Tech Talks

The 2-1 Rule and How to Define Fixed/Floating Bearings

Tech Talks by igus helping solve design engineering problems with motion plastics

Issue link:

Contents of this Issue


Page 0 of 2

When using drylin ® linear bearings and slides, it is important to ensure that all acting forces follow the 2:1 rule. In a nutshell, if either the drive force (Fa) or applied load force (Fs) are a greater distance than twice the bearing length (wx), then a binding or chattering of the system can occur. This distance is measured from these forces to the rail closest to the drive force, which should be defined as the fixed bearing side. It is always a good idea to spread these bearings as far apart as your design will allow. Example: When designing a four-bearing, two-rail system, and the two bearings on the fixed rail are 10-inches apart, then both the drive force and applied mass-force need to be within 20-inches of that rail. On the side closest to the drive force (Fa), you should spec fixed bearings and on the the other side, floating bearings. If you are using a one-rail system, you only need to use fixed bearings Defining a Fixed and Floating Side In a two-rail, four-bearing set up, it is important to define one rail as the fixed side: this should be the rail closest to the drive force. The other rail needs to be the floating side, which uses bearings with a little extra clearance: this should be the rail furthest from the drive force. You should only use two fixed bearings in any linear guide system to maximize the 2:1 ratio. Fixed bearings give the system precision and optimize the 2:1 ratio. Floating bearings do not affect this ratio and only act as guides in the direction of the applied load. Fixed – floating systems provide many benefits such as: • Optimizing the 2:1 ratio • Reducing the drive power needed to move the system • Minimizing wear so the bearings will last longer • Increasing the maximum permissible velocity • Maintaining better precision (floating bearings) in the system over its lifetime • Compensating for angular rail misalignments (floating bearings) so if a drive force is located in the center of the two rails, it is still beneficial to specify a floating side. Learn more at 2:1 Rule The And how to define fixed/floating bearings 2:1 Rule: permissible distances of the applied forces

Articles in this issue

Links on this page

view archives of Tech Talks - The 2-1 Rule and How to Define Fixed/Floating Bearings