Mendel i2 axes orientation

Hi,
I am constructing my Prusa Mendel i2 and I was unable to figure out some details about its axes. So the questions:
1. Do I correctly understand the axes orientations: X - is carriage which holds the extruder and its origin (zero) is on the left (if looking from front which is where heated bed drive mounted). Y - heated bed, origin is rear. Z - extruder, origin is bottom.
2. If 1. is correct, with such orientation it is left-handed coordinate system. But CAD software often has right handed system. How to overcome this? At which step of printing (preparation) I should convert the handedness?
3. Should I install endstops on each axis origin (I use Marlin firmware)? Is endstop a zero coordintate which is also "home position"? If yes, does it mean that Z-axis home position is bottom? But then I do not understand how to use it. The firmware does not allow positioning before the endstop (negative coordinates). So should Z-axis endstop be exactly on the bed level? (touching it?) But when I issue Z homing command the firmware drives the carriage at high speed just a bit past the endstop, than it rolls the carriage a bit back and precisely positions it at low speed. So the printing head will hit the bed in such case. What is the correct setup? Also does the extruder move to home after printing done? If yes, should not it move up, not down to the bed, where printed parts are lying?

Edited 1 time(s). Last edit at 01/23/2015 10:00AM by vagran.

Typically, the origin (0,0,0) is located on the front left corner of the print bed, touching the surface. This means that the X-carriage is to the far left, the bed is retracted toward the back of the printer and the nozzle is down all the way, very lightly touching the glass (or whatever surface material) of the print bed.

The end stops can be placed at either end (or both ends!) of each axis. The configuration.h file in Marlin will need to be changed to match the location of your end stops, and the end stops connected to the correct pins on the board.

---

-David

Find me online at:
Thingiverse
Instructables.com
LinkedIn
Facebook

Check out my FolgerTech Prusa i3 (plexi) at MindRealm.net

Oh, I understood at least one thing - the bed moving direction is inverted relatively to Y-axis direction, that confused me. So it is right handed. Thanks! But if it touches the surface, it will will hit it each time the head is positioned home (because of this high-speed first try overshooting). Is it OK? Will it scratch the bed surface if Z-home is reached first (before X and Y home)?

I would suggest placing a bit of masking tape on the surface of the bad at the front left corner (0,0) if you are worried about scratching the surface. You can also install your Z-min end stop a little higher during testing to stop the nozzle from hitting the bed, then move it back down when leveling the bed.

---

-David

Find me online at:
Thingiverse
Instructables.com
LinkedIn
Facebook

Check out my FolgerTech Prusa i3 (plexi) at MindRealm.net

OK, thank you for the answers!