How to install a press fit bearing

Each direct-acting press features a ram that produces up to 8. A pneumatic clamp device secures the piston in place during pin insertion. Force and distance monitoring triggers an audio sound and visual message to indicate whether the specific process is OK or not OK. Pistons are a good candidate for press-fit assembly, along with many other types of parts: bearings, rotors, gears, shaft collars and bushings. The first design factor is size.

Press-fit assembly involves the insertion of one part that is slightly larger than the mating hole. The assembly stays in place through friction and the force of the two parts pushing against each other.

Mike Brieschke, vice president of sales at Aries Engineering, says a 0. Parts in noncritical assemblies tend to have looser tolerances. Brieschke says a 2-inch-diameter bearing that is pressed onto a metal shaft, for example, could have a tolerance range of 0. In contrast, smaller bearings used for automotive parts, like transmission housings and engine components, often have a tolerance range of just a few microns.

Regarding shape, most press-fit parts are round, but they can also be oval, square, rectangular or triangular. Inserted parts may be solid or hollow. Keith Lowery, servo press product specialist at FEC Automation Systems, notes that nonround parts may require an extra step to ensure proper orientation, resulting in longer cycle times.

Large parts require a press that provides higher and more consistent force and sufficient part access. Part alignment is equally important for a good press-fit assembly, according to Natsume. He says the best way to prevent misalignment is to use the right tooling and fixturing. To enhance joint strength, part edges may be designed with indentations or projections.

Lowery says that knurls enable the inserted part to bite into the mating part and help prevent the joint from moving when exposed to high torque forces. In plastic and electronic assembly, grooves or barbs on the mating part help prevent the joint from being pulled apart. Press-fit parts are made of metal, plastic or rubber, and similar- or dissimilar-material parts can be joined.

When they are dissimilar, engineers should choose materials with similar coefficients of thermal expansion, but different hardness ratings. As an example, Lytle cites the pressing of a steel-encased rubber bushing into aluminum control-arm steering components for vehicles. Much high press-fit forces are required when one part is made of steel and one of aluminum.

Failing to do so when press-fitting a steel bearing in an aluminum housing, for example, could result in the latter expanding more than the steel—and the bearing falling out.

According to Rupprecht, die-cast metals and glass-fiber-reinforced plastics are brittle materials and must be press-fit with the exact amount of force. Pressing a hard part into a thin-walled aluminum or plastic part with too much force can easily disfigure the mating part. Burrs or particulates on the inserted part can also cause damage. Other types of plastics also have limitations. More flexible plastics, such as nylon, ABS and thermoplastic polyurethane, can better handle this stress, but may exhibit more stress relaxation over time.

When that happens, manufacturers have a couple options to overcome the problem. A very important point: avoid employing an impact tool to remove a press-fit bottom bracket.

You run the shaft, blunt end first, through the bottom bracket. You grab a hammer and bang away on the blunt end. The longer the bottom bracket has been in place, the harder the removal. Ok, not necessarily. Precisely machined tools, comprised of CNC-honed components, enable quick and gentle bottom bracket removal including BB92 along with all other types of press fit bottom bracket.

The video demonstrates in fine detail how to carry out installation or removal quickly and easily. For a summary keep on skimming down the page, or check out the video for detailed coverage of the procedure. First up, a simple grease preparation procedure is important. Applying a light smear of grease to both the bottom bracket bearing cups and the bottom bracket shell is advised.

Installation and, maybe more importantly, removal becomes easier. There is is no particular method of application. I would make the point though, that if you mess around with bikes a lot, you will be in frequent contact with a variety of chemicals in the oil, grease, and de-greasers you use over the years. Over the long term your skin will continually absorb tiny amounts. Over the long term that adds up. In the interests of reducing the odds of damage to your health somewhere down the track, keeping a barrier between your skin and these chemicals is beneficial.

Smearing grease on with a fine brush — a toothbrush will do the job — or fingers nitrile gloves are recommended is enough. All you need is a light smear across the 10mm where the bearing cup sits inside the BB shell. This tool is housed in a robust plastic shell with hard and durable — and flexible — closing clasps. The retaining cup is used for both installing and removing a BB92 bottom bracket. Its thread takes the bolt used to press-in a bottom bracket and also serves as the capturing vessel when you remove a bottom bracket.

This piece presses against, as well as inserting into, the bearing cup. The 22mm surface faces out. The 16cm bolt inserts through the piece and into the retaining cup. This piece presses the bottom bracket into position. The retaining cup helps to keep it square so the bearing cups are pressed into position on the correct plane.

Once the pressure is applied, this disc guides the BB squarely into position. There will sometimes be a tiny bit of sideways BB drift as soon as you begin turning the bolt. Getting the bolt finger-tight is enough. Provided the retaining cup is snug against the BB shell on the opposite side, you are good to go.

A few turns of the supplied 8mm allen wrench quickly moves the bearing cup into position. Fractionally turn the the bolt in the opposite direction to loosen the assemblage.

Then simply unscrew the retaining cup from the bolt. Mount the non-drive side BB92 bottom bracket cup onto the press piece and bolt.

The procedure is exactly the same installing the non-drive side. Installation is complete ready for crank installation. Often, vibrating or shaker-type applications vary from the above generality. Incorrect fits can cause premature bearing failure. Most general applications include inner ring rotation and a constant radial load. For these conditions, we recommend an interference fit between the shaft and bearing bore.

The level of interference will increase for heavier loads. When shaft conditions are stationary, and the radial load is constant, a moderate clearance fit between the shaft and bearing bore is an option. Your housing fit can be different from your shaft fit, and often is. Like the shaft fit, many conditions determine which fit is best. Considerations include the rotation of the inner or outer rings, type of load, and how easily it should be to install or remove the bearing from the housing. The amount of the radial load will also influence the choice of fit.

For indeterminate or varying load directions, avoid clearance fits. Imagine you are installing a bearing in an electric motor application. What type of shaft and housing fit do you need? In this situation, your inner ring will rotate, the applied load direction will be constant, and the outer ring is stationary. A transition fit is most appropriate for the housing bore because it will allow for easier installation as well as displacement for removal.

By reviewing the table in our Axis ball bearing Catalog , note that the appropriate fits are a k5 shaft fit of. Of course, this is only one example. Before selecting a housing or shaft fit, look to the application for guidance. The friendly engineers at Baart are always ready with helpful tips and advice.