Edger Familiarization & Pattern/Tracer Operation
Objective. Students will trace a frame shape using a manual or electronic tracer, store or cut the pattern, and verify that the traced shape matches the frame's eye size and DBL within ±0.5 mm.
This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.
VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.
Edger Familiarization & Pattern/Tracer Operation
Why Accurate Tracing Matters
Before an edger can grind a lens blank to fit a frame, it needs an exact map of the frame's opening — shape, size, and curvature. That map comes from the tracer. If the traced shape is off by even a millimeter, the finished lens may rock in the frame, leave gaps at the rim, or crack a rimless drill-mount. Accurate tracing protects the patient, protects expensive lens blanks, and protects your reputation as a technician. The ABO exam tests this knowledge directly, so mastering the tracer is foundational.
Key Frame Measurements
Two dimensions define a frame's optical geometry:
- Eye size (A measurement): the horizontal width of one lens opening, measured at its widest point.
- DBL (distance between lenses): the shortest distance between the two lens openings across the bridge.
These are stamped inside most frames in the format eye size ☐ DBL, for example 52 ☐ 18. After tracing, your stored shape must match both numbers within ±0.5 mm. Anything outside that tolerance means re-trace before you touch a lens blank.
The Electronic Tracer
An electronic tracer uses a stylus or probe that follows the groove (bevel channel) of the frame front while sensors record the three-dimensional path. The tracer converts that path into a digital shape file stored in the edger's memory. Most modern systems are interfaced directly: you trace at the tracer station, the shape transmits wirelessly or by cable, and the edger's display shows the outline ready for lens layout.
Tracing steps (electronic):
1. Clean the frame lens opening with a lint-free cloth. Debris in the groove can deflect the stylus.
2. Secure the frame in the tracer's clamp with the frame front level and the lens opening centered over the stylus port.
3. Lower or insert the stylus so it seats fully in the bevel groove.
4. Start the trace cycle — the probe travels around the inside of the frame opening automatically.
5. Inspect the on-screen shape. It should look like the frame opening without flat spots or spikes.
6. Read the displayed A measurement and DBL. Compare to the stamped values and to your own millimeter-ruler measurement. Both must be within ±0.5 mm.
7. Save the shape to the job number you created in the edger's job setup screen.
For rimless frames, most tracers use a demo lens or a factory template rather than a groove. Handle demo lenses carefully — they are brittle and the shape is the only reference you have. Some rimless systems allow direct tracing of the demo lens edge.
Manual Pattern Cutters
Older labs and some training environments use a manual pattern cutter. The instructor places a template (a thin plastic pattern) into the cutter, which trims it to the exact frame shape using a rotating drum and a metal template tracer arm. The resulting plastic pattern mounts in the edger's pattern holder and guides the grinding head mechanically rather than digitally. Even if your lab uses electronic tracing day-to-day, understanding the manual process shows you how shape data controls the edger — the logic is the same.
Label every pattern with: patient name or job number, frame brand/style, eye size, and date. File patterns in labeled envelopes or a pattern rack for the edging labs that follow.
Entering Job Data into the Edger
After the shape is stored, you enter the prescription and layout data into the edger's job setup screen. The critical fields are:
- Sphere, cylinder, axis — from the prescription.
- Add (if progressive or bifocal).
- Monocular PD (right and left separately) — calculated from the binocular PD on the fitting card.
- Optical center height (OC height) — the vertical position of the optical center relative to the datum line (geometric center line) of the lens opening.
- Lens material and coating type — tells the edger which wheel speed and coolant flow to use.
Always have a peer reviewer confirm every entry before grinding begins. One transposed digit — for example, entering a cylinder axis of 081 instead of 018 — can produce a lens that blurs the patient's vision even if edged perfectly.
Safety Rules at the Edger
- Eye protection (safety glasses or goggles) is required whenever the edger is running. The grinding wheel throws water-borne glass and plastic particles.
- Never reach into the edging chamber while the wheel is spinning. Wait for the cycle to end completely.
- Keep hands away from the stylus while the tracer is cycling.
- Report coolant leaks immediately — wet floors cause slips.
- Verify the lens blank is correctly chucked and the block is secure before starting a cycle. A dropped lens blank can shatter.
- Never start grinding without instructor or supervisor sign-off on the job data screen. Patient safety depends on correct prescription data being verified before material is removed.
Verification Before Grinding
The completion check for this lesson has two parts: (1) traced eye size and DBL must match reference measurements within ±0.5 mm on all three frames, and (2) job data must be confirmed error-free by instructor sign-off. Nothing runs until both checks pass. This is not a formality — it mirrors real-lab quality control and the professional standard the ABO credential represents.
Key terms9
Worked examples4
- Step 1 — Check eye size: 54.0 − 53.2 = 0.8 mm difference. The tolerance is ±0.5 mm, so 0.8 mm exceeds the limit.
- Step 2 — Check DBL: 17.4 − 17.0 = 0.4 mm difference. This is within ±0.5 mm, so DBL is acceptable.
- Step 3 — Conclusion: The eye size is out of tolerance; the DBL is within tolerance. The frame must be re-seated and re-traced before proceeding.
- Step 1 — Recall that binocular PD is the total distance from right pupil to left pupil, passing through the midpoint of the nose.
- Step 2 — For a symmetric patient, each monocular PD = binocular PD ÷ 2.
- Step 3 — 64 ÷ 2 = 32 mm.
- Step 4 — Enter 32 mm as the right monocular PD (OD) and 32 mm as the left monocular PD (OS) in the edger job setup screen.
- Step 1 — Calculate the datum line height from the bottom of the lens opening: 38 ÷ 2 = 19 mm.
- Step 2 — The OC is to sit 4 mm above the datum line, so OC height from the bottom = 19 + 4 = 23 mm.
- Step 3 — Enter 23 mm as the OC height in the edger's job setup screen.
- Step 4 — Verify: the fitting card segment height of 18 mm is below the OC height of 23 mm, which is consistent for a progressive design where the fitting cross sits above the near zone.
- Step 1 — Subtract the smaller value from the larger: 46.3 − 46.0 = 0.3 mm.
- Step 2 — Compare to the ±0.5 mm tolerance: 0.3 mm < 0.5 mm.
- Step 3 — The difference is within tolerance, so the trace is acceptable for this measurement.
The math in this lesson1
Materials: Electronic frame tracer (one per station), semi-automatic or automatic edger with digital interface, manual pattern cutter (demonstration), frame set (three styles including rimless), PD ruler, sample fitting cards, edger operation manual
Check: Traced eye size and DBL match instructor's reference measurements within ±0.5 mm on all three frames; job data entered into edger is confirmed error-free by instructor sign-off before any grinding begins.
Practice check8
Answer each question, then check it. Nothing is recorded; this is your own practice.
