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Activity 002: Troubleshooting Diagnosis Challenge

Activity ID: U4M4-ACT-002 Duration: 35 minutes Objective: Students will diagnose CNC routing problems from sample cut pieces and machine symptoms, then prescribe corrective actions using systematic troubleshooting methodology. Group Size: 3 students

Overview

Using a set of pre-cut sample pieces that exhibit common CNC routing defects, students will practice identifying problems, determining root causes, and recommending fixes. This activity builds critical diagnostic skills without risk to equipment.

Materials & Equipment Needed

  • 8 pre-cut sample pieces exhibiting specific defects (prepared by instructor in advance):
  • Sample A: Burn marks on profile edges (feed too slow)
  • Sample B: Chatter marks on pocket floor (vibration/resonance)
  • Sample C: Fuzzy top edges on plywood (upcut bit tearout)
  • Sample D: Oversized hole (tool deflection)
  • Sample E: Uneven pocket depth across surface (spoilboard not flat)
  • Sample F: Melted/welded edge on acrylic (RPM too high, feed too slow)
  • Sample G: Rough, splintered edge (dull tool)
  • Sample H: Good quality reference piece (correct parameters)
  • Magnifying loupe
  • Digital calipers
  • Diagnosis worksheet
  • Troubleshooting reference chart (from U4M4 slides)

Instructions & Procedure

Phase 1: Individual Assessment (12 minutes) 1. Each group receives all 8 sample pieces and the diagnosis worksheet 2. For each sample (A through G), independently identify: - The visible defect (describe what you see) - The probable cause (what went wrong) - The recommended fix (what parameter or setup change would correct it) 3. Compare each sample to Sample H (the reference) to calibrate your assessment 4. Use calipers to measure dimensional accuracy where relevant 5. Record all findings on the worksheet

Phase 2: Group Consensus (8 minutes) 1. Compare individual assessments within the group 2. Discuss any disagreements β€” use evidence from the samples to support your diagnosis 3. Arrive at a group consensus for each sample 4. Rank the defects from most dangerous to least dangerous in terms of operator safety

Phase 3: Scenario-Based Diagnosis (10 minutes) Without physical samples, diagnose the following scenarios from descriptions only:

Scenario 1: "Halfway through a 30-minute plywood cut, the sound of the router changes from a steady hum to an intermittent chattering. The operator notices the workpiece has shifted about 1/16" from its original position." - What happened? What should the operator do immediately? What caused it? How to prevent it?

Scenario 2: "A student is cutting ΒΌ" aluminum on the CNC router. The chips are small, dark blue/purple in color, and there is smoke coming from the cut area." - What do the chip color and smoke indicate? What parameters need to change? What additional measure is missing?

Scenario 3: "After completing a V-carve job on maple, the student notices the text looks perfect on the left side of the board but the letters on the right side are noticeably shallower." - What is the most likely machine/setup issue? How would you verify? How would you fix it?

Phase 4: Class Presentations (5 minutes) 1. Each group presents their most challenging diagnosis (1-2 minutes) 2. Other groups can challenge or add to the diagnosis 3. Instructor reveals the actual cause for each sample piece

Discussion Points

  • Which defect was hardest to diagnose? Why?
  • How does the "change one variable at a time" rule apply to troubleshooting?
  • In a production setting, which defects would cause you to stop production immediately vs. continue with adjustments?
  • How would you build a troubleshooting log that helps future operators?

Expected Outcomes

  • Students can visually identify 7 common CNC routing defects
  • Students can link visible defects to root causes with 80%+ accuracy
  • Students understand the safety implications of different defect types
  • Students can apply systematic troubleshooting methodology

Assessment Rubric

Criteria Excellent (4) Proficient (3) Developing (2) Beginning (1)
Defect Identification Correctly identifies all 7 defects with precise descriptions Identifies 5-6 defects correctly Identifies 3-4 defects Identifies fewer than 3
Root Cause Analysis Accurately links all defects to specific causes Most causes correctly identified Some causes identified Cannot determine causes
Corrective Action Specific, actionable fixes for all defects Reasonable fixes for most defects Vague or partial fixes No viable corrections proposed
Safety Prioritization Correctly ranks all hazards with justification Reasonable ranking with minor errors Incomplete ranking No safety consideration

Safety Considerations

  • Sample pieces may have sharp edges β€” handle carefully, especially aluminum and acrylic samples
  • Do not attempt to recreate defects on the CNC router without instructor supervision
  • This is a diagnostic activity β€” no machine operation required
  • If sample pieces include metal, wear cut-resistant gloves when handling

Last Updated: 2026-03-19