do i need endstops

I am building a prusa mendel i2 and and am currently doing the electronics. I am wondering if the endstops are completely necessary for the printer

how you going to tell it to stop and how will you achieve referencing?

You don't technically "NEED" endstops, but they make life a hell of a lot nicer.
Without them you have to manually reference 0,0,0 using G92 every time you power on or reset the printer.
I ran my first printer without endstops, but I wouldn't do it again.

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My blog [3dprinterhell.blogspot.com]

how do you have a reference point with no endstops?

Basically you power on the machine, you jog to 0 in each axis and enter G92 X0 Y0 Z0
which resets the coordinate system.

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My blog [3dprinterhell.blogspot.com]

but it would be easier for cheap enstops switches like i got for 98p each

You could even print one [www.thingiverse.com]

mechanical endstops are highly effectivve and cheap. You can get a pack for a few bucks or even go to your local electronics shop an grab momentary buttons/switches and get it that day, no need to wait for shipping, very easily. I really don't see the point in NOT getting endstops as they provide valuable infomration to the controller board at an extremely low cost...

Manually homing each axis before each print would seriously suck (please don't consider it). X and Y, maybe, but Z would involve re-leveling the print bed since it's impossible to turn both lead screws the exact same amount by hand. It may be a bit of extra complexity, but what do you expect when building a machine? If you want to buy an already made 3D printer, there are several that are probably just as cheap as the reprap and even if it costs a bit more, your time is still worth something. If you want to build one (and do it right), you need the endstop switches. This isn't the place to skimp if you're short on time or cash.

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Manually homing each axis before each print would seriously suck (please don't consider it).

While I have material for some 50 endstops lying around I still didn't build ones for my own printer (laziness). The trick to get away without endstops is simple: at the end of each print, move the print head to a known position. At the start of each print (more exactly: after resetting the controller) send a G92 with this known position.

Works beautifully. Also requires careful adjustment of acceleration and maximum speeds, of course. You should be able to run for weeks without step losses, which works perfectly fine here.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

I don't use end stop.

I just set up the software do that it always prints from zero. And I just move the head to the middle of the table and center the print part at zero before I slice it and print it.
So my zero is always where the head is after I reset the board

I also have to change the slicer so that it doesn't put gcodes that go home before it starts the print