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Activity 001: Facing, Turning, and Shouldering — Stepped Shaft Project

Activity ID: U8M2-ACT-001 Duration: 45 minutes Objective: Face, turn, and create a stepped shaft with two diameters to specified tolerances.

Overview

Students machine a stepped shaft from round aluminum stock, practicing facing, straight turning, and shoulder creation. The finished part must meet dimensional tolerances of ±0.003", reinforcing the importance of careful measurement and dial collar usage.

Materials & Equipment Needed

  • Metal lathe with three-jaw chuck
  • 6061 aluminum round stock (1" diameter × 4" long)
  • Right-hand turning tool (carbide insert, CCMT or DCMT style)
  • Digital calipers (0.001" resolution) or outside micrometer
  • Center drill (#2), drill chuck, tailstock
  • Cutting fluid (water-soluble)
  • Chip brush
  • Safety glasses (mandatory)

Instructions & Procedure

Phase 1: Setup (5 minutes)

  1. Mount the aluminum stock in the three-jaw chuck with 2.5" extending.
  2. Mount the right-hand turning tool in the tool post at center height. Verify with a scale against the workpiece.
  3. Center drill the exposed end for tailstock support.
  4. Bring up the tailstock with a live center for support during turning.
  5. Calculate RPM: Aluminum at 800 SFM with carbide, 1" diameter → RPM = (800 × 3.82) / 1 = 3056. Set to the nearest available speed (likely ~2500 RPM).

Phase 2: Facing (5 minutes)

  1. Face the end of the workpiece to clean up the saw cut.
  2. Take 0.010" per pass. Feed the cross slide smoothly from outside to center.
  3. Retract, return the cross slide, advance 0.010", face again until the surface is uniformly smooth.
  4. Zero the carriage dial collar at the finished face. This is your Z-axis reference.

Phase 3: Turning the Major Diameter (10 minutes)

  1. Target dimension: 0.875" ±0.003" for the first 1.5" of length.
  2. Current diameter: 1.000". Material to remove: (1.000 - 0.875) / 2 = 0.0625" radial.
  3. Take roughing passes at 0.025" DOC on the cross slide, power feed at 0.005 IPR.
  4. Leave 0.010" for the finishing pass.
  5. Finishing pass: 0.005" DOC, slower feed (0.003 IPR).
  6. Stop the lathe. Measure with calipers. Adjust if needed.
  7. Turn this section for a length of 1.500" from the faced end (use carriage dial collar).

Phase 4: Turning the Minor Diameter and Shoulder (15 minutes)

  1. Target: 0.625" ±0.003" for the remaining 1.0" of exposed length.
  2. Mark the shoulder location at 1.5" from the end.
  3. Begin turning the minor diameter starting from the free end, working toward the shoulder.
  4. Roughing passes: 0.025" DOC per pass.
  5. Leave 0.010" for finishing.
  6. Finishing pass to final dimension. Stop and measure.
  7. Square the shoulder: carefully face the step between the two diameters using the carriage handwheel for fine Z-axis control.

Phase 5: Measurement and Deburr (10 minutes)

  1. Remove the workpiece from the chuck.
  2. Measure both diameters at two locations (near the shoulder and near the end) and record.
  3. Measure the step length from the face to the shoulder.
  4. Deburr all sharp edges with a deburring tool or file.
  5. Record all dimensions on the inspection sheet.

Discussion Points

  • How did your actual dimensions compare to the target?
  • Did you notice a difference in surface finish between roughing and finishing passes?
  • What would you do differently to improve accuracy?
  • How does chip formation change between roughing and finishing?

Expected Outcomes

  • Stepped shaft with two diameters within ±0.003" of target
  • Square shoulder with clean transition
  • Smooth surface finish from finishing passes
  • Properly deburred edges

Assessment Rubric

Criteria Excellent (4) Proficient (3) Developing (2) Beginning (1)
Major Diameter Within ±0.001" Within ±0.003" Within ±0.005" Outside ±0.005"
Minor Diameter Within ±0.001" Within ±0.003" Within ±0.005" Outside ±0.005"
Shoulder Square, clean, at correct length ±0.005" Minor burr, within tolerance Rough shoulder, within ±0.010" Not square or significantly off
Surface Finish Smooth, consistent, no chatter marks Minor chatter or tool marks Visible roughness Very rough surface
Safety Practices All safety checks, key removed, glasses on Minor lapse, self-corrected Required prompting Unsafe behavior

Safety Considerations

  • Safety glasses mandatory at all times
  • Remove chuck key immediately after tightening
  • Never measure with the lathe running
  • Use the chip brush, not hands, to clear chips
  • Aluminum chips are sharp—handle finished parts carefully
  • Apply cutting fluid to reduce chip welding on aluminum

Last Updated: 2026-03-19