Bearings Basics

The REV Robotics 15mm Extrusion Building System primarily uses plastic acetal (Delrin/POM) molded bearings. These bearings have a maximum 9mm outer diameter (OD) which fit inside the 9mm inner diameter (ID) hole in the all the motion brackets and the bearing seat of the Extended Motion Pattern.

These Delrin bearings provide stable, low friction axle support in our nylon brackets. The two materials were carefully chosen because they have a very low coefficient of friction and are also incompatible materials, meaning that they will not stick together under extreme heat. These bearings come in three varieties.

End Cap Bearing


Short Through-bore Bearing


Long Through-Bore Bearing


End cap bearings are closed on one end, so when these bearings are placed on both ends of a shaft and fit into motion brackets the shaft is free to rotate but is fully constrained laterally (sideways).

Short Through-bore Bearings are low profile pass-through bearings intended to seat directly into any of the motion brackets. These low-profile bearings have a 3mm contact surface which makes them flush with one side of the motion plate. Shaft collars are recommended to laterally constrain the shaft.

Long Through-bore Bearings are full depth pass-through bearings which can be used with any of the motion brackets or the bearing pillow block. Unlike the end cap bearing, because a shaft can pass though this bearing, it can be used with the bearing pillow block to have a pivot between two fixed shaft ends. Shaft collars are recommended to laterally constrain the shaft.

There are number of different bearing, shaft collar, and motion bracket combinations that are recommended. See the image below for a visual representation of some of the recommended combinations.

How to Use?

The figures in the table below show several possible combinations for bearings, motion brackets, and pillow blocks. In these figures the brackets are all depicted as facing “up” but brackets can also point “down” just as well.

Motion Brackets and End Cap Bearings

Pillow Blocks and End Cap Bearings

Pillow Blocks and Long Through bore Bearings

Ball Bearings

The REV Robotics 15mm Extrusion Building System also uses metal ball bearings. These bearings come in two types, 8mm x 12mm Flanged Bearing (REV-49-1559) and the 5mm Hex Bearing Block (REV-41-1683). Ball bearings provide better performance in high load or high speed applications than the Delrin bearings.

Flanged Bearing

The 8mm x 12mm Flanged Bearing has a 12mm outer diameter (OD) which press fits into the 12mm inner diameter (ID) hole of the 15mm Metal Ball Bearing Mount V2 (REV-41-1452). The 8mm inner diameter (ID) of the bearing fits the 5mm Hex to 8mm Bearing Insert (REV-41-1528).

5mm Hex Bearing Block

The 5mm Hex Bearing Block has a pre-pressed in 5mm Hex Bearing. The block has mounting holes designed to match the Extended Motion Pattern.

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