5.4.1 Laboratories
• There are a total of eight laboratories to be submitted, others are included for the benefit of the student,
- basic measurement (no formal submission)
- dimensional measurements
- comparators
- optical metrology
- Manufacturing Processes (demonstration only - no formal submission)
- cutting forces
- surface texture
- roundness measurement
- interferometry
- SPC analysis with gauge talker III
- laser measurement (demonstration only, no formal submission)
5.4.1.1 - Lab Rules
• The general rules are simple,
1. Students must attend ALL labs, attendance at the demonstrations is also mandatory. missed laboratories will result in a loss of a mark.
2. Each laboratory must be done independently or in groups only when specified. COPYING WILL NOT BE TOLERATED, AND WILL BE DEALT WITH SEVERELY.
5.4.1.2 - How To Prepare for and Write-Up an Experiment
See the laboratory instructor.
5.4.1.2.1 - Basic Measurements
Purpose:
a) To determine the length of a component.
b) To introduce students to some fundamental measuring instruments
c) To determine possible causes of variation in measurement.
d) To introduce the concept of Standards, used in manufacturing
Component Drawing:
Procedure:
Use different instruments and different operators to measure the component length ‘L’.
Results:
Units -> Decimal inches
Tabulated Results:
Analysis of Results:
Which of the results is correct?
What accuracy is required?
What does accuracy depends upon?
Possible Causes of Variation:
• The Instrument - design, magnification (def. output/input), sensitivity (def. smallest input to provide a reliable output), condition & calibration.
• The Operator - experience, judgement, attitude, sense of touch or feel.
• The Component - flatness, parallelism, surface texture.
• Temperature - standard temperature (20°C or 68°F), different materials have different coefficients of linear thermal expansion.
• The Standards - grade & original accuracy, condition, traceability to primary standard.
5.4.2 Line Graduated Instruments
Purpose: To become familiar with the fundamental forms of measuring instruments. In particular scales, micrometers, vernier instruments, and transfer tools.
Procedure:
1. Record the measurements for the two parts below using scales (i.e., rulers) and transfer tools (e.g., calipers). Record the answers to the nearest 0.5mm or 0.02”
2. Use vernier instruments to measure the following parts. Record all lengths to the nearest .001”, or .02mm.
3. Using the instruments specified below, measure each of the parts. Record the dimensions to the appropriate number of decimal places. Where feasible, instruments may be checked against gauge blocks.
Questions:
1. Discuss the term ‘parallax error’, associated with the steel scale measurements.
2. Draw to some reasonable scale, a metric depth vernier set at a reading of 36.64mm.
3. A micrometer type instrument achieves magnification by two basic principles, explain these.
4. Explain the purpose of either Standard Rollers, or Hoke Gauge Blocks, used with a bench type micrometer.
5. List in order, the corrective adjustments necessary to calibrate a micrometer.
5.4.3 Comparators & Surface Plates
Part A - Comparators
Purpose: To give the student an understanding of the principals of measurement by comparison, and to be able to set up and use the comparators in the lab.
1. Set up the Valenite electronic column gauge to the master ring gauge. Then determine the actual diameter of the holes A, B, C in the test piece marked 2a.
2. Set up the Sheffield flow type pneumatic gauge using master pin gauges 0.7310” and 0.7292” (make one scale division equal to 0.0001”). Then determine the actual diameters of the brass pins A, B, C.
3. Set up and adjust the Sigma pressure drop pneumatic gauge to the master gauge 12.74mm. Then determine the actual diameters of the holes in the test piece marked 2b.
4. Set up and use the Sigma electronic comparator (set on a metric scale) to determine the length (ins.) of the other given component (cylinder)
Part B - Surface Plate
Purpose: To become familiar with the use of the surface plate as a reference plane, the use of the common accessory instruments.
5. a) Using the Mitutoyo electron height gauge, determine the two dimensions required, referenced from the base of the fixture. The units are inches.
b) Using the vernier height gauge with the test indicator attached, transfer the heights to the micrometer height gauge to determine the dimension from the reference line to the hole marked. The Units are millimeters.
Questions:
1. What advantages do electronic comparators have over mechanical comparators?
2. State one advantage, and one disadvantage of the air gauge compared to other principles of magnification.
3. In your own words, define “sensitivity” as applied to comparator type instruments.
4. List two important advantages of the granite surface plate over the cast iron plate.
5. What factors limit the accuracy in determining the dimensions, in exercise #5 b).
5.4.4 Toolmaker’s Microscope and Optical Projector
Purpose: To become familiar with measuring tools with optical magnification.
Part A: Toolmaker’s Microscope
1. Check the zero of the vernier protractor (under the eyepiece) as follows: - Set the protractor scale to zero. Then verify that the horizontal cross line (a) is parallel to the cross travel of the stage. To do this rotate the side micrometer knob and note that any object viewed through the eyepiece runs parallel to the cross line. If this is not correct see the instructor.
2. Set up the watch plate and measure the pin centre to centre distance. Record your measurements in decimals to four places. WARNING - If either micrometer head is turned to the full extent of its travel, it may become jammed.
3. Measure and record the pitch (axial spacing of the threads) of tap #1. Also measure and record the lead angle of the same tap. This will be the mean of the lead angles at the thread crest and root.
Part B - Optical Projector
4. a) Check the zero of the vernier protractor around the screen.
b) Check the magnification of the system. First set the protractor scale on zero. Then using the test pin gauge on the table, project the image (shadow) of the rod (you must measure the diameter of the pin by using the micrometer on the projector) onto the screen and adjust the table vertically until the tip of the shadow just contacts the horizontal cross line. Traverse the table horizontally with the micrometer. Note if the shadow moves in contact with the cross line. Then with the scale measure the width of the shadow. The width of the shadow divided by the actual diameter of the rod is the magnification.
5. Using the scale and tap #2, measure directly from the image on the screen the following thread dimensions.
a) major diameter
b) minor diameter
c) average pitch
6. For the given tap #3, measure the pitch (thread spacing) and the pitch diameter E using the micrometers on the projector. Calculate the lead angle. (see the text for descriptions of these terms).
7. Set up the Acme thread supplied, part #4, and measure the flank angles as shown below. Use the protractor on the screen. Record these angles and calculate thread lean.
Questions:
1. Suggest the reason why the cross lines on either instrument are broken lines and not solid lines.
2. Why, in exercise 3 above, is the lead angle calculated as the mean of the angles taken at the crest and root of the thread?
3. Provide a practical application to illustrate the importance of question #1.
4. Suggest reasons for errors in the total of angles θ1 and θ2 and the total angle θt
5.4.4.1 - Process Planning and Machining Demonstration
Purpose:
a) to observe a series of Machine Tool operations, in the manufacture of the component shown.
b) To introduce the students to the concept of Process Planning
Component Drawing:
Procedure:
1. Study the component drawing and the process planning sheet
2. Proceed to the machine shop to observe the part being made
CAUTIONS:
1. Power will be on in the machine shop.
2. For your safety, refrain from touching any machine buttons or levers.
3. Do not handle swarf (metal chips) from the cutting processes, they are hot, and sharp and WILL cause at least some harm.
Cutting Tool:
• High Speed Steel 3/8” tool bit
• Orthographic Views are shown (refer to text also, fig. 27-2)
Centre Drill & Machine Centre:
Surface Cutting Speed:
Process Planning Sheet:
5.4.5 Cutting Forces
Purpose:
To investigate the relationship of the cutting variables,
a) cutting velocity.
b) undeformed chip thickness (feed rate) to cutting force (tangential) Fc and lateral force (feed) Ft.
Procedure:
a) Take several cuts at different cutting speeds and note the readings of Fc and Ft and measured R.P.M. for each cut.
b) Take several cuts at different feed rates (undeformed chip) and note the readings of Fc and Ft for each cut.
Results:
a) Tabulate the results in the tables provided, and any other observations should also be written down.
b) Make graphs for the measured data.
c) Analyze and discuss the results (i.e., point out the obvious and subtle).
d) Write conclusions based on the analysis (i.e., draw some general conclusions based on the facts).
Questions:
1. Explain which of the test cuts requires the greatest H.P. at the tool.
2. If the machine efficiency is 60% calculate the minimum motor size required. For one of the cuts measure the deformed chip thickness t2, draw the merchants force circle diagram for that condition, determine the shear force Fs and calculate the co-efficient of friction on the tool face.
5.4.5.1 - Surface Texture
Purpose:
a) To observe a stylus type machine (Brown & Sharpe Surfcom 110B) in action, for the assessment of surface texture.
b) To evaluate the influence of machining variables, on the surface produced.
c) To analyze surface quality on different types of work material.
Exercises:
1. Test the calibration of the Brown & Sharpe Surfcom, using test specimens with known Ra values.
2. Investigate the effect of changes in the following machining variables on surface finish. The samples were produced on a 1.50 inch diameter bar of Mild Steel, turned between centres, using Tungsten Carbide tools. Note: typical results are provided. Plot graphs to show the relationship of each variable, to the surface texture produced. Analyze and comment on these results.
a) Cutting Speed
b) Tool Nose Radius
c) Feed
d) Depth of Cut
3. Take meter readings for the six specimens provided, i.e., Low carbon steel, aluminum, Brass, Bronze, Stainless Steel and Copper. Note: these surfaces were all machined using the same machining parameters. Discuss possible causes of significant differences in the readings obtained.
4. On the cylindrical part, the three surfaces were turned at different feed settings.
a) Find the meter reading for each surface.
b) Take a graphical trace of the “roughest” surface and determine the feed per revolution used to produce it.
c) Determine the value of ‘tp’ the bearing ratio, at a cutting depth of 50% of Rmax. (The distance between the highest peak and the lowest valley within the assessment length L).
Sample Results:
*************** INCLUDE TRACES FROM OLD LAB HERE
5.4.5.2 - Roundness Testing
Purpose:
a) To examine different methods of assessing Roundness and Concentricity.
b) To observe the Rank Taylor Hobson Talyrond in action and learn how to analyze the Polar Traces produced on this type of machine.
CAUTION: The Talyrond must never be started until the Professor or Technologist has lubricated the spindle bearing or expensive damage to the bearing may result.
Exercises:
1. Set-up the Talyrond with the 480 μin. reference “Radial Calibration Standard”. The standard should be centered visually using the annular rings on the table as the reference. After this, the coarse and fine centering knobs are used, to align the part axis with the machine bearing axis. This process is monitored on the machine head. When the magnification has been increased to a maximum, consistent with the entire trace remaining on the chart (x 2000 in this case) a polar graph is traced. The 2 1/2 inch stylus arm should be used for this. The “spike” length is measured using the transparent template, this value being compared with the standard value, to verify the correctness of the Talyrond.
2. a) Mount the stainless steel bar between the bench centres. Position the dial indicator to be in contact with the part at end A. Rotate the part and observe the Full Indicator Reading (F.I.R.). Repeat for end B.
b) Align the same part on the Talyrond, producing a polar trace for end A. Repeat for end B. Compare F.I.R. values obtained in part a) with the out of round values revealed in part b), explain any differences.
3. Align the inner bearing component on the Talyrond for testing the inside part diameter. At a high magnification setting, produce a polar trace to show not only out of roundness but also the magnified surface roughness. Leave the trace in position and change from normal to filter ‘B’ and trace over the original graph. Analyze the resulting traces and comment on the influences of filter ‘B’. Note: See the lecture notes for more details.
4. For the same component used in #3. Provide two traces on one graph, the first from the outside diameter the second from the inside diameter of the part. Show the calculation for eccentricity.
Questions:
1. Does the diameter of the trace on the chart have any relationship to the diameter of the part being checked?
2. Explain why the appearance of a polar trace involves considerable distortion, relative to the circular part it represents.
3. In exercise #4 the inside and outside profiles of the part shown, were examine for concentricity. Why is it necessary to adjust the Talyrond table levelling screws, before the two polar traces are produced?
******************* ADD IN SHEETS WITH POLAR TRACES
5.4.5.3 - SPC Analysis with Gauge Talker
5.4.5.4 - Interferometry
Purpose:
a) To understand the formation of interference bands.
b) To gain experience interpreting interference fringe patterns.
c) To assess Surface Texture using the Interference Microscope
Exercises:
1. Examine the lapped surfaces of old and new supplied gauge blocks, using an optical flat under a helium light (monochromatic light). The wavelength for helium = 23.2 μin. Sketch and explain the observed fringe patterns, evaluating the departure from flatness.
2. Determine the diameter ‘D’ of a cylinder, using an optical flat and the hoke gauge blocks. Set-up the items as shown in the sketch below. Obtain an interim dia. Di by measuring the cylinder on a bench micrometer. Select Hoke gauge blocks to build-up the height ‘H’ this being 0.0002” less than the measured value Di. Observe and count the number of fringes ‘n’ seen through the optical flat, over the width W of the Hoke gauge stack. Derive an equation by similar triangles and use this to calculate the cylinder diameter ‘D’.
3. Examine a “scratched” gauge block surface with the Interference Microscope. The view should be similar to the sketch on the next page. Estimate the depth of the scratch “S”, and the Surface Texture Ra by first calculating the full texture height “T”. Note: lambda for the Mercury light source = 20 μin.
Questions:
1. List the three characteristics of the fringes in a band pattern, from a flat surface, viewed through an optical flat under a monochromatic light.
2. The three examples shown below are views seen through an optical flat. Assume the optical flat makes contact with the LEFT ENDS of the surfaces. Draw the three sectional surface views A-A.
3. The sketches below are the Gauge Block Interferometer and the typical view seen through the eye piece of such an instrument. The height of the gauge block under test “G” is shown in the following equation:
4. Describe the nature of the surface being viewed through an optical flat, in the sketch below.
5.4.6 Assignments
5.4.6.1 - Metrology and Assembly
1. From the same set of gauge blocks build up the dimensions 3.2452” and 3.2462”. You must not use the same gauge blocks twice. Use the 83 piece gauge block set.
2. Determine what height is required to set up a 5” sine bar for an angle of 11°34’. Specify the gauge block stack required.
3. Design GO/NO GO gauges for an equilateral triangular hole that is to have each side 2.025”±0.002”.
4. Do complete drawings for a 3.000” hole shaft pair if they have a RC3 fit.
5.4.6.2 - Machining - Revised Assignment - Due First Class in January
1. A new lathe tool is to be used on cast iron work with a 6” diameter to make a 5” long rough cut in 3 passes. The operation conditions listed below were provided by the supplier or assumed. Calculate the parameters a) to e) as requested.
Cutting Speed = 300 fpm
Feed Rate = 0.008 ipr
Depth of Cut = 0.125”
Idle Horse Power = 0.25
Machine Efficiency = 0.90
a) Spindle RPM
b) Time to make the cut (min.)
c) Metal Removal Rate Q (in.3/min.)
d) Cutting Horse Power (HPc)
e) Minimum Machine Tool Motor HP.
2. The aluminum component below is to be turned on a lathe using a HSS tool. Develop a process plan, including offset for the taper, speeds, feeds, etc. Put the process plan in a list similar to the format shown. Assume a cost of $45.00/hr. for the lathe, and $25.00/hr. for all other pieces of equipment. State all assumption clearly, and justify numbers in the process plan with calculations or references.
5.4.6.3 - Quality Control
#1 Draw the detailed X, R, and s charts for the data below.
#2 What problems can be seen in this control chart?
#3. Draw the Pareto diagram for the data below. The data indicates the number of reported errors made when taking fast food orders by telephone
5.4.6.4 - Inspection Planning
#1.
a) Develop a double sampling plan OC curve given that,
N = 1000
n1 = 50
c1 = 2
r1 = 4
n2 = 100
c2 = 3
b) What is the AOQL?
