Drawer Slide 101
This blog will help you understand what drawer slides are as well as some of the terminology and considerations you should be conscious of when selecting a drawer slide to incorporate into your next project. Once you have an understanding of the basics, you should have a much easier time identifying what drawer slide is best for your application.
What is a Drawer Slide?
A drawer slide, or sometimes called a drawer roller, is a mechanism that allows for telescopic motion in one axis. They are commonly found in a wide range of household or office applications like desk drawers, kitchen cabinets, and pull out cutting boards but can be used in a wide range of applications that require linear extension and retraction. Drawer slides generally work by allowing one grove component to slide over a rolling component, which allows the entire mechanism to extend or retract. Drawer slides are not motorized but can be coupled with a linear actuator to provide greater stability. Generally, you will use a pair of drawer slides in any application and will most likely encounter two main types: Roller Slides and Ball-Bearing Slides.
Drawer Slides in Use
Types of Drawer Slides
1) Roller Slides
Roller slides consists of two components, the cabinet member and the drawer member, each having their own roller, usually made of plastic. As their names suggest, cabinet member mounts to a stable or grounded component, i.e. the cabinet, and the drawer member attaches to the moving component, i.e. the drawer. Each roller will fit into the groove found on the other member and will be at opposite ends of the mechanism when fully retracted with the cabinet member’s roller being at the front. As the mechanism is extended, the cabinet member’s roller allows the drawer member to move outwards and the roller of the drawer member follows in the grove of the cabinet member. When fully extended, the two rollers will meet. This two-roller design gives the mechanism horizontal stability and allows for level extension.
2) Ball-Bearing Slides
Ball-bearing slides make use of ball bearings instead of rollers to allow for the telescopic motion. They also make use of a third component, the intermediate member, which interfaces with two sets of ball bearings. The first set interfaces with the groves of the cabinet member and the intermediate member, while the second set interfaces with the groves of the intermediate member and drawer member. As the mechanism extends, the first component to move is the drawer member, which slides over the ball bearings between itself and the intermediate member. Once the drawer member reaches the end of the ball bearings, the intermediate member will begin to slide along the ball bearings between itself and the cabinet member until fully extended. Like the two-roller design, the ball bearings within each grove of the mechanism gives it horizontal stability and allows for level extension.
Example of a Ball-Bearing Drawer Slides
To Note: Some ball-bearing slides will allow for the drawer member to be disconnected, by pressing a release lever, from the rest of the mechanism for installation, but this is not always the case.
Generally speaking, ball-bearing slides provide greater durability and have larger load rating compared to roller slides. Heavy duty versions of ball-bearing slides are also available for harsher and heavier applications.
What About Slide Rails?
Slide rails, or also called linear guides, is another non-motorized mechanism that allow for linear motion. They consist of two basic components, the carriage and the rail. While there are different styles of slide rails, they generally work by having bearings, found within the carriage, that fit into the groves of the rail, which allows the carriage to slide back and forth along the rail. Slide rails are typically used in industrial and robotic applications, like CNC machines, where precise linear motion is need.
Example of a Slide Rail
While both slide rails and drawer slides allow for linear motion, the main difference between them functionally is that drawer slides are telescopic and slide rails are not. Practically, this means your drawer slide will collapse inwards, while slide rails will have a fixed length. There are also other differences, like thickness of the mechanism and load rating, that you’ll need to consider when choosing between the two mechanisms.
Considerations
Here are a few considerations and factors that you should consider when selecting or designing around a drawer slide. For this selection, I refer to the moving component as the drawer component and the stable component as the cabinet component for examples.
1) Load Rating
Load rating or load capacity is the maximum allowable load or weight the drawer slide can handle before failure and may be a key factor in deciding between a regular drawer slide or a heavy-duty one. This would seem straightforward; just ensure you don’t go over your limit, right? While your drawer slide might be able to hold 300lbs, doesn’t mean your design will. The load carried by your drawer slides will cause a shear stress on the mounting fasteners, for your drawer slides, and cause a corresponding force on your cabinet member. If these components cannot hold 300lbs, your design won’t either. To avoid unexpected failure, you should determine the load capacity for your entire design, knowing each individual component’s load rating as a limiting factor.
Shear Stress on a Bolt[1]
2) Max Extension
You are going to have an idea of how far you’d like your drawer slide to extend to. So, you’ll need a drawer slide with a max extension as long as your requirement. This will also determinate the total length and fully retracted length of your drawer slide. Generally speaking, your max extension will be equal to your fully retracted length and half of your total length. Your cabinet component and your drawer component will also need to be as long as your fully retracted length to ensure safe mounting of the drawer slide.
Simple Technical Drawing of a Ball-Bearing Drawer Slide
3) Thickness
The thickness of the drawer slide mechanism is another consideration you will need to factor into your design. The thickness of the mechanism will determine how much clearance you’ll need between your cabinet component and your drawer component. If these factors are constraining your design, then the thickness of your drawer slide will be a very important aspect of selecting the right one.
4) Mounting
Most commonly, you will mount each drawer slide on opposites sides of each other in a vertical configuration. Although, there are some that can be mounted on the bottom side of your drawer component or require only one draw slide, you should always follow what the manufacturer recommends. If your manufacturer does suggest bottom mount configuration is possible, always check to see if other factors, like load rating, are affected in that configuration. Another aspect to consider, related to mounting, is the hole pattern, which is for your fasteners. If you are getting parts machined for your project, you will to ensure you use the right hole pattern for your drawer slide as well as ensuring the holes are level.
Now that you understand the basics of drawer slides, you should feel confident in knowing what you are looking for in your next project. Browse our selection of drawer slides here at Firgelli Automations to find what suites your needs.
Reference:
[1] http://www.engineeringarchives.com/les_mom_singledoubleshear.html
