DC!) motor, therefore a little circuitry for rectification and voltage adaption was on the original PCB. I took off the parts needed and threw them on a PCB, the schematics are down below. If you want to reproduce this project and think you have a similar machine, you should be fine with little to no adaptions. The machine was a "Saeco Intuita" for reference. Please note that the 230VAC can be lethal and you have to take great care. I don't take any responsibility whatsoever if you build this yourself.
The grinder and circuitry
Schematics for rectification and voltage dropping
Case
To be able to actually use this mill in a useful way, a case and some extra parts had to be printed. The parts were drawn in solidworks, according to some rough measurements we took beforehands. stl, gcode and other stuff are in the repository.
Rendering of the case
Cut through the case
Result
In the end we printed a lid for dust protection and a small plunger to save our fingers. There's also a small video of it in action and some more photos which i will leave below.
View from the top into the mill
View from below
Video of the mill in operation