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KOBA Ball Bar®

KOBA ball bar

Special connecting devices are used to link the three ball bar segments together. These connectors ensure accurate line-up and help to guard against vibration. An optional, adjustable-height support is available for angular positioning.

Significant Features of the KOBA-Ball Bar

KOBA-Ball Bar on a horizontal arm CMM

Construction and Handling

Ball on the spring element between two distance tubes

The carrying body is a CFC-GFC aluminum box filled with foam, the most significant features of which are high rigidity, good vibration dampening and low weight. The number of individual elements depends on the total length. These elements are securely held together by fastening elements.

The fixing elements are ceramic balls connected over a spring elements which have retainers in their bases. The spring element provides freedom of movement in axial direction which is essential for perfect bonding between the ball and the distance tube. Stress is applied to the rods and the balls which are lined up by means of a clamping unit with reproducible force in the axial direction and which support themselves upon a fixed skewback (springer) at the opposite end, thereby avoiding changes in the length occurring due to varied pre-stress forces.

The tube elements are designed to enable self-centering of the skewbacks and the clamping units. The distance tubes are made of stainless steel or CFC and have a carbide three-point contact at the ends for the ceramic balls. This form of contact ensures the best repeatability of measured lengths.

Why are distance tubes available in two materials?
CFC distance tube with carbide 3-point contact

The KOBA-Ball Bar is mounted by means of a step bearing and a stable, adjustable height support; two supports can by used for horizontal mounting.

Because of its well-planned designed, a completely dismounted test body can be set-up within 20 minutes, by one person. Changing the position of the test body within the measuring volume can be made in minutes.

Ball Bar Calibration

Sample calibration certificate

Calibration of individual measuring lengths can be carried out by the user on an exact coordinate measuring machine of normal construction size, consequently the cost of calibration is greatly reduced. For the purpose of calibration, only the first supporting body elements is used. On this element a small number of measuring lengths, corresponding to the size of the measuring machine, are mounted using the clamping unit; the respective pairs (i.e, Ball 1-Rod 1-Ball 2 / Ball 2-Rod 2-Ball 3, etc.) are measured and the values of the distances of center points of balls are noted in a calibration document. More Ball Bar calibration details.

Ball Bar Application and Evaluation

The ball bar is adjusted and measured in various positions within the measuring volume according to the specific requirements. The arrangement can be carried out in the direction of individual axes, of diagonals in the measuring planes or of the space diagonals in the measuring volume of the CMM to be examined. The recorded measuring values can be evaluated in our GUK-KS software, which is independent of the CMM manufacturer and can administer up to 100 coordinate measuring machines.

Technical Data

Attainable lengths: 2000mm to 8000mm
Divisions (distance between balls): 200mm, 300mm, 400mm, 500mm - special distances on request
Useable vertical range of height: 250mm to 3000mm - depending on length
Probing elements: Ceramic balls, 30mm diameter
Distance tubes: Stainless steel or CFC tubes with carbide three-point contacts
Weight: approximately 8kg/m
Length of individual elements: maximum 1800mm
KOBA Ball Bar on CMM at PWM

Applicable SIC Codes: 3423, 3545, 5049, 5084
Applicable NAICS Codes: 332212, 333515, 423490, 423830