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Activity 002: Center Drilling, Through-Drilling, and Chamfering

Activity ID: U8M2-ACT-002 Duration: 40 minutes Objective: Perform center drilling, through-drilling with peck cycle, and chamfering operations on the metal lathe.

Overview

Students drill a through-hole in an aluminum workpiece using proper peck drilling technique, then chamfer both the hole entrance and the external edges. This builds skills in tailstock drilling operations and compound rest usage.

Materials & Equipment Needed

  • Metal lathe with three-jaw chuck
  • 6061 aluminum round stock (1.5" diameter × 2" long)

  • 2 center drill

  • 3/8" HSS twist drill
  • Jacobs drill chuck (#2 Morse taper arbor)
  • Right-hand turning tool (carbide)
  • Chamfering tool or 45° compound rest setup
  • Cutting fluid
  • Digital calipers
  • Safety glasses

Instructions & Procedure

Phase 1: Workpiece Preparation (8 minutes)

  1. Mount the aluminum stock in the three-jaw chuck with approximately 1.25" extending.
  2. Face both ends clean (re-mount to face the second end).
  3. After facing the second end, leave the workpiece mounted with the final faced end exposed.
  4. Turn the OD to a clean, consistent diameter and record the measured diameter.

Phase 2: Center Drilling (5 minutes)

  1. Mount the #2 center drill in the Jacobs chuck. Install in the tailstock.
  2. Calculate RPM for center drill tip diameter (~1/8"): RPM = (800 × 3.82) / 0.125 ≈ 2400 RPM.
  3. Set the nearest available RPM.
  4. Advance the tailstock to bring the center drill close to the workpiece face.
  5. Lock the tailstock to the bed.
  6. Apply cutting fluid. Feed the center drill into the workpiece using the tailstock handwheel.
  7. Drill until the countersink reaches approximately 1/3 of the diameter (about 3/32" depth into the countersink).
  8. Retract the center drill. Remove from the tailstock.

Phase 3: Through-Drilling (15 minutes)

  1. Install the 3/8" twist drill in the Jacobs chuck.
  2. Calculate RPM for 3/8" drill: RPM = (300 × 3.82) / 0.375 ≈ 3055 RPM (using 300 SFM for HSS in aluminum). Set to nearest available speed.
  3. Apply cutting fluid liberally.
  4. Begin drilling: advance the tailstock quill to feed the drill into the center-drilled hole.
  5. Peck cycle: Advance approximately 3/8" (1× drill diameter), then retract fully to clear chips. Re-apply cutting fluid.
  6. Repeat the peck cycle. Note chip formation—aluminum tends to produce long, stringy chips that must be cleared.
  7. Continue until the drill breaks through the opposite face. You will feel a change in resistance.
  8. Retract the drill completely. Remove from the tailstock.
  9. Measure the drilled hole with calipers. Record the diameter.

Phase 4: Chamfering (10 minutes)

  1. External chamfer: Set the compound rest to 45°. Using the turning tool, cut a small 45° × 0.030" chamfer on the exposed end of the workpiece. Feed with the compound handwheel.
  2. Hole entrance chamfer: Using a countersink or a 45° chamfer tool, chamfer the hole entrance to remove the burr and create a clean lead-in. Approximately 0.030" × 45°.
  3. Reverse the workpiece in the chuck and repeat chamfers on the other end.
  4. Deburr the hole exit (the break-through side will have a burr).

Phase 5: Inspection (2 minutes)

  1. Measure the hole diameter and record.
  2. Verify chamfers are consistent and clean.
  3. Record all dimensions on the inspection sheet.

Discussion Points

  • Why is center drilling necessary before twist drilling?
  • What did you notice about chip formation during the peck cycle?
  • What would happen if you tried to drill through without pecking?
  • How accurate was the drilled hole compared to the nominal drill size?

Expected Outcomes

  • Clean center drill hole as a pilot for the twist drill
  • Through-hole drilled with proper peck technique and no drill breakage
  • Clean chamfers on external edges and hole entrances
  • Understanding of the peck drilling process and its importance

Assessment Rubric

Criteria Excellent (4) Proficient (3) Developing (2) Beginning (1)
Center Drill Proper depth, centered, clean Slightly deep or shallow Offset or rough Cannot complete center drill
Peck Drilling Consistent pecks, good chip clearing, breakthrough controlled Minor peck inconsistency Infrequent pecks, chip packing Drill binding or breakage
Chamfering Consistent 45°, clean edges Minor inconsistency Uneven chamfer Cannot produce chamfer
Measurements All recorded, accurate 1 measurement missing Multiple missing No measurements taken

Safety Considerations

  • Secure the tailstock bed clamp before drilling—drilling forces can push the tailstock away
  • Retract the drill fully between pecks to clear chips—jammed chips cause drill breakage
  • Aluminum chips are sharp and hot—use chip brush, not hands
  • When the drill breaks through, resistance drops suddenly—maintain control of the handwheel
  • Cutting fluid is essential for aluminum drilling—dry drilling causes chip welding and drill failure

Last Updated: 2026-03-19