1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Comparison Measurement Unit 15

2. 15-2 Objectives Explain the principle of comparison measurement Identify four types of comparators and describe their use Measure to within.0005-in. (0.01-mm) accuracy with a dial indicator, mechanical and optical comparator, or air and electronic gages

3. 15-3 Comparison Measurement Process consisting of comparing measurement of part to known standard or master of exact dimension required Comparators –Any instrument used to compare size of workpiece to known standard –Incorporate some means of amplification to compare part size to set standard Standard usually gage blocks

4. 15-4 Dial Indicators Used to compare sizes and measurements to known standard and check alignment of machine tools, fixtures, and workpieces prior to machining Many work on gear and rack principle –Rack cut on plunger or spindle is in mesh with a pinion which is connected to a gear train –Any movement of spindle magnified and transmitted to pointer over graduated dial Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5. 15-5 Dial Indicators Generally two types –Continuous-reading dial indicator Numbered clockwise for 360º Regular-range –Only 2 ½ revolutions Long-range indicator –Digital and used to indicate table travel –Dial test indicator Reads both right and left from 0 Equipped with tolerance pointers

6. 15-6 Dial Test Indicators Perpendicular dial test indicators –Have spindle at right angles to dial –Used in setting up lathe work, table alignment Universal dial test indicator –Has contact point that may set through 180º arc –Used to check internal and external surfaces Metric dial indicators –Available both balanced and continuous-reading –Used for inspection purposes graduated 0.002 mm

7. 15-7 To Measure with a Dial Test Indicator and Height Gage 1.Clean face of surface plate and vernier height gage 2.Mount dial test indicator on movable jaw 3.Lower movable jaw until indicator point just touches top of gage block resting on surface plate 4.Tighten upper locking screw on vernier and loosen lower locking screw

8. 15-8 5.Carefully turn adjusting nut until indicator needle registers ¼ turn 6.Turn bezel to set indicator to zero 7.Note reading on vernier and record it 8.Raise indicator to height of first hole to measure 9.Adjust vernier until indicator reads zero 10.Note vernier reading again and record it 11.Subtract first reading from second and add height of gage block Metric Dial Indicator

9. 15-9 Mechanical and Electronic Comparators Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanical consists of base, column and gaging head Electronic uses Wheatstone bridge circuit to transform spindle moves to dial –May also be used as height gages

10. 15-10 To Measure with a Mechanical Comparator Clean anvil and master gage of required size Place master on anvil Carefully lower gaging head until stylus touches master and indicates movement of the needle Lock gaging head to the column Adjust needle to zero using fine adjustment knob and set limit pointer on the face

11. 15-11 To Measure with a Mechanical Comparator Recheck setting by removing master and replacing it Set tolerance pointers to upper and lower tolerances of part being checked Substitute work being gaged for master and note reading –Reading to right of zero, work too large –Reading to left of zero, work too small –Needle stops between tolerance pointers, OK

12. 15-12 Optical Comparators Projects enlarged shadow onto screen where it is compared to lines or to master form that indicates limits of dimensions or contour of part being checked Fast, accurate means of measuring workpiece with master Suited to checking extremely small or odd- shaped parts Available in bench and floor models

13. 15-13 Principle of the Optical Comparator Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Available in the following magnifications: 5X, 10X, 31.25X, 50X, 62.5X 90X, 100X and 125X Note: Use chart of same magnification as lens!

14. 15-14 To Check Angle of 60º Thread Using an Optical Comparator 1.Mount correct lens in comparator 2.Mount tilting centers on micrometer cross- slide stage 3.Set tilting centers to the helix angle of the thread 4.Set workpiece between centers 5.Mount vernier protractor chart and align it horizontally on screen

15. 15-15 6.Turn on light switch 7.Focus lens so clear image appears on screen 8.Move micrometer cross-slide stage until thread image centralized on screen 9.Revolve vernier protractor chart to show reading of 30º 10.Adjust cross-slides until image coincides with protractor line 11.Check other side of thread in same manner

16. 15-16 Mechanical- Optical Comparator Reed-type comparator Combines reed mechanism with light beam to cast shadow on magnified scale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17. 15-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. FIXED BLOCK Fixed steel block and free-reed block have reeds (2 pieces of spring steel) attached Upper ends of reed joined and connected to a pointer Movement of spindle attached to free-reed block will move it up and down (moving pointer to right or left) Light beam through aperture, movement of free block cause target to interrupt light beam, casting shadow on scale Principle of the Reed Mechanism

18. 15-18 Cutaway Section Showing Reed Mechanism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Upper part of reed deflects greater distance than the lower part

19. 15-19 To Measure with a Reed Comparator 1.Raise gaging head above required height, and clean anvil and master thoroughly 2.Place master gage or gage block buildup on anvil 3.Carefully lower gaging head until end of spindle just touches the master –Shadow will begin to appear on left side of scale 4.Clamp gaging head to column

20. 15-20 To Measure with a Reed Comparator Turn adjusting sleeve until shadow coincides with zero on the scale Remove gage blocks and carefully slide workpiece between anvil and spindle Note reading –If shadow to right of zero, part is oversize –If shadow to left of zero, part undersize

21. 15-21 Air Gages or Pneumatic Comparators Used to compare workpiece dimensions with master gage by means of air pressure or flow Two types: –Flow or column Indicates air velocity –Pressure indicates air pressure in system Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pressure-type air gage

22. 15-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Column-Type Air Gage Air passed through filter and regulator (10 psi) Air flows through tapered tube with float Rate of flow proportional to clearance Gage set to master Workpiece larger than hole size, float rises –Smaller, float falls

23. 15-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pressure-Type Air Gage

24. 15-24 Advantages of Air Gages Holes may be checked for taper, out-of- roundness, concentricity, and irregularity Gage does not touch workpiece Gaging heads last longer than fixed gages Less skill required to use this type Gages may be used a machine or bench More than one diameter may be checked at same time