In the introduction to our sliding guides series, we looked at different types of guides and their various applications. This article will focus on the specific differences between linear bushings and linear guides. There are many options for each of these products, and each manufacturer tends to use some creative marketing descriptions as an enticement to purchase their product (and thus adding to the confusion). Most of this potential confusion belongs to the linear guide camp, so we’ll first look at linear bushings.
Linear Bushing Image from iMall
If you need a quick and easy way to facilitate a linear motion profile, the linear bushing is a great choice, especially if you don’t have high tolerance or accuracy requirements. Usually, two shafts are used to support a traveling carriage with linear bushings that slide along the shafts. The shafts must be sized to support the load within an acceptable deflection tolerance – too much weight and the shafts will bend, causing a positioning error. The bushing to shaft interface is also relatively loose, which can cause issues with accuracy and repeatability. However, these errors are typically small, on the order of a few thousandths of an inch. The setup and maintenance are also very inexpensive compared to other options.
- Easy to install
- Easy to maintain and service
- Low friction
- Potential for positioning errors
- High speeds can cause problems
Linear Guide Image from MISUMI
Demanding applications usually have solutions with demanding costs. Linear guides offer a great load capacity and higher rigidity for two main reasons:
- The ball bearings are usually sitting in an R- or V-shaped groove instead of using a plain contact, from which some manufacturers are claiming thirteen times as much load capacity.
- The guides are sitting directly on a base, so there is no deflection. Even a small (1” by 1.5”) linear guide can support a dynamic load of around 2,000 pounds.
Linear guides are also extremely accurate- errors are usually measured in the micrometers (μm) range. The addition of a preload into the guide can also increase accuracy and repeatability. Instead of having a small clearance between the track and the ball bearings, an interference fit is used.
Proper lubrication is a must to maintain a low friction, but the added rigidity can really make a difference. These factors combine together to give a very smooth operation for the guide.
Linear Guide Image from Misumi
- Amazing accuracy and repeatability
- Higher load capacity and rigidity
- Higher cost
- Higher maintenance concerns
If you need to have high accuracy or high load capacity, there is nothing better than a linear guide. However, if you are just looking for a way to slide a mechanism back and forth, the linear bushing offers a great, low-cost alternative.
Still have questions, or have specific topics you would like us to cover in Part 3? Feel free to comment below, or email one of our experts at email@example.com.