The Right Linear Bearings for CNC Save Cost, Improve Reliability
Look inside a CNC machine, and you’ll find sophisticated recirculating ball linear bearings performing the mission-critical motion tasks. But when you go beyond the spindle and essential cutting or milling components, you’ll find auxiliary axes that don't have the high accuracy and precision requirements that are typically prescribed for expensive motion components.
One example of a non-mission-critical axis on a CNC machine is the basic door. When you choose an elaborate bearing to build a dependable, cost-effective door, you’ll have difficulties like:
- Deflection and alignment.
- Closing force.
- Contamination.
An Alternative Bearing Solution for CNC Doors That Solves Deflection and Alignment
Rollon has developed an alternative solution for doors and related auxiliary applications using our self-aligning Compact Rail bearings. Compact Rail eliminates the expensive, time-consuming and unnecessary process of machining mounting surfaces to near perfect flatness and adding special mounting fixtures during installation. For machine tool doors, both of those steps may be both ineffective and unnecessary. They’re ineffective because large, sheet-metal doors will deflect in use to undo the extra installation effort. And they’re unnecessary because self-aligning Compact Rail can accommodate deflection without the extra steps.
Compact Rail’s large roller bearings interact with a set of rail profiles that are designed to allow the rollers an extra degree or two of freedom to offset misalignment between rails. The alternative solution combines Compact Rail’s U and K rail profiles to support the slider. The U-style rail has a flat raceway that allows a roller freedom to translate in and out relative to the axial direction of the rail. The K-style rail has a geometry that allows for limited angular rotation of the roller, while still offering precise linear guidance. Together, these rails can absorb significant alignment errors in two axes: Parallelism on the horizontal plane and height differences between rails in the vertical plane. In addition to solving deflection and alignment problems, Compact Rail also offers:
- Low closing force. Together with its ability to tolerate misalignment without impeding motion, Compact Rail offers a low coefficient of friction (CoF) between 0.003 and 0.006 to make doors easy to open and close.
- Contamination resistance. Unlike recirculating ball linear bearings which have little clearance between balls and raceways, Compact Rail’s small ball bearings are permanently sealed within larger rollers. These larger rollers can roll over many chips that would otherwise stop a recirculating ball in its tracks. And seals and wipers can minimize contaminants on the rails.
A Cost-effective Bearing for Medium-precision CNC Motion
Not every motion on a CNC machine is mission critical. Because these machines have one or more axes that require lesser degrees of accuracy than a spindle, engineers have options to help lower costs while improving machine reliability. Machine builders can choose a more-compliant bearing like Rollon’s Compact Rail system on medium-precision CNC applications like doors, which can take some of the cost out of the machine and also improve its reliability in the field.
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