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Limits - Tolerances

Limits - Tolerances. Identify and use Dimensional Tolerancing in Engineering US 4438. Contents. Limits of size Tolerance Tolerance grades ISO Tolerance grades Tolerance grades and processes Questions One. Limits of Size.

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Limits - Tolerances

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  1. Limits - Tolerances Identify and use Dimensional Tolerancing in Engineering US 4438

  2. Contents • Limits of size • Tolerance • Tolerance grades • ISO Tolerance grades • Tolerance grades and processes • Questions One

  3. Limits of Size • It is not possible to make anything to an exact size even if you could you could not measure it • Everything is made within limits • A maximum size and a minimum size • The high limit is the largest size permitted and the low limit is the smallest size permitted

  4. Advantage • Reduces the cost of manufacturing • Nothing is made more accurate than it needs to be • Therefore • There are savings in the time taken • The cost of machinery used • The cost of measuring equipment used

  5. Tolerance • Tolerance is the difference between the high and the low limits about the basic size Minimum Size Maximum Size Tolerance Basic Size

  6. Tolerance Size = Tolerance Grade • Tolerance grades vary depending on the accuracy required • The greater accuracy the smaller the tolerance size • Tolerance grades vary depending on the basic size • The larger the basic size the larger the tolerance size There are 18 ISO tolerance grades Other systems have fewer

  7. ISO – IT (International Tolerance) Grades • IT01,  IT0,  IT1,  IT2,  IT3,  IT4, IT5 • Production of gauges and instruments. • IT6, IT7, IT8,  IT9,  IT10,  IT11,   • Precision and general Industry. • IT12, IT13,  IT14,   IT15,   • Semi finished products • IT16,   IT17,  IT18 • Structural Engineering Smaller Tolerances Greater Accuracy Larger Tolerances Greater Basic Sizes

  8. ISO IT Grades And Processes Larger Tolerances Cheaper Less Accurate Processes Indicates Process Range

  9. Questions • Answer in each case by clicking on the correct answer • A 200 mm basic size would have a bigger / smaller manufacturing tolerance than a 50mm basic size. • Reaming allows for the maintenance ofbigger / smaller tolerances than drilling • Manufacturing precision instruments would require the maintenance of bigger / smaller tolerances than manufacturing a G clamp • An ISO IT6 tolerance grade requires that a bigger / smaller tolerance be maintained than an ISO IT12 • The bigger / smaller the tolerances required the more expensive a part is to produce

  10. Giles Lancaster Marlborough Boys College 5 Stephenson Street Blenheim 03 578 0119 Ext 209 gilesl@mbc.school.nz

  11. The Three Sizes • Nominal Size • A size without specific limits of accuracy • Basic Size • Is the size about which the limits are set • It is the same for the hole and shaft • Actual Size • The size of the hole or shaft as measured • Note the measuring equipment has limits of accuracy as well

  12. Accuracy • Is how close the actual size is to basic size • The greater the accuracy the smaller the difference between the actual and basic size • The greater the accuracy required the greater the cost • More time • More expensive machining equipment • More expensive measuring equipment • Cost is asymptotic to accuracy

  13. No Try again

  14. Yes well done

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