Surface Texture:
Surface Roughness, Waviness,
and Lay
TECH 3421
Video Lecture
Importance of Surface Roughness
The topography of a surface affects:
● Friction
● Fit
● Aesthetic
● Corrosion resistance
● Optical properties
● Sealing performance
● Fatigue strength
Specifying Surface Finish
ISO Grade Numbers, N1, N2, etc.
Smaller number, smoother finish
Triangle Symbols (older designation)
More triangles, smoother finish (don’t use)
Ra (and other parameters)
Smaller number, smoother finish
ISO and ASME Standards
Other, specialty standards [SPI Mold Finish]
Standards for specifying and
determining surface texture
ASME Y 14.36M - Symbols,
ASME B46.1 - Surface Texture
ISO 1302
ISO 4287
ISO 4287
Profilometer (one of many types)
Background
How a record stylus works (worked)...
https://www.youtube.com/channel/UCivA7_KLKWo43tFcC
kFvydw
Measuring the Profile
The measured profile Includes roughness,
waviness, and errors of form It EXCLUDES: imperfections
such as scratches, dents, pits
and cracks
Roughness, Waviness, Form, and Lay
Separating Waviness from
Roughness
Waviness is filtered out. Notice that our stylus
already filtered out some short waves.
Cutoff filters out long waves.
The cutoff is a length. The
measured profile is chopped up
into these lengths.
Think of cutoff as tuning out the
bass of the signal. We just want
the treble.
Cutoff Separates Waviness from Roughness
Evaluation length is generally 5 cutoff lengths
A section of
the traversed
length is
discarded at
each end.
This is not
evaluated.
The Roughness Profile is Leveled
When chopped up, the roughness profile may
be rotated away from the nominal (ideal) from.
If so, it is rotated to be flat.
Roughness Can Now be Evaluated
Example: Ra
Ra is the average roughness. It is
the simplest and one of the most
commonly used roughness
parameters.
Units are length and can be
micrometers or microinches
Keep in mind:
0.001 mm is 1 micrometer [micron]
.001 inches plus one microinch is
.001001
There are about 40 inches in a meter
There are about 40 microinches
In a micrometer
𝝁m
𝝁in
Be consistent
with the other
units of the
drawing!
Ra
Same as CLA - Center Line Average and
arithmetic average (AA)
Analytical version
Ra
Notice that Ra
DEPENDS
On the cutoff!
See:
https://willrich.c
om/wpcontent/upload
s/2014/11/Surf
ace-TextureMeasurementFundamentals.
pdf
ASME Y14.36 - Roughness Symbols
Symbol rests on surface to be finished.
If no roughness is given, a note must be indicate
roughness value.
Complete Symbol
Ra is roughness average (in microinches or
micrometers [microns] ). Mu = micro
Horizontal line is required when
specifying anything to the right
of the check
Example Surface Texture Symbols
Lay Symbols
ASME Y14.36M - 2008
Lay Direction
Direction is relative to placement on the
drawing
Surface
Roughness
Comparator
Nice Rule of Thumb:
https://michmet.co
m/surfaceroughnessanalysis-averageroughnessbasics.htm
Typical Ra
values by
process
Keep in mind that there are
about 40 inches per meter
Surface Roughness Parameters
In addition to Ra, there are other parameters
that are sometimes measured, for example:
Ra; Rc; Ry; Rz; Rq; Rt; Rmax; Rp; Rv; R3z; Rsk; Rku; RPc; RSm;
Rz1max; S; HSC; RzJIS; Rppi; R™ a; R™ q; Rlr; Rmr; Rmr(c); R™ c;
Rk; Rpk; Rvk; Mr1; Mr2; A1; A2; Vo; Rpm; tp; Htp; R; Rx; AR;
These are used to characterize the shape and distribution of the
roughness. Is it mostly peaks, mostly valleys, are the peaks
spaced out or close together.
Rq
RMS Value - “Sees” peaks and valleys with
more sensitivity than Ra
Other Roughness Parameters
Other Roughness Parameters
Great reference:
Link
(also in references)
And this:
Understanding Surface Quality:
Beyond Average Roughness (Ra)
Case Study
Variation in taper surface
roughness for a single
design effects the wear rate
in total hip arthroplasty
Robert K. Whittaker Harry S. Hothi Antti Eskelinen Gordon W.
Blunn John A. Skinner Alister J. Hart
First published: 05 October 2016
https://doi.org/10.1002/jor.23456Citations: 8
Link
Measuring Roughness
Profilometer
Contact
Diamond stylus
Noncontact
Optical (laser triangulation)
Electron optical (SEM)
Start: 1:38
Example (Surftest J210)
Other References
See course site.
● Profile Parameters from ISO 4287
● Mitutoyo Quick Guide to Surface Roughness
Measurement