Just because I'm bored at uni:
- length of the circle with r=58 mm: ~360mm
- distance of tip traveled at 4000rpm in one minute: (4000*360)/1000 = 1440m
- speed [m/s]: 1440 / 60 = 24 m/s
This means the rotor will slam into your finger at approximately 86.4 km/u (24*3.6). I can tell you; your finger will lose the battle