Micromech is describing the FMB bearing as the ultimate in low-profile, high-precision rotary bearings for positioning systems where both precision and height are critical. The various bearing sizes are only 8.5 to 12.5mm tall yet they deliver radial and axial run-out from 10 microns down to 1 micron and wobble from 6 down to 2 micronrads.
The very thin and compact precision bearing is a turntable bearing designed to provide high-performance circular motion in as small a package as possible. The bearings are currently available in nine standard sizes with outside diameters ranging from 120 to 350mm and inside diameters from 40 to 250mm; for OEM applications, custom sizes are available up to 500mm OD to exactly match the application. They can support axial, radial and moment loads, have high rotary precision and repeatability, and provide significant cost savings of up to 50 per cent compared with classic turntable versions.
Classic turntables are designed by using a double pack of bearings that are often complex, making them costly because they use more components and also assembly must be done by trained workers. The FMB design is much simpler, with just one bearing having only one inner and one outer ring - thereby achieving significant cost savings.
The bearings are made from high-quality bearing steel grade 1.3505 with a through hardness of 60 +/-2HRc. If required by the application they can be manufactured in stainless steel grade 1.4034 or similar. The super-precision balls are made from bearing steel grade 1.3505 with a hardness of 62 +/-2HRc. These balls are spaced evenly in a PTFE-filled plastic cage. The bearings are manufactured in two quality grades, normal and precision grade, and are supplied by default with zero clearance.
FMB bearings can operate under different conditions and are therefore supplied in two preload classes V0 (0.02C) and V1 (0.08C). V0 is suitable for very smooth, almost friction-free operation, while V1 is suitable where the location requires high rigidity and is subjected to vibrations or large overhung loads.
The bearings are said to be very easy to install and they include a 0.5mm offset between the inner and outer races and counterbored holes to enable mounting directly onto flat surfaces.
The FMB bearings feature a single, four-point contact ball design, which consists of a single row of balls with a 'gothic arch' geometry raceway and PTFE-filled plastic ball cage with super-precision balls for low frictional torque. The specially designed raceways are finished by precision grinding and the balls are selected within a tolerance of 0.1 micron. Through this optimised design, the accuracy of these bearings is claimed to be unmatched by others and friction is extremely low.
Having this accuracy in a smaller, simpler package reduces design costs and envelope size, makes installation fast and easy, and also makes servicing simpler.