Transportable machining unit, structure and stack arrangement

Transportable machining unit for machining a workpiece with a tool, comprising a box-shaped support structure which can be placed on a support and which box-shaped support structure has a workpiece support plate which workpiece support plate can be used to support the workpiece to be machined, and a drive unit for mechanically driving the tool, which drive unit is arranged at least partially in the support structure and is fastened thereto ready for operation, so that the drive unit remains at least partially in the support structure during machining of the workpiece by the tool driven by the drive unit, wherein the support structure has support arms which, in a state, in which the support structure is placed on the support, define a footprint of the support structure, and which can be positioned selectively in a transport position or in a working position, wherein the footprint of the support structure is larger in the working position in at least one horizontal direction than in the transport position, the transportable machining unit further including one or more position sensors for detecting whether the support arms are in the working position, the transportable machining unit further comprising control electronics for controlling the drive unit, the control electronics comprising a safety device configured to receive detected positions of the support arms from the position sensors and to prevent the drive unit from being supplied with power if at least one of the support arms is not in the working position, wherein the safety device is configured to set the control electronics to a state in which they do not supply the drive unit with power if at least one of the support arms is not in the working position.