Understanding Precision
Finishing Processes

Precision isn’t achieved by technology alone – it’s driven by expertise.

At SAGA Engineering, decades of experience across materials, industries, and applications enable us to craft tailored, end-to-end surface finishing solutions using both conventional and super abrasive technologies, industries, and applications enable us to craft tailored, end-to-end surface finishing solutions using both conventional and super abrasive technologies.

What is Pitch Polishing?

Pitch polishing is a concept similar to the lapping process, except that it uses a pitch plate and much finer polishing media.

SAGA Engineering manufactures and uses single-sided polishing machines for optical components (e.g. optical flats, filters, prisms) and for refurbishing customer optical parts.

Typical component sizes range from 20 mm to 600 mm in diameter (though other sizes may be possible depending on machine and component).

Significant skill is required to achieve tighter tolerances of surface flatness, roughness, parallelism, and cosmetic finish than what is usually attainable via conventional lapping with coarser abrasives.

The pitch polishing process can yield very high surface quality, with typical Ra < 5 Å.

Pitch plates are semi-fluid surfaces (consistency similar to bitumen/asphalt), manufactured. Concentric, spiral, radial, or cross-hatch grooving may be hand-cut or machine-cut to allow abrasive slurry flow under the parts, improving polishing uniformity.

SAGA Engineering Pitch Polishing Machines / Systems?

SAGA Engineering offers a full line of pitch polishing machines and systems covering low-volume job shops to high volume industrial production.

Refurbishing and upgrade services are also offered for existing optical polishing machines. Typical optical polishing manufacturing limits on their (converted) “48 Air Bearing Machine” configuration:

Parameter	Value
Diameter	≤ 300 mm optical reference flat
Flatness	λ/20
Surface Roughness	≥ 5 Å rms
Cosmetic	Scratch/dig from 60-40 to 10-5

Pitch polishing is a concept similar to the lapping process, except that it uses a pitch plate and much finer polishing media.

What is Lapping?

Lapping is an averaging material removal process using loose abrasive particles (in slurry form) to modify the surface of a workpiece.

How Lapping Works

One or more parts are processed together in a batch.
Abrasive particles (e.g. Al₂O₃, SiC, diamond) are mixed with a liquid (oil or water) to form a “slurry,” acting as the cutting medium.
The slurry is placed on a rotating “lap plate.” The parts are held in retaining rings or carriers and dragged across the lap plate surface.
Highest material removal occurs where high points of the part surface contact the lap plate. The goal is to flatten and smooth surfaces.
The processed surface shows a matte (dull, non-reflective) appearance with multidirectional marks; very light micro-scratches may appear depending on abrasive size.

Factors Affecting Lapping

Material of the part: soft vs hard, brittle, exotic materials
Lap plate speed: must avoid vibration or displacement of the part
Down pressure: too high pressure (e.g. > 3 psi in conventional lapping) may “wipe” the part; for fine finishes, 2 psi or less is often recommended
Type, size, and friability of abrasive: Al₂O₃, SiC, B₄C, diamond, etc.
Lap plate flatness
Method of slurry charging / conditioning
Temperature and thermal behavior of the plate

Fundamental Theory & Process

Lapping is comparatively gentle (low pressure, slow speed, low removal rates).

The parts are placed on the lap plate (via carriers or rings), which has a film of slurry. The parts never directly touch the bare plate.

Abrasive particles in the slurry transfer cutting energy; concurrently, the lap plate wears. Conditioning rings help adjust radial positions to maintain flatness. The result is material removal, improved surface finish, and geometric flattening.

Lapping is an averaging material removal process using loose abrasive particles (in slurry form) to modify the surface of a workpiece

What is Polishing?

The abrasive is often used in conjunction with a pad (so it’s not always a loose-abrasive process). The pad itself is softer than the part.

Very little material is removed. The preceding surface must already be high quality (often lapped) before polishing.

Applications & Functions of Polishing

Enables sealing in high-pressure gas/liquid environments
Cosmetic surface finishes
Enables optical flatness measurement
Reduces surface and subsurface damage
Improves uniformity for epitaxial or deposited layers
Produces sharper cutting tool edges

Types / Modes of Polishing & Deburring

Fixed-abrasive films (i.e. captured abrasive) or lubricated systems

Soft or hard pads with conventional or special abrasive slurries

Pads using diamond slurry (water- or oil-based)

Hard pads with diamond compound + lubricant

Diamond slurry polishing using composite, metal, or other plates

Polishing is meant to produce a smoother, often reflective, surface by removing very small amounts of material (microns or sub-micron scale).

What is a Micron?

Because lapping and polishing are classified as micro-machining processes designed to produce low surface roughness and exceptional flatness, performance discussions are generally limited to the finer end of the scale.

However, not all lapping applications aim for ultra-precision. In many cases, the process simply ensures co-planarity — creating a uniform reference surface for subsequent manufacturing steps such as coating, bonding, or machining.

It’s important to note that firm capability data cannot be universally applied without reference to a specific material and process. Even when two components use the same abrasive and material, the results can differ significantly due to variations in process parameters such as pressure, plate condition, slurry composition, and dwell time. These interacting variables influence the final surface finish and flatness achieved.

Lapped Surface Roughness Capability

Under optimal conditions, SAGA Engineering’s lapping systems can routinely achieve surface roughness values of 1 micro-inch (0.0254 micron) or finer on dense, hard metals using very fine aluminum oxide abrasives.

This represents an industry-standard benchmark — sometimes referred to as a “trade show answer” providing a general indication of achievable performance rather than a specification guarantee, since every application is unique.

Units of Measurement Used to Define Flatness

One of the primary purposes of lapping is to produce a surface whose deviation from a true plane remains within a specified tolerance. In geometric terms, a plane is a two-dimensional surface defined by three points; flatness measures how far the real surface deviates from this ideal plane.

Design engineers can specify flatness using several measurement conventions, including:

Linear units:
Example – 0.0000116 in = 0.2946 µm
Light Band (λ):
Wave: equals two light bands (½ wave = 1 light band)
Fringe: equivalent to one light band

Different industries adopt different terminology — for example, optical manufacturers often specify flatness in light bands or waves, while mechanical engineers may use microns or micro-inches.

Understanding these units and their conversions is essential in multi-disciplinary precision work.

Flatness Measurement

Flatness can be measured using a variety of techniques, depending on the required resolution:

Dial Indicators:
A simple dial indicator can detect deviations from a reference plane; however, even high-precision versions resolve only about 0.000050 in (1.27 µm). This is insufficient for applications requiring tolerances below two light bands.
Optical Flat & Interferometer:
In advanced precision environments, SAGA Engineering employs optical flats and interferometers — instruments capable of resolving to fractions of a light band. These tools operate on the principle of Newton’s Fringes, where interference between monochromatic light waves produces a pattern of dark bands corresponding to variations in surface flatness.

This optical method enables precise visualization and quantification of deviations at the sub-micron level, ensuring that every SAGA-engineered surface meets the most demanding specifications

A micron (µm) is one millionth of a meter — the scale at which SAGA Engineering achieves precision and surface perfection.

What is Fine Grinding?

Instead of slurries, it uses diamond or CBN abrasives embedded in resin, metal, or vitrified bonds.

Fine grinding machines often adopt planetary kinematics similar to lapping machines but with the advantages of grinding technology.

Advantages of Fine Grinding vs Lapping

Feature	Traditional Lapping	Fine Grinding
Abrasive medium	Loose abrasive slurry	Fixed-abrasive (diamond/CBN) plates
Cleaning / swarf	Generates swarf, requires cleaning	Cleaner, minimal swarf disposal
Speed	Slower	Typically 3–20× faster
Finish / flatness	Good, but slower	Comparable flatness/roughness with improved throughput

SAGA Engineering’s fine grinding line would employ superabrasive wheels (diamond / black / amber CBN) with customized bond types. Wheels are also adaptable to various machine brands.

Grinding surface pattern, abrasive size, bond type, and thickness are customized per application. Vitrified bonds are often preferred for stability and flatness control.

Fine grinding (also called flat honing) is a process using fixed-abrasive (rather than loose) elements to achieve precision finishing.