Which side of the wheel or disc should face towards the machine? Is there a rotating direction?

For bonded wheels and discs, it is recommended to clamp type 41 cutting discs (type 41 is a normal flat cutting disc), always with the metal centre ring facing the machine flange. This ensures a flat contact surface and helps avoiding clamping failures. If there is no metal centre ring, then the side with the branding should face towards the machine flange.