Faculty of Engineering, Architecture and Science

Department of Mechanical and Industrial Engineering

Program: Mechanical Engineering/Industrial Engineering

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Introduction

The objective of this lab was to aid participating students in learning how to use optical

measuring tools. The lab consisted of 3 parts:

Part A - Optical Projector

Part B- Toolmakers microscope

Part C: Measurement Using Optical Flats

The optical projector works by projecting an image of the vertical pin (object used for

measurement) on its screen, where different scales are used to measure diameters and pitches.

Toolmakers microscopes’ are often used for making linear measurements on very small parts. In

this case, diameters of holes on a watch plate were measured. Optical flats are mainly used for

testing the flatness of surfaces with monochromatic light and a pattern of interference fringes. In

this case, a helium light source was used to measure the diameter of a cylindrical plug gage.

Procedure

Calibration1) Align the Zero mark of the Vernier protractor on the screen with the scale. 2) Use the vertical and horizontal pins to calibrate the machine further. Move the table

accordingly to align the pins with the horizontal marker on the screen to complete the calibration.

Magnification1) To measure magnification, align the vertical pin with the centre cross hair on the screen 2) using a ruler, measure the magnifies diameter of the pin on the screen (end to end)3) Then, using Vernier calipers, measure the diameter of the actual pin 4) Divide the magnified value by the actual value to get magnification number

Part A: Optical projector (Note: Divide all measurements by 50 to get unmagnified value)

1) Setup the object given to measure between the fixed pins on the table and move the table so the threads of the object are visible on the screen

2) To calculate the major diameter, measure the length of the threads from the top end to bottom end (Refer to figure 1)

3) To calculate the minor diameter, measure the length from the inner end on top to the inner end on the bottom (Refer to figure 1).

4) To find the average pitch, measure the horizontal distance from the top point of one thread to a thread 4 spaces away. Divide the number by 4 to find pitch.

Figure 1

5) Find the major and minor diameters and the pitch values again using the micrometer on the projector.

Part B: Toolmakers microscope 1) Calibrate the microscope by aligning the protractor scale with the 0 (Figure 2). Place a

ruler or a straight object under the microscope and while looking under the scope, see if the horizontal dotted line runs parallel to the straight object.

2) When calibrated, place the watch plate (Figure 3) under the scope such that the pins centre line is parallel to the horizontal cross line on the eye piece.

3) Measure the diameter of the holes on the watch plate by measuring the outer edge and then then inner edge.

4) Record values and subtract one from the other. 5) Repeat for hole two.

Figure 2 Figure 3

Part C: Measurement Using Optical Flats

1) Place optical flat on cylindrical plug gage.2) Moved the optical plate to get a resolution.3) Measured diameter of the cylindrical plug gage within the resolution with the

monochromatic helium light source (λ=23.2 μin) and other dimensions given (Figure 4).

Figure 4 Figure 5

Results

Part A

Part 2

There was a measured value of 6.25in with a ruler that had a resolution of 0.01”. After factoring the magnification of 50X the actual diameter was determined to be 0.125±1*10-4in.

Analysis of Pin diameter [table 1]

Measured diameter Magnification Actual diameter6.25±5*10-3in 50X 0.125±1*10-4in

Part 3

The major and minor diameters were measured with a ruler with a resolution of 0.00001”.davg=(dmin+dmaj)/2, davg was then converted to the actual diameter by multiplying it by the magnification of 50.

Analysis of Screw diameter [table 2]

Major diameter Minor diameter Average diameter Magnification Actual diameter9.53125±5*10-6in 7.34375±5*10-6in 8.4375±5*10-6in 50X 0.14875

±1*10-7in

4 pitches were measured with a ruler with a resolution of 0.0001”. This value was divided by four to determine the average pitch. After factoring the magnification of 50X the actual pitch was found.Pitch(4)/4=pitchavg

50*pitchavg=pitchactual

Analysis of Pitch [table 3]

4 Pitches Average Pitch Magnification Actual Pitch6.2815±5*10-5in 1.5704±5*10-5in 50X 0.031407±1*10-6in

Part 4

Two peaks and a pitch diameter were found using a micrometer with resolution of 0.0001”. The distance between the two peaks was the pitch. The pitch diameter and pitch formed a right angle tringle where the pitch diameter was adjacent to the lead angle and the pitch was opposite. Therefor tan-1(pitch/pitch diameter)=lead angle

Analysis of Pitch with a micrometer [table 4]

Peak 1 Peak 2 Pitch Pitch Diameter Lead angle0.1250±5*10-5in

0.1561±5*10-5in

0.0311±5*10-5in

0.1688±5*10-5in

10.44±0.01o

Part B

Two opposite points, Rn and Rn+1, of a hole were measured with a microscope with a resolution of 0.0001”. the distance between these points was the diameter. This was repeated for 2 other holes.

Left hole dimensions [table 5]

R1 R2 Diameter0.9608±5*10-5in 0.9140±5*10-5in 0.0468±5*10-5in

Right hole dimensions [table 6]

R3 R4 Diameter0.6506±5*10-5in 0.6305±5*10-5in 0.0201±5*10-5in

Center hole dimensions [table 7]

R5 R6 Diameter0.6990±5*10-5in 0.7605±5*10-5in 0.0615±5*10-5in

Part C

The equation below was used to find the plug gage diameter[N* (λ)/2]/0.95=(D/2)/(0.95+0.734+0.9420/2) where n=22 (the amount of light fringes), λ=23.2*10-6in and D was the diameter of the plug gage diameter.(1/n)/M= 0.0001 was used to find M the magnification

Plug Gage Analysis [table 8]

n(number of lines)

Magnification λ (wavelength) Plug Gage Diameter

Actual Diameter

22 454 23.2*10-6in 1.1578*10-3in 0.5257in

Analysis of Results

Part A

During part A of the experiment a micrometer and a ruler were used to measure values. When

measuring the diameter the ruler could have been inaccurate do to the experimenter having to

line up the ruler. To accurately measure the diameter the ruler must be held from one point to the

part of the circle that is the greatest possible distance away. It may have been difficult for the

experimenters to line this up properly.

Part B

During part B of the experiment a microscope was used. The vernier protractor had to be

manually lined up with the holes by the experimenter. This would allow errors to occur because

of a human’s limited ability to line it up.

Part C

During part C of the experiment an optical flat was used. The experimenters had to count the

amount of bright fringes on the optical flat. The light waves could have travelled a greater

distance than the measured n value but only the bright fringes (lines). The true value of n could

have been as much as 0.5 greater than what it was measured to be.

Conclusion and Discussion

In conclusion, this experiment familiarized the experimenters with measuring tools that use

optical methods. The measuring tools used include an optical comparator, a toolmakers

microscope, and an optical flat. The optical comparator was used to measure the magnification of

a pin by mathematically comparing the actual value of the pin with the magnified value of the

pin. This magnification was maintained as the tool was used to measure various dimensions on a

screw. The measured values of the screw include its major diameter, minor diameter, average

pitch, pitch diameter, and lead angle. There were many possible errors that could have occurred

during the experiment. To decrease the sources of error, certain precautions must be taken. The

thread must have been cleaned from all contaminates such as oil and dust. This will ensure

accuracy of each reading. The person who is reading the values should be the same person and

read from the same spot to avoid parallax error and keep data precise. This procedure helped us

familiarize us with the optical projector to measure the profiles of a thread by ourselves. We

were successfully able to measure all the essential measurements of a common thread. Tools

such as the optical projector are usually used to inspect manufactured parts in the industry.

The toolmakers microscope was used to measure the centre distance of the pins as well as the

diameter of the hole on the watch plate. There have been many errors which could have led to

insufficient results. For future procedures, it would be more practical to measure one edge of a

circle to the other edge, instead of center to center because there is a lot of visual judgment

required. Also, the same person should be adjusting and reading the values to maintain precision.

We accurately learned how to use the toolmakers microscope and we were able to successfully

measure the diameter and the distances between two holes. This tool is usually used to measure

minute details and is commonly used in the automotive and electronic industry.

Finally, the optical flat was used to view the light bands and count the number of bright fringes

that were displayed. The wavelength of the monochromatic helium light, the dimensions of the

setup, and the number of total fringes were values used in order to calculate the diameter of the

cylindrical plug gage. The fringe sharpness and the reflective properties of the flat may have

contributed to parallax errors. Using a more accurate and well maintained flat will improved the

accuracy of the results. This tool is usually used to calibrate metal parts.

Lab Questions

1. Errors in the measurement of the major diameter could be created due to multiple reasons.

There could be an issue with the calibration of the projector, or a malfunction during use. There

could be errors in the measurement due to environmental effects changing the dimensions on the

screw, like the pressure applied from the clamps. Additionally, errors could be created due to

parallax or a poor understanding on how the micrometer scale works. The errors to do with

calibration, parallax, environmental effects and understanding of the micrometer scale would be

systematic error. Errors due to the optical projector malfunctioning would be a random error.

The errors could be reduced by making sure that the device is properly calibrated before using it,

that the people using the device understand how to read its measurements and that the users take

the average of multiple measurements.

2. Errors in the measurement of the pin using the toolmakers microscope could be created due to

mistakes in orienting the pin with the cross-lines on the eyepiece, issues with reading the vernier

scale and vibrations changing the position of the pin. The errors to do with calibration and

knowledge of the vernier scale are systematic errors, whereas the error to do with vibration

would be a random error. The errors could be reduced by making sure that the people using the

device understand the vernier scale and that they have practice orienting the pin. The errors

could also be reduced by having larger knobs on the microscope to give the user more fine

tuning and by making sure that the microscope is located in an area with little vibration.

3. The optical projector and toolmakers microscope could have broken lines instead of solid lines

because it makes it easier to ensure that the object you are measuring is actually level with the

line. If the line were solid, you would not be able to notice if the edge of the object was slightly

slanted because the slant would be covered up by the solid, opaque line.

References

(n.d.). Retrieved February 2, 2015, from http://glink.hu/kezikonyv/menetek_images/thread.gif

(n.d.). Retrieved February 2, 2015, from https://courses.ryerson.ca/bbcswebdav/pid-2897598-dt-

content-rid-4611110_2/courses/mec322_w14_01/metrology_lab_w2014.pdf

(n.d.). Retrieved February 2, 2015, from http://www.nist.gov/calibrations/upload/75-975.pdf

MM-200 Toolmakers Microscope | Measuring Microscopes | Video & Microscope Measuring |

Products | Nikon Metrology. (n.d.). Retrieved February 2, 2015, from

http://www.nikonmetrology.com/en_US/Products/Video-Microscope-Measuring/

Measuring-Microscopes/MM-200-Toolmakers-Microscope