Choosing a Process
Last updated September 26, 2026
OpusFab offers five processes: CNC Machining (milling), CNC Turning, SLA resin printing, SLS nylon printing, and metal 3D printing (DMLS/SLM). There is no single best process. The right choice depends on what your part needs to do. Work through the five questions below, then confirm against the comparison table.
1. What is the geometry?
- Mostly round, symmetrical around one axis (shafts, pins, bushings): CNC Turning.
- Prismatic with flat faces, pockets, and holes (brackets, plates, housings): CNC milling.
- Complex organic shapes, internal channels, lattices, or interlocking parts: SLS in plastic or metal printing in metal. Additive processes build layer by layer, so tool access is not a constraint.
- Fine detail and smooth surfaces (small text, sharp edges, cosmetic faces): SLA.
2. Does the part need to perform like the final product?
If the part will take real mechanical load, heat, or chemical exposure, material properties matter more than speed:
- CNC parts are cut from solid stock, so strength matches the raw material exactly.
- SLS nylon is tough enough for many functional uses, clips, brackets, ducts, but printed parts can have directional weaknesses along layer lines.
- SLA resin is more brittle and best kept to visual or light-duty parts.
- Metal printing produces dense metal parts for demanding applications where machining cannot reach the geometry.
Early concept models and fit checks do not need production-grade strength, so SLA or SLS will usually get you an answer faster and cheaper.
3. How tight are your tolerances?
- CNC machining holds ±0.05mm standard on the platform. Use it for precision fits and mating features.
- SLA holds ±0.5mm standard. SLS and metal printing are in a similar printed-part range, with some shrinkage as parts cool.
If only a few features are critical, one common approach is printing the part and finish-machining the precision interfaces. See Tolerances explained.
4. How many parts do you need?
Instant quotes cover 1 to 100 units per part. Within that range:
- One to ten units: 3D printing usually wins on cost and speed because there is no setup or tooling.
- Ten to one hundred units: compare directly. CNC unit prices drop with quantity, and for simple geometries machining can undercut printing even at low volumes.
- Above 100 units, or multi-part assembly files: request a custom quote from the upload or edit screen.
The fastest way to decide is to upload the STEP file once and switch the process in the quote editor to compare prices side by side.
5. What is the budget and timeline?
3D printing has little setup cost, so single parts are cheap and fast. CNC costs more per part at quantity one because of programming and fixturing, but scales well. Metal printing is the most expensive option per part and is justified mainly by geometry that cannot be machined. Production speed (Standard or Expedited) is a batch-wide choice in the totals bar; see Production speed.
Comparison table
| Process | Type | Typical materials | Surface | Standard tolerance | Strength | Best for |
|---|---|---|---|---|---|---|
| CNC Machining (milling) | Subtractive | Aluminum, steel, plastics | Smooth, tool marks | ±0.05mm | Full stock strength | Functional, precision prismatic parts |
| CNC Turning | Subtractive | Aluminum, steel, plastics | Smooth, tool marks | ±0.05mm | Full stock strength | Shafts, pins, round parts |
| SLA | Additive (resin) | Standard Resin | Smoothest of printed | ±0.5mm | Low, brittle | Visual prototypes, fine detail |
| SLS | Additive (nylon powder) | Nylon | Grainy matte | ±0.5mm range | Good, tough | Functional plastic parts, complex geometry |
| Metal printing (DMLS/SLM) | Additive (metal powder) | Aluminum, steel, titanium alloys | Rough, often finish-machined | Looser than CNC | Near full metal strength | Complex metal parts CNC cannot reach |
Material lists change over time; check the dropdowns in the quote editor for the current live list, and see Materials overview.
Still not sure?
Upload the part and let the quote do the comparison: prices and lead times update instantly when you change the process. Automatic DFM analysis also flags geometry that a chosen process cannot make, with a “DFM Warning” pill in the quote table. See Understanding your quote and DFM overview.