Isthmus Engineering and Manufacturing Co-op (IEM) is a co-operative that produces robots and robotic services for other industries. As a worker’s co-operative in the United States, it allows considerable autonomy to its workforce in making decisions, including on production methods. In IEM we found that tacit knowledge and tinkering/hobbying were important parts of the co-operative functions. Although the co-operative was a radical, worker-centred organisation, its position within the supply chain of primarily profit-making, private firms meant that workers did not always have the autonomy to conduct the projects that they would want to be involved in. In the conclusion, we remark on the possibilities of co-operative organisation for collective decision-making and for prefiguring more democratic and less exploitative workplaces and societies.