Collaborative robots, such as the KUKA LBR iiwa, UR series from Universal Robotics, and many more, have opened new fields of applications in industries through human-robot collaboration. However, despite up to seven rotational degrees of freedom typically offered by commercial collaborative (and industrial) robots, the operational reach is often not sufficient. This prevents these robots from reaching into and operating within confined spaces autonomously or in collaboration with human co-workers. To overcome these limitations, this paper presents a custom-made, open-source, affordable robot arm extension to be mounted on commercial or custom-made robots. The developed solution adds three additional degrees of freedom, including a 0.5 m linear rail. These additional degrees of freedom of the robot extension significantly increase the reach and ability of industrial and collaborative robots to operate in narrow environments. The developed extension is demonstrated by extending a KUKA LBR iiwa 14 collaborative robot operating various insect farming use cases, including tasks such as reaching into crates for insect rearing, operating within caged enclosures, and material handling over a wider workspace. Furthermore, simulations are used to provide insights into the extended reach of the robot. Simulation results show an increase in total operational space by up to \(110\%\) , and a \(200\%\) increase in positions reachable from \(\ge 50\%\) of tested orientations, compared to a baseline KUKA iiwa.