Working Drawings


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fits and tolerance

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Working Drawings

  1. 1. Working Drawings S. P. Gaikwad
  2. 2. First, here’s what we talked about last time… Applying Tolerances
  3. 3. Representing Tolerance Values ∙ Tolerance is the total amount a dimension may vary and is the difference between the maximum and minimum limits. (A) Tolerance = .04 (B) Tolerance = .006 ∙ Tolerances are represented as Direct Limits (A) or as Tolerance Values (B).
  4. 4. Important Terms of Toleranced Parts A System is two or more mating parts. Nominal Size is used to describe the general size (usually in fractions). Basic Size – theoretical size used as a starting point for the application of tolerances (written in decimals).
  5. 5. Important Terms of Toleranced Parts Actual Size is the measured size of the finished part after machining. Limits – the maximum and minimum sizes shown by the tolerance dimension. The large value on each part is the Upper Limit, the small value = Lower Limit.
  6. 6. Important Terms of Toleranced Parts Allowance – the tightest fit between two mating parts. (The minimum clearance or maximum interference).
  7. 7. Important Terms of Toleranced Parts Maximum Material Condition (MMC) The condition of a part when it contains the greatest amount of material. Least Material Condition (LMC) The condition of a part when it contains he least amount of material possible.
  8. 8. Important Terms of Toleranced Parts Piece tolerance The difference between the upper and lower limits of a single part (.002 on the insert in this example, .004 on the slot.). System tolerance The sum of all the piece tolerances. For this example (.006)
  9. 9. Fit Types: A Clearance Fit occurs when two toleranced mating parts will always leave a space or clearance when assembled. An Interference Fit occurs when two toleranced mating parts will always interfere when assembled.
  10. 10. Functional Dimensioning Functional Dimensioning begins with tolerancing the most important features. Then, the material around the holes is dimensioned (at a much looser tolerance). Functional features are those that come in contact with other parts, especially moving parts. Holes are usually functional features.
  11. 11. Occurs when dimensions are taken Tolerance Stack-up from opposite directions of separate parts to the same point of an assembly. Dimensioned Dimensioned from the from the left. right. AVOID THIS!!!
  12. 12. Avoiding Tolerance Stack-up Tolerance stack-up can be eliminated by careful consideration and placement of dimensions. (Dimension from same side). Better still, relate the two holes directly to each other, not to either side of the part. The result will be the best tolerance possible of ±0.005.
  13. 13. Today’s Lecture - Week 10: Working Drawings Generally, a complete set of Working Drawings for an assembly includes: 1.) Detail Drawings of each non-standard part. 2.) An Assembly or Subassembly drawing showing all the standard parts in a single drawing. 3.) A Bill of Materials (BOM). 4. A Title Block.
  14. 14. A Detail Drawing of a Single Part Called a Lever
  15. 15. Assembly Drawing of a Piston & Rod containing 8 parts. An assembly drawing normally consists of the following: 1. All parts drawn in their operating position 2. A parts list or Bill of Materials (BOM) 3.Leader lines with balloons indicating all parts. 4. Machining and assembly instructions
  16. 16. Detail Drawing of the retainer ring used to fasten the rod to the piston.
  17. 17. Multiview Sectioned Assembly Drawing of a Spring Pack containing… Drawing Number Part Numbers
  18. 18. Pictorial Assemblies Sectioned Assembly
  19. 19. Pictorial Assemblies Technical Illustration (Exploded) Assembly
  20. 20. …contain... Title Blocks A. Name & Address of Company B. Title of the Drawing C. Drawing Number D. Names and dates of drafters, checker, issue date , contract number, etc. E. Design Approval F. Additional Approval Block G. Drawing Scale H. Federal Supply Code for Manufacturers J. Drawing Sheet Size K. Actual or estimated weight L. Sheet Number
  21. 21. Parts Lists The information normally included in a parts list is as follows: 1. Name of the part. 2. A detail number for the part in the assembly. 3. The part material, such as cast iron or bronze. 4. The number of times that part is used in the assembly. 5. The company assigned part number. 6. Other information, such as weight, stock size, etc.
  22. 22. Record any changes - Revision Blocks in upper-right corner Found
  23. 23. General tolerance note for inch and millimeter dimensions
  24. 24. ANSI drawing sheets with “zones” located on the border.
  25. 25. Tabular Drawings
  26. 26. Fastening Devices Fastening is a method of connecting or joining two or more parts together, using devices or processes. Mechanical Fastening –Process that uses manufactured devices (Nuts and Bolts) Bonding – Using material (Glue, Welding) Forming – Using component shape itself (HVAC, Tupperware, Velcro)
  27. 27. Threaded Fasteners First Application of a screw thread was developed by Archimedes to lift water. 1800’s Joseph Whitworth – English Standard Screw Threads 1864 – US Screw Thread Standard 1946 – ISO Develops Metric Standard 1948 – US Develops Unified Standard
  28. 28. Standard Thread Notations: Internal Threads Form Chart External Threads
  29. 29. Specifying Tap Drill Size: A Tap is a tool used to make threads in holes. A Die is used to make external threads.
  30. 30. Thread Representation:
  31. 31. General Types of Fasteners:
  32. 32. Finished vs. Unfinished Bolts: The difference between a finished and Unfinished hex head bolt is a washer Under the head of the finished bolt.
  33. 33. Nuts:
  34. 34. Cap Screws: Notice the chamfer (Also found on bolts).
  35. 35. Machine Screws: Machine Screws are finished with flat bottoms instead of chamfered corners. A ½” Hex Head Machine Screw is used on this week’s assembly drawing.
  36. 36. Set Screws:
  37. 37. Shoulder Screw: Check Appendix 33 for the dimensions of the shoulder screw required for this week’s assembly drawing
  38. 38. Retaining Rings:
  39. 39. Lock Washers:
  40. 40. Pin Types:
  41. 41. Standard Key Types:
  42. 42. Rivets:
  43. 43. Rivets:
  44. 44. Springs:
  45. 45. Create a complete set of Working Drawings
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