As-machined vs as-printed: the default finishes

Every part needs a finish selection, but the most common choice is no finish at all. On OpusFab the default is called Raw (As-Machined) for CNC parts and As Printed for 3D printed parts. Both mean the same thing: the part ships with the surface the machine left on it, with no secondary processing.

Raw (As-Machined) for CNC parts

An as-machined part comes straight off the mill or lathe. The surface shows visible tool marks: fine, regular lines or arcs left by the cutting tool. Small burrs on edges are removed (deburring is part of standard production), but no polishing, blasting, or coating happens after that.

What to expect:

• Appearance: metallic, with visible tool paths. Flat faces often look quite clean; curved or pocketed surfaces show more marking.
• Feel: smooth enough to handle, but not a uniform texture.
• Dimensions: nothing is added or removed, so an as-machined part holds the tightest achievable tolerances. This matters if you are working to standard CNC tolerances.
• Corrosion: bare metal. Aluminium will oxidise slowly and can stain; steels can rust. For long-term protection, see Anodizing.
• Conductivity: the surface stays electrically conductive, which coatings like anodising would remove.

As Printed for 3D printed parts

An as-printed part comes off the printer with the surface the printing process produces. As Printed is currently the only finish option for 3D printed parts; what that surface looks like depends on the process:

• SLA resin: perfectly smooth with faint layer lines, the closest in feel to an injection moulded part. Usually slightly translucent unless the resin is opaque. See What is SLA 3D printing?
• SLS nylon: a grainy, matte, slightly porous surface from the powder bed, more textured than SLA, but the parts are generally stronger. See What is SLS 3D printing?
• Metal printing (DMLS/SLM): a rough, matte metallic surface with visible layer texture, rougher than a machined surface. See Metal 3D printing (DMLS/SLM)

Support contact points may leave small marks where the part was attached to the build platform or support structures.

When the default is fine

The default finish is the right call in more situations than you might think:

• Prototypes and test parts, where you are checking fit and function
• Internal or hidden components that nobody will see in the final assembly
• Structural brackets and fixtures inside enclosures
• Parts that need the tightest possible dimensions, since no coating adds thickness
• Anything you need as fast as possible, since no finishing step is added

When to move past the default

Secondary finishes currently apply to CNC machined parts. Choose one when the part needs one of these:

• A clean, uniform look: bead blast or sandblast hides tool marks and gives a consistent matte surface.
• Colour: anodising (aluminium) or powder coating.
• Corrosion resistance: anodising for aluminium, zinc or chrome plating for S45C/4140 steel, powder coating for a barrier layer on other metals.
• Wear resistance: PVD coating for a hard, thin surface.

Printed parts do not currently have secondary finish options; CNC machining and sandblasting of printed metal parts are planned down the track.

Cost and lead time

The defaults add zero cost and zero lead time. Every other finish adds both, since the part goes through an extra process after it is made. If you are unsure whether you need a finish, ordering the first prototype as-machined or as-printed is the fast, cheap way to find out: on CNC parts you can always add a finish on the production run.