Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Screw Jack - Effort Force vs. Load

Screw jacks and effort forces.

A screw jack is a mechanical device that can increase the magnitude of an effort force.

Screw jack - load and effort force

The effort force for a screw jack when neglecting friction can be expressed as

F = (Q p) / (2 π R)                                 (1)

where

F = effort force at the end of the arm or handle (lb, N)

Q = weight or load (lb, N)

p = pitch - distance or lead of thread in one turn  (in, m)

R = lever-arm radius (in, m)

Pitch is the distance between screw grooves and is commonly used with inch sized products and specified as threads per inch. Lead is the linear travel the nut makes per one screw revolution. The pitch and lead are equal.

The torque acting on the screw can be calculated as

T = F R                                 (2)

where

T = torque (lb in, Nm)

Example - Screw jack without friction

If the load on a screw jack is 50000 lb, the lever-arm is 20 inches and the pitch equals 1/8 inches - the effort force can be estimated to

F = ((50000 lb) (1/8 in)) / (2 π (20 in))

    = 49.8 lb

The torque acting on the screw can be calculated

T = (49.8 lb) (20 in)

    = 995 lb in

    = 82.9 lb ft

Example - Metric Screw Lift

A M24 metric screw with pitch 3 mm is used in a mechanical screw lift with load 225 kN. The lever arm is 0.5 m. The effort force required can be calculated as 

F = ((225000 N) (0.003 m)) / (2 π (0.5 m))

    = 215 N

The torque acting on the screw can be calculated

T = (215 N) (0.5 m)

    = 107 Nm

Screw Jack Calculator - without Friction - Imperial Units

Calculate torque and effort force acting on the lever arm.

Screw Jack Calculator - without Friction - Metric Units

Calculate torque and effort force acting on the lever arm.

Note the difference between mass and weight!

Screw Jack with Friction

For motion in the same direction as the load (load assist the screw jack), the effort force can expressed as

F = Q ( (2 π μ r - p) / (2 π r + μ p) ) (r / R)                                   (2)

where

r = pitch radius of screw (in)

μ = friction coefficient

For motion in the opposite direction as the load (load resists the screw jack), the effort force can expressed as

F = Q ( (2 π μ r + p) / (2 π r - μ p) ) (r / R)                                 (3)

Related Topics

  • Mechanics

    The relationships between forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more.
  • Statics

    Forces acting on bodies at rest under equilibrium conditions - loads, forces and torque, beams and columns.

Related Documents

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .

Citation

This page can be cited as

  • The Engineering ToolBox (2009). Screw Jack - Effort Force vs. Load. [online] Available at: https://www.engineeringtoolbox.com/screw-jack-d_1308.html [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter

















































11.4.12

.