Calculating the needed force to turn a stub with 7.5 nm

[Trkp]

Hi Guys
I have a stub I need to fasten with 7,5 Nm. Around it, I have 6 small tongues which are activated by pneumatics.
The tongues clamp on the cyan surface, and are not allowed to make any scratches.
How do I calculate the the needed radial force on the cyan surface in order to turn/tighten the stub with 7.5 Nm
All measurements is in mm
Best Regard
Trkp

 

[rb1957]

so coefficient of friction ? how much normal load to develop the required tangential load ?
tangential load (per tongue) is 1.25 Nm/0.0056m = 223N
CoF = 0.01? radial load = 22300N

If you're serious about not damaging the stub, then radius the edges of the tongues (so they don't dig into the stub)

another day in paradise, or is paradise one day closer ?