Copyright 2008 Society of Manufacturing Engineers. FUNDAMENTALS OF TOOL DESIGN Gaging & Inspection Tool Design SIZE.

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1 FUNDAMENTALS OF TOOL DESIGN Gaging & Inspection Tool Design SCENE 1. GI06A, tape FTD40, 13:13:28:00-13:13:49:00 wide, parts being air gaged GI06B, CGS: Tolerance BECAUSE OF THE LIMITS OF MANUFACTURING, ALL PART DIMENSIONS ARE MADE WITHIN A SPECIFIED WORKING TOLERANCE, WHICH IS THE TOTAL PERMISSIBLE AMOUNT BY WHICH A DIMENSION MAY VARY FROM A SPECIFIED SIZE. SCENE 2. GI07A, tape FTD40, 13:19:44:00-13:20:00:00 part being gaged GI07B, CGS: Nominal Value/Dimension GI07C, ANI: design drawing, zoom in, nominal value and tolerance GI07D, ANI: highlight nominal value GI07E, ANI: highlight tolerance WHEN PROVIDING TOLERANCES, DESIGNERS RECOGNIZE THAT NO TWO WORKPIECES, DISTANCES, OR QUANTITIES CAN BE EXACTLY ALIKE. FOR THIS REASON, AN IDEAL, UNATTAINABLE CONDITION, REFERRED TO AS A NOMINAL VALUE, OR DIMENSION, IS SPECIFIED AND THE DEGREE OF ERROR, OR TOLERANCE ACCEPTABLE FROM THAT DIMENSION IS STATED. SCENE 3. GI08A, CGS: Allowance GI08B, tape 661, 15:07:52:00-15:08:15:00 zoom out, dowel pin inserted into assembly ALLOWANCE IS SOMETIMES CONFUSED WITH TOLERANCE. ALLOWANCE IS THE MINIMUM CLEARANCE SPACE INTENDED BETWEEN MATING PARTS AND REPRESENTS THE TIGHTEST PERMISSIBLE FIT. SCENE 4. continue previous shot GI09A, ANI: shaft

2 GI09B, ANI: shaft with plus GI09C, ANI: shaft with minus GI09D, ANI: hole GI09E, ANI: hole with plus GI09F, ANI: hole with minus GI09G, ANI: hole GI09H, ANI: shaft in hole FOR EXAMPLE, IF A SHAFT THAT IS ONE INCH FOUR HUNDRED AND NINETY EIGHT THOUSANDTHS (1.498 ) PLUS ZERO (0.000 ) MINUS THREE THOUSANDTHS OF AN INCH (0.003 ) IS TO FIT A HOLE ONE INCH FIVE HUNDRED THOUSANDTHS (1.500 ) PLUS THREE THOUSANDTHS OF AN INCH (0.003 ) MINUS ZERO (0.000 ), THE SMALLEST POSSIBLE HOLE SIZE IS ONE INCH FIVE HUNDRED THOUSANDTHS (1.500 ) AND THE LARGEST SHAFT SIZE IS ONE INCH FOUR HUNDRED AND NINETY EIGHT THOUSANDTHS (1.498 ). SCENE 5. continue animation GI10A, ANI: shaft in hole allowance GI10B, ANI: shaft in hole tolerance THUS THE ALLOWANCE IS TWO THOUSANDTHS OF AN INCH (0.002 ) AND THE MAXIMUM CLEARANCE, OR TOLERANCE, IS EIGHT THOUSANDTHS OF AN INCH (0.008 ), BASED ON THE MINIMUM SHAFT SIZE AND MAXIMUM HOLE DIMENSION. SCENE 6. GI11A, tape FTD37, 10:18:37:00-10:19:02:00 zoom out, workpiece being gaged at machine GI11B, tape FTD37, 10:12:56:00-10:13:16:00 zoom out, inspection gages GI11C, tape FTD37, 10:05:25:00-10:05:38:00 zoom out, master gages being used to calibrate gage GAGE TOLERANCE GENERALLY IS DETERMINED FROM THE AMOUNT OF THE SPECIFIED WORKPIECE TOLERANCE. FOR FIXED, LIMIT- TYPE WORKING GAGES, GAGE TOLERANCE IS GENERALLY SET AT TEN PERCENT OF WORKPIECE TOLERANCE. THE TOLERANCE OF

3 INSPECTION GAGES IS USUALLY FIVE PERCENT OF WORK TOLERANCE. MASTER GAGES, THOSE USED TO CHECK THE ACCURACY OF OTHER GAGES, ARE USUALLY TEN PERCENT OF GAGE TOLERANCE. SCENE 7. GI12A, ANI: chart showing four classes of gage tolerances GI12B, tape FTD37, 10:26:07:00-10:26:28:00 zoom out, parts being gaged GI12C, tape FTD40, 13:29:33:00-13:30:30:00 zoom out, part being gaged with multiple gages FOUR CLASSES OF GAGEMAKERS TOLERANCES HAVE BEEN DEVELOPED BY THE AMERICAN GAGE DESIGN COMMITTEE AND ARE IN GENERAL USE. THESE FOUR CLASSES ESTABLISH MAXIMUM VARIATIONS FOR ANY DESIRED GAGE SIZE, WITH THE DEGREE OF ACCURACY NEEDED DETERMINING THE CLASS OF GAGE USED. SCENE 8. continue previous shot GI13A, CGS: Class XX Class X Class Y Class Z THESE GAGE CLASSES INCLUDE: DOUBLE X, X, Y, AND Z. SCENE 9. GI14A, ANI: chart showing four classes of gage tolerances, class XX gages CLASS DOUBLE X GAGES ARE PRECISION- LAPPED TO THE VERY CLOSEST TOLERANCES FEASIBLE. THESE GAGES ARE USED PRIMARILY AS MASTER GAGES AND FOR FINAL CLOSE- TOLERANCE INSPECTION. SCENE 10. GI15A, ANI: chart showing four classes of gage tolerances, class X gages CLASS X GAGES ARE PRECISION-LAPPED TO

4 CLOSE TOLERANCES. THESE GAGES ARE USED FOR SOME TYPES OF MASTER GAGE WORK AND AS CLOSE-TOLERANCE INSPECTION AND WORKING GAGES. SCENE 11. GI16A, ANI: chart showing four classes of gage tolerances, class Y gages CLASS Y GAGES ARE PRECISION-LAPPED TO SLIGHTLY LARGER TOLERANCES THAN CLASS X GAGES. THESE GAGES ARE USED AS INSPECTION AND WORKING GAGES. SCENE 12. GI17A, ANI: chart showing four classes of gage tolerances, class Z gages CLASS Z GAGES ARE PRECISION-LAPPED. THESE GAGES ARE USED AS WORKING GAGES WHERE TOLERANCES ARE LARGE AND THE NUMBER OF PIECES TO BE GAGED IS SMALL. SCENE 13. GI18A, tape FTD37, 10:27:17:00-10:27:53:00 zoom out, parts being gaged GI18B, CGS: Unilateral Bilateral AFTER DECIDING THE TOLERANCE FOR A SPECIFIC GAGE, THE DIRECTION, PLUS OR MINUS, OF THE ALLOWANCE MUST BE DECIDED. TWO BASIC SYSTEMS, THE UNILATERAL, AND THE BILATERAL, AND THE MANY VARIATIONS OF THOSE SYSTEMS ARE USED WHEN MAKING THIS DECISION. SCENE 14. GI19A, CGS: Unilateral GI19B, ANI: unilateral system showing the gage tolerance zone included in the work tolerance zone GI19C, tape FTD40, 13:17:37:00-13:18:08:00 zoom out, parts being gaged IN THE UNILATERAL SYSTEM, THE WORK TOLERANCE ZONE INCLUDES THE GAGE TOLERANCE ZONE. THIS MAKES THE WORK

5 TOLERANCE SMALLER BY THE SUM OF THE GAGE TOLERANCES, BUT GUARANTEES THAT EVERY PART PASSED BY SUCH A GAGE, REGARDLESS OF THE AMOUNT OF THE GAGE SIZE VARIATION, WILL BE WITHIN THE WORK TOLERANCE ZONE. SCENE 15. GI20A, CGS: Bilateral GI20B, ANI: bilateral system showing half minus and half plus relative to the high and low limits of the work tolerance zone IN THE BILATERAL SYSTEM, GO AND NO-GO GAGE TOLERANCE ZONES ARE DIVIDED INTO TWO PARTS, HALF MINUS AND HALF PLUS RELATIVE TO THE HIGH AND LOW LIMITS OF THE WORK TOLERANCE ZONE. SCENE 16. GI26A, tape FTD37, 10:19:26:00-10:19:53:00 parts being gaged GAGES CAN WEAR BEYOND USEFULNESS UNLESS SOME ALLOWANCE FOR WEAR IS BUILT IN. ONE METHOD USES A PERCENTAGE OF THE WORKING TOLERANCE AS THE WEAR TOLERANCE. ANOTHER IS TO CREATE A STANDARD BEYOND WHICH THE GAGE IS NOT USED. SCENE 17. GI27A, tape FTD40, 13:31:07:00-13:31:33:00 zoom out, c.u. gaging of part GI27B, tape FTD46, 19:02:38:00-19:03:02:00 worn gaged being lapped GAGE WEAR SURFACES ARE MADE OF HARDENED ALLOY STEEL FOR MEDIUM PRODUCTION, AND CHROMIUM-PLATED STEEL FOR GREATER VOLUME. TUNGSTEN CARBIDE IS OFTEN USED FOR HIGH PRODUCTION AND SUPERIOR WEAR RESISTANCE. WORN CONTACT SURFACES ARE

6 COMMONLY GROUND, PLATED, REGROUND AND LAPPED TO SIZE. SCENE 18. GI28A, tape 541, 05:04:38:00-05:04:58:00 pan of physical primary standard objects TO ENSURE ACCURACY, GAGING AND MEASUREMENT TOOLS ARE CALIBRATED TO KNOWN PRIMARY STANDARDS, SUCH AS GAGE BLOCKS, WHICH PROVIDE A COMMON REFERENCE FOR MEASUREMENT STANDARDIZATION. SCENE 19. GI29A, CGS: Gage Blocks GI29B, tape 541, 05:09:00:00-05:09:54:00 zoom in, gage blocks used in calibrating precision measuring gage GAGE BLOCKS ARE MACHINED AND PRECISION LAPPED TO VERY FLAT, HIGHLY ACCURATE SURFACES, AND ARE PRODUCED FROM HARD, STABLE MATERIAL, SUCH AS CHROMIUM- CARBIDE STEEL. SCENE 20. GI30A, CGS: Surface Plates GI30B, tape 538, 02:16:13:00-02:16:33:00 wide, tilt down, sine plate being calibrated on granite surface plate, cut on action to next image GI30C, tape 538, 02:10:40:00-02:10:53:00 c.u., sine plate being calibrated on surface plate IN ADDITION TO GAGE BLOCKS, MEASUREMENT AREAS TYPICALLY UTILIZE SURFACE PLATES, WHICH ARE FLAT PLANES PRODUCED FROM HARD, HOMOGENEOUS GRANITE OR CAST IRON. SURFACE PLATES HOLD EXTREMELY TIGHT TOLERANCES, AND ARE USED AS A REFERENCE SURFACE FROM WHICH DIMENSIONS OR OTHER MEASUREMENTS ARE TAKEN.