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

8. Handle precision measuring instruments with care

9. 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.

10. Direct reading instruments

11. 1. Steel Rules

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

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

14. 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

15. 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)

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

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

18. 2 types of indicators a. dial b. test
some can be used to make linear measurement
discriminations range from 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”

19. 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

20. Angle measuring instruments (not for measuring angularity)

21. 1. Plate protractor
discrimination of 1 degree

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

23. 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

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

25. 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”)

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

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

28. Common set has 81 to 88 blocks

29. Range in thickness from .050 to 4.0”

30. 3 Grades
grade 1 = lab
grade 2 = inspection
grade 3 = shop

31. Grade on tolerance = +/- .000002”

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

33. Use as few combinations as possible when stacking

34. 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

35. Wringing gage blocks

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

37. Checking with optical flats

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

39. Accessories
scribes
bases
screw sets

40. Other machines
Optical comparator
Coordinate measuring machine (CMM)