I always put them concave down (concave edges on the blade) as the concave edges tend to be a bit sharp - I would prefer they gouge the blade rather than the more long lived disc
Hmmmm well atleast I don't feel so silly now asking, as it does seem there's not a great concensus on the right way to orient. That said i don't sduppose there's a huge difference in effect. I need to buy some more as I'm well and truly due to change the bolt & nuts over - when you resharpen the blades you can get a bit slack about this but I'm aware of the danger metal fatigue can have on such parts and it's best to change rather than a blade suddenly detatching at several thousand RPM!
