Miniature Bearings: An Overview (Defining and Typical Materials; Part 1)

The miniaturization movement in manufacturing has been going on for quite some time, with its pace constantly accelerating. To accommodate the space constraints of ever-shrinking everything, the demand for smaller and smaller bearings continues to grow larger and larger. This is where miniature bearings come in. They are found in so many industries today including robotics, defense, medical/dental, and power tools. The list goes on and on.

Miniature Bearing - Defined

So, what exactly is a miniature bearing? It comes down to size. Generally speaking, it’s one with an outside diameter less than ½”, and a bore size as small as .0250”. They are available in both metric and imperial dimensions. It’s interesting to note that the smallest ones are so tiny and precise, they still need to be assembled by hand! Miniature bearings are available in both radial and angular configurations.

Typical Materials

Miniature bearings are available in a variety of materials including stainless steel, chrome steel, ceramic and beryllium copper. The ideal choice depends mostly on the application, and in some cases, budget. Let’s take a look at each:

Stainless Steel - is the most popular material today. In the United States, 440C is the preferred variety. Stainless steel bearings are hardened to a higher level, allowing for higher speeds and load ratings. They also provide excellent longevity and corrosion resistance, making them ideal for medical and dental applications. In fact, any use where the bearing could be exposed to the elements would benefit from stainless steel. Interestingly, overseas manufacturers tend to select 400 series steel, which is a little softer.

52100C Chrome Steel - For less threatening environments, 52100C Chrome Steel will get the job done at a better price point than stainless. It’s also softer than 440C, and therefore easier to machine. It’s ideal for light duty, moderate speed applications such as vacuum motors. Lower speed applications include computer fans and ATM printers. These are just a few of many products that use chrome steel miniature bearings.

Ceramic – Ceramic hybrid bearings are widely used in electric motors, aerospace applications, performance racing vehicles, laboratory equipment, underwater applications and more. Any application that requires higher speeds, lower friction and longer life are ideal for ceramic hybrid bearings. Ceramic bearings are becoming more popular today due to their favorable characteristics. They are extremely lightweight, practically impervious to the elements, and boast a much longer lifespan than metallic ones. However, all of this does come with a drawback: ceramic bearings tend to be approximately double the cost than metallic ones. But for certain applications, such as mission and safety critical ones in military and aerospace, reliability and longevity are much bigger factors than price tag. Another benefit is that they handle high speeds extremely well with very little, if any, lubrication. This makes them perfect candidates for applications such as machine tool spindles, which commonly fail due to lack of proper lubrication.

Beryllium Copper (BeCu) - This material was somewhat popular in the past, but is becoming obsolete. The biggest benefits are its ability to conduct electricity, along with good strength and hardness. However, when producing BeCu bearings, a toxic gas is emitted. The risks and associated costs to process them has grown significantly over the years, making them more impractical to produce.