Scissor Lift Jack Review & Equations

Credits:
Calculations proof contributed by:
Jean-Philippe Major
Jeffrey Trembley
Dominic Pellerin

Equations and Calculators updated: April 20, 2012

To submit an improved mathematical proof(s) (yes, we know parts of proof has an acedemic sign (-) imperfection) send a pdf with proper credits to webmaster-at-engineersedge.com.

A scissor lift (jack) or mechanism is device used to extend or position a platform by mechanical means. The terms "Scissor" comes from the mechanism utilized which is configured with linked, folding supports in a crisscross 'X' pattern. The extension or displacement motion is achieved applying of force to one of the supports resulting and an elongation of the crossing pattern.

The force applied to extend the scissor mechanism may be hydraulic, pneumatic or mechanical (via a lead screw or rack and pinion system).

Design Equations for Scissor Lift:

For a scissor lift that has straight, equal-length arms, i.e. the distance from the horizontal-jack-screw attachment (or horizontal hydraulic-ram attachment) point to the scissors-joint is the same as the distance from that scissor-joint to the top load platform attachment.

Scissor Jack Equation With Load Applied At Center Pin:

Free Body Diagrams:

Static Equations

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