Περιγραφή θέματος

  • Learning objectives

    Σύμπτυξη όλων Ανάπτυξη όλων
      1. Demonstrate a correct single point (stippling impact) with consistent force, angle and contact time.
      2. Produce short patterned runs with regular spacing, consistent burr morphology and predictable visual density.
      3. Diagnose and correct three common execution faults (under-strike, over-strike, angular misalignment) and perform a basic recovery.

      Prerequisites

      • Lesson 1 (Cultural Context) and Lesson 2 (Tools & Materials) completed.
      • Familiarity with holding a punch and basic hammer control (two-handed steady strike).
      • Workpiece clamped and surface prepared (clean, smooth, appropriate hardness) — see Lesson 3.

  • Materials & equipment

      • Workpiece: thin metal plaque (e.g., silver, brass, pewter, or an aluminium test panel). Specify alloy and thickness in instructor notes.
      • Punches: prick punch (30°–60° tip) for fine dots; centre punch (~90°) for larger dots; optional automatic centre punch.
      • Hammer (light jeweller’s hammer / brass mallet), anvil or support block (rigid, massy), clamp/vice.
      • Marking tools: scribe, dividers, pattern template.
      • Safety PPE: eye protection, gloves, hearing protection if mechanical punch used.

  • Quick overview of the physical principle

    • Pointillé is a displacement technique: each impact produces a crater plus a raised burr; visual effect depends on punch geometry, force magnitude, orientation and spacing. The relationship between these execution parameters and resulting deformation is the basis for visual control and automated assessment in the simulator.

  • Micro-action step sequence

    • Step 0 — Setup & orientation (preparation)

      • Intent: ensure stable backing and repeatable strike geometry.
      • Parameters: workpiece flatness ±0.5 mm; backing mass sufficient to prevent rebound; surface cleaned and smooth.
      • Action: clamp workpiece to anvil or rigid block; align punch perpendicular to target surface using a light jig or finger guide. Mark first dot with scribe.
      • Cue: no movement or bounce of workpiece on low-force hand taps.

      Step 1 — Single-impact calibration (experiment to set force)

      • Intent: find the strike force that creates a crater with a clean burr without cracking or excessive flow.
      • Parameters to record: pulse force (qualitative) or hammer light/medium; punch angle 0° ± 5° (vertical); contact time ~instant (hammer impulse). In simulator terms: force magnitude, vertical alignment, acceptable angle deviation.
      • Action: on a scrap area, deliver 3 strikes at increasing force (light → medium → firm). Inspect crater depth, burr height, and any flange cracking.
      • Expected visual cue: small, crisp crater with consistent burr; no radial cracks or tearing. If burr is absent → increase force slightly; if metal fractures or spreads excessively → reduce force.

      Step 2 — Establish spacing & rhythm for a short run

      • Intent: create a repeatable rhythm and spacing for pattern building.
      • Parameters: target center-to-center spacing for fine shading: ~1.5–2× crater diameter; for denser shading use ~1× diameter. Maintain strike repetition period (rhythm) for uniform burr formation.
      • Action: use dividers or a template to mark a short row of 5–8 target points. Practice striking at calibrated force, keeping the punch orientation constant between impacts (use your elbow/forearm as a guide).
      • Cue: uniform crater size and burr morphology across row; consistent reflectance under side lighting.

      Step 3 — Building shaded areas (density control)

      • Intent: vary dot density to produce tonal gradients.
      • Parameters: spacing, punch size, strike force. Closer spacing → darker (matte) appearance because burrs merge; wider spacing → lighter (highlights).
      • Action: for gradient, execute sequential rows where center-to-center spacing systematically decreases. Maintain identical strike force and angle.
      • Cue: gradual change of surface reflectance and micro-shadowing across the gradient.

      Step 4 — Cornering, curvature and pattern transitions

      • Intent: maintain spatial continuity when pattern changes direction or crosses form curvature.
      • Parameters: adapt spacing on curves so apparent density remains constant (projected spacing rule). For convex forms, slightly increase spacing; for concave, decrease.
      • Action: mark guide lines; when turning, place transitional dots with intermediate spacing and inspect for evenness.
      • Cue: no abrupt gaps or clustering visible at transitions.

      Step 5 — Finishing strikes and burr management

      • Intent: remove undesired burrs or flatten for specific effects.
      • Parameters: light burnishing or filing force; angle management.
      • Action: where burr is too prominent, use a light burnishing tool or fine abrasive to reduce height; for a matte background, leave burrs intact; for polished foregrounds, selectively remove burrs.
      • Cue: target reflectance and tactility achieved without scratching pattern.

      Step 6 — Final inspection & correction

      • Intent: quality assurance against criteria (size, spacing, burr uniformity).
      • Checklist: crater diameter uniform ±10%; spacing tolerance consistent relative to chosen density; no radial cracks; intended visual gradient achieved. Use magnified inspection or side lighting.

  • Typical errors, diagnostics & recovery paths

      • Under-strike (too shallow): crater too small / no burr → correction: increase force slightly, keep angle vertical. If repeated under-strikes produced, check backing rigidity.
      • Over-strike (excessive force): flange tearing, metal thinning or cracks → correction: stop, anneal area if alloy allows, reduce force; use lighter punch or different punch geometry.
      • Angular misalignment: elongated or asymmetric crater → correction: re-align punch with jig or guide; retrain elbow/shoulder support. Simulated detection: angle deviation beyond semantic threshold triggers corrective prompt.
      • Irregular spacing: visible rhythm break → correction: re-scribe pattern lines or use template; practice tempo with metronome to stabilise rhythm.