I once did an H&S course on grinding machines and the first thing i learnt was to safely guard it it would be imposible to use a bench grinder as all the rotating stones would be fully encased so you introduce a segmental opening and safety is out the window and is reliant on the opperator to be trained and sensable, Given mans quest for inovation we try to make machines do things they wernt intended to do to make tasks easier and quicker . A lot of the vids on You Tube are show off ideas with no safety thoughts gone into and because the internet is a mass media resouce more people see monkey do and hence more accidents ACCIDENTS are just that unplaned and can happen to the best of us no matter how expert we are we can only try to be as safe as possible and use our sence to stay in one piece ( undead ,mangled , maimed ,dispatched to another world ) ps thanks Monty Python