Team SILK SX28-72, Instruction Manual

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SX28-72 Flange Facing Machine
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APPENDIX B SURFACE METROLOGY
First profile graphs of roughness texture were produced over fifty years ago by a German Engineer,
Gustav Schmalz. His graphs allowed differential magnification of vertical and horizontal axes so that a
visual assessment of surface could be made.
These profile graphs did not provide the direct indications of magnitude required by workshops. Of the
usual ways of measuring a wave from the deepest individual roughness depth of surface (R Max) was
too dependent on extremes e.g. dirt or scratches.
Conventional statistical terms like RMS present instrumental difficulties: The compromise is to use Ra
previously known as C.L.A. (Centre Line Average) which can be determined on a purely geometrical
basis and easily measured on an electrical instrument.
Ra This is the arithmetic mean of the departure of the profile of the surface from the mean line.