Re: strange marks on S76 blades
Just for the record(not a record) but debris from a 9" angle grinder will travel in still conditions 60Ft and will at that range stick to auto glass, the sparks you see start life at about 1200Degree's and transfer that heat (or variations of it) to whatever they land on and will burn through Plastic coated steel roofing sheets with ease, if using a cutting disc (not a grinding disc) these sparks will be the hottest when cutting through High Carbon steel.
Leave your Auto or Heli or Plank at least 100mtrs away from any halfwit with any sort of grinding or cutting equipment.
Vfr