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Activity 001: Cut Parameter Optimization β€” Speed Test Matrix

Activity ID: U5M2-ACT-001 Duration: 45 minutes Objective: Students will cut a series of test lines at varying speeds on mild steel to identify the optimal speed for a given amperage, learning to read cut quality indicators. Group Size: 2-3 students

Overview

Using a standardized test plate, students will make 5 cuts at different speeds while holding amperage constant. By comparing drag lines, dross, kerf width, and edge quality across all cuts, students will identify the optimal speed window and understand the consequences of cutting too fast or too slow.

Materials & Equipment Needed

  • CNC plasma table (or hand-held torch with guide rail for manual operation)
  • 12 gauge (0.105") mild steel plate, minimum 12" Γ— 8"
  • Plasma cutter set to 40A with air
  • Welding helmet (shade 9)
  • Full PPE: FR jacket, leather gloves, boots, hearing protection, respirator
  • Digital calipers
  • Magnifying loupe (10Γ—)
  • Permanent marker and straightedge
  • Speed test evaluation worksheet
  • Fire extinguisher within 15 feet

Instructions & Procedure

Phase 1: Setup & Safety Briefing (10 minutes) 1. Set up the test plate on the cutting table with solid work clamp connection 2. Instructor reviews emergency procedures, E-stop location, fire extinguisher location 3. Mark 5 parallel cut lines (6" long, 1.5" apart) on the test plate 4. Verify plasma cutter settings: 40A, air at 65 PSI, correct consumables for 40A

Phase 2: Speed Test Cuts (20 minutes) Cut each line at a different speed. For 12-gauge steel at 40A, the manufacturer recommends approximately 80 IPM.

Cut # Speed % of Recommended Expected Result
1 40 IPM 50% (very slow) Wide kerf, excessive top melting
2 60 IPM 75% (slow) Good penetration, some excess melting
3 80 IPM 100% (recommended) Optimal cut quality
4 100 IPM 125% (fast) Increased dross, steeper drag lines
5 120 IPM 150% (very fast) Heavy dross, may not fully penetrate

For each cut: 1. Ensure proper standoff height (0.060"–0.080") 2. Initiate the cut and travel at the designated speed 3. Complete the full 6" length 4. Allow the plate to cool before inspection

Phase 3: Analysis & Measurement (15 minutes) For each of the 5 cuts, evaluate and record:

  1. Drag line angle: Use the loupe to observe the angle of drag lines on the cut face
  2. Vertical = too slow
  3. Slight trail (5°–15Β°) = optimal

  4. Heavy trail (>20Β°) = too fast

  5. Dross: Rate bottom-edge dross on a 1-5 scale:

  6. 1 = No dross
  7. 3 = Moderate, easily removed

  8. 5 = Heavy, requires grinding

  9. Kerf width: Measure with calipers at top, middle, and bottom of each cut

  10. Top edge quality: Rate 1-5 (1 = sharp/clean, 5 = excessively rounded/melted)

  11. Complete the comparison table on the worksheet

  12. Identify the optimal speed range (should align with cuts 2-3)

Discussion Points

  • How did kerf width change with speed? Why?
  • What would happen if you increased amperage to 55A β€” how would the optimal speed change?
  • Which cut would be acceptable for a part that needs to be welded? Which would not?
  • How would these results differ on ΒΌ" plate with the same amperage?

Expected Outcomes

  • Students can visually identify optimal cut speed from drag line angle and dross
  • Students understand the relationship between speed and cut quality
  • Students can use a speed test to dial in parameters for unfamiliar materials/thicknesses

Assessment Rubric

Criteria Excellent (4) Proficient (3) Developing (2) Beginning (1)
Safety Compliance All PPE, all procedures followed Minor PPE reminders needed Multiple safety corrections Significant safety concerns
Measurement Accuracy Consistent, precise measurements Reasonable measurements Inconsistent measurements Unable to measure effectively
Quality Assessment Correctly identifies optimal speed with justification Identifies correct speed Identifies approximately correct speed Cannot determine optimal speed
Analysis Depth Connects observations to underlying physics Good understanding of relationships Partial understanding No connection between parameters and results

Safety Considerations

  • Full plasma cutting PPE required for all participants (see U5M1-SAFE-001)
  • Welding screens must be deployed to protect others in the shop
  • Fire watch required during and 30 minutes after cutting
  • Allow test plate to cool 5+ minutes before handling for measurement
  • Use pliers or tongs to handle hot material β€” mark with "HOT" if leaving unattended
  • Ensure water table is at proper level (if applicable)

Last Updated: 2026-03-19