1 / 37

Tolerancing

Outline. Why tolerancing?Engineering tolerancesGeometric tolerances. Why tolerancing?. Setting limits to dimensionsDefine manufacturing limitsBilateral ? plus and minus valueUnilateral ? either plus or minus value is zeroStandard tolerancesApply to all dimensionsIndividual toleranceApplies

kallima
Download Presentation

Tolerancing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. Tolerancing MECH 2012 Winter 2011

    2. Outline Why tolerancing? Engineering tolerances Geometric tolerances

    3. Why tolerancing? Setting limits to dimensions Define manufacturing limits Bilateral – plus and minus value Unilateral – either plus or minus value is zero Standard tolerances Apply to all dimensions Individual tolerance Applies to one dimension only

    4. Why tolerancing? (continued 2) Baseline for tolerances Prevents tolerance build-up Baseline should be a functional part of the device Edge of a plate Axis of a whole in plate Edge or axis of a hole in a structure Shoulder of a shaft (usually not end of a shaft!) Tolerances between holes and shafts – standard fits

    5. Why tolerancing? (continued 3) Costs of tolerances The smaller the more expensive Always only as small as really required Standard tolerances should be “large” Design for tolerances as large as possible while maintaining function and safety! Can given dimensions with small tolerances be manufactured? Consider change of tolerances due to temperature Environment – summer and winter Operating conditions – engine Humidity Dust build-up ...

    6. Engineering Tolerances A tolerance is: Physical dimension Measured value Space between a bolt and a nut Space between balls or rollers and the cage in bearings A tolerance can be specified as: Percentage of nominal value Maximum deviation of nominal value Standard that defines values Symmetrical or asymmetrical

    7. Engineering Tolerances (continued 2) Tolerance is different from safety, but an adequate safety factor will take into account relevant tolerances as well as other possible variations Determine how wide the tolerances may be without affecting other factors of the outcome of the process Scientific principles Engineering knowledge Professional experience Experimental investigation assessing the effects of tolerances Process control and quality assurance to make sure that tolerances are within specified values

    8. Engineering Tolerances (continued 3) International tolerance grades (IT) Standard (size) tolerances are divided into two categories: hole and shaft Hole basis represents a system of fits corresponding to a basic hole size – the fundamental deviation is H Shaft basis represents a system of fits corresponding to a basic shaft size – the fundamental deviation is h The tolerance zones are specified in international tolerance grade numbers, called IT numbers

    9. Uni- and bilateral Tolerances

    10. Uni- and bilateral Tolerances

    11. Dimensions from one Edge – No Stacking

    12. Dimensions from one Edge – No Stacking (continued 2)

    13. Dimensions from one Edge – No Stacking (continued 3)

    14. Dimensions from one Edge – No Stacking (continued 4)

    15. Type of Fit

    16. The Hole Basis System is used preferably

    19. International tolerance grades (IT)

    20. Tolerances of Bearings (and other Machine Elements) Get ID, OD and width tolerance from bearing manufacturer => Choose appropriate dimensions and tolerances in design Width tolerance typically -0.06 to -0.10mm (SKF) Bearing Tolerance Fields (SKF)

    21. Dimensions on Shaft that require individual Tolerances

    22. Dimensions on Shaft that require individual Tolerances Distance from shoulder on shaft to groove for snap ring Snap ring groove dimensions Shaft diameter for bearings to achieve proper fit as suggested by bearing manufacturer Distance between sprocket and gear Shaft diameter for gear and sheave Distance from bearing shoulder (on right) to gear Cut out for key …

    23. Bosch Hedge Trimmer Cutting Blade Drive Mechanism

    24. Bosch Hedge Trimmer Cutting Blade Driver

    25. Bosch Hedge Trimmer Cutting Blade Driver – Assembly Tolerances

    26. Geometric Tolerances Dimensioning based on geometric shape of an object Flatness Roundness Straightness Circularity Cylindricity ... Datum – point, axis or surface used as a starting reference point for dimensions and tolerances

    27. Geometric Tolerances (continued 2)

    28. Datum Axis and Planes

    29. Possible Shape without Geometric Tolerances

    30. Flatness

    31. Straightness

    32. Circularity

    33. Circularity

    34. Perpendicularity

    35. Continuum Hip Cup System (Zimmer Inc.)

    36. Articulation Tolerances of Metal-Metal Hip Implants Tolerance range of cup and inlay sphere approximately 0.01mm Circularity range of 0.001mm – very difficult to manufacture Very low clearance for optimal lubrication in body If tolerances and material combinations are not correct => excessive wear and revision surgery within a few years

    37. References Bethune, J.D. 2002. Engineering Graphics with AutoCAD 2002. Prentice Hall Norton, R.L. 2006. Machine Design – An Integrated Approach. Prentice Hall Shigley, J.E., Mischke, C.R., Budynas, R.G. 2004. Mechanical Engineering Design McGraw Hill http://www.mitcalc.com/doc/tolerances/help/en/tolerancestxt.htm Tolerances and fits http://www.roymech.co.uk/Useful_Tables/Drawing/draw_geom.html Geometric Tolerances SKF Bearings Catalogue

More Related