As-machined surface finish

As-Machined Aluminum Finish

As-machined means the part ships exactly as it leaves the CNC — cleaned and deburred, but uncoated. It's the fastest, cheapest, and most dimensionally honest finish there is.

The engineering question isn't whether as-machined looks good enough; it's whether your part's environment lets you keep the advantages of bare aluminum.

Upload CAD for Quote Talk to an Engineer on WhatsApp

What this finish is

Bare metal, controlled — not unfinished

An as-machined finish is defined by what we control at the spindle: surface roughness from toolpath strategy, uniform edge breaks from planned deburring, and cleanliness from washing and packaging. There is no coating step — the surface you see is the cut aluminum itself, with faint, regular tool witness lines.

Bare aluminum self-passivates instantly with a thin natural oxide, which protects it adequately in dry indoor service. What that oxide doesn't do is resist fingerprints, salt, or repeated handling — which is exactly the boundary where anodizing starts earning its cost.

Surface roughness
Ra 1.6 µm standard on milled faces; Ra 0.8 µm on request for functional surfaces.
Dimensional impact
Zero — the only finish that adds nothing to your tolerances.
Conductivity
Full electrical and thermal conductivity at every surface.
Lead time & cost
The fastest and cheapest option: no finishing house in the loop.
Appearance
Bright metallic with visible, regular machining marks; not color-stable over years of handling.

Benefits

Why engineers specify as-machined

The right reasons to skip coating are functional — dimension, conductivity, schedule — not just budget.

Zero dimensional growth

H7 bores and press fits ship exactly as machined — no film-thickness compensation, no post-coat gauging.

Full conductivity

Grounding, EMI bonding, and thermal interfaces work at every face without masking plans.

Lowest cost and fastest delivery

Removing the finishing step removes days of lead time and a line item from the quote.

Re-machinable and probe-able

Reference surfaces stay measurable and can be re-cut at rebuild — why fixture datums ship bare.

Nothing to peel or chip

No coating means no coating failures — relevant for parts flexed, pressed, or re-worked in service.

Honest prototyping

Fit-check prototypes in bare metal validate machined dimensions before finishing enters the equation.

Typical applications

Where as-machined parts belong

Bare aluminum is the standard choice anywhere the part lives indoors, gets handled rarely, or must stay exactly the size we cut it.

Fixtures and tooling datums

Reference faces on fixture plates and inspection tooling stay uncoated so they can be probed and re-certified.

Internal mechanism parts

Spacers, blocks, and brackets inside dry enclosures — coating adds cost without adding life.

Prototypes and fit checks

First articles and EVT hardware where dimensional truth matters more than looks.

Grounding and RF hardware

Bonding surfaces and RF test hardware that need bare-metal conductivity everywhere.

Thermal interfaces

Heat sink bases and cold plate faces where any film adds thermal resistance.

Short-life production aids

Assembly aids and line tooling with service lives too short to amortize finishing.

Design considerations

Specifying as-machined correctly

The drawings that go wrong say 'no finish' and stop. These callouts make bare parts arrive the way you imagined them.

Specify Ra, not 'smooth'

Write Ra 1.6 (or 0.8 on functional faces). 'Good machined finish' means something different in every shop — a number is inspectable.

Call out the edge condition

'Break all edges 0.3–0.5 mm' turns deburring into a spec. Handled parts and seal paths deserve explicit edge callouts.

State cleanliness and preservation

Bare aluminum stains from fingerprints and coolant residue. Specify wash, gloves-only handling, and VCI or oiled packaging for storage.

Mark cosmetic faces anyway

Even bare parts have a show face. Identify it so we fixture and pack from the other sides.

Know the environment boundary

Dry indoor service: bare is fine for years. Humid, coastal, or handled daily: budget for clear anodize now rather than corrosion complaints later.

Plan for mixed finishing

Parts can ship bare now and anodize later only if dimensions were planned for it — say so at RFQ if a coated version may follow.

Compatible aluminum grades

How each alloy behaves left bare

Alloy chemistry decides both how good the machined surface looks and how long it stays that way.

Alloy	Suitability	Engineering notes
6061-T6	Excellent	Clean bright finish, good natural oxide — the standard bare-part alloy
7075-T6	Good indoors only	Crisp machined surfaces, but pits in humid air — don't ship it bare outdoors
2024-T351	Poor	Corrodes quickly bare; we plan chem-film or anodize on 2024 by default
5052-H32	Excellent	The one alloy that genuinely tolerates bare wet service — expect a duller machined finish
MIC-6	Excellent	Standard for tooling plate — matte grey factory faces often ship as-supplied

Comparing coatings instead? Return to the aluminum surface finishes hub or read the full anodized aluminum CNC machining guide.

Quote your as-machined aluminum parts

Send STEP and PDF with Ra, edge-break, and cleanliness callouts — or tell us the environment and we'll confirm bare is the right call. Engineering review within one business day.