• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • Advertise
  • Subscribe

Linear Motion Tips

Covering Linear Motion Systems, Components and Linear Motion Resources

  • News
    • Editor’s blog
    • Industry news
    • Motion Casebook
  • Applications
  • Slides + guides
    • Ball + roller guides
    • Track roller (cam + wheel) guides
    • Crossed-roller slides
    • Linear bearings
    • Plastic + composite guides
  • Drives
    • Ball + lead + roller screws
    • Belt + chain drives for linear
    • Rack + pinion sets
  • Actuators
    • Ball + leadscrew driven
    • Belt + chain driven
    • Linear motors
    • Mini + piezo + voice coil
    • Rack + pinion driven
    • Rigid-chain actuators
  • Encoders + sensors (linear) + I/O
  • Stages + gantries
  • Resources
    • Suppliers
    • Video

How to calculate combined static load

★ By Danielle Collins 3 Comments

Static load capacity is an important factor in linear bearing selection. While dynamic load capacity is used to calculate bearing life, static load capacity indicates how much load the bearing can withstand before permanent damage occurs to the balls and/or the raceways. Even when they’re not moving, linear guides often experience a combination of both forces and moments, all of which contribute to the combined static load that the bearing sees.

The combined static load (sometimes referred to as the equivalent static load) takes into account the various types of loading that a bearing is subjected to at standstill.

A linear guide rail with one bearing can experience forces in both the Y and Z directions, and moments can occur about any of the three axes: X, Y, and Z. This means that there can be as many as five different components to the static loading.

Combined Static Load
Image credit: SKF Group

However, most applications use more than one linear bearing on a rail, and demanding applications typically use two rails with one, two, or sometimes three or more bearings per rail. The benefit of multiple bearings per rail, and multiple rails used in parallel, is that moment loads are resolved into forces. Because linear bearings generally have higher load capacities than moment capacities, using multiple bearings to counteract moment loads will typically yield increased bearing life.


For one rail with one bearing:Combined Static Load

Combined Static Load


For one rail with two bearings:Combined Static Load

Combined Static Load


For two rails with two bearings:Combined Static Load

Combined Static Load


For two rails with four bearings:Combined Static Load

Combined Static Load


Where:

Fcomb = combined static load

Fy, Fz = external forces in Y (lateral) and Z (vertical) directions

Mx, My, Mz = external moments about the X (roll), Y (pitch), and Z (yaw) axes

C0 = static load rating

Mt0 = static roll moment rating (moment about the X axis)

ML0 = static pitch and yaw moment rating (moment about Y and Z axes)

For many linear bearings, the moment ratings about the Y (pitch) and Z (yaw) axes are equal and are denoted as ML0.


Once the combined static load has been calculated, it can be used to determine the static load safety factor. The static load safety factor is calculated by dividing the basic static load rating (C0) by the static equivalent load of the most heavily loaded bearing. The recommended safety factor is given by the manufacturer, based on the type of loading and the usage conditions—low, moderate, or high impact loads and vibrations. It often ranges from 1 to 8, and is used to ensure that the bearing never experiences a load that will cause permanent plastic deformation of the balls or raceways.


Application Note: Preload creates an internal force on the bearing. This internal force is counteracted as an external load is applied. For most linear bearings, when the applied load is equal to or greater than 2.8 times the preload force, preload can be disregarded in bearing life and static loading calculations.

For example, if a bearing has a dynamic load capacity of 25,000 N and a preload of 2%, an external load of 1,400 N (25,000 * 0.02 * 2.8) or greater will be sufficient to overcome the internal preload force.

 

Feature image credit: PILETEST

 

You Might Also Like

Filed Under: Applications, Ball + roller guides, Slides + guides (all) Tagged With: bearing life, calculation, combined static load, linear guide, static load

Reader Interactions

Comments

  1. vijay says

    ★ at

    For my project I am going to use a single lm rail with two slider blocks. the first one carries 10.5 kg and the second one carries 2.3 kg . the full length required is 1 metre .how do i select a lm rail for the above task ? please help me choose the dimensions of rail and block along with necessary calculations.

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

LEARNING CENTER

Design World Learning Center
“lmt
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for Design Engineering Professionals.
“linear

RSS Motion Control Tips

  • Day 1: New technologies at Automate 2025
  • Festo showing multi-axis positioning systems at Automate
  • Rollon marks 50 years of innovation with global expansion
  • New brushless slotless motor for industrial power tools from Portescap
  • PI releases V-308 stage with 10-nm motion resolution

RSS Featured White Papers

  • Robotic Automation is Indispensable for the Logistics Industry’s Continued Growth and Success
  • Reliable Linear Motion For Packaging Machines
  • Technical Brief – “Understanding the Extensive Benefits of Total Linear Positioning Systems.”

Footer

Linear Motion Tips

Design World Network

Design World Online
The Robot Report
Coupling Tips
Motion Control Tips
Bearing Tips
Fastener Engineering
Wire and Cable Tips

Linear Motion Tips

Subscribe to our newsletter
Advertise with us
Contact us
About us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy