Using Eggshells in compost,
I have always just chucked the eggshells in the compost bin. Looks like that is not do anything any good.
All though it does get rid of them.
Jerry Coleby-Williams suggests eggshells in your worm farm to add lime. I watched Jerry on Gardening Australia on the 17/8/2013 building a worm farm. (He gave the simplest and easiest instructions I have ever seen). He ground the eggshells in a mortar and pestle, till they had a coarse sand texture.
link to fact sheet. http://www.abc.net.au/gardening/stories/s3827415.htm
link to video http://youtu.be/ZN3cACBUWjI
One thing I know from my Grandmother is if you want to grind eggshells they need to be dry to grind up well.
I remember my Grandmother would always dry eggshells in a slow oven then crush them with a rolling pin till very small unrecognisable pieces. She fed this to the hens to give them calcium and always said very important to crush them up well otherwise the hens could attack their own eggs.
The article below is a great help, from this I understood if I want to use eggshells and get the calcium/lime out of them, I need to grind them up thoroughly to release the calcium.