Lesson 3 – Deterministic Polishing Theory

What You Will Learn

Define deterministic polishing.
Explain the purpose of a removal function.
Describe how dwell time controls material removal.
Understand the role of metrology in process control.
Explain why deterministic polishing improves manufacturing accuracy.

What Is Deterministic Polishing?

Deterministic polishing is a manufacturing process that predicts how much material will be removed before polishing begins. Instead of relying on operator experience, the process uses measurements, mathematical models, and CNC machine control to produce consistent results. The goal is simple: remove exactly the amount of material needed to bring the optical surface within specification. Because every polishing cycle is based on measured data, the process is repeatable and produces predictable results from part to part.

Measuring Before Polishing

Every deterministic polishing cycle begins with metrology. Instruments such as interferometers or profilometers measure the current surface and compare it to the desired optical prescription. The resulting error map shows exactly where material must be removed. High spots require additional polishing, while areas already within tolerance receive little or no correction. Accurate measurements are essential because the polishing program is built directly from this data. Poor measurements lead to poor polishing results.

Understanding the Removal Function

Every polishing tool removes material in a predictable pattern called the removal function. This pattern depends on several factors, including tool size, polishing pressure, abrasive, speed, and polishing pad material. Once the removal function has been measured, software uses it to calculate how long the polishing tool should remain at every point on the surface. A stable removal function is one of the keys to successful deterministic polishing. If the polishing tool changes because of wear or contamination, the software predictions become less accurate.

Dwell Time and Material Removal

One of the simplest ways to control polishing is by changing dwell time. Dwell time is the amount of time the polishing tool remains over a particular location. If the tool spends more time in one area, more material is removed. If it moves quickly across another area, less material is removed. By changing dwell time across thousands of locations, the CNC machine gradually corrects the optical surface until it closely matches the desired shape. This process is repeated until the required accuracy is achieved.

Interactive Removal Function Simulator

The Removal Function Simulator lets you adjust dwell time and observe how it changes the amount of material removed from the surface. As you experiment, you’ll see how small changes in polishing time affect the final optical figure. This exercise demonstrates one of the most important principles of deterministic polishing: accurate control of material removal depends on understanding the removal function.
Interactive Removal Function Simulator

Interactive Removal Function Simulator

Adjust dwell time and watch the simulated polishing pass reshape the optical figure.

Set the Polishing Pass

Dwell Time 5.0 s

0.5 s20 s

Removal Width Medium

NarrowWide

Correction Position Center

LeftRight

Watch the response: Greater dwell time increases removal depth. A pass that is too long can create an overcorrection.

Live Process Display

Peak Removal 0.55 µm

Correction Volume 0.38 mm³

Final Figure Error 0.31 µm

Removal Footprint Current polishing pass

Figure Correction Before versus after

Before

Removed

After

The current dwell time produces a controlled correction that reduces the high spot without overcorrecting it.

Deterministic polishing combines accurate measurements with predictable material removal to manufacture complex optical surfaces. By controlling dwell time and following carefully calculated toolpaths, manufacturers can produce optics with exceptional precision. The next lesson introduces Preston’s Law and explains how polishing pressure and relative velocity determine material removal rates.

Introduction to Subaperture Polishing

Curriculum

Lesson 3 – Deterministic Polishing Theory

What You Will Learn

What Is Deterministic Polishing?

Measuring Before Polishing

Understanding the Removal Function

Dwell Time and Material Removal

Interactive Removal Function Simulator

Interactive Removal Function Simulator

Set the Polishing Pass

Live Process Display

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