Working with Linear Bushings Pt. 2: Bushing Comparisons

Linear guiding devices are the most frequently used motion elements on automation equipment for palletizing, transferring, positioning and assembling. Here, linear bushing application tips will be explained along with comparisons of [1] Linear Bushings, [2] Linear Guides, and [3] Plain Bushings.

Comparison of Linear Bearing Characteristics

Three linear guiding types are roughly compared below.

∆- good

O- insufficient

bushings

Relationship of the characteristics above and the structures are explained below.

Relationship Between Characteristics and the Structures of Linear Bushings

(1) Differences in Load Capacities

Linear Bushings vs. Plain Bushings

a) Linear motion units with linear bushings and plain bushings have suspended guide shafts supported on the ends and the shafts would deform under high load (Photo 1).
For vertical motion applications where the load is not applied horizontally on the shaft, this problem does not exist and a compact design is possible.

Linear Guides

b) Excellent load capacity due to the rails directly mounted on bases.

(Photo 2)

photo1andphoto2

 

(2) Friction Coefficient Differences

These differences are due to the differences in sliding methods (rolling motion or sliding motion). These differences will directly affect the selection of driving actuator.

a) Low Friction Resistance = Little Fiction force = Possible to drive with small motors = Converts Rotary motion to Linear motion
b) High Friction Resistance = Large Fiction force = Requires large torque/force = Push directly with linear cylinder

friction

Proceed with Caution

1. The high friction coefficients affect driving actuator selections and operation heat generation. The plain bushings are not suitable for frequent motion at high speeds.
2. Air cylinders are not easily controllable for acceleration and deceleration velocities. But some soft-stop mechanisms such as shock absorbers will need to be installed to achieve high speed operations and vibration control.

 

(3) Differences in Guide Accuracy

This parameter is mainly determined by clearances between the rails and bearings.

a) Linear bushings are used with round shafts, and operate with small amount of clearances such as “Clearance Fit: g6” or “Medium Fit: h5”
b) Linear guides are used as pairs of dedicated rails and precision bearings in “Slight Clearance (0~3 μm) or “Pre-load (-3~0μm).
c) Guiding accuracy of plain bushings are lower since they are used with shaft clearances larger than linear bushings.

 

Bearing Load Contact Types

Bearing contact arrangements of linear bushings and linear guides are different. Linear bushings have Point Contact arrangement and localized contact pressures are high. This design is not suitable for heavy loads.  Linear guides use rails with concave grooves that are shaped to fit the spherical shape of the bearing balls and the contact arrangement is a Surface Contact. Applied loads are distributed over the contact areas which allows for heavier loads. The contact arrangement differences reflect on the load capacities of these systems ([Fig.1] & [Fig.2]).

load

Environmental Resistance Characteristics and Maintainability

This is determined by the construction material.

a) Linear bushings and linear guides depend on the lubrication used for long term reliability thus they cannot be used in environments exceeding the environmental resistance of the lubrication used because debris may get into the bearing balls.

b)Plain bushings can be used without any lubrication and has higher environmental adaptability and better maintainability.

 

There are a variety of characteristics of bearings and bushings to consider when designing your application.  They are a versatile mechanical part which can be used in many ways.  For long lasting designs, it is best to stay within the parameters of each part or keep spares on hand for easy replacement in the field.  Seeing side by side comparison of each type will help determine what will work best in your design.  Thus ends the second series of working with linear bushings.  Happy Designing!

Share this Story
Load More Related Articles
Load More By Carlicia Layosa
Load More In Featured Articles

One Comment


  1. AshBox

    November 22, 2016 at 5:16 am

    Great Work. Thanks for sharing.

    Reply

Leave a Reply

Your email address will not be published. Required fields are marked *

*

Check Also

10 Tips About MISUMI’s 10th Edition Mechanical Automation Components Catalog

You asked for it, we answered! The 10th ...

Get articles like this sent to your inbox every week:

Subscribe to our Channel

Follow Me @usa_misumi

Like us on Facebook

FOLLOW @ INSTAGRAM

  • Discover even more MISUMI components for your designs. Get your copy today! Link in bio.  #80Sextillion #design #catalog #engineering #MISUMI #components #manufacturing #engineeringdesign
  • We are excited to be in Charlotte for the Linear Guides Master Class. Our head instructor, John Williams, is explaining ball contact force with a Master Class stress ball! Want to attend the next class? View the course schedule for upcoming classes. #MasterClass #80sextillion #LinearGuides #engineering
  • We’re getting ready for Master Class in Charlotte next week! Want to attend? There’s still time to register. Link in bio #MasterClass #80sextillion
  • Thank you to everyone who attended the MISUMI Catalog Summer Event! It was a perfect day with robots, ice cream and catalogs! Want to get a catalog? Link in bio for ordering #catalogs #engineering #designengineer #designengineering #summer #configuredtohavefun
  • Fresh Linear Guides debuting at the San Diego Master Class today. Want to attend the next class? Check the course schedule for upcoming classes. #80sextillion #engineering #linearguides
  • MISUMI was in attendance today at the Innovative Automation Event. Thanks to everyone who stopped by to speak with the team! #80sextillion #automationengineering
  • Put your best foot forward #MISUMI #80sextillion #socks
  • The Master Class dream team! We are excited to launch our Aluminum Extrusion Master Class.  #80Sextillion