1. Lab # 5: Surface Roughness Test
4/19/2019
Lab # 5: Surface Roughness Test
Eng. Ibrahim Kuhail
Eng. Ahmed Al Afeefy

2. Lab#5: Surface Roughness Test
4/19/2019
Objectives
To understand surface roughness terminology and its parameters.
To be able to use surface roughness measurement instrument.
To know how PERTHOMETER M1 can be used to measure surface roughness

3. Lab#5: Surface Roughness Test
4/19/2019
Introduction
Surface finish is a characteristic of any machined surface. It is sometimes called surface texture or roughness.
The design engineer is usually the person that decides what the surface finish of a work piece should be. They base their reasoning on what the work piece is supposed to do.

4. Lab#5: Surface Roughness Test
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Introduction cont.
There are two principal reasons for surface control:
To reduce friction: When a film of lubricant must be maintained between two moving parts, the surface irregularities must be small enough so they will not penetrate the oil film under the most severe operating conditions.
To control wear: Surface finish is also important to the wear service of certain parts that are subject to dry friction, such as machine-tools bits, threading dies, stamping dies, rolls, clutch plates, and brake drums.

5. Lab#5: Surface Roughness Test
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Roughness
Roughness is a measurement of the small-scale variations in the height of a physical surface. It consists of surface irregularities which result from the various machining process. These irregularities combine to form surface texture.
This is in contrast to large-scale variations, which may be either part of the geometry of the surface or unwanted 'waviness'.
Roughness is sometimes:
An undesirable property, as it may cause friction, wear, drag and fatigue,
A beneficial property, as it allows surfaces to trap lubricants and prevents them from welding together.

6. Lab#5: Surface Roughness Test
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Roughness Parameters
Roughness Height: It is the height of the irregularities with respect to a reference line. It is measured in millimeters or microns or micro inches. It is also known as the height of unevenness.
Roughness Width: The roughness width is the distance parallel to the nominal surface between successive peaks or ridges which constitute the predominate pattern of the roughness.
Roughness Width Cut Off: The greatest spacing of respective surface irregularities to be included in the measurement of the average roughness height. It should always be greater than the roughness width in order to obtain the total roughness height rating. It is used to differentiate between roughness and waviness. The cut-off length should be at least 2.5 times the peak-to-peak spacing of the profile roughness. This means that at least two peaks and valleys are found in each cut-off length.

7. Roughness Parameters cont.
Lab#5: Surface Roughness Test
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Roughness Parameters cont.
Lay: the direction of predominant surface pattern produced and it reflects the machining operation used to produce it.
Waviness: the irregularities which are outside the roughness width cut off values. Waviness is the widely spaced component of the surface texture. This may be the result of work piece or tool deflection during machining, vibrations or tool runout.
Waviness Height : the peak to valley distance of the surface profile, measured in millimeters.
Waviness Width: the peak to peak distance of the surface profile, measured in millimeters.

8. Roughness Parameters cont.
Lab#5: Surface Roughness Test
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Roughness Parameters cont.

9. Surface Texture Parameters cont.
Lab#5: Surface Roughness Test
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Surface Texture Parameters cont.
Ra: Arithmetical mean deviation. The average roughness or deviation of all points from a plane fit to the test part surface. The average roughness is the area between the roughness profile and its center line divided by the evaluation length. This is the parameter that has been used universally for many years and the European and ISO standards now more generally use Rz

10. Surface Texture Parameters cont.
Lab#5: Surface Roughness Test
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Surface Texture Parameters cont.
Rv (Valley): Lowest valley. The maximum distance between the mean line and the lowest point within the sample. It is the maximum data point height below the mean line through the entire data set.
Rp (Peak): Highest peak. The maximum distance between the mean line and the highest point within the sample. It is the maximum data point height above the mean line through the entire data set.
Rt (PV): Maximum peak-to-valley height. The absolute value between the highest and lowest peaks.

11. Surface Texture Parameters cont.
Lab#5: Surface Roughness Test
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Surface Texture Parameters cont.
Rtm: Mean peak-to-valley roughness. It is determined by the difference between the highest peak and the lowest valley within multiple samples in the evaluation area. For profile data it is based on five sample lengths. ISO, n=5
Ry (Rmax): Maximum peak-to-valley roughness. The vertical distance between the top of the highest peak and the bottom of the deepest valley within the sampling length. It is the maximum of all the peak-to-valley values.

12. Surface Texture Parameters cont.
Lab#5: Surface Roughness Test
4/19/2019
Surface Texture Parameters cont.
Rz: Ten-point height. The average absolute value of the five highest peaks and the five lowest valleys over the evaluation length.
Rz ISO: Average peak-to-valley profile roughness. The average peak-to-valley roughness based on one peak and one valley per sampling length. The single largest deviation is found in five sampling lengths and then averaged

13. Equipment Perthometer
Lab#5: Surface Roughness Test
4/19/2019
Equipment
Perthometer
It is characterized by a multitude of functions. After carrying out a measurement, periodic and non-periodic profiles can be identified and the cutoff set according to standards automatically, such that unintentional non-standard measurements are excluded

14. Perthometer Features Measuring range up to 150 µm (6000 µin)
Lab#5: Surface Roughness Test
4/19/2019
Perthometer Features
Measuring range up to 150 µm (6000 µin)
Measuring units µm/µin selectable
Standards: DIN/ISO/JIS
Tracing lengths 1,75 mm; 5,6 mm; 17,5 mm (0,07 in; 0,22 in; 0,7 in)
Cutoff 0,25 mm/0,8 mm/2,5 mm (0,01 in/0,032 in/0,100 in)
Reduced cutoff selectable
Number of sampling lengths selectable from 1 to 5
Automatic selection of filter and tracing length confirming to standards
Phase-corrected profile filter as per DIN EN ISO 11562
Parameters as per DIN/ISO/SEP: Ra, Rz, Rmax, RPc and JIS: Ra, Rz
Automatic scaling according to the profile amplitude
Printing of roughness profile and measuring record
Dynamic pick-up calibration
Blocking of instrument settings to prevent unintentional modifications

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17. Example 1 Parameter Value Total length( Lt) 5.6 mm Cut-off length (Lc)
Lab#5: Surface Roughness Test
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Example 1
Parameter
Value
Total length( Lt)
5.6 mm
Cut-off length (Lc)
0.8mm
Measured Length (Lm)
5.6-(2*0.8)=4mm
Average Roughness (Ra)
0.937µm
Average Roughness Depth (Rz)
6.26 µm
Maximum peak-to-valley (Rmax)
6.89 µm
RPc (0.2,-0.2)
90/c
Vertical Scale Division
2.5 µm

18. Example 2 Parameter Value Total length( Lt) 1.75 mm
Lab#5: Surface Roughness Test
4/19/2019
Example 2
Parameter
Value
Total length( Lt)
1.75 mm
Cut-off length (Lc)
0.25mm
Measured Length (Lm)
(1.75 – 2 (0.25)) = 1.25mm
Average Roughness (Ra)
0.9555µm
Average Roughness Depth (Rz)
6.22 µm
Maximum peak-to-valley (Rmax)
9.14 µm
RPc (2.5,-2.5)
16 / c
Vertical Scale Division
5 µm

19. Lab#5: Surface Roughness Test
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Question