An old urban legend that has been recently revived surrounding cranes, excavators and other construction equipment with a fully-rotating upper cab concerns whether it is possible to cause it to unscrew itself simply by spinning it enough times in the same direction.
This is simply untrue, and whilst most of the time people who mention the possibility of an excavating machine spinning 16 times and disassembling are typically joking or taking advantage of an old rumour to avoid reckless use, it is also impossible given the design of the machinery.
The main reason why this is not true is that an excavator cab is connected to the tracks and lower structure through a slew ring system, which is a system of bearings, mounts and caging that is designed to slowly but consistently turn in the same direction.
Because of their robust design, they will typically lock up rather than unscrew, and even this will happen throughout thousands of hours of constant turning. This is what it is designed for, and any slew ring that can allow even slight loosening of this rotational mechanism is defective.
As well as this, gravity and friction will keep the upper cab from disconnecting from the excavator unit, and these opposing forces will stop the rather fanciful idea that the excavator’s upper machinery will launch itself from the bottom part.
Excavators are not designed to swing quickly and uncontrollably, but instead will rotate in a controlled mechanism for hundreds of thousands of cumulative hours and millions of rotations with appropriate maintenance.
It is more likely that the excavator’s hydraulic system would overheat and thus stop the rotational forces long before the slew ring could be damaged in any meaningful way.
Whilst excessive rotation could potentially wear out an excavator over a considerable amount of time, 16 rotations in one direction are nowhere near enough to cause any issues.
https://www.britannica.com/technology/excavating-m...
