Superfinishing and Isotropic Superfinishing

Mechanical finishing · Mechanical

Superfinishing removes grinding peaks from bearing and gear surfaces with very fine abrasive action.

CNC machining CastingHigh cost $$$$Unchanged

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Reference page — Superfinishing is not in the instant-quote configurator. Upload the part, name the finish in the notes, and an engineer quotes it with the part.

Superfinishing and Isotropic Superfinishing on a machined part

What is Superfinishing?

Isotropic or chemically accelerated mass-finishing systems, often described as REM-class processes, reduce directional texture across complex parts.

How it works

Conventional superfinishing oscillates a fine abrasive stone, often in the 600–1200 grit class, against a slowly moving journal or race under light pressure. Isotropic systems use nonabrasive or fine media with chemistry that forms a soft conversion layer which is repeatedly removed from high points. Typical finished Ra is about 0.02–0.20 µm (0.8–8 µin), reducing asperity contact while changing macrogeometry far less than grinding. Measure the final texture under ASME B46.1 or ISO 21920.

Why specify it

Produces Ra about 0.02–0.20 µm (0.8–8 µin)
Reduces friction and break-in wear
Removes directional grinding peaks
Improves bearing-area ratio

Where it falls short

Does not correct major form error
Specialist equipment and chemistry increase cost
Chemically accelerated cycles require alloy validation
Edge protection may be needed

Superfinishing at a glance

Superfinishing is a middle-of-the-range finish; its best score is cosmetic quality (65 of 100), at a high cost. It adds little corrosion protection. Surface hardness is not rated: the finish leaves the part's own surface.

Corrosion protectionMinimal5 / 100

Surface hardnessNot rated—

Cosmetic qualityGood65 / 100

LubricityGood55 / 100

Relative costHigh75 / 100

Each score is 0–100 against every finish in this catalog. Corrosion comes from salt-spray life (ASTM B117, log scale) and hardness from the finish layer's Vickers or pencil hardness; cosmetic, lubricity and cost are FabDigit's engineering assessment. Economy on the radar is the inverse of cost.

Superfinishing key numbers

Typical values from the governing specifications and shop practice; bars are this finish against the highest value among mechanical finishing finishes.

Thickness0 µm0 mil

Thickness: No coating; typical resulting Ra 0.02–0.20 µm (0.8–8 µin).
Electrical: Unchanged
Appearance: Smooth low-gloss to reflective surface with greatly reduced directional lay.

Specifications for Superfinishing

The documents a drawing cites to define this finish, with the Type / Class rows that apply. Each links to a page explaining the standard.

Drawing call-out

SUPERFINISH BEARING JOURNAL Ø25 TO Ra 0.10 µm MAX AFTER GRINDING; MAINTAIN DIAMETER TOLERANCE AND ROUNDNESS 0.003 mm

Which materials take Superfinishing?

Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library.

Material family	Verdict	Notes
Stainless Steel	Yes	Suitable with alloy-compatible abrasive or chemistry.
Steel	Yes	Primary substrate for gears, races, and journals. Validate case-hardened stock removal limit
Magnesium Alloy	With care	Possible with non-sparking media and fire-safe dust control.
Nickel Alloy	With care	Specialist process development is required.
Titanium	With care	Requires specialist chemistry and hydrogen-control review.
Zinc Alloy	With care	Soft die-cast zinc cuts quickly and can embed media.
Aluminum	Limited	Soft aluminum embeds abrasive and does not hold a bearing-race superfinish.
Brass	Limited	Soft brass smears under stone or tape superfinishing.
Copper Alloy	Limited	Soft copper smears; not a typical superfinish substrate.
Polymer	No	Superfinishing is for hard metal journals and races, not polymers.

How Superfinishing is applied, and what it does to the part

1Pre-grind to geometry
2Select stone or isotropic chemistry and media
3Superfinish under controlled load
4Neutralize and clean if chemical
5Inspect Ra form and material ratio

Dimensions	Removes microscopic peaks with little macrogeometry change, but stock removal and edge effects must be qualified on precision parts.
Build-up per side	0 µm — No buildup; microscopic peaks are selectively removed.
Masking	Usually needed. Protect edges, fits, threads, and surfaces not intended for chemically accelerated treatment.
Electrical	Unchanged
Appearance	Smooth low-gloss to reflective surface with greatly reduced directional lay.
Added lead time	3–10 working days on top of the bare part

Design rules for Superfinishing

What to decide on the drawing before the part goes to the finisher.

Finish geometry before superfinishing.The process removes peaks but not major form error.
Specify Ra and material-ratio needs.Friction depends on more than average roughness.
Validate alloy chemistry.Accelerated isotropic processes are chemistry-sensitive.
Protect sharp edges and threads.Mass action can alter exposed features.

Superfinishing versus the alternatives

Finishes engineers weigh against Superfinishing, and when each wins.

Finish	Corrosion	Hardness	Cosmetic	Cost	Choose it when
Superfinishing this page	5	—	65	$$$$	—
Lapping Superfinishing vs Lapping →	0	—	70	$$$$	when flatness of a planar face is primary
Honing Superfinishing vs Honing →	0	—	25	$$$	when a bore requires cross-hatch and geometric correction

SuperfinishingLapping

The radar overlays Superfinishing with Lapping, its most common alternative — chosen when flatness of a planar face is primary. Scores in the table are 0–100 across every finish in the catalog.

Cost, lead time and compliance

Relative cost

Superfinishing and Isotropic Superfinishing is a high-cost finish ($$$$): more expensive than about 80 % of the finishes FabDigit quotes.

Finishing is priced per part with a lot minimum, from FabDigit's own China-side rates. The exact figure appears on the instant quote once the part is uploaded.

Lead time and compliance

Added lead time	3–10 working days
RoHS	Compliant
Notes	Chemically accelerated systems require controlled bath, neutralization, and waste treatment.

What Superfinishing is used for

Bearing races
Crankshaft journals
Transmission gears
Aerospace rolling contacts

Superfinishing — frequently asked

what is isotropic superfinishing

It removes directional machining peaks to create a more uniform low-roughness surface. Chemically accelerated mass-finishing variants repeatedly form and remove a soft surface layer at high points.

what Ra does superfinishing achieve

Typical production results are about Ra 0.02–0.20 µm (0.8–8 µin). The incoming grind, abrasive, time, load, and alloy control the result.

what is REM finishing

REM is a trademark associated with proprietary chemically accelerated isotropic finishing processes. It is often used informally as a process class, but drawings should identify the approved supplier process and measurable result.

superfinishing vs polishing

Polishing often prioritizes gloss and can change edges and form. Superfinishing targets load-bearing peaks and friction while preserving previously ground macrogeometry.

does superfinishing improve gear life

Reducing asperity peaks can lower friction, scuffing risk, and break-in debris. Life improvement depends on load, lubrication, hardness, geometry, and the verified final texture.