What does Layer Height and Density have to do with print quality and functionality?

Layer height affects quality directly in the fact it controls how visible the layers are. The smaller the layer height the less visible and more solid looking the model will be. Density directly affects strength in that it creates more surface are for each layer to bond to. What would be stronger, a layer that is bonded all the across for edge to edge or a layer that is bonded on at the perimeter? Or 20% of the layer versus 99%?

Printed the following geared keychain(http://www.thingiverse.com/thing:561175). when I inserted smaller gear the plastic cracked on center hub. Does print resolution change strenght. How do I prevent this for future builds.

Thanks.

What was your fill setting? More than resolution, speed and temp affect strength. Slower is always better even if you can't wait. So the best option is the best resolution at slowest speed and max fill for ultimate strength.

Thanks.