3) GD&T

Question 1

What is GD & T?

Answer 1

• Geometrical dimensioning and tolerancing.
• International language used on eng drawings to describe the size, form, orientation and location of part features.

Question 2

The finished accuracy of a machined product depends on what?

Answer 2

Manufacturing tolerances of the manufacturing processes used.

Question 3

Describe the symbols describing a feature:

Answer 3

Far left: geometrical tolerance symbol
Left: cylindrical tolerance symbol
Right: Tolerance value
Far right: Datum Letter

Question 4

What are the 3 levels of datum plane?

Answer 4

Primary, Secondary, Tertiary

Question 5

What is maximum material condition?

Answer 5

When a hole measures to its smallest size, or a shaft measures to its largest size.

E.g shaft 20 +/- 0.5 measuring to 20.5.

Question 6

What is least material condition?

Answer 6

When a hole measures to its largest size or a shaft measures to its smallest size.

Question 7

What should a dimensional inspection plan include?

Answer 7

• A list of measurements to be made
• What gauges and instruments to be used
• The procedure for each measurement
• The gauging limits for each measurement
• Identification of calibration/ accuracy/ repeatability issues of the gauges and instruments.

Question 8

What are the steps of a dimensional inspection plan?

Answer 8

1. For every part - part function, dimensions to be/not to be inspected, acceptance/rejection of dimensions and the ramifications.
2. Manufacturing processes used to manufacture the component.
3. Measurement equipment to be used.
4. Measurement uncertainties which will be introduced.
5. Acceptance of bad/good features and the ramifications.
6. Identify the most likely distribution of measurement data.
7. Creation of a written document which details the above issues.