| Established in 1952 | |
Page: 1790 |
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A Ball Bar (Dumbbell) is the major tool for functional "Performance Evaluation of Coordinate Measuring Machines" According to ANSI B89.4.1-1997. A Ball Bar (Dumbbell) consists of two very round spheres of exactly the same size firmly attached to opposite ends of a rather long rigid bar. The accuracy of a Ball Bar (Dumbbell) has a single major limitation. A conventional free standing Ball Bar (Dumbbell) will bend when the contact force of the measuring probe is applied to it. The longer the Ball Bar (Dumbbell), the greater the bending. With all of the automatic error correcting computer power, it should be easy enough to compensate for these Ball Bar (Dumbbell) deflections. However, these corrections turn out to be a good deal more complex than they first appear. The resulting deflection of the Ball is a rather complex vector function of gravitational sag, some simple bending and a large twisting moment. This is all complicated by the fact that there is no deflection at all on the very ends of the Ball Bar (Dumbbell). The end result of this complexity is that the C.M.M. and its software see two much smaller diameter spheres with the distance between their centers much further apart then the true dimension. |
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Cantilever Ball Bar shown with stand and
collar
( priced separately ) |
For C.M.M.s of ordinary quality, these shortcomings are of little or no consequence. The bending is fairly repeatable and the limited resolution and accuracy of ordinary machines presented little challenge for the free standing Ball Bar (Dumbbell).
With the advent of the new generation of high end C.M.M.s, a new higher accuracy Ball Bar (Dumbbell) is required.
An advance in Ball Bar (Dumbbell) technology now corrects these errors by providing two additional spheres just behind the master spheres.
These two hardened steel spheres are rigidly attached to the Ball Bar (Dumbbell) shaft.
The additional spheres are used to Kinematically support the Ball Bar (Dumbbell) in a very rigid manner, while leaving the full surfaces of the master spheres exposed for measurement.
These two kinematic couplings that support the Ball Bar (Dumbbell) are mounted near the very ends of a robust aluminum supporting structure that resists all bending.
The very rigid aluminum structure is only used as a support mechanism for the Ball Bar (Dumbbell). Its high rate of thermal expansion does not in any way influence the inter ball dimension of the steel Ball Bar (Dumbbell) itself.
The kinematic coupling that holds the first support sphere consists of three precision spheres located in a circle and rigidly mounted to the aluminum structure. The other coupling consists of two precision lapped cylinders rigidly mounted to the aluminum structure, to form a Vee-Block, that locates the second support sphere. There is a powerful rare earth magnet just below each of the couplings that pulls the support spheres solidly down against the kinematic couplings.
The Way Out Ball Bar ( Dumbbell ) support is often used with the Cantilever Ball Bar ( Dumbbell ).
| Part Number | Description | Price |
|
WO-1-2
|
100 STD BB ///// 200 CANT BB
|
$ 605.71
|
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WO-2-3
|
200 STD BB ///// 300 CANT BB
|
$ 547.55
|
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WO-3-4
|
300 STD BB ///// 400 CANT BB
|
$ 547.55
|
|
WO-3.5-4.5
|
350 STD BB ///// 450 CANT BB
|
$ 547.55
|
|
W0-4-5
|
400 STD BB ///// 500 CANT BB
|
$ 440.63
|
|
WO-4.5-5.5
|
450 STD BB ///// 550 CANT BB
|
$ 440.63
|
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WO-5-6
|
500 STD BB ///// 600 CANT BB
|
$ 571.05
|
|
WO-5.5-6.5
|
550 STD BB ///// 650 CANT BB
|
$ 546.55
|
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WO-6-7
|
600 STD BB ///// 700 CANT BB
|
$ 564.13
|
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WO-6.5-7.5
|
650 STD BB ///// 750 CANT BB
|
$ 580.45
|
|
WO-7-8
|
700 STD BB ///// 800 CANT BB
|
$ 649.20
|
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WO-7.5-8.5
|
750 STD BB ///// 850 CANT BB
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$ 659.80
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WO-8-9
|
800 STD BB ///// 900 CANT BB
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$ 688.40
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WO-9-10
|
900 STD BB /// 1000 CANT BB
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$ 697.95
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| < CMM-16 Page 1, Cantilever Ball Bar (Dumbbell) | ||
Copyright © 1999,
revised 2008, Micro Surface Engr. Inc. |
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