Basic Metrology Practices Iss1.ppt
- 1. Basic Metrology Practices © 2000 Taylor Hobson
- 2. Principles of Measurement The Principle of linear measurement is essentially a comparison of the piece under test with a known standard. Two systems are generally used: - Metric System - Imperial or English System Working standards are calibrated against master standards. The calibration or testing of measuring tools and instruments usually requires special equipment. Ensure instruments are maintained in a serviceable condition: - Keep instruments clean, avoid misuse. - Return instruments to cases when not in use. - Keep the inside of the cases clean. - Do not attempt to dismantle an instrument.
- 3. Rules, Calipers & Squares Steel Rule Only one possible reading at edge of ruler By using a steel rule properly, parallax errors are avoided. These are apparent differences in dimensions caused by changing the point of observation.
- 4. Rules, Calipers & Squares Outside Calipers Calipers are used for measuring or comparing distances and sizes. Outside measuring calipers legs are curved and turn inwards. Outside Spring Caliper Outside Caliper
- 5. Rules, Calipers & Squares Inside Calipers Inside measuring calipers legs are straight and turn outwards. Inside Spring Caliper
- 6. Rules, Calipers & Squares Engineers Square Engineers squares are used for checking Squareness and Flatness of components. They are also used for marking out (in conjunction with a scriber). Engineers Square
- 7. Gauges Feeler Gauges NB: Feeler gauges should be wiped with a clean cloth before and after use. If grease or dirt is trapped, a false reading may be given. Feeler Gauges are manufactured from accurately rolled shims and are used to measure gap sizes from 0.05mm up to about 1.25mm (0.002 to 0.050 inches). The numbers are marked on the gauge to give the thickness and thus the gap width. Feeler Gauges
- 8. Gauges Radius Gauges Radius gauges are usually made of tool steel and cut with an inside and outside radius of a stated size. The gauges are grouped with other sizes to make a set. An accurately machined component can be easily compared with the profile of a radius gauge. Radius Gauges
- 9. Gauges Pitch Gauges NB: Both Pitch gauges and thread, should be clean and free of burrs. It is useful to hold the screw up to a light to see small gaps. Use the full length of the gauge for greater accuracy. A screw pitch gauge has a set of teeth which are of a known thread form. The gauge is used to determine the pitch of a thread on a bolt or screw of any diameter.
- 10. Gauges Screw pitches Metric Screw Thread: Other screw thread types include: UNF - Unified Fine UNC - Unified Coarse BA - British Association BS Whitworth (BSF, BSP & Conduit) - British Standard Where: p = pitch of the thread d = depth of the thread r = radius at the top and bottom of the threads
- 11. Gauges Ring Gauges A Ring Gauge is a precision-sized gauge used for size control of external diameters/bars. It can be fitted over a bar end and moved along the length to test for roundness and accuracy of diameter.
- 12. Gauges Plug Gauges A Plug Gauge is an precision-sized gauge which is used for size control of internal diameters/holes. Go No-Go gauges are double ended. If the Go end is sized to 20mm, the No-Go end is slightly bigger, i.e. 20.020mm. If the Go end fits in the machined hole and the No-Go end doesn’t then the hole is the an acceptable size. The tolerance on the gauges can vary and each gauge is usually specific to a particular job.
- 13. Now it’s Your Turn! Try the Exercises in Section 1 of the Worksheet.
- 14. The Micrometer is an instrument for measuring and comparing thickness. Micrometers Frame Locking Ring Barrel Thimble Anvil Measuring Faces Spindle Micrometer Screw Fixed nut Slotted to adjust play in threads Thimble Sleeve Thimble Cap Ratchet Stop
- 15. Micrometers Using a Micrometer Hold the frame in your hand, gripping with the 2nd, 3rd & 4th fingers Rotate the thimble with the ratchet stop if fitted. Ensure uniform pressure is applied, so a consistent reading is achieved. Ratchet Stop
- 16. Ratchet Stop Micrometers Using a Micrometer If a ratchet stop is not fitted, take care when turning the thimble. Do not apply to much pressure, as this can damage the measuring faces and cause excessive wear of the screw threads.
- 17. Micrometers Using a Micrometer When measuring round objects, roll the object over the anvils to ensure a reading is taken at the largest diameter.
- 18. Micrometers Using a Micrometer When checking square objects, the micrometer should be adjusted until there is no angular movement. Take measurements in two or three places to check parallelism of material.
- 19. Micrometers The Metric Micrometer 1mm Barrel 1/2mm Thimble 50 divisions (1 division =1/100mm) The pitch of the screw in a metric micrometer is ½mm. 1 rev of the thimble = ½mm. The beveled edge of the thimble is divided into 50. Each graduation = 1/50th of ½mm (1/100mm or 0.01mm).
- 20. Reading (3) Thimble Barrel Reading (1) Reading (2) Micrometers Reading the Metric Micrometer Read the number of whole mm divisions visible on the barrel. Read the number of ½mm divisions visible on the barrel. Read the line on the thimble which coincides with the axis line.
- 21. Micrometers Reading the Metric Micrometer Reading (3) = 0.22mm Thimble Barrel Reading (1) = 10mm Reading (2) = 0.50mm Whole mm divisions visible…… 10 = 10.00mm ½mm divisions visible…………. 1 = 0.50mm Line on the thimble……………… 22 = 0.22mm Total Reading…………………….. = 10.72mm
- 22. Micrometers The Imperial Micrometer 0.025” Barrel 0.100” Thimble 25 divisions 1 division =1/1000 (0.001) The pitch of the screw in an imperial micrometer is 0.025”. 1 rev of the thimble = 0.025”. The beveled edge of the thimble is divided into 25. Each graduation = 1/25th of 0.025 (0.001”).
- 23. Micrometers Reading the Imperial Micrometer Read the number of long vertical divisions visible on the barrel. Read the number of smaller divisions visible on the barrel. Read the line on the thimble which coincides with the axis line. Reading (3) Thimble Barrel Reading (1) Reading (2)
- 24. Micrometers Reading the Imperial Micrometer Larger divisions visible………… 2 = 0.200” Smaller divisions visible………. 1 = 0.025” Line on the thimble…………….. 6 = 0.006” Total Reading……………………. = 0.231” Reading (3) = 0.006” Thimble Barrel Reading (1) = 0.200” Reading (2) = 0.025”
- 25. The Micrometer Depth Gauge is used for measuring depths of shoulders and holes. Micrometer Depth Gauges Thimble Barrel Head
- 26. Micrometer Depth Gauges Using the Micrometer Depth Gauge Screw back the spindle to clear the bottom of the hole and place Micrometer head over the hole. Adjust the thimble until the head touches the bottom of the hole. Read off the hole depth.
- 27. Micrometer Depth Gauges Reading the Micrometer Depth Gauge Read the number of whole mm divisions on the barrel. Read the number of ½mm divisions on the barrel. Read the line on the thimble which coincides with the axis line. NB: Remember the scale is reversed from an ordinary micrometer.
- 28. Micrometer Depth Gauges Reading the Micrometer Depth Gauge Whole mm divisions ……………. 9 = 9.00mm ½mm divisions ……….…………. 1 = 0.50mm Line on the thimble……………… 29 = 0.29mm Total Reading…………………….. = 9.79mm
- 29. Now it’s Your Turn! Try the Exercises in Section 2 of the Worksheet.
- 30. The Vernier Caliper is an instrument for measuring sizes of components. Vernier Calipers Nibs Beam Jaw Beam Scale Top Vernier Scale (Imperial) Clamping Screws Clamping Block Bottom Vernier Scale (Metric) Fine Adjustment Screw Wheel Movable Jaw (Integral with Vernier)
- 31. Vernier Calipers Using Vernier Calipers With the clamping screws released, hold the calipers in one hand, the thumb rested on the fine adjustment screw wheel. Move the jaw forward with the thumb, until contact is made with the component.
- 32. Vernier Calipers Using Vernier Calipers Lock the jaws with the other hand and adjust the jaws to just grip the work piece with the fine adjusting screw. Remove the caliper and read off the dimension.
- 33. Vernier Calipers The Metric Vernier Caliper The Beam Bottom Scale is 10mm divided into 10 (1mm). Each 1mm is divided into 2 (0.5mm). On the Bottom Vernier Scale, 12mm divided into 25. (12/25 =0.48mm) - Each division is 0.48mm. Difference is 0.5 - 0.48 = 0.02mm. 10mm 0.5mm 0.48mm Beam Bottom Scale Bottom Vernier Scale
- 34. Vernier Calipers Reading the Metric Vernier Caliper Read the scale to the left of the 0 on the bottom Vernier. Read the mark where the Vernier Scale is Exactly the same as the Beam Bottom Scale. Beam Bottom Scale Bottom Vernier Scale Reading (1) Reading (2)
- 35. Vernier Calipers Reading the Metric Vernier Caliper Bottom Vernier Scale reading…. = 30.50mm Mark where scales are aligned... 14 (x 0.02) = 0.28mm Total Reading……………………… = 30.78mm Beam Bottom Scale Bottom Vernier Scale Reading (1) 30.5mm Reading (2) 14
- 36. Vernier Calipers The Imperial Vernier Caliper 0.024 inch 0.025 inch 1 inch Beam Top Scale Top Vernier Scale The Beam Top Scale is 1 inch, divided into 10. Each of the 10 is divided into 4 (0.025 inch). On the Top Vernier Scale, 6/10 is divided into 25. (1/25 of 6/10 = 0.024 inch)- Each division is 0.024 inch. Difference is 0.025 - 0.024 = 0.001 inch.
- 37. Vernier Calipers Reading the Imperial Vernier Caliper Read the scale to the left of the 0 on the Top Vernier. Read the mark where the Vernier Scale is Exactly the same as the Beam Top Scale. Beam Top Scale Top Vernier Scale Reading (1) Reading (2)
- 38. Vernier Calipers Reading the Imperial Vernier Caliper Top Vernier Scale reading……… = 3.225 inch Mark where scales are aligned... 16 (x 0.001) = 0.016 inch Total Reading……………………… = 3.241 inch Beam Top Scale Top Vernier Scale Reading (1) 3.225 inch Reading (2) 16
- 39. Vernier Calipers Using Digital Calipers Digital Calipers are operated in the same way as Vernier Calipers. Just read off the digital display (can be switched between Metric and Imperial).
- 40. The Vernier Height Gauge is mostly used to measure surface heights and for making precise markings on components. The gauge has a sharp finger attached which can be used for both purposes. Vernier Height Gauge Metric Scale Imperial Scale Fine Adjustment Clamp Clamping Screw Base Finger Clamp Fine Adjustment Screw Finger
- 41. Vernier Height Gauge Using the Vernier Height Gauge The Height Gauge can be used to measure the height of a component. In this case, the height of the component is the same as the Vernier Gauge reading.
- 42. Vernier Height Gauge Using the Vernier Height Gauge The Height Gauge can be used to measure the Underside of a component. In this case, the height of the component is the Vernier Gauge reading plus the height of the Finger (7.95mm).
- 43. The Vernier Protractor is used for precisely measuring angles on components. Vernier Protractor Blade Clamp Screw Blade Dial Clamp Main Scale Vernier Scale
- 44. Vernier Calipers Using a Vernier Protractor Most protractors are graduated 0 to 90 degrees reading in two directions. The Blade can be slid round to any position and clamped. One side is flat to allow it to lie flat on a workpiece.
- 45. Vernier Protractors The Vernier Protractor The 12 divisions on the Vernier equal 23 degrees on the main scale. Each of the 12 divisions is 11/12th of a degree, 1 Vernier div is 1/12th degree = 5 mins 12 Vernier Divisions
- 46. Vernier Protractor Reading the Vernier Protractor Read the number of whole Degrees visible on the main scale. Read the number of mins where the Vernier Scale is Exactly the same as the main scale. Reading (1) Reading (2)
- 47. Vernier Protractor Reading the Vernier Protractor Whole degrees visible……………... = 52 Mark where scales are aligned….. = 40 Total Reading………………………... = 52 degs 40 mins Reading Left to Right Reading (1) 52 Reading (2) 40
- 48. Vernier Protractor Reading the Vernier Protractor Whole degrees visible……………… = 127 Mark where scales are aligned….. = 20 Total Reading………………………... = 127 degs 20 mins Reading Right to Left Reading (1) 127 Reading (2) 20
- 49. Now it’s Your Turn! Try the Exercises in Section 3 of the Worksheet.
- 50. Slip blocks are used as standards for precision length measurement in the Engineering Industry. Slip Blocks
- 51. Slip Blocks Four Grades of Accuracy Workshop Grade Inspection Grade Calibration Grade Reference Grade Care of Block Gauges When not used, Slips should be kept in their Case. Avoid Excessive Handling - Don’t touch lapped faces. Wipe slips clean before and after they are used. Use soft linen or cambric cloth to clean slips. Least Expensive Most Expensive
- 52. Slip Blocks Wringing Slips Select the blocks needed to make up the pack and clean them. Start with the biggest pair and twist them at 90° under slight pressure.
- 53. Slip Blocks Wringing Slips For slips less than 1.27mm (.05 inch) wring by sliding together. To prevent scratches on slips, protector blocks can be used on the ends on stacks (2mm) which are cheaper to replace.
- 54. Slip Blocks Calibration Charts Blocks are calibrated by comparing them to master gauges The deviation of each slip is recorded and included in the block set stating the error. For High accuracy the calibration chart is essential.
- 55. Slip Blocks The Effect of Cumulative Errors Error due to deviation from true size. Errors due to grease or dirt between ringing faces. Errors due to expansion caused by exposing gauges to strong light or excessive handling.
- 56. Choosing a Measuring instrument Basic Rules Choose instrument in keeping with the tolerance and dimensions to be measured. Use an instrument that gives a direct reading wherever possible. Don’t use damaged or worn instruments. Instrument resolution is not always the accuracy to which it can be used. Inbuilt accuracy's often exceed resolution. NB: The larger the size being measured, the more difficult it will be to attain a high standard of accuracy.
- 57. Choosing a Measuring instrument Instrument Or Measurement Type of Measurement Range Value of smallest Graduation (Resolution) Suggested Reliability Steel Rule Direct 150 – 600mm 6 - 24 in .5mm .02in ±.5mm ±.02in Depth Gauge Direct 150mm 6in .5mm .02in ±.5mm ±.02in Calipers Transfer 150mm 6in none ±.5mm ±.02in Vernier Calipers Direct 600mm 24in .01mm .001in ±.05mm ±.002in Vernier Depth Gauge Direct 300mm 12in .01mm .001in ±.05mm ±.002in Vernier Height Gauge Direct 600mm 24in .01mm .001in ±.05mm ±.002in Micrometers Direct 0-25mm 0-1in .01mm .001in ±.01mm ±.001in Direct 25-50mm 1-2in .01mm .001in ±.01mm ±.001in Inside Micrometers Direct 2.5-130mm 0.1-5.2in .01mm .001in ±.01mm ±.001in Depth Micrometers Direct 0-300mm 0-12in .01mm .001in ±.01mm ±.001in Slip Gauges End Standard Up to 100mm Up to 4in .001mm .0001in .0005mm .00001in
- 58. Checking Surface Texture Roughness average index The Roughness average (Ra) index is an accepted method of measuring surface finish. The table shows a series of surface textures which can be produced by various manufacturing processes.
- 59. Checking Surface Texture Using Comparison Plates Comparison plates are a range of blocks machined to various calibrated surface textures, each texture measured in microns (µm) and micro-inches (µin).
- 60. Checking Surface Texture Visually ... Clean work piece and appropriate comparison plate. Compare the workpiece and plate from many different angles. The workpiece finish should be at least as good as, if not better.
- 61. Checking Surface Texture ... or by Touch Draw your fingernail lightly over the comparison plate. Repeat the operation on the workpiece and note any differences. The workpiece finish should be usually better than the plate.
- 62. Checking Surface Texture With an Instrument Pickup Stylus Pickup Mount Traverse Unit and Electronics Controls and Display Pickup Lead
- 63. Checking Surface Texture With an Instrument Pickup Stylus Measurement Length Surface to be measured The Pickup is pulled across the surface for a pre set distance. A diamond tip stylus measures the roughness of the surface. The result in Ra (Roughness average) is shown on the display.
- 64. Checking Surface Texture With an Instrument A typical Ra result taken on a Surtronic instrument is shown.
- 65. Checking Surface Texture What is Ra? Mathematically, Ra is the arithmetic average value of the profile departure from the mean line, within a sampling length. A method of visualising how Ra is derived is as follows: Graph A: A mean line X-X is fitted to the measurement data.
- 66. Checking Surface Texture What is Ra? Graph B: The portions of the profile within the sampling length “l” and below the mean line are then inverted and placed above the line. Graph C: Ra is the mean height of the profile above the original mean line. Ra
- 67. Checking Surface Texture Ra has its Limitations All the above profiles have different form, but the Ra value is the same. Other parameters are used to calculate these differences. Ra Ra Ra Ra
- 68. Now it’s Your Turn! Try the Exercises in Section 4 of the Worksheet.
- 69. Any Questions?
- 70. Basic Metrology Practices © 2000 Taylor Hobson