Phase 2 SRG-4600 - Calibration and Environmental Factors; Ignoring Vibration in Gaging Environment; Misunderstanding Calibration Procedures

9.Ignoring vibration in the gaging environment Many surface finish gages are used on production floors,
where vibration from manufacturing equipment may interfere with the measurement signal. Some skidless
gages have a built-in "static mode" function to assess this condition. With the traverse motor turned off
and the stylus in contact with a surface, any signal generated is the result of ambient vibration. Vibration
effects can be reduced or eliminated by relocating the gage near a bearing wall, by isolating the gage with
vibration-absorbing rubber pads or a high-density table, or by removing it from the area altogether. It
may also be possible to identify and eliminate the source of vibration.
10.Misunderstanding calibration Surface finish gages are verified against test patches or specimens
whose surface characteristics are known and certified. If gage results do not agree with the characteristics
of the specimen, the gage must be adjusted. The nature of the adjustment differs considerably between
simple, non-computer-driven gages, and sophisticated computerized ones. Simple gages are generally
checked against a roughness patch with either a triangular or sine-wave profile. If the gage reads other
than the patch's calibrated value (usually around Ra 125 μ"), a potentiometer is adjusted to bring results
into agreement with the specimen. In this case, it is the "back end" or calculating portion of the gage that
is being adjusted. The "front end"--the raw input data--is untouched. The reverse applies to computer-
driven gages, where the backend consists of the software algorithms that turn raw data into numerical
results. As the algorithms cannot be modified, the way the gage perceives the raw data at the front end
must be adjusted. Skidless gages are usually calibrated against a stepheight specimen, then a
multiplication factor is entered into the computer to adjust signal gain from the transducer before it
reaches the algorithm software. From that point on, all data entering the computer is corrected by the
same multiplication factor.
References
1.Tabenkin,A.,:SurfaceFinish:AMachinist'sTool,ADesignNecessity,ModernMachineShop.April1996
2.Tabenkin,A.,:SurfaceFinishMeasurementBasics,QualityMagazine.September2004
3.Tabenkin,A.,:Wheredowegowronginsurfacefinishgaging?,QualityinManufacturing.November/December1998.
4.Sander,M.:APracticalGuidetotheAssessmentofSurfaceTexture,FeinprufGmbH,Goettingen1989
5.ANSI/ASMEB46.1‐2002SurfaceTexture,SurfaceRoughness,WavinessandLay,AmericanSocietyofMechanical
Engineers,2002
6.ANSI/ASMEY14.36M‐1996(R2002)SurfaceTextureSymbols‐Metricversion,AmericanSocietyofMechanicalEngineers,
1996
7.Nugent,P.,MacKenzieD.,DevelopmentsinSurface(andForm)MeasurementTechnology(PresentationforCaterpillar),
October2006.
8.Vorburger,T.,Raja,J.,SurfaceFinishMetrologyTutorial(NISTIR89‐4088),U.S.DepartmentofCommerce,National
InstituteofStandardsandTechnology,June1990.
Note:Parametercalculationsinthispresentationareshownfordiscussionandpurposesofillustrationonly.
Refertothe
ANSI/ASMEB46.1‐2002SurfaceTexture,SurfaceRoughness,WavinessandLayforactualcalculationsandmethodsof
evaluation