5663N acting axially on a flat dry joint between two flat circular faces.
O/D = 0.0635m…I/D = 0.0534m.
Hard' Steel to Hard' Steel.
Assuming friction Co-Eff' of 0.42.

Need to find the torque (Nm) at which the joint is likely to start slipping…

So have been using:-
T = [/3] * [[Do^3-Di^3]/[Do^2-Di^2]]

(u=Co-Eff')
(R=Axial Force)
(Do=O/D)
(Di=I/D)

And getting about 70Nm.

Anyone used to these calcs, (possibly even have a spreadsheet/program) & could possibly check them for me ?

The 'rule of thumb' calc for bolts is: axial force = (5 * torque)/ diameter, assuming a coefficent of friction of 0.3 at all interfaces (bolt head, washers, threads, etc etc), so the formula looks about right. Not checked the numerical usage though.

hmmm, thinking it through………..

It's not moving, therefore the greatest force is closest to the axis. However if this were to slip here, the next bit moving outwards is still gripping. So nothing moves untill the outer edge does.

Fy=cFx (x= perpendicular in my head, y is in the same plane as the interface)

T=FyDz (Dz is distance for the axis (outer diameter), same plane as the interface, but perpendicular to y)

T/Dz=cFx

T=151Nm

well? what was the answer?