Proper endstop location for 12" i3v questions

I am apologizing in advanced for the following noob question. I am the definition of a beginner. Essentially, I'm trying to better grasp how the endstops work. I understand that when I autohome the printer, it moves in the direction of the endstops and once it triggers them it knows it's in the home position for that axis. And that home position can be adjusted by adjusting the physical location of the endstops. My first question is where should the home position be exactly. I know it's in the back right corner of the i3v when your are looking at it from the front, but how far from each edge of the build plate should the nozzle be? Basically where should my x and y home positions be? For the z-axis, I understand where my home position should be.

Now, on to my next question which may be more specific to the newer i3v 12". When I adjust my y-end stop, I run into two issues. Either the endstop is too close to the front of the printer and my nozzle actually hits the relay built into the heated bed when the x-carriage moves left and right, or it's too far away from the front of the printer and when the y-axis moves the full 300 mm away from the front, the y-axis idlers hit the back of the printer. So it seems like it's impossible to utilize the full 300mm without hitting something. So for any users who have had experience with this printer, did you have this issue with the y-axis and if so how did you solve it. Or, what could I be doing wrong that is creating this issue for me.

And finally, this is a question im sure most 3d printer users could answer. What tells the printer to stop when it's moving in the direction opposite the endstops as in there is no endstop to tell it when it's reached the physical boundary of the printer? Is this just accomplished by not building anything larger than 300mm x 300mm x 300mm or would the printer actually stop itself if a command told it to go beyond its limit. Like if I manually commanded the x carriage 300 mm away from the endstop, would it automatically stop if I told it to keep going or would it just start skipping steps. Is there a place in the firmware where you tell the printer the physical limits of the printer and to stop when it reaches them.

If you made it this far, I sincerely thank you for taking the time to read this. If you have any comments/ suggestions, please let me know!

Thanks,

Preston

It's a matter of personal preference, but I found it made sense to move "home" to the front-left corner. That way I have improved access for wiping filament from the hot end as it heats up. To keep the x-carriage out of the way at the end of a print, my ending gcode includes moving the nozzle to the right-rear corner. I didn't want to mess with printer firmware settings at the time, so I just relocated the x and y endstops and reversed the x and y motor connectors at the electronics board to cause the motors to move in the opposite direction.

On my 8-inch i3v, I found the x-axis was also short from the advertised 200mm. Most probably wouldn't care, but I took on getting those last few millimeters available to me as a challenge. It took some minor modifications to achieve the full 200mm.

FWIW, the print bed on the 200mm printer has (or at least used to have) a square silkscreened on the top that could be used as an end-stop positioning guide. The "back edge" has about 3mm clearance between the edge of the heat bed and the square. The front edge has about 8mm clearance, and the sides about 6. I'd see how far your nozzle can travel to your endstop side without anything mechanically stopping it. If the nozzle can get to the edge of the bed, adjust that end stop so you're maybe at least a few mm inside of that. Then see how far you can command the nozzle to move from that endstop. If it seems like you can get more than 300mm, I'd go back and futz with the endstop to center the movement between the edges of the bed. If you're short from 300mm, one option is to move the endstop closer to the bed edge, as long as the printer mechanically lets you to.

Both the slicer and the printer firmware can keep you from trying to print something that is too large. The slicer shouldn't let you place an item that is larger than what it has been told your bed size is, and the printer will automatically truncate any commands to go beyond what it thinks your range is. Key to at least the latter is performing a homing operation every time you turn on the printer or reset the electronics. Otherwise the printer will default to thinking the zero positions on each axis is where ever the nozzle was at turn on/reset. BTW - multiple early adopters of the 300mm printer from MakerFarm found their prints were being "cut off", only to eventually realize they had received electronics configured for a 200mm printer, not 300mm.

In general, the endstop is the farthest out that axis will ever be able to travel, so the kind of deceptively simple answer is to put it at the furthest point you want the printer to be able to move.

If you have a single nozzle and you're doing simple printing, you should probably adjust it so the nozzle is right at the edge of the glass, enabling you the largest possible envelope. This is the simplest setup and would be a good place to start.

If you have dual extruders or if you want to get off the edge of the glass to prime the nozzle, then you may wish to move further off the glass, knowing that you'll have to tell your slicer that it can't print there.

I am running a double extruder, and I want my left-hand nozzle to be able to reach the right-hand edge of the glass, so I designed an underslung X limit switch mount that allows me to move much further to the right to be able to do this: http://www.thingiverse.com/thing:945481

I then have start- and end-gcode to move around and do special stuff, like priming the nozzles and wiping them on the edge of the glass. You don't have to do any of this to start out, or ever if you don't want. I would just keep it simple for now and set it to the edge of the glass.

Thanks for the quick replies. I figured out everything thanks to you guys. Seems like my Y-axis won't quite be 300mm but that's ok. It's pretty close. I'll definetly be setting up that double extruder one of these days. Very well designed. Thanks again.