CNC CNC Lathe Turning Operations 3 — Questions and Answers
Question 1: In CNC lathe programming, G96 activates:
- Constant RPM mode
- Constant surface speed (CSS) mode (Correct answer)
- Thread cutting cycle
- Peck drilling cycle
Correct answer: Constant surface speed (CSS) mode
G96 enables Constant Surface Speed mode, where the controller automatically adjusts spindle RPM as the tool moves to different diameters.
Question 2: What is the function of the G70 finishing cycle on a Fanuc-style CNC lathe?
- Rough-turns the OD profile
- Performs a finishing pass along a defined profile (Correct answer)
- Centers the workpiece
- Performs a groove cycle
Correct answer: Performs a finishing pass along a defined profile
G70 is the finishing cycle that traces the part profile defined in the G71 or G72 rough turning sequence to remove the finishing allowance.
Question 3: A negative rake angle on a turning insert:
- Reduces cutting forces significantly
- Provides a stronger cutting edge (Correct answer)
- Increases chip curl away from the workpiece
- Decreases heat generation
Correct answer: Provides a stronger cutting edge
A negative rake angle creates a stronger, more supported cutting edge, making it suitable for interrupted cuts and hard materials.
Question 4: What does 'dwell' (G04) accomplish in a CNC lathe program?
- Pauses axis motion for a specified time or revolutions (Correct answer)
- Dwells at the tool change position
- Activates the tailstock
- Enables threading mode
Correct answer: Pauses axis motion for a specified time or revolutions
G04 causes the machine to pause all axis motion for a programmed time (seconds) or spindle revolutions, useful for cleaning up grooves or facing.
Question 5: When programming an internal boring operation, the X-axis values are:
- Larger as the bore diameter increases (Correct answer)
- Smaller as the bore diameter increases
- Always negative values
- The same as OD turning values
Correct answer: Larger as the bore diameter increases
In boring, moving to a larger X value increases the bore diameter because the tool moves away from the spindle centerline.
Question 6: Which insert grade is best suited for high-speed finishing of aluminum on a CNC lathe?
- Uncoated carbide P-grade
- PCD (polycrystalline diamond) (Correct answer)
- Cermet grade
- CBN (cubic boron nitride)
Correct answer: PCD (polycrystalline diamond)
PCD inserts are ideal for high-speed aluminum finishing because diamond is extremely hard, has low friction with aluminum, and provides exceptional surface finish.
Question 7: What is the primary purpose of a chip breaker groove on a turning insert?
- To increase insert hardness
- To curl and break chips into manageable lengths (Correct answer)
- To reduce insert cost
- To improve thermal conductivity
Correct answer: To curl and break chips into manageable lengths
The chip breaker groove curls the chip so it fractures into short segments, preventing long stringy chips that can tangle around the workpiece or tool.
CNC CNC Lathe Turning Operations 3
In CNC lathe programming, G96 activates: