5.5. Describe the term datum 5.6. Specify a.25-diameter hole with a..375 diamete

Question

5.5. Describe the term datum

5.6. Specify a.25-diameter hole with a..375 diameter *.25 deep counterbore in ASMEY 14.5 standard.

5.7. How many threads per inch does a ¼-20 thread have?

5.8. In what units is roughness measured in inches? In metric?

5.9. Why is reading material specifications important?

5.10. What additional part features are controlled by GDT that cannot be controlled by conventional tolerancing?

5.11. What is maximum material condition M

5.12. What is least material condition L?

5.13. Describe the positional relationship between GDT datum planes?

Explanation / Answer

a) Datum:

This is like a reference point whose co-ordinate is known or assumed. This is the reference point at which the calculations and measurements are made.

c) It has 20 threads per inch (TPI). The numeber 20 represents the TPI.

d) It is measure in micro-inches and micro-meters.

e) Specification of the material is required to describe the quality and quantity of different materials required. Specification is necessary to specify the machine and tools to be engaged for a material and thus enables to procure them beforehand.

g) MMC: Maximum Material Condition or for short, MMC, is a feature of size symbol that describes the condition of a feature or part where the maximum amount of material exists within its dimensional tolerance. eg. If it is a hole or internal feature: MMC = smallest hole size. If it is a pin or external feature: MMC = largest size of the pin.

h) LMC: Least material condition is a feature of size symbol that describes a dimensional or size condition where the least amount of material (volume/size) exists within its dimensional tolerance. eg. If it is a hole or internal feature: LMC = largest hole size. If it is a pin or external feature: LMC = smallest size of the pin.

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