Because I believe every 'bot should have at least one of these, I made a video. Behold: http://www.youtube.com/watch?v=2iGnlqBLn5s&sns=em

I started with the latest Mechanical Endstop on thingiverse from MakerBot (v1.0), which is for the Gen4 electronics, cleaned up the traces to make it easier to make at home, and then made a few.

I quickly realized that I would need support parts to make these work in my Cupcake, and so far I have the Z Minimum (down) working and a good start on the X and Y supports as well.

I have provided the PDF I used for toner transfer, the sourcefikes for the board and the schematic in Eagle, and the OpenSCAD and STL files for the two parts needed for the Z-Minimum endstop.

Move the traces further from the screws so a home-etched board doesn't need tape to not short on the screws/nuts.
Add a LED position on the back of the PCB in case the shelf is printed in non-clear plastic.
X and Y stages.

These boards should also work well with the Mendel inspired x and y carriage lowrider by twotimes http://www.thingiverse.com/thing:4213 With that the X and Y endstops are already done, and you only need the Z!

These are preliminary instructions for those familiar with electronics, and only for the Z-min endstop. I'll post more info as I develop the other stages and test more.

First, etch or buy 3 or 6 of the boards. The boards are all the same for all three axes. You only need three for full operation of homing, but 6 will keep it from driving completely into the side.

Next, solder the components in place, except for the microswitches. They will go on the back of the board. Be careful about the orientation, it does matter! You might wait until you have the printed parts ready so you can make sure it lines ip properly.

Next, print the parts. Currently that's one Z-shelf and one Z-slider. The slider is actually more of a plunger and allows you to adjust your height precisely. I made the center hole in the slider/plunger just the right size so a 3mm scew will self tap it, but you might need to clean it out with a drill or a round file first. You just want to make sure it's tight enough it won't move with vibration but loose enough that you can make fine-tuning adjustments without having to have large tools.

Place the board onto the z-shelf as shown, with the switch pointing up an the pins through the board into the dip in the shelf. Then place the long 3mm screws into the sides of the slider, and put nuts on the ends, threading them almost till you run out of threads. Place nuts into the holes in the from of the shelf and screw the two screws into them, as shown in the picture. Tighten them until the slider just sits on the switch without clicking it, and make sure it doesn't stick on or off and moves freely. Then tighten the nuts down on top of the board while holding the screws from turning.

Attach the assembly to the endstop position on the right-inside of the cupcake. I used 3mm screws and the holes on the back of the shelf were just the right size to self-tap with a little pressure. Don't over tighten.

Teat to make sure the z-stage will come down and click the switch without lifting the stage at all.

Now, with a cd-rom cable connect your board to the stepper driver. Todo: add instructions for splicing an Ethernet cable to a carom cable for old stepper drivers. This was designed to work with either Gen4 electronics (untested) or my triple axis stepper driver. http://www.thingiverse.com/thing:4526 When it's connected to power, clocking the switch should make the led light up.

Now, in the inboard preferences screen in RepG, change the endstop setting to "Non-Inverted..." and save the setting and restart the motherboard.

Add this to your start code (see the example start code file to see how I use it):

G161 Z (Home down on Z)

Now your bot will go down till the light lights up, and set that as Z-zero! Once you have it tuned right, you won't have to worry about get the nozzle just in the right... and then moving it up or down during the first layer untill it's right. You just center x and y by hand and tell it to go!!

I'm working on the x and y, and soon those will be fix up the same way.