Accurate Measurement of Radial Air Bearings

Measuring the diameter of radial air bearings is a deceptive task, one which teams often attempt with their coordinate measuring machines (CMM’s) before reaching out to New Way for support. Because CMM’s perform a large quantity of measurement averaging and graphite deflects under point probes, CMMs are not the appropriate tool for this task. The most accurate method of measuring the ID and OD of our radial bearings is by using an ID micrometer with a cross pattern measurement technique.

Because carbon/graphite air-bearing surfaces are porous and can deflect under point contact, we do not rely on a CMM or a traditional bore gauge. Instead, we use a method designed specifically to avoid surface deformation and provide a true functional diameter.

1. Create a “full circle” reference using paired bearings – Radial air bearings are machined in sets—usually two or four at a time—so each bearing in the set shares the same geometric cutting path. Before removing them from the fixturing, we position two bearings directly across from one another to form a complete circular geometry. This gives us an accurate, continuous diameter to measure.
2. Measure the inside diameter (ID) using an ID micrometer – An ID mic (inside micrometer) is used instead of a bore gauge because it uses flat contact pads, not spring-loaded points that can dent or deflect graphite.
   The ID mic is set between the two opposing bearings, and we measure the effective diameter.
3. Use a controlled “cross pattern sweep” for accuracy – To avoid point loading and ensure repeatability:
   1. The technician lightly drags the ID mic left to right until a faint, consistent drag is
   felt.
   2. Then the mic is moved front to back the same way.
   3. The true diameter is the position where an equal, minimal drag is felt in both
   directions.

This cross-pattern technique ensures:

• No gouging or deformation of the graphite
• A stable, repeatable feel-based measurement
• A true representation of the functional bearing diameter

This method has been validated against pin gauges and ring gauges and provides the most consistent results across all radial sizes.