Established in 1952		Page: 3310
		Technical Data Sheet # CMM1 Page 2

Standard Ball Bar ( Dumbbell ) for Evaluation of
Coordinate Measuring Machines

per ANSI / ASME B89.4.1-1997

Archival Standard

In the past, the actual distance between the two spheres was not known to a high degree of accuracy. In fact, many Ball Bars were actually made adjustable. The basic concept was that the Ball Bar was a volumetric check of the measuring machine envelope and nothing more.

There is an interest in using the Ball Bar as an archival or distance standard. A recently developed material with extremely good long term dimensional stability, Invar™, brings the Ball Bar to gage block status. The National Institute of Standards and Technology in Gatersberg, Maryland, USA will supply legal certification of Ball Bars to gage block accuracy.

Low-Expansion Material

One unique approach being used for some applications is to build Ball Bars out of materials that have little or no thermal growth.

Glassy Ceramics, although very fragile, are excellent. Invar is the number one choice, but its long term dimensional stability is questionable, therefore these Ball Bars can only be used for volumetric checks at present. The temperature of the measuring machine environment must be well controlled for successful use of these low-expansion Ball Bars.

Our entire Ball Bar product line is now available in Invar with a low thermal coefficient of expansion of 0.68 microinches per inch per degree Fahrenheit, one tenth that of steel.

Elevated Temperature

Another approach for coping with elevated thermal conditions in the measuring machine environment is to build Ball Bars out of the same material as the parts being measured. These Ball Bars are made quite long to maximize the elevated thermal effect.

An Aluminum or Titanium Ball Bar that is calibrated for length at standard temperature can be used to establish the exact corrections to be applied. This is done by measuring these artifacts on the C.M.M. in the elevated thermal environment.

Bal-tec will give fast, economical delivery of Ball Bars which are custom-made from any available material.

Inventory

A finished inventory of the six most popular lengths of the Standard Ball Bars is maintained for immediate shipment.

An inventory of component parts is stocked to quickly produce custom lengths of Ball Bars.

Individual Ultra Precision Balls or matched pairs of these balls will be sold to anyone who may prefer to produce their own Ball Bars or other calibration devices (see Technical Data Sheet CMM-8, Page 2.).

Each of the Standard Ball Bars is shipped in an individual heavy duty plastic storage container.

Each of the Ball Bars is assigned an individual serial number that is permanently stamped into the bar.

A general certification of conformance stating the nominal size and roundness of the spheres is supplied with each Ball Bar at no cost.

An individual inspection certification that is traceable to the National Institute for Standards and Technology giving the exact size and sphericity of each ball, with polar charts documenting the sphericity, will be supplied at a cost of $60.00 per Ball Bar.

Five Most Popular Ball Bar ( Dumbbell ) Sizes