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Measurement and Standards: KOBA-step Step Gages
Phone (586) 759-2400
www.pmargage.com www.shoppwm.com 1111
Fax (586) 759-2423
Step GagesStep GagesStep GagesStep Gages A complete system for monitoring coordinate
measuring machines.
Measurement and StandardsMeasurement and StandardsMeasurement and StandardsMeasurement and Standards
Measurement and Standards: KOBA-step Step Gages
Fax (586) 759-2423
2222 www.pmargage..com www.shoppwm.com
Phone (586) 759-2400
Step Gages, At a GlanceStep Gages, At a GlanceStep Gages, At a GlanceStep Gages, At a Glance
⊕ Available in five standard
lengths: 420, 620, 1020,
1540 and 2020mm
⊕ The gage body is manu-
factured using special
steel, stabilized by a long
aging process which
provides 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 in
its installed position.
⊕ The unique form of the KOBA-step body configuration produces
identical principal planes that provide the neutral bend feature at
specified, marked bearing points along the gage body.
⊕ The gage blocks and faces are cylindrical in form with lapped faces
on either end of the cylinder. As the cylinder approaches the gaging
surface it is tapered to allow easy access for measurement and
cleaning of the gage faces.
⊕ Ceramic gage blocks
⊕ Gage faces are spaced in 20mm nominal increments. The diameter
of the gage faces is 5mm. Gage cylinders are available in either steel
or ceramic.
⊕ Gage faces are not set to exact nominal positions for measurement—
this provides higher testing variation against a certified nominal data-
base. KOBA sources for certification are PTB, NIST, DKD and Works
(in-house).
⊕ Access for probing 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.
⊕ Gage faces are held along the center line fiber of the gage body which
allows the gage to be held horizontally, vertically or on various inclines
without spacing deformation, this is accomplished through the gages
neutral-bend body design. ⊕ The 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 set-ups ⊕ Purpose-built transport containers minimize the risk of damage
during transportation. ⊕ Also available in a “mini” version for users of smaller CMMs
-6
Measurement and Standards: KOBA-step Step Gages
Phone (586) 759-2400
www.pmargage.com www.shoppwm.com 3333
Fax (586) 759-2423
Step Gages for Checking the Accuracy of Step Gages for Checking the Accuracy of Step Gages for Checking the Accuracy of Step Gages for Checking the Accuracy of
measurement uncertainty grid (right). The top and bottom boundary lines
produce a funnel shaped outline with the neck of the funnel measuring
2A (A = the figure specified by the manufacturer for length measurement
uncertainty, irrespective of length). 95% of all the test measurements must
lie within, or on, the boundaries. A quantitative analysis is made simply by
counting the number of measurements which lie outside the boundary lines.
Gage Face Position PlotGage Face Position PlotGage Face Position PlotGage Face Position Plot
It is possible to test the positions Lp of the gage faces as distances from the
datum face using the step-gage. If the relevant length errors ∆ Lp given by
position measurement in line with VDI guideline 2617 part 3 are entered in
a plot, then it is possible to see both the position of the test length and
also the sequence, for example, if the measurement points in a run are
connected by straight lines. With individual gage blocks this is not possible
because they do not have any true common reference point and are not
situated on a measurement line.
A gage face position grid (right),
similar to the length measure-
ment uncertainty grid, is used
for analysis. The outline is sym-
metrical and similar in shape to
a butterfly with a width of 1A
across the waist. The parame-
ters in this case correspond to
the appropriate figures A1, K1, B1
and so on. As this grid is moved along the measured length L, at least 95%
of all the measurements must always lie within or on the boundary lines,
meaning that all the measurement points must do so consistently whatever
the position of the waist. This ensures that any pairing of two gage faces
(even from different runs) in the form of outside, inside or face-to-face dimen-
sions will also lie inside the funnel of the length measurement uncertainty
grid. Thus, the grid forms a combined graphic expression of both the equa-
tions given above for all points of measurement.
Comparisons Between the Test Standards Comparisons Between the Test Standards Comparisons Between the Test Standards Comparisons Between the Test Standards
Gage Blocks and Step GagesGage Blocks and Step GagesGage Blocks and Step GagesGage Blocks and Step Gages
Apart from the step-gage, parallel gage blocks are the reference standards
known for the greatest accuracy of length. However gage blocks are rela-
tively flexible and have to be mounted at the AIRY points (symmetrical spac-
ing a = 0.57735 x L) so that they are free of bending moments if the parallel-
ism of the gage faces is to be maintained. The gage blocks for the individual
test lengths can be individually placed one behind the other for shorter
lengths and next to one another for longer lengths. When this is done, how-
ever, there is no way of obtaining the different gage points along a line of
measurement which are desirable for measurement purposes.
As is normal with all measurement standards, the KOBA-step step gage
should be recalibrated after a certain period. We recommend the first
calibration after one to two years and successive recalibration after two
to three years.
Alignment of the KOBAAlignment of the KOBAAlignment of the KOBAAlignment of the KOBA----stepstepstepstep
To define the position and orientation of the KOBA-step respective to the
measuring line within the measuring volume, we recommend proceeding
as follows:
As the gage body with the fixed cylindrical gage blocks has been designed
symmetrically to both sides, one of the external side surfaces and the upper
external surface at the end of the large U-groove can be used for alignment.
Any points which are as large as possible can be sensed at either the side
surface or at the upper external surface. Both places so defined are squared
off mathematically. A parallel line 27.5mm to the side surface and 30mm to
the upper surface is the measurement line situated on the neutral fiber.
It is also possible to use both ends of the 7 x 10mm interior groove for the
alignment and proceed in a similar way as before. The distance from the
wall of the groove and the floor of the groove to the line of measurement is
5mm in both directions.
Figure 11, KOBA-step vertically oriented along the Z-axis, standing in the base. This
alignment is also suitable for checking height gages as shown in Figure 12 (right)
Measurement and Standards: KOBA-step Step Gages
Fax (586) 759-2423
8888 www.pmargage..com www.shoppwm.com
Phone (586) 759-2400
Practical UsePractical UsePractical UsePractical Use
Practical experience using the
KOBA-step step gage to check
the accuracy of coordinate
measuring machines and
access and interpret the results
has demonstrated the useful-
ness and potentially high
information yield of the “length
measurement uncertainty”
method. The advantage lies in
the fact that the measurement
is carried out at precision gage
faces using the normal gaging
procedure and, in general, the
manufacturer’s standard processing software. It is a good idea to make full
use of the opportunities offered by the step gage since (a) the unidirectional
and bidirectional gaging of the inside and outside dimensions, (b) the di-
mensions between similarly oriented surfaces and successive dimensions
from a given point occur even in the routine measurement of work pieces
and (d) the measurements which have been obtained can all be correlated
with one another as desired even after the event. What is more, a series of
measurements at all the gage faces in succession provides a large amount
of interrelated information and requires only a short time for measurement.
Since the length measurement uncertainty characteristic depends very
much on the geometry of the coordinate measuring machine, the lines
along which measurements are made should be as follows:
⊕ 3 to 4 measurement lines which are diagonal in 3 dimensions (i.e.,
along the diagonals of an inscribed cube—at an angle of approximately
35° - or along the diagonals of the cuboid shape representing the
measured space).
⊕ 2 diagonal lines of measurement in each coordinate plane (i.e.,
along the diagonals of a square—at a gradient of 45° - or the diagonals
of a rectangle).
⊕ At least one line of measurement parallel to each coordinate axis.
At least 18 suitable lines of measurement have to be selected in order to
arrive at a complete definition of the 18 geometrical cuboid characteristics
of the entire measurement volume.
It must be stressed that reliable measurement results for a complex system
cannot be achieved unless stylus probes are included. Checking the CMM
without mechanical contact, i.e., without using a probe, will not result in a
comprehensive statement about the accuracy of the measuring machine.
Figure 13, KOBA-step shown with swivel support and
base, illustrated at various inclines.
Figure 14, KOBA-step, shown with
swivel support and base, size 1,
for accommodating a 1020mm
long step-gage.
Measurement and Standards: KOBA-step Step Gages
Phone (586) 759-2400
www.pmargage.com www.shoppwm.com 9999
Fax (586) 759-2423
Conducting Formal Acceptance Procedures and Monitoring the Conducting Formal Acceptance Procedures and Monitoring the Conducting Formal Acceptance Procedures and Monitoring the Conducting Formal Acceptance Procedures and Monitoring the
Precision of Machine Tools and Robotic Dimensional Gaging SystemsPrecision of Machine Tools and Robotic Dimensional Gaging SystemsPrecision of Machine Tools and Robotic Dimensional Gaging SystemsPrecision of Machine Tools and Robotic Dimensional Gaging Systems
The KOBA-step gage can be used for checking the positioning accuracies
of machine tools and articulated-arm robotic dimensional gaging systems,
applications where it offers the same elegant approach and speed as when
checking coordinate measuring machines. The swivel support and base
accessories are required for this application.
Regular use of the KOBA-step for monitoring dimensional gaging precision
of machine tools is essential to total quality assurance. Complete quality
assurance demands more than the mere precision dimensional gaging of
finished work and components; regularly monitoring the dimensional gaging
precisions of those machine tools employed in fabrication is indispensible.
Finished products must be machined to within prescribed dimensional
tolerances if they are to pass final acceptance checks. Regularly monitoring
machine tool dimensional gaging precision provides valuable information on
the degrees to which work and component dimensional tolerances are
maintained during machining operations.
Figure 15, KOBA-step installed on a swivel
support and base, shown here spanning
the major diagonal of the workspace of a
vertical milling machine equipped with a
dimensional gaging head.
Figure 16, KOBA-step shown horizontally
aligned along the x-axis of the rotary bed of
a machine tool equipped with a dimensional
gaging head.
Figure 17, KOBA-step shown aligned
vertically for checking the z-axis of a
machine tool equipped with a dimensional
gaging head
Figure 18, KOBA-step shown installed on
a flexible machining center to verify its
positioning accuracy (the center’s dimensional
gaging head is integrated into its tool chuck.)
Measurement and Standards: KOBA-step Step Gages
Fax (586) 759-2423
10101010 www.pmargage..com www.shoppwm.com
Phone (586) 759-2400
KOBAKOBAKOBAKOBA----step Ministep Ministep Ministep Mini
A system for calibrating and monitoring
multi-sensor measuring instruments
and coordinate measuring instruments
of small measuring volume.
The KOBA-step mini is a step gage with
a reduced cross section and gage
block distance resized according to the
measuring length and measuring task.
The advantages of the regular sized
step gage, such as cylindrical gage
block embedded in the neutral fiber of
the carrying body and access on three
sides, have been maintained. The
length and distance of the gage blocks
were reduced to 10mm according to
the total lengths which allows recognition of local errors of the measuring
instrument. The cylindrical gage blocks are made of zirconia ceramic and
are corrosion and wear resistant.
The KOBA-step Mini system is completed by the swivel support, which is
included, allowing the Mini to be mounted horizontally, vertically or in the
volume.
Traceability to the National Length Standard is guaranteed by DKD, PTB
or Works calibration.
Standard Lengths:Standard Lengths:Standard Lengths:Standard Lengths:
Nominal Lengths,
MM
Number of
Castellations /
Probing Faces
Division,
MM
Overall Length,
MM
210 11 / 22 10 220
310 16 / 32 10 330
Includes: KOBA-step Mini with zirconia ceramic probing elements, base
and swivel support for positioning from 0° to 90° (horizontally or vertically)
and an aluminum storage case.
Measurement and Standards: KOBA-step Step Gages
Phone (586) 759-2400
www.pmargage.com www.shoppwm.com 11111111
Fax (586) 759-2423
Standard Nominal LengthsStandard Nominal LengthsStandard Nominal LengthsStandard Nominal Lengths
The nominal length of a step gage is the distance from the first gage face to the last gage face.
Special sizes on request up to 2500mm.
CrossCrossCrossCross----section of holdersection of holdersection of holdersection of holder: 55x55mm Length of castellationsLength of castellationsLength of castellationsLength of castellations: 20mm
Space between castellationsSpace between castellationsSpace between castellationsSpace between castellations:
20mm (10mm for 210 and 310mm
step gages)
CrossCrossCrossCross----section of cylindrical gage section of cylindrical gage section of cylindrical gage section of cylindrical gage
blocksblocksblocksblocks: 10mm diameter
The following characteristics are identical for all lengths listed above:
210 22 220 —
310 22 330 —
AccessoriesAccessoriesAccessoriesAccessories
Swivel Support Lockable in positions –50° to 50° in 5°
increments
Base, Size 1 For mounting swivel support to step gages
420, 620 and 1020
Base, Size 2 For mounting swivel support to step gage
1540 and 2020
StorageStorageStorageStorage
Step Gages 420, 620
and 1020
Includes one storage box for gage, clamps
and swivel support and one box for the base
CalibrationCalibrationCalibrationCalibration
PTB U = 0.2µm + 0.8 x 10-6 x L
DKD U = 0.2µm + 0.5 x 10-6 x L
Works U = 0.6µm + 1.5 x 10-6 x L
NIST U = 0.22µm + .18 x 10-6 x L
“L” is the distance between any measuring faces in meters.
Step gages 1540 and
2020
Includes one storage box for gage, clamps,
one box for the swivel support and one box
for the base
Measurement and Standards: KOBA-step Step Gages
Fax (586) 759-2423
12121212 www.pmargage..com www.shoppwm.com
Phone (586) 759-2400
Step GageStep GageStep GageStep Gage
⊕ Ceramic Gage Blocks
⊕ Corrosion resistant body
⊕ Includes aluminum
transport / storage case
⊕ 210 and 310mm step gages
include a swivel support and
a base
Order Number Material Nominal
Length
Number of
Blocks
Contact
Points
KOB-420STEPCER Ceramic 420 11 22
KOB-620STEPCER Ceramic 620 16 32
KOB-1020STEPCER Ceramic 1020 26 52
KOB-1540STEPCER Ceramic 1540 39 78
KOB-2020STEPCER Ceramic 2020 51 102
KOB-210STEPCERS Ceramic 210 11 22
KOB-310STEPCERS Ceramic 310 11 22
Swivel Arm Support:Swivel Arm Support:Swivel Arm Support:Swivel Arm Support:
⊕ Swivel arm and clamps
⊕ Swivels and locks in position
–50° to 50° in 5° increments
⊕ Includes aluminum transport /
storage case
⊕ Requires Base for use (base is partially visible in photo at left)
Order Number Description
KOB-####SWISUP Locking, swivel support for Step-gages
(replace “####” with the nominal length of the step gage).
Note: 210 and 310 step gages include a swivel support.
Measurement and Standards: KOBA-step Step Gages
Phone (586) 759-2400
www.pmargage.com www.shoppwm.com 13131313
Fax (586) 759-2423
Step Gage Base 1 and 2:Step Gage Base 1 and 2:Step Gage Base 1 and 2:Step Gage Base 1 and 2:
⊕ Mounts swivel arm to
the step gage
⊕ Includes aluminum transport /
storage case
Order Number Description
KOB-####Base-1 Base for step gages 420, 620 and 1020
KOB-####Base-2 Base for step gages 1540 and 2020
(replace “###” with the nominal length of the step gage).