Had a sensor issue recently with the fan on our 6m Rapid system disc drill. Removing the speed sensor from its housing revealed the end had been deeply scored opening it up a fair bit. The fan bearings sounded well but having removed the drive motor the female coupling on the end of the fan shaft seemed to "wobble" about a bit, looking up in the housing it was possible to see something sticking out of the securing roll pin. Once it was all apart it was easy to see that there were 2 roll pins but these had shattered with part of the inner sliding out into the path of the sensor.

Looking at an old shaft the coupling on that was held with an odd sized solid pin and a couple of tack welds. Unable to find some round steel to suit the holes diameter, it was a case of getting the broken bits out and finding a couple of suitable new roll pins. In a bid to stop the coupling waving around again in the future I stuck a couple of reasonable tack welds to hold it tight and take the shock loads off of the roll pins