# Machine Dynamics Questions and Answers – Computer Aided Analysis for Four Bar Mechanism

This set of Basic Machine Dynamics Questions and Answers focuses on “Computer Aided Analysis for Four Bar Mechanism”.

1. In a CAD package, mirror image of a 2D point P (5, 10) is to be obtained about a line which passes through the origin and makes an angle of 45° counterclockwise with the X-axis. The coordinates of the transformed point will be
a) (7.5, 5)
b) (10, 5)
c) (7.5, -5)
d) (10, -5)

Explanation: Coordinates of D in x-axis is (10,0) and in y-axis is (0,5)
So coordinates are (10,5)

2. In a CNC program block, N002 G02 G91 X40 Z40…, G02 AND G91 refer to
a) Circular interpolation in counterclockwise direction and incremental dimension
b) Circular interpolation in counterclockwise direction and absolute dimension
c) Circular interpolation in clockwise direction and incremental dimension
d) Circular interpolation in clockwise direction and absolute dimension

Explanation: G02 – Circular interpolation in clockwise direction
G91 – incremental dimension

3. For generating Coons patch we require
a) A set of grid points on surface
b) A set of control points
c) Four bounding curves defining surface
d) Two bounding curves and a set of grid control points

Explanation: Coons patch or surface is generated by the interpolation of 4 edge curves. A linear interpolation between four bounded curves is used to generate a Coons surface, also called as Coons patch. The method is credited to S. Coons who developed this concept for generating a surface.

4. NC contouring is an example of
a) Continuous path positioning
b) Point-to-point positioning
c) Absolute positioning
d) Incremental positioning

Explanation: Contouring is the most complex flexible and the most expensive type of machine tool control. It is capable of performing both PTP and straight cut operations. In addition to the distinguishing feature of the contouring NC system is their capacity for simultaneous control of more than one axis movement of machine tool illustrates the versatility of continuous path NC. Milling and Turning are the common examples of the use of conturing control.

5. The tool of an NC machine has to move along a circular arc from (5, 5) to (10, 10) while performing an operation. The center of the arc is at (10, 5). Which one of the following NC tool path commands performs the above mentioned operation?
a) N010 G02 X10 Y10 X5 Y5 R5
b) N010 G03 X10 Y10 X5 Y5 R5
c) N010 G01 X5 Y5 X10 Y10 R5
d) N010 G02 X5 Y5 X10 Y10 R5

Left hand G41
Right hand G42
Tool-Height Compensation
Positive G43
Negative G44
Cancel tool-height compensation G49

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Tool-radius compensations make it possible to program directly from the drawing, and thus eliminate the tool-offset calculation
G41 (G42) Dxx
Dxx: the radius of tool to compensate is saved in a memory unit that is named Dxx
G41/G42 is directly related with direction of tool movement and which side of part is cut.

6. During the execution of a CNC part program block NO20 GO2 X45.0 Y25.0 R5.0 the type of tool motion will be
a) Circular Interpolation – clockwise
b) Circular Interpolation – counterclockwise
c) Linear Interpolation
d) Rapid feed

Explanation: G02 – Circular interpolation in clockwise direction
G91 – incremental dimension

7. In a 2-D CAD package, clockwise circular arc of radius, 5, specified from P1 (15,10) to P2 (10,15)will have its center at
a) (10, 10)
b) (15, 10)
c) (15, 15)
d) (10, 15)

Explanation: Coordinates of P in x-axis is (15,10) and in y-axis is (10,55)
So coordinates are (10,10)

8. In an NC machining operation, the tool has to be moved from point (5,4) to point (7,2) along a circular path with center at (5,2). Before starting the operation, the tool is at (5, 4). The correct G and M code for this motion is
a) N010 G03 X7.0 Y2.0 I5.0 J2.0
b) N010 G02 X7.0 Y2.0 I5.0 J2.0
c) N010 G01 X7.0 Y2.0 I5.0 J2.0
d) N010 G00 X7.0 Y2.0 I5.0 J2.0

Explanation: G02 – Circular interpolation in clockwise direction
G91 – incremental dimension

9. In computer aided drafting practice, an arc is defined by
a) Two end points only
c) Radius and one end point
d) Two end points and center

Explanation: Two end points and center defines an arc.

10. In finish machining of an island on a casting with CNC milling machine, an end mill with 10 mm diameter is employed. The corner points of the island are represented by (0, 0), (0, 30), (50, 30) and (50, 0). By applying cutter radius right compensation, the trajectory of the cutter will be
a) (-5, 0), (-5, 35), (55, 35), (55,-5), (-5,-5)
b) (0,-5), (55,-5), (55, 35), (-5, 35), (-5,-5)
c) (5, 5), (5, 25), (45, 25), (45, 5), (5, 5)
d) (5, 5), (45, 5), (45, 25), (5, 25), (5, 5)

Explanation: Radius of trajectory = 5cm

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