Lead Screw Formulas

Torque required to drive load W using a lead screw with pitch p and efficiency, e

Ttotal=Tfriction+Tacceleration

Tfriction=F/2ppe

F=frictional force in ounces

P=pitch in revs/inch

e=lead screw efficiency

F=mW (for horizontal surfaces)

ms=coifficient of static friction

W=load weight

Taccel=1/g(Jload+Jlead screw+Jmotor)w/t

W=2ppv

Jload=W/(2pr)2

Jlead screw=(pLrR4)/2

 

T=Torque, oz-in

W=angular velocity, radians/sec

T=time, seconds

V=linear velocity, in/sec

L=length, inches

R=radius, inches

r=density, ounces/in

G=gravity constant 386in/sec2

Lead Screw Efficiency

Type

Effeciency %

 

High

Medium

Low

Ball-Nut

95

90

85

Acme metal nut

55

40

35

Acme plastic nut

85

65

50

 

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