Surface Roughness

1. TITLE

Surface Roughness Measurement

2. OBJECTIVE

a) To obtain the value of roughness of a specimen by the CENTER LINE

AVERAGE (CLA) or ROUGHNESS AVERAGE (Ra) method by using a

Computerized Roughness Measuring Machine.

b) To compare the value of roughness of a specimen by the Center Line Average

(CLA) and average roughness (Ra) method.

c) To study the causes of different value of roughness of a specimen between CLA

and Ra method.

d) To study the necessary precaution needed for this experiment.

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3. INTRODUCTION

Figure 1: Sketch depicting how a probe stylus travels over a surface

Roughness is a measure of the texture of a surface. A surface can never be

perfectly smooth and will always have two components of surface texture namely

roughness and waviness as shown in figure above. They may vary from fine to coarse

according to the machine process used. Roughness is quantified by the vertical

deviations of a real surface from its ideal form. If these deviations are large, the surface

is rough; if they are small the surface is smooth. Roughness is typically considered to

be the high frequency, short wavelength component of a measured surface.

Roughness plays an important role in determining how a real object will interact

with its environment. Rough surfaces usually wear more quickly and have higher friction

coefficients than smooth surfaces. Although roughness is usually undesirable, it is

difficult and expensive to control in manufacturing. Decreasing the roughness of a

surface will usually increase exponentially its manufacturing costs.

In some cases, the physical geometry of the measuring instrument may have a

large effect on the data. This is especially true when measuring very smooth surfaces.

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4. SPECIMEN & EQUIPMENT

a) Specimen – piston cylinder

b) A computerized Surface Roughness Machine

c) Digital planimeter

5. PROCEDURES

Machining Processes

1. A cut off wavelength of 0.8mm by 8 sections were selected on the machine. The

machine were set to a vertical magnification to auto and horizontal magnification

too 100.

2. The component is placed on the auto leveling table at a suitable position such

that when pick up head is lowered, its stylus contacts the surface of the

specimen.

Figure 2: Computerized Surface Roughness machine

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L

5. The machine was set; the measurement is ready to be recorded.

6. The roughness profile graph for the specimen was obtained.

Manual Processes

Figure 3: Roughness Profile

1. Three peaks on the profile graph were selected.

2. Two vertical lines were drawn for the three peaks.

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CLA Line

L

CLA Line

3. A centerline (CLA) line was drawn.

4. The areas above and below the CLA line was measured using a digital

planimeter. Three measurements were taken and the average of the

measurements was calculated.

5. The value of CLA was calculated.

6. The computerized result for CLA was compared with the manual result.

6. RESULTS & DATA ANALYSIS

i. The value of Ra from computerized result is 3.48 µm.

ii. For manual calculation, we must calculate the CLA and the percentage error.

CLA = ΣA / ( L x Mv )

where:

∑A = sum of the area above and below the centerline

L = sample length

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Mv = vertical magnification

Percentage of error = x 100%

iii. The value of L = 10 cm and Mv = 2100.

Area above the line(m2)

Area below the line(m2)

Sum of area above and below the line(m2)

A1 0.00025 0.00064 0.00089

A2 0.00022 0.00060 0.00082

A3 0.00022 0.00062 0.00084

ΣA = (0.00089+0.00082+0.00084) / 3

= 8.5 x 10 -4 m 2

CLA = ΣA / ( L x Mv )

= (8.5 x 10-4 )/ (10 x 10-2 x 2100 )

= (8.5 x 10-4 )/ 210

= 4.048 µ m

Percentage of error = x 100%

= x 100%

= 16.32%

7. DISCUSSIONS

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From the result, the roughness value that we get using Center Line Average

(CLA) method is 4.048µm and the percentage of error is 16.32%. The percentage of

error that we get is acceptable since the value is still below 20%. If the value of

percentage of error is above 20%, the error is considered large. There are some errors

that occur during the experiment which caused the percentage of error value equal to

16.32% which is the inconsistent of hand movement. When the hand movement is not

consistent, the result will be affected. The inconsistent of the hand movement cannot be

controlled since it is normal for each people. In our opinion, we believe that the value of

Ra is depends on the peak value and how often the peak is occur. If the peak occurs in

many time and high, it will affect the value of area and directly affect the value of

roughness that we get from manual calculation. Since the value of Ra is get from the

computer, we know that it will give the most accurate value compare to the manual

result. The manual result will give us more error since it can be affected by environment

factor.

One of the causes of incorrect measurement is the selection of the wrong cutoff

wavelength. Selecting the incorrect cutoff length could make the values appear larger or

smaller than the desired values. The cutoff wavelength must be at the centre wave or

close to the center of wave. The tracing speed of the person who is conducting this

experiment is also not the same. In this experiment, we use three different people to

measure the profile of the surface roughness. So, the speed between the three of us is

not the same. It may differ according to the method of our group members. If the trace

speed is too high, it will effect the measurement data because it will cause the data

recorded is not exactly as the exact value. It also will cause the distortion to occur when

the tracing speed is too high.

Other than that, one of our group member was used the left hand to measure the

profile of surface roughness. It will affect the result because the instrument is more

suitable for people who use the right hand to handle this instrument. When handling this

instrument, suddenly we stop the measuring process and will proceed the process to

complete the measurement. So, when we proceed the process, some mistakes will

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occur during the proceeding the process. The instrument may not stay in contact with

the surface continuously. So, when this happen it will cause the error to occur.

The environment condition also will influence the reading of the result. During the

measurement process, if the table or papers are move during measurement, the error

will occur. The digital planimeter is the sensitive instrument, so it must be carefully

handle to avoid the error from occur. Finally, the error may occur if the surface to put the

graph paper has dirt. If there any dirt appeared, the accuracy of measurement for area

above and below centerline will decrease. This is because of the sensitivity of the digital

planimeter.

There are several precautions that should be taken and considered to ensure

accurate data and result is obtained. Firstly, students should ensure that the profile

graph paper is clean from any dirt and positioned correctly and neatly on the table.

Other than that, students should handle the digital planimeter carefully and not to touch

the screw at the back of the planimeter. This is because it will affect our reading. To

obtain accurate results, students should consider taking three measurements and

calculating the average. Also, students should make sure that the person who is in

charge of measuring the graph area has steady hands and of the same person to get

accurate and consistent results.

8. CONCLUSION

From this experiment, we found that the value of the roughness of the specimen

by using CLA method is greater than the Roughness Average (Ra) method. The error is

acceptable since the percentage of error is less than 20%. To overcome this error, we

should do the experiment carefully by considered the precaution in this experiment.

Other than that, in order to get the result that is close to the Ra method, we must take at

least three times reading. The more reading that we take, the more accurate value we

will achieved. Besides, we also must know the error that might occur in this experiment

to prevent the mistake occur in the next time.

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As a conclusion, the objective of this experiment is successfully achieved since

we had got the value of roughness by using CLA method or Ra method. We also have

succeeded to determine the error and the method to overcome the error in this

experiment.

9. RECOMMENDATION

Students should take measurements using the digital planimeter at least three

times and calculate its average. This is to ensure accurate data and result is obtained. It

is also recommended that the students should pick the suitable place on the table to put

the roughness profile graph so that the person who is going to use the digital planimeter

is comfortable when measuring. Students should handle the equipment with care

especially the digital planimeter as it is a very sensitive equipment. The screw below the

digital planimeter should not be disturbed to ensure exact and accurate measurements

were taken. It is recommended that the same student who measures the area of the

graph using the digital planimeter should also calculate the area of the graph

themselves.

Nowadays, the quality of product is very important in manufacturing area since

many companies are competing with each other. Usually, the product which has rough

surface is undesirable. This problem is difficult and expensive to control in

manufacturing. So, we must have a machine that can measure the roughness of the

product. The Computerized Roughness measuring machine are recommended because

it can reduce the problem error and faster than manual method. This machine is also

more accurate than manual method. We suggest that each company has this kind of

machine so they can determine their product surface roughness and improve of it from

time to time.

10.REFERENCES9

a) http://claymore.engineer.gvsu.edu/~jackh/eod/manufact/manufact-84.html

b) http://www.mfg.mtu.edu/cyberman /quality/sfinish/terminology.html

ASSIGNMENT: Roundness

Objective

1. To calibrate a Dial Gauge using Calibration Tester

2. To find the error on each reading of the dial Gauge

3. To obtain the accuracy of the gauge

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Introduction

Roundness can in general is defined as ‘trueness of form’ of a circular part.

Some of the common causes of out of roundness are clamping distortion, rotational

imperfections in the process of manufacture, vibration, heat, strain induced during

machining, strain released after machining and residual surface texture left by the

process. A study of roundness and its measurement is essential in order to specify the

required roundness. The roundness of parts like spindles, bearings is very important

since the proper functioning of these parts is crucial for generating a round part. To get

an effective functional of parts, it is essential that the parts should conform to their

geometry, roundness in this case as close as possible

Apparatus

Calibration Test Piece (of roundness 11.2m), centering tool, stylus arm 63.5mm, roundness chart paper.

Procedure

1. The calibration test piece is placed on the turn table. The stylus arm is adjusted

until it gets near the test piece. The pen shift knob is set to the centre position.

The magnification is set to x100.

2. The stylus arm is adjusted until it touches the test piece right position. The

needle is ensured to be at the centre.

3. The turn table is switched on after we switched on the power supply. The test

piece is adjusted using centering meter with in range.

4. Step 1-4 is repeated by changing the magnification to x200, x500, x1000 and

x5000. The needle is checked if it is within range in the centering meter

everytime we changed the magnification. The test piece is adjusted using

centering tool.

5. The roundness polar graph is inserted into polar graph recorder after the

magnification reached x5000 and ensured that it is in correct position.

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6. The chuck clamping knob is turned clock wise until the graph is rotating. The

record button is pressed once. The recording pen is ensured that it is plotting the

profile of the test piece on the graph paper.

7. The chuck clamping knob is turned anti clock wise direct. The graph paper is

taken out from the recorder.

8. The result is analyzed using Transparent Template. If the value of result is equal

to or close to the value given by the test piece, calibration is completed and the

machine can be use for measurement.

Findings

Peak, P value: 1.4 µm

Valley, V value: 1.6 µm

P + V = 3 µm

Conclusion

From our observation, we know that all round object is not exactly in round

shape. It can be in cylinder or oval shape. To observe whether the object is exactly

round or not, we can see by using roundness measuring machine. For example, a

piston is actually in cylindrical shape although we see it roughly in round a shape.

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