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Activity 002: Bowl Interior Hollowing and Finishing

Activity ID: U7M4-ACT-002 Duration: 45 minutes Objective: Hollow the interior of a bowl mounted in a scroll chuck, achieving consistent wall thickness and a smooth interior surface.

Overview

Continuing from Activity 001, students mount their bowl (by the tenon) in the scroll chuck and hollow the interior. This activity covers interior tool rest positioning, progressive hollowing technique, wall thickness monitoring, and interior finishing.

Materials & Equipment Needed

  • Wood lathe with scroll chuck (bowl from Activity 001 mounted by tenon)
  • Bowl gouge (1/2" and 3/8"), round-nose scraper
  • Inside/outside calipers or bowl wall-thickness gauge
  • Safety glasses, face shield, dust mask, hearing protection
  • Sandpaper (150, 220, 320 grit)
  • Danish oil or food-safe finish (if making a food bowl)
  • Paper towel pads for finish application

Instructions & Procedure

Phase 1: Chuck Mounting and Setup (5 minutes)

  1. Mount the bowl in the scroll chuck by the tenon created in Activity 001.
  2. Tighten the chuck firmly using the chuck key. Verify the bowl seats flat against the jaw faces.
  3. Bring up the tailstock with a live center to the bowl face as a safety backup for initial cuts.
  4. Set the tool rest across the bowl face, 1/4" from the surface, at center height.
  5. Set speed to 800-1000 RPM (the blank should now be round and balanced from exterior turning).
  6. Hand-rotate to verify clearance.

Phase 2: Opening the Interior (15 minutes)

  1. Start the lathe. Using the 1/2" bowl gouge, make an initial cut at the center of the bowl face, scooping toward you to remove the first bit of material.
  2. Widen the opening by cutting from the rim area inward toward the center in a sweeping arc. The gouge flute should face approximately 10 o'clock.
  3. Remove material in layers—do not try to reach full depth immediately. Each pass should deepen the interior by approximately 1/2".
  4. Reposition the tool rest inside the bowl as the interior deepens. Always stop the lathe before adjusting the tool rest.
  5. Continue progressive hollowing: widen and deepen with each pass layer.
  6. Once the tailstock center is no longer needed (after several layers are removed), retract and lock the tailstock.

Phase 3: Refining Wall Thickness (15 minutes)

  1. As the interior approaches final depth, begin checking wall thickness with calipers.
  2. Target wall thickness: 3/8" to 1/2" consistent from rim to base.
  3. Work the walls to consistent thickness using the 3/8" bowl gouge for finer control.
  4. The bottom should flow smoothly into the walls with no sharp internal corners.
  5. Use the round-nose scraper for final smoothing of the interior, especially near the bottom where gouge access is limited. Present the scraper at or below center height.
  6. Check wall thickness at multiple points: rim, mid-wall, and base. Aim for +/- 1/16" consistency.

Phase 4: Sanding and Finishing (10 minutes)

  1. Sand the interior: start at 150 grit (500 RPM), progress through 220 and 320.
  2. Hold sandpaper in a folded pad. Be careful around the rim edge—sandpaper can catch on sharp edges.
  3. Stop the lathe and hand-sand with the grain as a final step.
  4. Apply finish:
  5. For decorative bowls: Danish oil or friction polish
  6. For food-contact bowls: mineral oil or walnut oil (food-safe)
  7. Apply with a paper towel pad at 300 RPM. Wipe off excess.
  8. Allow to dry. Inspect the finished interior for consistent color and coverage.

Discussion Points

  • What was the most challenging aspect of interior hollowing?
  • How did you manage tool rest positioning as the interior deepened?
  • Where was wall thickness most difficult to keep consistent?
  • How does interior curve relate to exterior curve for good wall thickness?

Expected Outcomes

  • Fully hollowed bowl with smooth interior profile
  • Consistent wall thickness (3/8"-1/2") throughout
  • Smooth interior surface after sanding
  • Applied finish with even coverage
  • Interior and exterior profiles that complement each other

Assessment Rubric

Criteria Excellent (4) Proficient (3) Developing (2) Beginning (1)
Hollowing Technique Smooth progressive cuts, good tool control Minor catches, self-recovered Rough cuts, required instructor guidance Cannot maintain control during hollowing
Wall Thickness Consistent 3/8"-1/2" throughout (+/- 1/16") Minor variation (1/4" thick spot) Significant variation Broke through wall or excessively thick
Interior Profile Smooth flowing curve, no ridges Minor ridges smoothed with scraper Visible steps or ridges after sanding Rough, uneven interior
Finish Quality Even sanding progression, consistent finish coat Minor sanding marks, adequate finish Visible scratches, uneven finish Rough surface, blotchy finish

Safety Considerations

  • Tailstock support recommended during initial hollowing passes
  • Reposition tool rest frequently—never turn with a large gap between rest and workpiece
  • Interior hollowing creates significant tool overhang—keep the tool rest as close as possible to the cutting area
  • Stop the lathe before reaching inside the bowl for any reason
  • Be cautious when sanding the rim area—the edge can catch sandpaper
  • Use food-safe finishes only for bowls intended for food contact

Last Updated: 2026-03-19