Established in 1952

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Coordinate Measuring Machine
Probe Characterizing Spheres On A Post

The PM series is the least expensive of the Coordinate Measuring Machine Probe Characterizing Fixtures. Despite its low price, this fixture is manufactured to the very highest quality standards. The ultra precise datum spheres of either 1.00 inch (25.4mm) (Part number PM-UB-B 100), or 0.750 inch (19.05mm) (PM-UB-B 75), or 0.500 inch (12.7mm) (PM-UB-B 50) diameter use this common fixture. These spheres are made of very fine-grained, high carbon, high chromium stainless steel. It is through-hardened to 58 Rc for wear-resistance and ultra cold cycled for long-term dimensional stability.

The 10mm (0.3937") (Part number PM-UB-B 39) sphere is made of micro-grained tungsten carbide and is mounted on a 0.125 inch (3.175mm) diameter tungsten carbide stem that is 0.850 inch (21.59mm) long.

This allows much greater measuring access to this smaller diameter sphere. The extremely high rigidity of tungsten carbide greatly reduces the elastic deformation of the smaller diameter sphere by the probe contact force, and yields a reduced bending moment of the support stem. Tungsten carbide is orders of magnitude more wear-resistant than hard steel. This material is very corrosion resistant, it will not rust.

The maximum departure from a perfect geometry on all of these spheres is 2.5 micro inches (63.5 nm). This tolerance is considered to be the limit of commercial metrology. This is twice as accurate as the quality requirements for "Performance Evaluation of Coordinate Measuring Machines ANSI/ASME-B89.4.1-1997" and ten times as good as high quality bearing balls. The specific size of all of these balls is held to a tolerance of +0.000020" (508nm). The quality of the surface texture is maintained below 0.5 micro inches (12.7nm) Ra. Spheres of this quality are simply not available from any other commercial source.

In keeping with the very rugged design, the ball is not simply glued on top of the post, but is reinforced by a long metal pin that penetrates deep inside the ball and the post so that a minor tap will not send the ball rolling across the room. This hole is drilled in the ball using special computer-controlled Electrical Discharge Machining (EDM) techniques which do not disturb the original quality of the balls.

For maximum stability, the post of the probe characterizing sphere is supported by a robust steel platform.

The post that supports the Ultra Precise Sphere and connects it to the platform is of rugged steel construction measuring 1-1/4 inch ( 1.25", 31.75 mm ) diameter at the base by 2-3/8 inch ( 2.375", 60.33 mm ) long.

The extremely robust 4 inch ( 101.6mm ) diameter, 1-1/2 inch ( 1.5", 38.1 mm ) thick steel platform (Part Number PLT-4 see Technical Data Sheet 6.A.) is used to couple the characterizing sphere to the CMM table.

The central portion of the bottom of this platform is relieved to provide an anular ring of contact. The surface of this ring is precision lapped flat to provide the most stable location possible with the measuring machine table. This robust 5.2 pound ( 2.3 kg ) assembly has a counter-bored tie-down hole provided for either a 3/8 inch ( .375", 9.525 mm ) or a 10mm diameter socket head cap screw.

In order to facilitate the connection and removal of the post, a 3/16 inch ( .1875", 4.76 mm) diameter clearance hole through the post is provided. A removable pin made of high tensile stainless steel is supplied as a handle.

Some accessories which are available for use with the probe characterizing spheres include a 45 Angle Block (Part Number BLK-45) used to incline the sphere and post at an angle for easier access. A 1-1/4 inch ( 1.25", 31.77 mm ) diameter by 3 inch ( 76.2mm ) long extension post (Part Number P-EP3) and 6 inch ( 152.4 mm ) long extension post (Part Number P-EP6) can be used to extend the height of the Probe Characterizing Spheres.

Probe Sphere Prices

Part #	Ball Diameter		Ball Material	Price	Purchase
Click link for IGES file
PM-PB-B75	19.0500 mm	0.7500"	Hardened Stainless Steel	$178.73
PM-PB-B100	25.4001 mm	1.0000"	Hardened Stainless Steel	$178.73
PM-UB-B39	10.0000 mm	0.3937"	Tungsten Carbide	$198.77
PM-UB-B50	12.7000 mm	0.5000"	Hardened Stainless Steel	$198.77
PM-UB-B75	19.0500 mm	0.7500"	Hardened Stainless Steel	$198.77
PM-UB-B100	25.4001 mm	1.0000"	Hardened Stainless Steel	$198.77
PM-UB-B100R	25.4001 mm	1.0000"	Hardened Stainless Steel, The Runt	$198.77
PM-SAT-B50	12.7000 mm	0.5000"	Hardened Stainless Steel	$178.73
PM-SAT-B75	19.0500 mm	0.7500"	Hardened Stainless Steel	$178.73
PM-SAT-B100	25.4001 mm	1.0000"	Hardened Stainless Steel	$178.73
PM-SAT-B100-C	25.4001 mm	1.0000"	Ceramic	$185.34
PM-SAT-B100-SN	25.4001 mm	1.0000"	Silicon Nitride	call us
PM-SAT-B100-AO	25.4001 mm	1.0000"	Aluminum Oxide	$185.34
PM-SAT-B100 -ZO	25.4001 mm	1.0000"	Zirconium Oxide	call us
Post Length - 2.375" (60.33 mm), Post Diameter - 1.250" (31.75 mm)

	PM-PB-B75 / PM-UB-B75 Standard Probe Sphere
	PM-PB-B75R / PM-UP-B75-R The Runt Probe Sphere
	PM-PB-B100 / PM-UB-B100 Standard Probe Sphere
	PM-PB-B100R / PM-UP-B100-R The Runt Probe Sphere
	PM-B0-200 The Big One