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 www.igus.com/drylin
2:1 Rule
The
And how to define fixed/floating bearings
2:1 Rule: permissible
distances of the applied
forces
