Rapid Fabrication: Choosing a Method
Printing, laser cutting, machining, bending and casting compared, with a scored choice and cost against quantity.
The options at a glance
| Method | Speed | Cost | Good for | Limits |
|---|---|---|---|---|
| Cardboard, foam, wood mock-up | Hours | Lowest | Size, shape, layout, ergonomics (see Low-Fidelity Prototyping: Mock-ups and Models) | Not strong; not accurate |
| FDM 3D printing | Hours to a day | Low | Complex shapes, brackets, enclosures (see 3D Printing) | Layer lines; weaker across layers; ±0.1 to 0.3 mm |
| Resin printing | Hours to a day | Low to medium | Small, detailed, smooth parts | Brittle; messy post-processing |
| Powder printing (SLS, MJF) | Days (service) | Medium | Tough nylon parts, no supports, small batches | Rough surface; service only |
| Laser-cut sheet | Minutes to hours | Low | Flat parts, enclosures, plates and brackets (see Laser Cutting) | Flat only, unless joined or bent; kerf to allow for |
| CNC machining | Hours to days | Medium to high | Strong, accurate metal and plastic parts (see CNC Machining) | Set-up time; needs CAM skill |
| Sheet-metal bending | Days | Medium | Brackets and enclosures; strong | Bends need allowance; special tools |
| Silicone molding and resin casting | Days | Medium | Small runs of soft or detailed parts | Need a master part; fumes and mess |
| Breadboard / perfboard / dev boards | Hours | Low | Electronics proof of concept (see Electronics in a Prototype) | Unreliable contacts; not for high speed or power |
| Custom PCB | A week or two | Low to medium | Reliable electronics (see PCB Prototyping) | Wait for fabrication; fixes mean a new board |
What accuracy to expect
| Process | Typical tolerance | Notes |
|---|---|---|
| FDM 3D printing | ±0.2 mm or ±1 % | 0.1 to 0.3 mm layers; anisotropic |
| Resin (MSLA) printing | ±0.1 mm | Smooth; brittle |
| SLS / MJF nylon | ±0.3 mm or ±0.3 % | Tough; no supports |
| Laser cutting | ±0.1 mm (kerf 0.1 to 0.3) | Flat parts; edge taper |
| CNC milling | ±0.05 mm (±0.01 with care) | Metals and plastics; fixtures |
| Sheet-metal bending | ±0.2 to 0.5 mm | Bend allowance |
| Urethane casting | ±0.3 mm or ±0.3 % | Silicone molds, 20 to 25 parts |
| Waterjet | ±0.1 to 0.2 mm | Thick sheet; no heat effect |
Typical values for good machines and parts of up to 100 mm. Larger parts and poor settings do worse; see Tolerances by Process and Surface Finish.
Scoring the options
When two or three methods look possible, a weighted decision matrix makes the trade-off explicit. Choose the criteria, give each a weight (summing to 1), score each option from 1 (poor) to 5 (excellent) and add up weight × score.
Worked example: a bracket prototype
Weights: speed 0.35, cost 0.25, strength 0.25, finish 0.15.
| Option | Speed | Cost | Strength | Finish | Weighted score |
|---|---|---|---|---|---|
| 3D print (FDM) | 4 | 4 | 3 | 3 | 3.60 |
| Laser-cut plywood | 5 | 5 | 3 | 3 | 4.20 |
| CNC-machined aluminum | 2 | 2 | 5 | 5 | 3.20 |
- Laser-cut plywood scores 0.35 × 5 + 0.25 × 5 + 0.25 × 3 + 0.15 × 3 = 4.20: the highest, so it is the best first prototype.
- If strength matters most (strength 0.5, speed 0.2, cost 0.2, finish 0.1), the scores become:
| Option | Score with strength weighted 0.5 |
|---|---|
| 3D print (FDM) | 3.40 |
| Laser-cut plywood | 3.80 |
| CNC-machined aluminum | 3.80 |
CNC aluminum moves from last to a tie for first (3.8 each) and the 3D print drops to 3.4: the result depends on what you value. Choose the weights before you score, not after, and check how sensitive the ranking is to them.
Cost against quantity
| Quantity | 3D print | Laser cut | CNC | Urethane casting | Injection molding |
|---|---|---|---|---|---|
| 1 | $6.00 | $27.50 | $148.00 | $403.00 | $8000.80 |
| 5 | $6.00 | $7.50 | $52.00 | $83.00 | $1600.80 |
| 25 | $6.00 | $3.50 | $32.80 | $19.00 | $320.80 |
| 100 | $6.00 | $2.75 | $29.20 | $7.00 | $80.80 |
| 1000 | $6.00 | $2.53 | $28.12 | $3.40 | $8.80 |
Worked example: where the break-even points fall
- Each process has a set-up cost S and a cost per part c: total = S + c × q. A process with a higher set-up and a lower per-part cost wins above the quantity q = (S2 − S1) ÷ (c1 − c2).
- Using the models in the figure: 3D print ($6 per part) against laser cutting ($25 + $2.50): laser wins above (25 − 0) ÷ (6 − 2.5) = 7.1 parts; print against CNC ($120 + $28): CNC never wins on cost (it costs more per part), only on strength and accuracy; print against casting ($400 + $12): casting wins above 133 parts; casting against molding ($8 000 + $0.80): molding wins above 3 455 parts (see From Prototype to Production).
- At one part, printing is cheapest; at 25 parts, laser cutting (if the part is flat); at 1 000 parts, casting; molding only beyond a few thousand.
- The models are illustrative: replace them with your own quotes.
Time and cost of one part, by process
Worked example: one bracket, three ways
- 3D print: a part of 40 cm³ of PLA (density 1.24 g/cm³) is 50 g. At a printer rate of 15 g/h that is 3.3 h; filament $1.24 plus machine time $4.96 at $1.50/h = $6.20.
- Laser cut: a flat part with 1.2 m of cut path at 15 mm/s takes 80 s (1.3 min): at $30/h that is $0.67 plus sheet material of about $5.00 (3 mm plywood at $6 per 0.18 m² sheet; the part uses 0.15 m² of it): $5.67.
- CNC: 1.0 h set-up and CAM plus 0.5 h running at $60/h = $90 for one part, about 15 times the print.
- The cheapest first is not always the right one: the CNC part is accurate and strong, which may be what you need to test (see The Prototyping Process and Its Stages).
Materials for prototypes
| Material | Stiffness (E) | Strength | Density | Strength per density |
|---|---|---|---|---|
| PLA (printed) | 3.5 GPa | 40 MPa | 1.24 g/cm³ | 32.3 MPa per g/cm³ |
| PETG (printed) | 2.1 GPa | 45 MPa | 1.27 g/cm³ | 35.4 MPa per g/cm³ |
| Nylon PA12 (SLS) | 1.7 GPa | 48 MPa | 1.01 g/cm³ | 47.5 MPa per g/cm³ |
| Plywood (birch, 3 mm) | 9.0 GPa | 40 MPa | 0.68 g/cm³ | 58.8 MPa per g/cm³ |
| Acrylic (cast) | 3.2 GPa | 70 MPa | 1.18 g/cm³ | 59.3 MPa per g/cm³ |
| Aluminum 6061-T6 | 69.0 GPa | 240 MPa | 2.70 g/cm³ | 88.9 MPa per g/cm³ |
| Mild steel | 200.0 GPa | 250 MPa | 7.85 g/cm³ | 31.8 MPa per g/cm³ |
Typical values: printed parts are weaker across layers and depend on the print settings; plywood depends on the grain; all values change with temperature. See Material Properties and Filament Materials.
- Match the material to the question: if the question is fit, plastic is fine; if it is strength, test in the real material or one with the same stiffness.
- Plastics creep and soften: PLA softens near 55 to 60 °C (a car in the sun); use PETG, ABS or nylon for heat.
- Wood moves with humidity; sheet metal springs back after bending.
Finishing and post-processing
- Printed parts: remove supports, sand, fill and paint for appearance models (see Post-processing and Finishing); vapor smoothing and annealing for strength.
- Laser-cut parts: wipe the charred edges, sand lightly, and glue with wood glue or solvent cement.
- Machined parts: deburr, anodize or paint; specify the finish on the drawing.
- Presentation: a coat of primer and paint makes a rough print look like a product, which is useful for user tests, but do not confuse looks with function.
Safety
- 3D printers: hot ends, moving parts, fumes from ABS and resin; ventilate and use a smoke alarm (see Troubleshooting and Safety).
- Laser cutters: never leave them running; fire, fumes (never cut PVC) and eye protection (see Laser Safety, Fire and Fumes).
- Machining: chips, rotating tools, workholding (see Workshop Safety).
- Casting resins are sensitizers: gloves, ventilation and care.
Troubleshooting
| Problem | Likely cause | Try |
|---|---|---|
| Part is the right shape but does not fit | Process tolerance and warping | Print test coupons; add 0.2 to 0.4 mm clearance (see Mechanisms, Fasteners and Snap-Fits) |
| Printed part snaps along the layers | Layer direction against the load | Rotate the part; thicker walls; use PETG or nylon |
| Laser-cut edges are charred or tapered | Too slow or too much power; focus off | Test grid of power and speed; air assist; mask the surface |
| CNC part is too expensive for a prototype | Too much fidelity | Print or laser-cut first; machine only the parts that need it |
| Cannot decide between methods | No criteria | Score the options and check the sensitivity to the weights |
| Lead time much longer than quoted | Service queue, finishing, shipping | Ask for dates; order early; keep a local backup method |
Related
- Prototyping Techniques: the overview of this guide.
- Mechanisms, Fasteners and Snap-Fits: joining the parts you make.
- Sourcing, Services and Outsourcing: when to buy the service.
- 3D Printing, Laser Cutting and CNC Machining.
FAQ
Should I 3D print or laser-cut my prototype?
Laser cutting is faster and cheaper for flat parts and enclosures made of sheet; 3D printing is better for shapes with depth and curves. Many projects use both. Score the options against what matters.
When is CNC machining worth it for a prototype?
When the part must be strong, accurate or in a specific metal, and the question depends on that. Otherwise print or cut first.
How many parts before I should switch process?
Compute the break-even from the set-up and per-part costs: typically a few tens of parts from printing to laser cutting or casting, and several hundred to thousands before a molding tool pays back.
Is a 3D print strong enough to test?
For fit and function at low loads, yes. For strength, test in the real material or a printed material with margin, and take the layer direction into account.
What is the cheapest way to make a small batch of 20?
Usually laser cutting for flat parts, a printer farm for 3D shapes, or urethane casting from one master for complex parts.
References
- Ulrich, K. T. and Eppinger, S. D., Product Design and Development, McGraw-Hill (concept selection matrices).
- Gibson, I., Rosen, D. and Stucker, B., Additive Manufacturing Technologies, Springer.
- Kalpakjian, S. and Schmid, S., Manufacturing Engineering and Technology, Pearson (process capabilities).
Last reviewed: October 2026. Prices, speeds and tolerances are typical or illustrative: use quotes for your parts.