It took some time to find optimal places and constructions for the limit switches at the ends of the axes. Unlike what I would expect, for the Sainsmart control board the switches connect to a common 5V instead of ground, so it’s not possible to use the chassis for a common ground connection.
Because the driver board has only 4 inputs and each axis has 2 limit switches the two switches for each axis are connected in series to one input.
One very important switch is the emergency stop. This is directly connected to the motor controller board so that it will work even if the driver software would hang. While waiting for the ‘production’ button to arrive I mounted a temporary one.
To make sure that also the spindle motor is stopped immediately in case of an emergency this is connected to the mains power via the relais on the control board.