How do nozzle changes work?

Hi – I’m a complete noob to 3D printing. I’m looking at the Monoprice Maker Select printer, and had a question about nozzles.I’ve heard that to print with carbon fiber, glow in the dark, and other exotic filaments, it’s generally a good idea to use a nozzle with some kind of reinforced or hardened metal – I’ve also seen that you can get faster print times (sacrificing detail) with a larger nozzle, and more detail (sacrificing time) with a smaller nozzle.I was wondering how the process of changing nozzles works. For example, if I wanted to try out this Volcano nozzle pack, I assume I’d have to buy a new hotend for them to fit in. However, that would (I assume) let me use other E3D nozzles, too – which there are plenty of sizes for and looks like a fairly good ecosystem.Is changing the hotend simple, like – unscrew old one, screw new one in, change settings, or is it way more complicated? Are hot ends even compatible across printers, or do I have to find one that will work with my printer? http://ift.tt/2a7nKA3

Z calibration issue prusa i3 mk2

I have an issue on my printer where it will slam into the build plate on the z calibration. The weird thing is that it only hits in the middle back point of all 9 points. I was just wondering if anyone had any ideas what to do, or if it had happened to other people before. The last print I ran worked perfectly and now I can’t get past the calibration. Thanks for any help you may be able to give me. http://ift.tt/2ag4TQN