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Objective
The learner will be able to:
- Evaluate the importance of comparison measurement
- Analyze measurements made with rulers
- Identify comparison measuring instruments
- Examine angular measurements taken with protractors
Orienting Questions
ļ¼ Do rulers measure parts accurately?
ļ¼ Is comparison measurement effective in machining?
ļ¼ Do fixed gages accurately portray their solid counterparts?
Helpful Tips
ļ¼ You can select the to read more about it.
ļ¼ If needed, there are CLOSED CAPTION buttons on the YouTube
videos that will enable you to read along while you watch. The Closed Caption buttons are located bottom right of the video screen.
ļ¼ Take time and explore about the subject by selecting the links in
each section of this module.
Comparison Measurement
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INTRODUCTION
Measurement is one of the main responsibilities of a machinist. Measurements are dictated by the dimensions on blueprints. describe the size of part. The
level of accuracy required by those dimensions relate to the tolerances.
describe the variation of the dimension that is allowable. Tolerances will determine the type of measuring instrument and if itās a useable part.
is referred to as measurements that have a
level of accuracy within 1/64ā, 0.5 millimeters, or 1 degree. These tolerances described are not considered as having a high level of accuracy. In this module we will take a look at the different tools used in comparison measurement and their level of accuracy.
COMPARISON INSTRUMENTS
used in machining are flat metal piece that has graduations engraved, dividing
the ruler into inch or metric parts. These flat metal rulers (see Figure 1 ) are the most common comparison measurement tool used in machining. It is important that a machinist know the uses for the ruler and its limits. The type of ruler used will dictate the level of tolerance that can be achieved. Many different styles, widths, and lengths are available. Rulers are typically used to measure linear distances. Measurements are more easily read when the ruler is not lying flat. It is also a good practice to line up a major graduation with the edge you are measuring from. Just remember to subtract that amount from the measurement that you are reading.
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are twice as thick as flex rulers and have an attachment on their end called a hook. The hook enables the ruler to hook to the edge of the part for more accurate measurements. Rigid rulers are stiff, will not flex, and is the most expensive of the three. High quality steel is used to prolong the life of the ruler.
All rulers have metric counterparts. Some rulers can be purchased that only read in the metric system. Metric rulers are read much the same way that inch rulers are. They have divisions graduated in millimeter and half-millimeter increments. There are quick-reading dimensions that are placed every 5 to 10 millimeters.
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Note: Fractions are converted to lowest terms.
Figure 2: Measuring in Inches (Ladell Humphries, 2013)
CALIPERS
In comparison measurement the ruler is the standard that all other comparison measurement tools are gaged by. The measurements that are compared are taken with transfer measuring instruments. A caliper is one kind of transfer measurement tool. have two legs that make contact with the parts surfaces and they are
compared to a ruler to obtain the measurement. Calipers can also be used to scribe radii.
Calipers can measure outside and inside diameters (see Figure 3 ). A slide caliper has a built in ruler that allows measurements to be read directly and not transferred. The most common type of caliper that is used for comparison measurement is the spring type caliper (see Figure 4 ). This type can measure both inside and outside dimensions. The measurement taken has to be compared to a standard such as a ruler.
20/32 or 5/8ā
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ADJUSTABLE SQUARES
are used to check perpendicularity. This is referred to as checking for
squareness. A square has one corner that measures at 90 degrees. Note, most squares do not measure distance; however, adjustable squares have a steel ruler as a blade with āgraduationsā.
(see Figure 5 ) have two pieces that can be adjusted
and disassembled. The beam contains a locking mechanism that will hold the blade. The blade is a ruler that has graduations on it. The adjustable square can check height, depth, and squareness. The combination set is another example of an adjustable square. It contains a blade, square head, center head, and a protractor. The blade is also a ruler that has graduations for quick reading. The square head, in combination with the blade, can be used to check perpendicularity. Along with a 90 degree edge it also has a 45 degree edge that can check that one type of angle. The center head will find the center of a cylinder. The protractor will check angles within 180 degrees.
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Figure 5: Adjustable Square (Ladell Humphries, 2013)
Blade/ruler Square
Adjustment Screw
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Figure 6: Protractor measuring at 90 0 degree angle (Ladell Humphries, 2013)
ACTIVITY
Record the measurements taken with the ruler in lowest terms as a fraction and the decimal equivalent from the images below (see Figure 7 ). The scale used on the ruler is 32nds.
Helpful Tip:
90 0 degree Measurement at the zero witness mark
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Activity 1: Images
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Figure 7: Activity 1 Measurement Assignment (Images by Ladell Humphries, 2013)
Name: Activity #1 Measurement Sheet Image # Measurement Explanation Example 2 1/8 or 2. 125 The ruler I am using is marked in 1/8 inch increments. I looked at where the edge of the whole object meets with the marks/dashes on the ruler. The edge of the object is 1 mark past the whole number 2. The reading is 2 and 1/8 inches. 1 2 3 4 5 6 7
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Figure 8: representation of Radius Gages (Humphries, Eddie, 2013)
ANGLE GAGES
, while very similar to radius gages, are used to compare angles on
parts to standard angular sizes. They come in sets that range in size from 5 degrees to 90 degrees. Angular sizes are also checked by protractors but are used when a closer degree of accuracy is required.
SCREW PITCH GAGE
A is used to determine the distance between threads. It does
not measure the size of the threads. It compares the thread pitch on a part to a leaf that has a threads per inch designation engraved on it. Each leaf (see Figure 9 ) has a different thread pitch cut into it. The screw pitch gage comes in inch or metric versions.
1/8 radius gage
1/4 radius gage
3/8 radius gage
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Figure 9: Screw Pitch Gage (also known as Thread Pitch Gage) (Humphries, Eddie, 2013)
ACTIVITY
List and explain the purpose of comparison measurement tools in Figure 10 below. Assignments are to be turned in to the class dropbox.
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MAJOR CONCEPTS (HEADING 1)
KEY CONCEPTS
Summarize the module into a small list of major concepts (I would aim for between 3 and 5 and be sure that some relate to your learning outcomes). Use bullets to distinguish each concept and write a few sentences explaining the concept.
- Measurement is a critical component of machining. Without it, machinists cannot validate a part that has been completed. Machinists are required to analyze dimensions and tolerances that are located on blueprints. The level of accuracy and features of the part will dictate the use of comparison measurement.
- Rulers are the most common comparison measuring tool available. They come in a variety of lengths, and graduations. The ruler is the gage that all other comparison measurement tools are standardized to with exception to fixed gages. Rulers may have graduations in inch or metric systems.
- Fixed gages are flat templates that represent the feature that is to be machined. These tools give the machinist a way of evaluating if the feature matches the form of the gage or if further machining is required.
KEY TERMS
Dimensions Tolerances
Comparison Measurement Rulers
Graduations Calipers
Squares Fixed gages
LABS
PHYSICAL LABS
MTT122 is a corequisite of MTT
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ASSESSMENT
ANSWERS TO ACTIVITIES
ACTIVITY # 1
Name: Activity #1 Measurement Answer Sheet Image #
Measurement Explanation
1 3 5/32 or 3.15625 Check studentās explanation to see if the student is reading the measurement correctly. 2 4 1/8 or 4.3125 For example, āThe ruler I am using is marked in 1/ inch increments. I looked at where the edge of the whole object meets with the marks/dashes on the ruler. The edge of the object is 1 mark past the whole number 4. The reading is 4 and 1/8 inches. 3 4 5/16 or 4.3125 Another example, āThe ruler I am using is marked in metric or decimal so the marks/dashes read as tenths of a centimeter (millimeter). The edge of the object is 5 marks past the whole number 4. The reading is 4 and 5/16 inches. 4 5 9/16 or 5.
5 5 23/32 or 5.
6 7 or 7.
7 6 3/16 or 6.
