CNC Surface Finishing & Post-Processing

Question 1

What does the surface finish symbol 'Ra' represent in machining drawings?

Accepted Answer

Arithmetic average roughness of a surface profile

Answer

Maximum peak-to-valley roughness height

Answer

Root mean square of surface deviations

Answer

The total range of surface texture values

Question 2

Which of the following surface finish values represents the smoothest machined surface?

Accepted Answer

16 Ra (micro-inches)

Answer

125 Ra (micro-inches)

Answer

63 Ra (micro-inches)

Answer

32 Ra (micro-inches)

Question 3

What machining operation is typically used to achieve a surface finish of 8–16 Ra micro-inches on a bore?

Accepted Answer

Reaming or fine boring

Answer

Rough boring

Answer

Drilling

Answer

Counter-boring

Question 4

Which CNC operation produces lay marks parallel to the direction of cutter travel?

Accepted Answer

Peripheral (side) milling

Answer

Face milling with a large shell mill

Answer

Ball nose contouring

Answer

Boring with a single-point tool

Question 5

When a drawing calls for a 'ground' surface, which post-processing step is implied?

Accepted Answer

Cylindrical or surface grinding to achieve fine tolerance and finish

Answer

Hand-filing to remove burrs

Answer

Sandblasting for texture

Answer

Anodizing before machining

Question 6

What is the primary purpose of a 'spring pass' or 'cleanup pass' at the end of a CNC turning sequence?

Accepted Answer

To remove tool deflection error by repeating the final cut with no additional infeed

Answer

To rough out excess material quickly

Answer

To change the spindle speed automatically

Answer

To check the part with the probe cycle