Page 60 - EDM Today Winter 2025

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QUALITY CORNER | CONTINUED

Another very useful value reported for surface roughness is R z, whose defi nition is depicted in Figure 12.

R z
R z is the average maximum peak to
valley distance of fi ve consecutive
sampling lengths within the measur-
ing length. R z is very useful to deter-
mine the approximate total depth of
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Figure 12EDM Today Magazine
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the surface roughness and gives a
good approximation as to how much
in order obtain a “clean” surface.
A Final Sobering Note on Surface
Roughness
Despite the fact they we report
surface roughness measurements in
either microinches or microns, there
is considerable variability in those
numbers. According to Mitutoyo,
”roughness measurement values,
particularly the vertical parameters R t, R z, R z1max and R a, vary in the approximate range of -20% to +30%.”
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Even re-running the same test will usually not give an identical result!
In addition to the aforementioned EDM Today articles, those interested in further details concerning surface
roughness should download the excellent Mitutoyo PDF QUICK GUIDE TO SURFACE ROUGHNESS
MEASUREMENT Bulletin 2229 from their website.
Roger Kern | Principal Consultant | International Technology Professionals | www.itp4edm.com

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