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MIME 1650 Laboratory 1

Measurement

Objective

The student should learn the basic skills of measuring an object using some standard tools

and methods.

Introduction

Measurements are an important part of being an engineer. Any engineer should have a

good feel for the dimensions and tolerances of his or her design. In order to do so, an

understanding of the tools used to take those measurements is necessary. A part with

tight tolerances requires a very accurate tool. Tight tolerances cost more time and

money. Part of the expenditure is in the measuring devices. On the other hand, a part

with loose tolerance will cost time and money. It costs money because the part has a high

rejection rate and it costs time because time is wasted on a part that does not work. A

concept of measurements is needed for finding the median between these two.

An example of where the tools come into play is, when measuring an object, a ruler could

be used for a much looser tolerance than that provided by a micrometer. A ruler is very

easily to read and easy to use where as a micrometer is a little more difficult and time

consuming to use. A Go-No Go Gage is very fast in its use where as a Vernier caliper

takes more time. There are also standards that tools have to adhere to. This guarantees

that one caliper will measure the same as another.

Agenda

In this lab, the tools that the student will be using are the following

• Steel Ruler • Vernier Caliper • Micrometer • Go − No Go Gage • Sine Bar • Surface Roughness Machine. • Optical Comparator

Steel Ruler:

This measurement device is one that should be familiar to most people. There is a

slight difference with this ruler than with those used in your kindergarten days.

The inches of this ruler can be divided into 16-ths and 32-nds. When reading this

instrument, it is most accurate to read it perpendicular to the surface. The

measurements from this device should be recorded in their fractional form.

Conversion to decimal is not necessary.

Vernier Caliper:

This measurement device is a little trickier to use than the steel ruler. The Vernier

scale is easy once you grasp the concept. For the Vernier caliper, it is accurate

down to 0.001 of the desired unit. The 1/10 inches on this caliper are divided by

four instead of 5. This means that you must use 0.025” for your increment instead

of 0.02.

How to use this device:

1. First start with each inch. The zero on the Vernier scale is the measurement point. (The Vernier scale is the scale that is on the sliding

part of the caliper. One scale is inches. The other scale is mm.) Before

reading that inch, make sure the zero line is completely lined up with or

past that inch’s tick mark.

2. Read the tenths place.

3. Read the one hundredths place. (Remember that it is in 0.025)

4. Read the Vernier scale. This part is the hardest part of using this instrument. You have to take the scale on the sliding part of the caliper

and find the line that matches up with any tick mark on the stationary part

of the ruler. You then read that number off of the vernier scale and

multiply it by 0.001. Since the hundredths measurement is only in

quarters, this scale “fills in the gaps” to make the measurement more

accurate.

5. Sum them up.

6. Make sure the answer seems logical. If you get a measurement of 2.022 inches and the line between the zero and the 2” mark barely line up, then

chances are you really have 1.997 inches.

Dial Caliper:

The Dial Caliper is an instrument that utilizes a small gear rack that drives a

pointer on a circular dial. The Dial Caliper is read in a manner similar to the

Vernier Caliper. Instead of reading a Vernier scale, the reading taken by the dial

is the amount that goes in the hundredth’s place. This eliminates trying to

decipher which of the small lines is in direct alignment with the Vernier Scale

Micrometer:

This instrument is similar to the Vernier caliper but instead of a sliding clamp,

you have a rotating spindle. This instrument is even more accurate. It allows the

measurer to have up to 0.0001 accuracy.

The inch marks are on the shaft and are divided up into tenths and hundredths.

There is a scale similar to one like the scale on the Vernier caliper. It is the

sideways scale on the back.

How to read a micrometer.

1. See if it is a 0-1”, 1-2” or 2-3” micrometer. Put the lowest number in the ones place.

2. Read the tenths increment. 3. Read the hundredths increment. (Note: The increment is in fourths.) 4. Read the thousands place by observing the lowest number on the spindle that is

closest to the center line.

5. Read the number on the sideways scale on the back and multiply it by 0.0001 6. Sum the read amounts. 7. Make sure the amount seems logical.

Go −−−− No Go Gage:

This instrument is very useful in very quick measurements. The way the tool

works is by inserting either end into the hole that you desire the radius. The end

either goes in, or it is a “no go”. The diameter is noted of each end.

Sine Bar:

This method requires a little bit of trigonometry. It is useful in determining the

angle of a side. To set this system up you need to lay a sine block of at given

length L, on the block to be observed.

There are Sine Plates included with the sine bar. These plates have their thickness

noted on the slot in which they are placed as well as inscribed on the side. These

are to be placed under both ends until the angle of the sine bar is that of the work

piece. With a little manipulation, the sine bar can have the first height to be zero,

thus eliminating a calculation. The calculation for the angle is as follows:

 

  

 − =θ

−

L

hh 121sin

L

Surface Roughness:

The surface roughness comes into play when

considering the effects of friction on a moving part.

This instrument is a stylus based instrument that

measures the surface roughness by means of the

vibration on the needle. The average of these peeks

is taken and an amount is displayed on the screen.

The number displayed is multiplied by the setting on the output device.

Optical Comparator:

An optical comparator is an instrument

that projects a greatly magnified image

of a part feature onto a screen for

examination. The part is placed on the

worktable in the path of the light beam.

Since the part is opaque, a shadow is

produced which is magnified and then

projected onto the screen. The screen is

designed to allow angle and length

measurements. Use the elevation wheel

to bring the part into view. Move the part

in or out (toward or away) to coarsely

focus. Use the focus knob to finely focus.

Use the Horizontal Travel Knob to bring

the view to the center of the screen.

Align etched line on rotating screen with

the angle of the shadow on the screen by

turning the angle knob. Read the angle

from the Vernier scale. Use the optical

comparator to measure the slope of the

provided block.

Procedure

• Measure each aspect of the block three times with each instrument. (Sine Bar can be used just once.)

• Record the measurements taken on data sheet. • Average each section. • Compare measurements between instruments.

Light source

Part

Elevation Wheel Fine Focus Knob

Vernier Scale

Horizontal Travel Knob

Angle

Knob

Report Requirements

1. Why is the accuracy of the tools important? 2. What does measuring have to do with engineering? 3. What is one tool you used that was the fastest to measure with? 4. What was the slowest? 5. What was the most accurate? 6. What do you think is the best tool to use to get enough accuracy but that does not

take a very long time to use?

θ

Data Sheet

Measurement 1 2 3 Average

Steel Ruler

L1

L2

H

W

D

Vernier Caliper

L1

L2

H

W

D

Micrometer

L1

L2

H

W

D

Go-No Go

Sine Bar (θ )

Optical

Comparator (θ )

Surface

Roughness