Page 95 - Mechanical Engineer's Data Handbook

84 MECHANICAL ENGINEER'S DATA HA

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2.7.4 The wedge
(k)
Wedge angle u = tan -

Force Q normal to wedge face F = 2Q(p cos u + sin a)
Force Q normal to force (F), F = 2Q tan(u + 4)
where: p = tan 4.

o=tan-'(z) (for n starts)
i Torque to lower load TL =- WD tan(6 - 4)

2
Torque to raise load TR = - tan(6 + 4)
WD
2
tan 6
Efficiency q =
tan@ + 4)
Maximum efficiency qma, =

Mechanical advantage MA=-=cot(O+d)
W
F
XD
Velocity ratio VR = -
2.7.5 Friction of screw thread P
Square section thread Vee thread

For a vee thread the 'effective coefficient of friction'
Thread angle 6 =tan- (for one start)
nD Pe = P Sec B