| Established in 1952 | |
Page: 3300 |
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The Super Ball Bar (Dumbbell) Thing (Part # SBB-TH-1) was originally developed as a fast, almost automatic Monday morning check for the United States Air Force to evaluate the performance of Coordinate Measuring Machines ( CMM ) in accordance with the ANSI B89.4.1-1997 specification. The importance of an interim checking device was brought home by an Air Force study, which indicated that the majority of C.M.M.s are not functioning properly at the time of their annual re-calibration. |
 The Bal-tec Ball Bar Thing |
The Super Ball Bar (Dumbbell) Thing consists of a very rigid assembly that holds two Ultra Precision Cantilever Ball Bars ( see our page, "The Cantilever Ball Bar", page number 1410).
Each Ball Bar (Dumbbell) consists of two ultra precise spheres of exactly the same diameter securely attached to opposite ends of a rather long rigid bar. One Ball Bar (Dumbbell) is held horizontal and the second is inclined at an angle. The two Ball Bar (Dumbbell)s are indexed at 90 degrees to each other. ( see our page, Standard Ball Bar ( Dumbbell ) for Evaluation of Coordinate Measuring Machines, for more information about ball bars. )
The base ring assembly of the device is rigidly fixed to the C.M.M. table through a central threaded stud.
There is an entire family of Dual Threaded Adapter Screws available, (see Technical Data Sheet C.M.M.-14 Table #1) that will match any thread size on the C.M.M. table to the standard M10 x 1.5 thread in the center of the base ring assembly.
There are three 3/4 inch ( 0.75", 1.9 cm ) diameter precision spheres securely attached to the lower surface of the upper rotating assembly.
These three spheres are positioned to sequentially mate with eight pairs of precision lapped Kinematic cylinders. These matched pairs of cylinders are located every 45 degrees around the annular face of the base ring.
In operation, the upper rotating assembly is lifted up out of contact with the Kinematic cylinders by approximately 25 P.S.I. of air pressure. The assembly is indexed to the next position and it is then lowered into position as the air pressure is released.
The end result of the horizontal and the angled Ball Bars being indexed to the eight 45 degree positions is the generation of a three dimensional Ball Plate with thirty two physical coordinates.
Although a length calibration of the Ball Bar (Dumbbell)s is not essential, it does give an added level of certainty to the evaluation.
To resist any deflection caused by the contact force of the C.M.M. measuring probe, these Ball Bar (Dumbbell)s are Kinematically supported on robust Aluminum rails. One of the Ball Bar (Dumbbell) spheres sits in a precision three ball Kinematic cup at one end of the aluminum support rail while the other is supported in a cradle formed by two precision cylinders at the other end. There is a powerful rare earth magnet in the center of each of the Kinematic couplings that holds the Ball Bar (Dumbbell) rigidly in position.
The robust aluminum rails are simply rigid supporting devices and their high rate of thermal expansion is not involved in the measurement of the steel Ball Bar (Dumbbell)s.
On Direct Computer Controlled C.M.M.s, the location of both Ball Bar (Dumbbell)s in all eight positions can be programmed or taught to the computer memory one time, so that all future measurements can be carried out automatically.
The proper use of Ball Bar (Dumbbell)s for the "Performance Evaluation of Coordinate Measuring Machines" is outlined in ANSI B89.4.1-1997 specification. This is available from the American National Standards Institute. 25 West 43rd Street, 4 floor, New York, NY 10036, USA Tel: 1.212.642.4900, Fax: 1.212.398.0023
| Part # | Description | Price | Purchase |
| BB-TH-1 | BALL BAR THING WITH TWO BALL BARS | $5640.00 |  |
http://www.precisionballs.com |
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