# Unit 09 - Tolerance, limits and fits - Lesson element - Teacher instructions (DOCX, 295KB) 24/02/2016

```Unit 9: Mechanical Design
LO1: Be able to use graphical and engineering
drawing techniques to communicate design
solutions
Tolerances, Limits and Fits
Instructions and answers for teachers
These instructions should accompany the OCR resource ‘Tolerances, Limits and Fits’ activity which supports
Cambridge Technicals in Engineering Level 3.
The Activity:
This activity offers an
This activity offers an
opportunity for English
opportunity for maths
skills development.
skills development.
!
Suggested
timings:
1 hour
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Activity 1: Tolerances, Limits and Fits – Application
Teachers might begin this activity by explaining that interference fits provide a secure assembly as they
require a certain amount of force to be applied to assemble the component. In cases where such
interaction is not required clearance fits can be used.
Pin in a bicycle chain
Interference
Key in a lock
Clearance
Coin in a coin slot
Clearance
Gudgeon pin in a piston
Interference
Cap on a marker pen
Interference
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Activity 2: Tolerances, Limits and Fits – Symbols
Teachers might explain that there are preferred hole-basis and shaft-basis fits specified in
(ISO 286-1:2010).
Shaft tolerance Zone: C
Fundamental Deviation: D
Hole tolerance Zone: B
International tolerance grade number: E
Basic Size: A
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Activity 2: Tolerances, Limits and Fits – Calculation
Learners should use the supplied tables in order to answer the problems give.
a)
Clearance fit; Maximum Clearance 345 &micro;m; Minimum Clearance 145 &micro;m
b)
Transition fit; Maximum Interference 39 &micro;m; Maximum Clearance 10 &micro;m
c)
Interference fit; Maximum Interference 42 &micro;m; Minimum Interference 1 &micro;m
Further details of the process of obtaining the required answers with visualisation is available at:
http://www.amesweb.info/FitTolerance/FitTolerance.aspx
Teachers might develop further similar problems for learners to solve.
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