CNC Machine 2 — Questions and Answers
Question 1: What does the term 'backlash' refer to in a CNC machine's lead screw system?
- The rebound of a tool after a deep cut
- The lost motion between the screw and nut due to mechanical play (Correct answer)
- The reversal of spindle direction
- The vibration caused by high feed rates
Correct answer: The lost motion between the screw and nut due to mechanical play
Backlash is the small amount of lost motion caused by the gap between mating lead screw and nut threads, which can cause positioning errors.
Question 2: Which CNC machine component converts rotary motor motion into linear table movement?
- Encoder
- Ball screw (Correct answer)
- Servo amplifier
- Proximity sensor
Correct answer: Ball screw
Ball screws convert the rotary motion of a servo motor into precise linear movement of the machine table or axis.
Question 3: On a CNC machining center, what is the purpose of the automatic tool changer (ATC)?
- To sharpen dull cutting tools automatically
- To store and swap tools into the spindle without manual intervention (Correct answer)
- To measure tool length during cutting
- To cool tools during high-speed machining
Correct answer: To store and swap tools into the spindle without manual intervention
The ATC stores multiple tools in a magazine and automatically exchanges them in the spindle, reducing cycle time and manual intervention.
Question 4: What machine parameter describes the maximum distance an axis can travel from its home position?
- Feed rate limit
- Soft limit (travel limit) (Correct answer)
- Backlash compensation value
- Rapid traverse override
Correct answer: Soft limit (travel limit)
Soft limits are programmable boundaries set in the controller that prevent axis travel beyond the machine's physical range.
Question 5: A CNC router experiences chatter marks on a flat pocket. Which machine-related cause should be investigated first?
- Incorrect G-code format
- Worn or loose spindle bearings (Correct answer)
- Incorrect coolant concentration
- Wrong tool material grade
Correct answer: Worn or loose spindle bearings
Worn or loose spindle bearings allow radial runout that causes chatter and surface finish defects, especially during milling operations.
Question 6: What is the function of a machine tool's 'home position' (reference point)?
- The safest position for loading workpieces
- The fixed machine datum from which all coordinates are referenced (Correct answer)
- The position where tool changes occur
- The location of maximum spindle speed
Correct answer: The fixed machine datum from which all coordinates are referenced
The home position is a fixed machine reference point established at startup so the controller knows the absolute position of all axes.
Question 7: Which type of CNC machine guide system provides higher rigidity and load capacity for heavy-duty cutting?
- Linear roller guides
- Box way (flat way) guides (Correct answer)
- Round column guides
- Air bearing guides
Correct answer: Box way (flat way) guides
Box way guides provide greater surface contact area and inherent damping, making them superior for heavy cuts and vibration resistance.
CNC Machine 2
What does the term 'backlash' refer to in a CNC machine's lead screw system?