HW9 Hints & Tips


HW9.1
Use Eqn. 16.4 or 16.5 to calculate the pitch diameter of Acme screws.  If you use an effective thread friction of 0.2066, you should get 1888 in*lb of torque required.  Friction would have to be 0.054 for the screw to unscrew on its own.


HW9.2
Tangent of the lead angle is 0.127.  Torque would be 53.03 Nm.


HW9.3
Look up the pitch of a coarse M10 screw in Table 16.9.  Calculate the pitch diameter: CrestDiameter-0.75*Ht, with Ht from Eqn. 16.2.  Don't use Eqn. 16.4 because that is for Acme threads and this is a 60° thread.  Preload should be 43.7kN.  Either calculate the tensile area with Eqn. 16.34 or just look it up in Table 16.9. Tensile stress should be 753.5 MPa.  From Table 16.7, that's going to require a bolt of minimum grade 10.9.