Overview

A code wheel etching process makes the slotted discs used in optical and magnetic encoders by dissolving radial slots and reference marks out of thin metal, rather than stamping or laser-cutting them. Stainless steel 304/316L/430 and nickel alloys 0.10–0.50 mm thick are laminated on both faces, exposed with the slot pattern and developed, then sprayed with ferric chloride so hundreds of radial windows open at once with clean, burr-free walls. Because every slot on the disc is etched in the same bath, the radial slot width and angular pitch stay uniform from the hub to the rim.

For an encoder disc the numbers that set resolution and accuracy are radial slot width and concentricity, and code wheel etching controls both from the artwork stage. Side etch is compensated at roughly 0.6–0.8 × thickness per side so a 0.10 mm slot holds ±0.01 mm, while the pattern is registered to the centre bore to keep runout low. The chemical route leaves no burr or heat-affected edge to scatter the optical beam, and the same film repeats the slot geometry identically across a production batch.

Parameter Window

• Available Materials: stainless steel 304/316L/430, nickel 200, copper C1100
• Material Thickness Range: 0.10–0.50 mm (0.15–0.30 mm typical)
• Tolerance: radial slot width ±0.01 mm, angular pitch ±0.05°, concentricity ≤ 0.02 mm to bore
• Minimum Feature: 0.08 mm slot width, 0.10 mm web at 0.15 mm stock, 200–2000 lines per revolution
• Surface Options: passivated, blackened/matte anti-reflective, electropolished, hub-bonded, protective liner
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork & Registration — Generate the radial slot pattern from the line count and reference the datum to the centre bore, compensating side etch at 0.6–0.8 × thickness per side.
2. Material Selection — Choose 304 for general use or 430 for magnetic encoders, and verify thickness, flatness and inclusion level.
3. Cleaning & Lamination — Laminate dry-film resist on both faces so narrow slots and the index mark are fully protected.
4. UV Exposure — Expose the radial artwork with the bore as datum, checking that the pattern is truly concentric on the sheet.
5. Development — Wash out unexposed resist to open every slot, then inspect the narrowest webs under magnification.
6. Etching — Spray ferric chloride to cut the slots through, holding dwell so slot width and wall verticality stay on target.
7. Stripping & Finishing — Strip resist, neutralize, then blacken or passivate for low reflectivity and bond to the hub if required.
8. Inspection & Packaging — Verify slot width, angular pitch and concentricity optically, then pack flat between rigid liners.

Core Advantages

1. Uniform radial slot width: All slots etch in one bath, so width holds from hub to rim and resolution is even.
2. Low runout to bore: Artwork registered to the centre bore keeps concentricity within 0.02 mm for stable readback.
3. Burr-free optical edges: Chemical removal leaves no burr or recast to scatter the beam or flicker the signal.
4. Fine line counts: 0.08 mm slots and up to 2000 lines per revolution are practical on thin stock where stamping would distort.
5. Batch-to-batch repeatability: One film reproduces the slot geometry identically, so encoder output matches across lots.
6. No die, fast line-count changes: code wheel etching changes a film to move the line count, so a new resolution is sampled in days without a stamping die.

Typical Applications

• Incremental optical encoders: Slotted 304 discs that generate A/B pulses for motor feedback.
• Absolute encoder discs: Multi-track patterns with an index slot for position readback.
• Magnetic encoder wheels: 430 stainless discs where slot geometry modulates the magnetic field.
• Servo and robotics: High-line-count discs for precise speed and angle control.
• Metrology and rotary tables: Reference discs with tight concentricity for calibration.
• Consumer and appliance knobs: Low-cost slotted wheels for volume control and menu selection.

Design Notes & Process Considerations

1. Datum to bore: Reference the slot pattern to the centre bore, not the outer edge, since concentricity drives signal quality.
2. Slot width versus thickness: Keep slot width at least 0.8 × thickness, or webs bow and the duty cycle drifts.
3. Angular pitch: State line count and allowed angular error, and let a test disc confirm the accumulated pitch error.
4. Surface reflectivity: Specify blackened or matte finish when an optical reader is used, to suppress stray reflection.
5. Flatness and handling: Discs are thin and wide; call out flatness per 100 mm and rigid packaging to avoid bending.
6. Burr and cleanliness: code wheel etching should ship burr-free and particle-free, because a single clogged slot drops a pulse.