Surface Finishing & Post-Processing Flashcards
6 cards from real CNC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Surface Finishing & Post-Processing flashcards as text
What does the surface finish symbol 'Ra' represent in machining drawings?
Answer: Arithmetic average roughness of a surface profile
Ra is the arithmetic mean of the absolute deviations of the surface profile from the mean line, the most widely used surface roughness parameter.
Which of the following surface finish values represents the smoothest machined surface?
Answer: 16 Ra (micro-inches)
Lower Ra values indicate smoother surfaces; 16 Ra is finer than 32, 63, or 125 Ra.
What machining operation is typically used to achieve a surface finish of 8–16 Ra micro-inches on a bore?
Answer: Reaming or fine boring
Reaming or fine boring with sharp tooling and proper feeds produces 8–16 Ra finishes, which are required for precision fits.
Which CNC operation produces lay marks parallel to the direction of cutter travel?
Answer: Peripheral (side) milling
Peripheral milling cuts along the edge of the end mill, leaving lay marks aligned with the cutter feed direction.
When a drawing calls for a 'ground' surface, which post-processing step is implied?
Answer: Cylindrical or surface grinding to achieve fine tolerance and finish
A 'ground' callout means the surface is finished by grinding, achieving tolerances and finishes beyond what turning or milling alone can produce.
What is the primary purpose of a 'spring pass' or 'cleanup pass' at the end of a CNC turning sequence?
Answer: To remove tool deflection error by repeating the final cut with no additional infeed
A spring pass re-runs the final tool path without additional depth, allowing the tool to spring back to its true position and clean up any deflection-caused material.