±0.01mm across 96 slits / Measured on optical comparator
Optical Components | Encoder Disk | Laser Micro Cutting & Etching
Optical Encoder Disk
Project Brief
A metal optical encoder disk with radial slits and thin retaining ribs. The slits chop light as the disk spins; the ribs hold the ring together. Slit width is 0.15 mm, rib width is 0.1 mm. If either dimension drifts or the edge is not clean, the encoder signal gets noisy.
We cut these from 0.2 mm stress-relieved 304 stainless steel shim. The material is soft and warps easily under heat, so the cutting sequence matters more than the laser power itself.
Production Problem
They had been running these through a stamping die. After roughly 8,000 pieces, the die wore enough that slit width spread from 0.15 mm to 0.18 mm. The ribs also thinned unevenly. They tried chemical etching next; the edges came out rough with micro-undercuts and burrs that scattered light. Their QC rejected batches because the optical signal-to-noise ratio dropped below their spec.
They sent us a bag of rejected parts and asked if laser could hold the geometry without the tooling wear or the edge fuzz.
Process Development
First run: we cut one slit at a time in a clockwise spiral. The disk bowed by 0.05 mm because heat pooled on one side. We scrapped the batch.
Second run: we switched to a radial alternating pattern—cut one slit at 12 o'clock, then 6 o'clock, then 3 o'clock, then 9 o'clock, working outward. This balanced the heat input enough that flatness stayed within 0.01 mm across the full 80 mm diameter.
We also had to slow the feed rate for the last 2 mm of each slit. If we ran the same speed all the way through, the laser overshot the end point and left a tiny hook that caught light. Dropping the feed to 30 % for the exit fixed it.
After cutting, we passivate in citric acid for 20 minutes to remove the micro-slag layer, then blow out the slits with dry nitrogen. No mechanical deburring—we tried that once and it rounded the slit corners, which changed the optical duty cycle.
These slit, rib, and flatness constraints inform custom metal encoder-disk design for optical sensing assemblies.
Verification Results
Minimum 0.08mm after cut / No breaks in 10k+ cycles
30× inspection, no visible edge break / Flat within 0.005 mm
Finished Part
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