THE "BIG ONE" ( PART NUMBER BO-PM-B200 ) IS A GIANT 2.00 INCH (50.8MM) DIAMETER PRECISION SPHERE MOUNTED ON A RUGGED 2.00 INCH (50.8MM) DIAMETER BY 2-1/2 INCH (63.5MM) HIGH STEEL POST.

IT WAS DEVELOPED FOR THE EVALUATION OF COMPUTER NUMERICALLY CONTROLLED MACHINING CENTERS ACCORDING TO ANSI/ASME B 5.54.1992. IT IS ALSO USED AS A PROBE CHARACTERIZING SPHERE ON SOME COORDINATE MEASURING MACHINES. THE LARGE TARGET IS PARTICULARLY WELL-SUITED FOR USE ON BIG MACHINES AND ON MULTI-SPINDLE MACHINES.

SOME OF THESE TESTS INCLUDE MACHINE TOOL REPEATABILITY, TEMPERATURE VARIATION ERROR, HYSTERESIS, FEATURE ACCURACY, PALLET CHANGE REPEATABILITY, TOOL CHANGER REPEATABILITY, DRIFT, VIBRATION AND COMPLIANCE.

THE SURFACE AREA OF THIS 2.00 INCH ( 50.8MM ) DIAMETER SPHERE IS 12.566 SQUARE INCHES ( 319.19 SQUARE MM ) WHICH IS FOUR TIMES THE 3.1416 SQUARE INCH (79.797 SQUARE MM) AREA OF THE STANDARD 1.00 INCH ( 25.4 MM ) DIAMETER SPHERE COMMONLY USED.

THE 2.00 INCH (50.8MM) DIAMETER PRECISION SPHERE IS MADE OF VERY FINE GRAIN HIGH CHROME, HIGH CARBON STAINLESS STEEL THAT IS HARDENED TO 58 HRC FOR WEAR RESISTANCE AND COLD CYCLED FOR LONG-TERM DIMENSIONAL STABILITY. THIS LARGE DIAMETER COMPONENT IS LAPPED SPHERICAL WITHIN 5 MILLIONTHS OF AN INCH (127NM) AND HAS A SURFACE FINISH BELOW 0.7 MICRO INCHES (17.78 NM) RA. THE EXACT DIAMETER OF THE SPHERE CAN BE CERTIFIED TO 10 MILLIONTHS OF AN INCH (254NM).

THIS DESIGN USES A UNIQUE HIGH STRENGTH CONNECTION TO JOIN THE PRECISION SPHERE TO THE POST. AN ELECTRICAL DISCHARGE MACHINE ( EDM ) IS USED TO DRILL A CONCENTRIC HOLE DEEP INTO THE ALREADY FINISHED SPHERE. THIS SPACE AGE PROCESS USES MILLIONS OF TINY BURSTS OF ELECTRICAL ENERGY TO ERODE A HOLE INTO THE PRECISION SPHERE WITHOUT AFFECTING THE ORIGINAL QUALITY. THE END OF THE POST HAS A CORRESPONDING HOLE DRILLED IN IT. AS THE HIGH STRENGTH GLUE IS APPLIED TO THE ASSEMBLY, A STEEL PIN IS INSERTED BETWEEN THESE HOLES TO FORM A VERY STRONG CONNECTION.

THE FLAT BASE OF THE MOUNTING POST IS RECESSED TO LEAVE AN ANNULAR RING FORMING A STABLE CONNECTION FOR THE SPHERE.

THE POST OF THE "BIG ONE" IS PROVIDED WITH AN ATTRACTIVE BLACK OXIDE FINISH THAT RESISTS CORROSION. A 1/4 INCH (6.35MM) DIAMETER CLEARANCE HOLE IS CROSS-DRILLED THROUGH THE POST AND A HIGH TENSILE STAINLESS STEEL PIN IS PROVIDED TO TIGHTEN AND TO REMOVE THE DEVICE FROM ITS MOUNT.

A M10 X 1.5 TAPPED HOLE IS MACHINED IN THE CENTER OF THE FLAT BASE OF THE POST TO PROVIDE A STRONG MEANS OF ATTACHMENT. THIS CONFIGURATION IS STANDARD THROUGHOUT THE PRODUCT LINE SO THAT ALL COMPONENTS ARE INTERCHANGEABLE.