1 / 40

Measuring Instruments

Measuring Instruments. Metrology. science of weights and measures. Discrimination. degree to which a measuring instrument divides a basic unit of length. 10 to one rule for discrimination.

jseaver
Download Presentation

Measuring Instruments

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Measuring Instruments

  2. Metrology • science of weights and measures

  3. Discrimination • degree to which a measuring instrument divides a basic unit of length

  4. 10 to one rule for discrimination • a measuring instrument should discriminate 10 times finer than the smallest unit that it will be used to measure • instrument lands between two lines - do not use to measure

  5. Parallax error • the apparent shift of an object when viewed from different angles

  6. Calibration • Process by which a measuring instrument is compared to a known standard • The international prototype kilogram is a platinum iridium alloy, created in 1879, that is the standard by which all the world’s weight measurements are calibrated. It is lock in a Paris vault and is only brought out on very rare occasions • The length of a meter is defined by the distance light travels in a vacuum in 1/299,792,458 seconds

  7. Handle precision measuring instruments with care

  8. Use of precision measuring instruments • keep calibrated • when possible, take readings while the instrument is in contact with the work piece • on cylindrical work pieces, check twice - 90 degrees apart • best temperature is 68 degrees F.

  9. Direct reading instruments

  10. 1. Steel Rules

  11. 2. Calipers (Can be Vernier, Dial, or Digital Reading) • Outside • Inside • Depth

  12. 3. Micrometers (Can be Vernier, Dial, or Digital Reading) • Outside • frame, anvil, spindle, sleeve, thimble • Inside • Depth

  13. Comparison measuring instruments • comparing to a known standard • represents a known distance • used in conjunction with an instrument that has the capability of showing measurement • sometimes referred to as transfer measurement • direct reading instruments should be used whenever possible

  14. Common types • 1. spring calipers • 2. telescoping gages • 3. small hole gages • 4. adjustable parallels • 5. radius gages • 6. thickness gages • 7. planer gages (similar to adjustable parallels)

  15. 8. Squares • a. machinists combination square set • protractor • centering head • b. solid beam square • c. cylindrical square

  16. 9. Indicators • balanced vs. continuous readings • mounting must be rigid • magnetic bases • flexible link holding arms • height gage applications (test)

  17. 2 types of indicators • a. dial • some can be used to make linear measurement • discriminations range from .00005 to .001” • ranges are from .003 to 2.0” • b. test • used for comparisons only (no direct measurements) • discrimination approx .0005” • range of about .030”

  18. Angle Terminology • acute angles = < 90 degrees • right angles = 90 degrees • obtuse angles = > degrees • full circle = 360 degrees • 1 degree = 60 minutes of an arc • 1 minute = 60 seconds of an arc • radian = metric unit of angular measurement

  19. Angle measuring instruments (not for measuring angularity)

  20. 1. Plate protractor • discrimination of 1 degree

  21. 2. Bevel protractor • part of the machinists combination set - discrimination of 1 degree

  22. 3. Universal bevel protractor • includes a vernier scale • measure to accurately to within 5 minutes of a degree (remember there are 60 minutes in one degree

  23. 4. Sine bar • 5” and 10” center spacing of cylinders

  24. To find angles with the sine bar: • elevate the sine bar with adjustable parallels until the indicator reads zero at each end of the workpiece • parallel is removed and measured with a micrometer • transpose the sine bar elevation formula and solve for the angle • sin of the angle = elevation / sin bar length (5 or 10”)

  25. Gage blocks • permit comparison between working measurement and instruments of mfg.

  26. Uses: • calibration of measuring instruments • establishment of precise angles (with sine bars) • positioning of machine tools and cutting tools • used to set snap gages

  27. Common set has 81 to 88 blocks

  28. Range in thickness from .050 to 4.0”

  29. 3 Grades • grade 1 = lab • grade 2 = inspection • grade 3 = shop

  30. Grade on tolerance = +/- .000002”

  31. Tolerance on a stack of 30 gage blocks assembled to represent 20”?

  32. Use as few combinations as possible when stacking

  33. Care • avoid unnecessary contact with hands • clean with proper solvents • handle and lay on lint free cloth • don’t leave blocks rung for extended periods of time • spray with a preservative

  34. Wringing gage blocks

  35. Main cause of gage block wear is wringing poorly cleaned blocks

  36. Checking with optical flats

  37. Wear blocks • used in applications where direct contact is made • usually .050” or .100”

  38. Accessories • scribes • bases • screw sets

  39. Other machines • Optical comparator • Coordinate measuring machine (CMM)

More Related