KOBA-step® Gage Bar

Available in five standard lengths: 420, 620, 1020, 1540 and 2020mm
The body of the gage is manufactured using special steel stabilized by a long aging process, providing dimensional stability
Material expansion is U = 11.5 x 10^-6 / 6°C
Distortion free support of the gaging cylinder faces is accomplished by a patented, machined form shaped to hold each cylinder firmly at its installed position.
The unique form of the KOBA-step body configuration produces identical principal planes tha provide the neutral bend feature at specified, marked bearing points along the gage body.
The gage block and faces are cylindrical in form, with lapped faces on either end of the cylinder. As the cylinder approaches the gaging surfaced the form is tapered to allow easy access for measurement and cleaning of the gage faces.
Gage blocks are available in ceramic.
Gaging faces are spaced in 20mm nominal increments. The diameter of the gaging faces is 5mm. Gage cylinders are available in steel or ceramic.
For measurement, gaging faces are not set to exact nominal positions - this provides higher testing variation against a certified nominal database. KOBA offers optional DAkkS calibration.
How the KOBA-step meets ISO 10360 Requirements
Access for probing of gage faces is available through a) holes on the side of the body, b) the longitudinal groove or c) at either open end of the gage body.
KOBA-step is ideal for horizontal and vertical quills operating from "under-the-table" type machines.
Gaging faces are held along the center line fiber of the KOBA-step body which allows the gage to be held horizontally, vertically or on various incline orientations without spacing deformation, accomplished through the gages neutral-bend body design.
Swivel base option provides proper clamping and support at bearing points and allows angular positions to be made quickly.
Leveling feet and handles provide fast and safe setups.
Purpose-built transport containers minimize the risk of damage during transportation.
The KOBA-step gage bar is also available in a "mini" version for users of small CMMS.

Step Gages for Checking the Accuracy of Coordinate Measuring Machines

In industrial metrology, actual physical bodies of known length which can be contacted by mechanical sensors have an important part to play as reference standards when measuring geometrical parameters. They have become increasingly important for assessing the accuracy of two and three-axis coordinate measuring machines (CMMs) which employ mechanical sensors. Checking the length measurements uncertainty has proved to be a highly informative and economical method for the acceptance testing and ongoing monitoring of CMMs. The Step-gage can be used for this in a great variety of ways given, for example, the advantages of uni-directional and bi-directional targeting and of measurements from all the gage faces along the line of measurement in succession while needing only a short time for preparation and measurement. Local errors can be detected in the CMM and characteristics can be derived for individual coordinate axes of the machine.

With the aid of the length measurement uncertainty, the manufacturer or user can specify and check the accuracy of a coordinate measuring machine to establish its suitability for length measurement. This fundamental task in metrology is of particular importance due to the fact that in practice the majority of measuring requirements are for the measurement of lengths. "Length measurement uncertainty" is defined by VDI/VDE guideline 2617, part 2.1 as the uncertainty with which a CMM allows the precisely known distance between two points on two mutually parallel gage faces situated in succession along a line of measurement to be remeasured. Figure 1 sows a measurement of this kind being made, taking as an example an individual parallel gage block with an outside length Le which is arranged obliquely in three dimensions and whose length is remeasured by successive contacts with the block with the probe head in positions I and II.

On the step gage, spacing of different kinds for making test measurement are all available simultaneously, as follows:

Outside dimension Le, e.g. with the probe head in positions I and II (figure 2)
Inside dimension Li, e.g. with probe head in positions III and IV (figure 3)
Rear-face to rear-face dimension Ls, e.g. with probe head in positions III and V (figure 3
Front-face to front-face dimension Lx, e.g. with probe head in positions VI and IV (figure 3)
Positional length Lp of a gage face from the datum gage face, e.g with probe head in positions VI and 0 (figure 3)

The illustrations show only one of many options available for each type and size of spacing. The value of the length measurement uncertainty is generally given in the form of a length-dependant formula: U = A + K x L </= B

Figure 2, Castellated step gage arranged obliquely in three dimensions on the table of a coordinate measuring machine, with an outside length Le being measured.

Figure 3, Step gage arranged obliquely in three dimensions on the table of a CMM, showing measurement of an inside dimension Li, of and outside dimension Ls or of the position Lp of a gage face as a distance from the datum face.

A distinction should be made between the figure U1 specified for one-dimensional test measurements along a coordinate axis (with terms A1, K1, B1), the figure U2 for two-dimensional test measurements made diagonally in a coordinate place (with terms A2, K2, B2) and the figure U3 for three-dimensional test measurements made diagonally in the three-dimensional space defined by the coordinates (with terms A3, K3, B3).