Tolerances
Muhtasari
Nothing is ever made to size. Cut a hundred pieces of timber to 300 millimetres and you will have a hundred pieces measuring between about 299 and 301, and if you measure them precisely enough, no two will be identical. That is not a failure of skill, it is how making works, and a designer who has not accepted it will produce drawings that cannot be manufactured and will spend their career blaming the workshop.
A tolerance is the amount by which a dimension is allowed to differ from the size on the drawing, and it is the designer's statement of how much variation the product can survive. This lesson covers working accurately using tolerances, how a range of materials are cut, shaped and formed to designated tolerances, and why tolerances are applied during making activities at all. You will calculate limits, work with percentage tolerances, see why errors accumulate and how a datum stops them, and decide how tight a tolerance ought to be, which is the judgement that separates a designer from somebody who writes small numbers. This is designing and making principles content, examined in Section C of Paper 1.
Malengo
- Work accurately using tolerances. How a range of materials are cut, shaped and formed to designated tolerances. Why tolerances are applied during making activities.
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Maelezo ya Somo
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Tathmini ya Somo
Hongera kwa kukamilisha somo la Tolerances. Sasa kwa kuwa umechunguza dhana na mawazo muhimu, ni wakati wa kuweka ujuzi wako kwa mtihani. Sehemu hii inatoa mazoezi mbalimbali maswali yaliyoundwa ili kuimarisha uelewaji wako na kukusaidia kupima ufahamu wako wa nyenzo.
Utakutana na mchanganyiko wa aina mbalimbali za maswali, ikiwemo maswali ya kuchagua jibu sahihi, maswali ya majibu mafupi, na maswali ya insha. Kila swali limebuniwa kwa umakini ili kupima vipengele tofauti vya maarifa yako na ujuzi wa kufikiri kwa makini.
Tumia sehemu hii ya tathmini kama fursa ya kuimarisha uelewa wako wa mada na kubaini maeneo yoyote ambapo unaweza kuhitaji kusoma zaidi. Usikatishwe tamaa na changamoto zozote utakazokutana nazo; badala yake, zitazame kama fursa za kukua na kuboresha.
- A dimension is given as 30 plus 0.3 minus 0.2 millimetres. What is the tolerance? A. 0.1 millimetres B. 0.2 millimetres C. 0.3 millimetres D. 0.5 millimetres Answer: D
- A length of 400 millimetres has a tolerance of plus or minus 1.5 per cent. What are the limits? A. 398.5 and 401.5 B. 394 and 406 C. 385 and 415 D. 340 and 460 Answer: B
- Four spacers each 5.0 plus or minus 0.1 millimetres thick are stacked. What is the maximum possible height of the stack? A. 20.1 millimetres B. 20.2 millimetres C. 20.4 millimetres D. 24.0 millimetres Answer: C
- Dimensioning every feature from one chosen face rather than from the previous feature is done in order to A. save drawing time. B. prevent errors from accumulating. C. reduce the material cost. D. avoid the need for a tolerance. Answer: B
- Why should a designer avoid specifying a tolerance tighter than the process can achieve? A. It makes the drawing harder to read B. It produces rejects and raises the cost without improving the product C. It is not allowed by the specification D. It removes the need for a datum Answer: B
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