As I know it, a 'kunstbohrer' is a derivative of the 'forstner drill bit'. The 'kunstbohrer' has 'teeth' (spurs)... the 'forstner drill bit' has cutters (blades - superior finish).
So my translation for a 'kunstbohrer' is 'multispur (cylinder) bit' - or 'sawtooth (cylinder) bit'.
I am SURE it not a 'spade drill bit'. I have seen adjuatable drill bits (mostly spade drill bits), but I have NEVER seen a 'multispur bit' that was adjustable!
'Machine' drill bits (conic top - different angles for different metals) are used for drilling metals; the prefix 'machine' is oftem used in connection with metal working.
Hope this helps..... a translation to German is available for an (alcohol free) beer... Guelle Axel!