Minimum shaft diameter as per AS1403 Table 2 Formula 3 for power applied and torque reversal conditions.
This equation is equivalent to Australian Standard AS1403-2004 Table 2 Formula 3. It should be used only in cases where design and operating conditions match those described in the standard.
Try different values for Dtry until Dtry and DminAS1403F1 are as close as possible.
If value of FR is unknown use 0.45 * FU .
For values of KS see Clause 8.1 and Figure 1.
For values of K see Clause 8.2.