# Use of floating carriage type of micrometer - Metrology & Quality Control

Q.  Which of the following statements is true?
- Published on 07 Aug 15

a. In three wire method, each flank of a thread is touched by a wire in axial plane section and this is valid only for a thread having rank angle
b. Compression error is always subtracted from effective diameter value obtained
c. Floating carriage type of micrometer is used for two wire method ----
d. The value of θ is assumed 30o while calculating best wire diameter for Withworth thread

ANSWER: Floating carriage type of micrometer is used for two wire method ----

#### Discussion

• Sravanthi   -Posted on 26 Oct 15
Three wire method

- This method is used to measure the pitch or effective diameter.

- Generally best wires are used because diameters of these wires have contact with thread flanks at pitch diameter.

- Accurate results in this method are obtained only if thread angle is correct and wires have contact with straight portion of the flank.

Compression errors:

- The force exerted on wires by the micrometers result in compression errors. The diameter measured decreases due to the force applied by micrometer and leads to some degree of compression.

- Compression corrective = 0.001 (F 2/3 / E 1/3 ) is the formula to calculate compression error. Here, F is the force applied by micrometer in Newton's, E is the effective diameter.

Floating carriage micrometer

- This micrometer is used for two wire method.

- Least count available for floating carriage micrometers are 0.001 mm, 0.002 mm, 0.005 mm, 0.0002 mm.

- The head stock of this micrometer has precision measuring screw with compensating devices. This is used to ensure error free reading.

Whitworth thread: The value of θ is assumed as 55o while calculating best wire diameter.

## ➨ Post your comment / Share knowledge

Enter the code shown above:

(Note: If you cannot read the numbers in the above image, reload the page to generate a new one.)