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Computer Aided Design (CAD)

Computer Aided Design (CAD). Week 10 :: Limits, Fits and Tolerances. Limits and Fits Example Application. Clearance Fit. Interference Fit. Limits and Fits - Terminology. TRANSITION FITS. INTERFERENCE FITS. CLEARANCE FITS. Limits and Fits - Terminology. POSITIVE.

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Computer Aided Design (CAD)

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  1. Computer Aided Design(CAD) Week 10 :: Limits, Fits and Tolerances

  2. Limits and FitsExample Application Clearance Fit Interference Fit

  3. Limits and Fits - Terminology

  4. TRANSITIONFITS INTERFERENCEFITS CLEARANCEFITS Limits and Fits - Terminology

  5. POSITIVE Limits and Fits – Background to BS ‘Selected Fits’ SELECTED FITS NEGATIVE

  6. Limits and Fits – Background to BS ‘Selected Fits’ SELECTED FITS

  7. Limits and Fits – Classification • H11-c11 – Extra loose running fitProvides a large clearance. Gives easy assembly. • H9-d10 – Loose running fitUsed where ease of assembly is required (e.g. pulleys) • H9-e9 – Easy running fitSuitable for smaller parts, e.g. camshafts etc. • H8-f7 – Normal running fitGood quality fit which can be easily produced. • H7-g6 Close running or Location fitExpensive to produce. • H7-h6 Precision slide or Location fitPrecision Slides with good lubrication under constant Temp.

  8. Limits and Fits – Classification • H7-k6 – Push or easy keyring fitLocation of parts which are not dismantled often. • H7-n6 – Tight keyring fitTight assembly of long parts where H7-k6 isn’t sufficient. • H7-p6 – Light drive fitUsed to secure steel parts. Dismantel & renewal required. • H7-s6 – Heavy drive fitPermanent assembly of ferrous parts. Shrunk-fit required.

  9. Limits and Fits - Question • Consider a Drive pulley and shaft assembly (shaft = Ø40). The keyway provides positive drive rotation.The required fit is H7-h6.Calculate:the Maximum and MinimumLimits for the size of Hole & Shaft.

  10. Limits and Fits - Solution • Ø40 H7 = +25 upper 0 lower I.E.: Max Limit of Size of Hole: 40 + .025 = 40.025 Min Limit of Size of Hole: 40 – 0 = 40.000 • Ø40 h6 = -16 upper 0 lowerI.E.: Max Limit of Size of Shaft: 40 - .016 = 39.984Min Limit of Size of Shaft: 40 – 0 = 40.000

  11. Limits and Fits - AutoCAD

  12. Machining and Surface Texture 3.2 3.2 Machining of Surface (removal of material) is Prohibited! Surface Roughness of 3.2 µm(Machining Optional) Machining of Surface is Required

  13. Machining and Surface Texture All surfaces are to be machined. A value can be added as necessary. Typical Drawing with Surface Roughness

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