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MWA30 Chapter 2

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MWA30 Chapter 2

  1. 1. Tolerances Slide 1 Tolerance is the measurement variation allowed so that the item is acceptable. 𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 = 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 − 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 Nominal value is the target value for a measurement. 𝑛𝑜𝑚𝑖𝑛𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 = 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 + 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 2 The manufacturing tolerance is the difference between the maximum acceptable dimension and the minimum acceptable dimension. It can be expressed in several ways: • 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒 • 𝑛𝑜𝑚𝑖𝑛𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 ± 1 2 𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 • 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒 −0 +𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 • 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒 −𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 +0
  2. 2. Slide 2 Activity 2.3 – Tolerances in Carpentry (textbook page 98) • You are making a wooden stool that will look like the one shown below. • Your measurements will have a tolerance of 1 16 of an inch Calculate the maximum and minimum values of the dimensions for the legs, top and bottom crosspieces and seat.
  3. 3. Slide 3 𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 = 1 16  1 2 𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 = 1 2 1 16 = 1 32 Points to consider: • The seat diameter and seat thickness doesn’t need to be as accurate as the other measurements, since these dimensions don’t affect any of the other measurements. To show that the dimensions can be anywhere within the  range, the measurements should be written as nominal value  1 2 (tolerance) • The leg length, leg width, top cross-piece length, bottom cross-piece length, and the cross-piece diameter are dimensions that need to fit with other pieces of the wooden stool. Therefore, it would be safest to make them slightly larger, and then sand them down to size if they are too big. To show this, the measurements could be written as 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒 −𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 +0
  4. 4. Slide 4 Maximum Value Minimum Value Measurement with tolerance Seat diameter = 14 1 8 + 1 32 = 14 4 32 + 1 32 = 14 5 32 = 14 1 8 − 1 32 = 14 4 32 − 1 32 = 14 3 32 = 14 1 8 " ± 1 32 " Seat thickness = 1 1 2 + 1 32 = 1 16 32 + 1 32 = 1 17 32 = 1 1 2 − 1 32 = 1 16 32 − 1 32 = 1 15 32 = 1 1 2 " ± 1 32 "
  5. 5. Slide 5 Maximum Value Minimum Value Measurement with tolerance Leg length = 26 + 1 32 = 𝟐𝟔 𝟏 𝟑𝟐 = 26 − 1 32 = 25 32 32 − 1 32 = 25 31 32 = 𝟐𝟔 𝟏 𝟑𝟐 " − 𝟏 𝟏𝟔" + 𝟎 Leg width = 1 3 4 + 1 32 = 1 24 32 + 1 32 = 𝟏 𝟐𝟓 𝟑𝟐 = 1 3 4 − 1 32 = 1 24 32 − 1 32 = 1 23 32 = 𝟏 𝟐𝟓 𝟑𝟐 " − 𝟏 𝟏𝟔 " + 𝟎 Reminder: 𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 = 1 16
  6. 6. Slide 6 Max Value Min Value Measurement with tolerance Top cross- piece length = 7 1 2 + 1 32 = 7 16 32 + 1 32 = 𝟕 𝟏𝟕 𝟑𝟐 = 7 1 2 − 1 32 = 7 16 32 − 1 32 = 7 15 32 = 𝟕 𝟏𝟕 𝟑𝟐 " − 𝟏 𝟏𝟔" + 𝟎 Bottom cross- piece length = 9 + 1 32 = 𝟗 𝟏 𝟑𝟐 = 9 − 1 32 = 8 32 32 − 1 32 = 8 31 32 = 𝟗 𝟏 𝟑𝟐 " − 𝟏 𝟏𝟔" + 𝟎 Cross piece diameter = 1 1 4 + 1 32 = 1 8 32 + 1 32 = 𝟏 𝟗 𝟑𝟐 = 1 1 4 − 1 32 = 1 8 32 − 1 32 = 1 7 32 = 𝟏 𝟗 𝟑𝟐 " − 𝟏 𝟏𝟔" + 𝟎

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