Porous graphite air-bearing components as applied to machine tools Page: 7 of 45
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Figure 2. AIR BEARING STEADY REST - CAPTIVE DESIGN.
Several significant linear-motion air-bearing applications have been made for continuous
machining and inspection use. One of the more significant applications has been the use of the
linear-motion ram, shown in Figure 3, to provide a third improved axis of measurement
capability to a precision jig borer having 30 inches (0.763 m) of travel with a laser interferometer
measuring system. Flexibility and ease of fabrication are prime advantages of the design (Figure
4). The small pads are easily lapped to a flatness of 10 microinches (0.254 gm). The spherical
seat provides automatic alignment of the bearing pad to the ram, and the adjustment-screw
arrangement allows microinch film clearance without the costly fabrication of microinch
tolerances. In addition, maintenance is simplified since the pad is removable without disassembly
of the housing. Ram travel over 30 inches (762 mm) was straight within 50 microinches
(1.27 gm) in one plane and 75 microinches (1.9 gm) in the other plane. The measuring accuracy
over the 30 inches (762 mm) of travel was 75 microinches ( 1.9 gm).
With the development of the graphite impregnation technique, noncaptive air bearings are now
feasible for large-mass, small-force applications such as encountered in some machining and many
inspection applications. Two such applications were recently made to a tape-controlled turning
and boring machine tool, shown in Figures 5 and 6, by replacing the roller bearings with both
self-aligning and fixed-air-bearing pads. A view of the self-aligning pads is presented in Figure 7.
Both systems have been evaluated and are presently being used in normal machine operations.
Results of the evaluation studies of the slide made to date indicate good stability during
operation for a range of tool moments over the entire range of its capacity. In this case, the slide
is limited by design to 2000 inch pounds (226 Nm) of moment due, primarily, to the fact that
limitations in the support area came about in adapting the system from the original roller-bearingMRR74 - 02
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Rasnick, W. H.; Arehart, T. A.; Littleton, D. E. & Steger, P. J. Porous graphite air-bearing components as applied to machine tools, article, January 1, 1974; Tennessee. (https://texashistory.unt.edu/ark:/67531/metadc1055862/m1/7/?q=%22~1~1~1%22~1: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.