As much as I like the design of the RepRap/Prusa/Mendel type 3D printer, there is one thing I never got happy with: these tiny endstop holders that attach to the smooth rods! These are quite fragile and tend to break if you fasten them too much ... and if you don't fasten them tightly they easily move around by the slightest touch.
So my goal was to design new endstop holders which do not attach to the (usually greasy) smooth rods, and, thus, are less prone to being moved inadvertently...
The first type of endstop I present here is for the x-axis. It attaches to Jonas Kuehling's left (motor) or right (idler) Improved Prusa X-end. It is anchored by the X-end's front clamp screw, which has to be changed from the original M3x15 to M3x20 in order to pass through the endstop holder base plate. Use some washers on the screw head to adjust the thread height coming out at the top so that it will reach into the nut cavity, but not protrude into the slide cavity.
The endstop is designed to work with a standard 20x6mm micro-switch, which has a two screw holes spaced by 9.5mm. I found it easiest to widen the 2mm holes with a 2.5mm drill bit and then cut an M3 thread into them (using an M3 tap or just a clean cut M3 screw). The switch itself is screwed onto to the slide arm, which offers several positions to find the best location of the switch. Once the optimal position is found, the slide arm is fixed to the base plate with a M3x12 screw and the corresponding nut.
The provided SCAD file is highly parametrized, so that it can easily be adapted to special needs.
Ready-to-print STL files are provided for mounting the endstop either on the motor or the idler side. Also I included a wide choice of STL files for the slide arm: Including for arm lengths of 60/90/120mm and for mounting the switch vertically or horizontally in either high or low position. Choose the arm which fits best you particular installation.