# Engineering Metrology Questions and Answers – Tool Maker’s Flats and High Precision Surface Plates

This set of Engineering Metrology Interview Questions and Answers focuses on “Tool Maker’s Flats and High Precision Surface Plates”.

1. What is the shape of the tool maker’s flats?
a) Circular
b) Rectangular
c) Square
d) Triangular

Explanation: Tool maker’s flats are small circular surface plates which are used for the high precision measurement work.

2. Which of the following is not true about tool maker’s flats?
a) Tool maker’s flats should be free from inclusions
b) Tool maker’s flats are of less hardness
c) Working surfaces are produced by lapping
d) Should be located in a stirred atmosphere

nswer: b
Explanation: Tool maker’s flats should be free from inclusions which after proper heat treatment gives a high hardness. Working surfaces are finished by lapping to possess a high degree of accuracy and uniformity.

3. Why are shallow grooves provided in larger flats?
a) To minimize the possibilities of uneven hardening
b) For design purpose
c) To maintain high accuracy for a longer period
d) To make them lighter

Explanation: A shallow groove is provided around the periphery of larger flats to avoid uneven hardening and for easy handling.

4. Which of the following is not true about the requirements of material selection for tool maker’s flats?
a) Suitable surface for the wringing purpose
b) High degree of rigidity
c) Wear resistance

Explanation: Material should have a proper surface so that gauges can be wrung on to it and it should have a high degree of rigidity and freedom from warping. Material should reflect radiant heat.

5. What is the tool maker’s flat size which generally uses both the faces as a working surface?
a) 30 to 45 mm
b) 50 to 75 mm
c) 75 to 100 mm
d) 100 to 200 mm

Explanation: Both the faces are highly finished in the range of 50-75 mm size and both are used as working surface and above this range it has only one face finished as working surface.
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6. Which of the following hardness is given by Solid steel tool maker’s flats?
a) 93HRC
b) 83HRC
c) 73HRC
d) 63HRC

Explanation: Solid steel tool maker’s flats after proper heat treatment gives a hardness of 93HRC or 850HV as high hardness is a desirable property for precision flats.

7. What is the minimum thickness of top in a high precision surface plate?
a) 20 mm for 350 mm dia
b) 25 mm for 250 mm dia
c) 30 mm for 250 mm dia
d) 20 mm for 250 mm dia

Explanation: Minimum thickness of top in a high precision surface plate is 20 mm for 250 mm dia, 25 mm for 300 mm dia and 30 mm for 350 mm dia.

8. What is the advantage of granite over cast iron in making surface plates?
b) Won’t rust by moisture
c) Strength for given weight is high
d) No need of inserts and fasteners

Explanation: Granite absorbs radiant heat which is a disadvantage. Granite won’t rust by moisture but may distort. Strength of cast iron is more than granite for a given weight.

9. Which of the following is true regarding high precision surface plates?
a) The top of high precision plate projects about 32 mm beyond the framing
b) The top of high precision plate projects about 32 mm below the framing
c) The top of high precision plate projects about 12 mm beyond the framing
d) The top of high precision plate projects about 12 mm below the framing

Explanation: The top of high precision plates is machined around the sides and generally projects approx 12 mm beyond the framing.

10. What is the minimum total depth in high precision surface plates for 300 mm dia (nominal size)?
a) 60
b) 70
c) 80
d) 90

Explanation: Minimum total depth for 250, 300, 350 mm dia is 70, 80, 90 mm respectively.

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