# Engineering Metrology Questions and Answers – Coordinate Measuring Machines

This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Coordinate Measuring Machines”.

1. What precise movement does CMM have?
a) Precise movement in x coordinate
b) Precise movement in x and y coordinates
c) Precise movement in y and z coordinates
d) Precise movement in x, y and z coordinates

Explanation: Co-ordinate measuring machines are useful for three dimensional measurements. These machines have precise movements in x,y and z coordinates which can be easily measured and controlled.

2. Which type of CMM is most suited for large heavy workpieces?
a) Cantilever type
b) Bridge type
c) Horizontal boring mill type
d) Floating bridge type

Explanation: Bridge type CMM is more difficult to load. It less sensitive to mechanical errors. Horizontal boring mill type is best suited for heavy and large workpieces. Highly accurate type is vertical bore mill type but is usually slower to operate.

3. Which direction is sensed by a linear measurement transducer used in CMM?
a) Positive direction only
b) Negative direction only
c) Both positive and negative direction
d) Not used to sense directions

Explanation: Each slide in CMM is equipped with the help of a precision linear measurement transducer in 3 directions. It gives digital display and also senses a positive or negative direction. These are manufactured in both computer-controlled models and manual.

4. What is the accuracy of present day co-ordinate measuring machine?
a) 10 microns
b) 5 microns
c) 2 microns
d) 1 micron

Explanation: Co-ordinate measuring machines of present day are three-axis digital read-out type and these machines work up with an accuracy of 10 microns. Resolution of present day co-ordinate machine is 5 microns.

5. What is the name of an element which uses inductive coupling?
a) Inducto conduct
b) Inductosyn
c) Conductosyn
d) Conducto induct

Explanation: CMM utilize a measuring element known as Inductosyn data element. It uses inductive coupling between conductors and the conductors are separated by a small air gap. As Inductosyn is not subjected to wear, it does not develop inaccuracy.
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6. Which principle is used in the three master guideways and probe location?
a) Principle of dynamic design
b) Principle of static design
c) Principle of kinematic design
d) Principle of effective design

Explanation: In the probe location and three master guideways, the principles of kinematic design are used. Whole machine is supported on a 3-point suspension with its massive granite work table.

7. What is the cause of translational errors in CMM?
a) Error in scale division
b) Error in straightness
c) Twisting error
d) Roll error

Explanation: Translational errors result from errors in the division of scale and straightness error perpendicular to the corresponding axis direction. Errors in scale division are known as positional errors. Error in straightness is the cause of translational errors.

8. Which of the following is not related to the geometrical accuracy of CMM?
a) Straightness of axes
b) Squareness of axes
c) Position accuracy
d) Axial length measuring accuracy

Explanation: Geometrical accuracy concerned with the straightness of axes, position accuracy and squareness of axes while total measuring accuracy concerns volumetric length measuring accuracy and axial length measuring accuracy.

9. How many measurement parameters are considered in checking axes accuracy of straightness in CMM?
a) 2
b) 4
c) 6
d) 8

Explanation: Six measurement parameters need to be considered in the straightness of axes. Straightness of x-axis measured in y and z directions. Straightness of z-axis in x and y directions and of y-axis in x and z directions.

10. How many reference gauges are measured for volumetric length measuring accuracy in CMM?
a) 2
b) 3
c) 4
d) 5

Explanation: It is defined as the difference between the reference length of gauges, oriented freely and the corresponding results from the machine. 3 reference gauges are measured. Their lengths corresponding to approx. 1/3, 1/2 and 3/4 of the full travel of the longest axes.

11. Which of the following is true for trigger type probe system used in computer controlled CMM?
a) Bucking mechanism is a 2 point bearing
b) Current coordinate position stored when circuit is close
c) Contacts of point bearing arranged at 90 degree
d) Contacts of point bearing act as electrical micro switches

Explanation: The “buckling mechanism” in trigger type probe system is a 3 point bearing, the contacts of which are arranged around the circumference at 120 degrees. These contacts act as micro switches.

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