This is another adapter that allows to motorise a Hario Skerton manual coffee grinder with a standard hex shaft electric screwdriver (like an IXO as shown in the photo).
The difference with the other models that can be found on Thingiverse, is that this one can be mounted without having to remove the handle or nut. This means the grinder won't fall apart if you topple it over, and you can switch to manual at any time.
Do not use any tool that spins faster than about 3 revolutions per second, this could damage your Skerton.
It is obvious that this part must be printed to be as strong as possible, because it will need to withstand quite a bit of force. Any type of filament will probably do, but I recommend ABS or PETG. Print it nice and slow with not too thick layers, with the fan disabled except when absolutely necessary (e.g. for the hex shaft which could become a blob without extra cooling). Use a high infill, at least 50%, although 100% may be the best choice. Print with a high number of perimeters for extra strength, I used 4.
A PETG model I printed was able to withstand the force of the IXO being jammed on a stubborn coffee bean, but it eventually broke at a weak point caused by me messing up the fan settings. I printed another one in rigid.ink ABS filament, and that one held for quite a long time until I broke it by making a wrong move with the IXO. I was actually amazed at how strong a home-3D-printed part can be.
Update 2016/12/30: I added an alternative model that accepts a hex shaft, this should be less prone to breaking. Even if you don't have a metal hex shaft handy, you can still print the provided 1-inch shaft, which might be more robust than the upwards-pointing shaft that is integrated in the other model, because the layers will be perpendicular to the torque forces. Still, you will need a damn strong filament and print with many perimeters to give this shaft any chances of survival. I tried one in ABS which broke eventually. I then tried one in PLA, which to my surprise has held up so far.
I'll be honest about the fact that this more of a novelty than something really practical, unless you can have it printed in metal or some other nearly indestructible material. Even the strongest of typical filaments will not be able to survive if you tilt your electric drill too much, which puts undue strain on the base of the hex shaft and breaks it. Even the alternative model that accepts a separate hex shaft and is much more robust, still is not terribly practical. If you are too lazy to grind your coffee manually, buy a motorised grinder ;)
The photos show the part printed with rigid.ink PETG and silver ABS.
Next to the regular models, another one with a pre-made tiny support is provided, which can help with blobby filaments to get an accurate print of the small overhang at the bottom (just cut off the support with a knife).
If you want to print the hex shaft, a raft is highly recommended because you should print the shaft with many perimeters or a high infill, and this will increase the risk of it warping during printing. Print it with the strongest filament you have. The shaft STL model has exact dimensions, you may need to sand it down a little bit for it to fit in your drill.