When using systems with two parallel rails, one side must be designated as the “fixed” rail, and the opposite side as the “floating” rail.
The “fixed” bearing rail should be positioned closest to the driving force. This rail will determine the precision of the system; no system should contain more than two “fixed” bearings.
The “floating” rail should be the rail located furthest from the drive force. It should only act as a guide, and will compensate for misalignment or errors in the system ensuring proper functionality.
The mounting surfaces for rails and bearings should have a very flat surface (e.g. milled surface) in order to enhance performance. Variations in these surfaces may be compensated for by using floating bearings.
See the different installation variations (right).
Fixed bearing carriage4
Floating bearing carriage LLZ or LLY
Lateral installation option with floating bearing in z-direction
Horizontal installation option with floating bearing in z-direction
Horizontal installation option with side-mounted carriage and floating bearing in y-direction
Automatic compensation of parallelism errors
The 2:1 Rule
When using drylin® linear guides, it is important to ensure that the acting forces follow the 2:1 Rule (see drawing, right). If either the load or the drive force (F) is greater than twice the bearing length (1x), then a binding or interrupted motion may occur.
If the location of the drive force or load can not be changed, simply increase the distance between the bearings, or create a counterbalance to move the center-of-gravity back within the 2 to 1 ratio.
This principle applies regardless of the load or drive force. It is a product of friction and is always related to the fixed bearing. The greater the distance between the drive force and the guide rail, the higher the degree of wear and required drive force.
The 2:1 rule,
1. Floating bearing, 2. Fixed bearing
Failure to observe the 2:1 rule when using drylin® linear guides can result in uneven motion or other problems. Such situations can often be remedied with relatively simple modifications.