Manufacturing Expertise

Fabrication and machining are the two primary processes that turn raw metal into engineered parts. Engineers who understand the difference, and more importantly, when to use each, make better design decisions earlier, avoid expensive first articles, and get parts that perform as intended.

This guide covers what distinguishes fabrication from machining, when each process is the right choice, when to combine them, and how material selection and design for manufacturability principles affect the decision.

For a complete overview of custom metal fabrication processes, see our expert guide to custom metal fabrication.

What Is the Difference Between Fabrication vs. Machining?

The core distinction is how each process creates a part.

Fabrication works with stock material, sheet, plate, tube, structural section, and shapes it through cutting, bending, joining, and assembly. The starting material approximates the finished shape; fabrication operations form it into the required geometry. Welding joins multiple pieces into a larger assembly. The process is additive and formative rather than subtractive.

Machining is subtractive. A CNC mill or lathe removes material from a solid workpiece using rotating cutting tools, gradually cutting the finished part from a block or bar. Machining produces precise features, bores, pockets, threads, contoured surfaces, to tolerances that fabrication processes cannot reliably achieve.

Both processes are used on most complex metal assemblies. Understanding where each adds value, and where it adds cost without benefit, is what drives better part design.

When Should You Use Fabrication?

Fabrication is the right choice when:

• The part is a large structural assembly. Welded frames, machine bases, enclosures, and conveyor structures are economical in fabrication. Machining a machine base from solid billet is rarely justified when welded plate and tube can achieve equivalent stiffness at a fraction of the material cost.
• Thin-walled geometry is required. Sheet metal fabrication produces complex thin-walled shapes, enclosures, brackets, panels, that would require extremely deep cuts and long cycle times to machine from solid. Forming is faster and more economical.
• Volume is too low for stamping or casting tooling. Fabrication requires no hard tooling. A prototype weldment can be produced from a drawing in days. A casting or stamping requires tooling that may take weeks and cost thousands.
• The design calls for joining dissimilar sections. Welding allows structural tube, plate, and machined components to be combined into a single assembly in ways that solid machining cannot achieve.

When Should You Use CNC Machining?

CNC machining for prototypes and production parts is the right choice when:

• Tight tolerances are required. Machined features routinely hold +/- 0.001″ or tighter. Fabricated and welded assemblies operate at +/- 0.010″ to +/- 0.060″ depending on process and overall size. When a precision bore, precise hole location, or flat reference surface is required, machining is the process.
• Complex 3D geometry is specified. Contoured surfaces, pockets, undercuts, and internal features that cannot be formed or welded require 3-axis or 5-axis CNC milling. The geometry of a machined part is defined by the tool path, not the available stock shapes.
• The part is solid and relatively small. Machined parts are typically smaller components, shafts, housings, brackets, flanges, where removing material from a billet or bar produces the geometry efficiently.
• Surface finish requirements are high. Machined surfaces achieve Ra 32–125 µin as-machined; with additional grinding or polishing, Ra 8–16 µin is achievable. Fabricated surfaces are rougher and more variable.

For a detailed breakdown of CNC machining for prototypes and how to evaluate process options, see our guide on CNC machining for prototypes.

When Should You Combine Fabrication and Machining?

Most complex assemblies use both. The structural shape comes from fabrication; the precision features come from machining. Common combination approaches:

• Weld-fabricated frames with machined reference surfaces: A structural welded frame has its mounting pads and reference surfaces machined flat after welding. Welding distorts the overall geometry; machining brings critical interfaces back to tolerance.
• Fabricated enclosures with precision machined cutouts: Sheet metal enclosures are formed and welded, then transferred to a mill for precision hole patterns, tapped features, or mating surface machining.
• Machined components integrated into weld assemblies: Precision machined housings, shafts, or flanges are welded into fabricated structural assemblies where the machined features maintain precision alignment.

At Bravo Team, machining and fabrication operate under the same roof. When an assembly requires both processes, the handoff is a conversation between machinists and fabricators, not a purchase order to a second partner.

“We have engineers that are designing, pulling stuff out of their head, creating it in 3D in a model, and then once that’s finalized, what we are able to do here in the machine shop is take that from the computer screen and create that part into the world. We bring it to life.”   Rich Neal, Director of Manufacturing, Bravo Team

How Does Design for Manufacturability Affect the Fabrication vs. Machining Decision?

Design for manufacturability (DFM) principles directly govern when fabrication or machining is the right process for a given feature. Getting this decision right at the design stage prevents expensive process changes after drawings are released. See our guide on design for manufacturability decisions for the full DFM framework.

Key DFM principles for fabrication vs. machining decisions:

• Reserve tight tolerances for machined features. Calling out +/- 0.005″ on a welded flange location is a conflict. Either machine that feature after welding or relax the tolerance to what fabrication can hold.
• Use fabrication for structural geometry, machining for precision interfaces. A machine base is a fabricated structure; the mounting interface where a linear rail or motor bolts on is a machined feature.
• Avoid deep internal features that require machining from solid. A pocket or internal passage that can be fabricated from formed sheet and welded is almost always faster and more economical than machining it from billet.
• Material selection affects process choice. Aluminum 6061 machines excellently and welds with some care. Aluminum 7075 machines beautifully but is very difficult to weld, if welding is in the design, 7075 is the wrong alloy choice.

“As I start to conceptualize what I think might be a good solution for a specific problem that we’re facing, I’ll run it by some of our experienced machinists and get their input on it.”   Gregory Helfrich, Mechatronics Engineer, Bravo Team

How Does Materials Selection Affect the Fabrication vs. Machining Decision?

Materials selection engineering is part of the fabrication vs. machining decision, not a separate upstream step. The material a designer specifies affects which process is viable, what tolerances are achievable, and what the finished part costs. For a full framework on materials selection for engineering parts, see our guide on materials selection for engineering prototypes.

Material-process interactions:

• Aluminum 6061-T6: Excellent machinability; good weldability with appropriate filler. A strong candidate for combined fabrication-machining assemblies. Loses temper in the weld heat-affected zone, specify post-weld heat treatment if HAZ mechanical properties are critical.
• Carbon steel A36: Good machinability and excellent weldability. The workhorse material for fabricated structural assemblies. Lower cost than aluminum or stainless for most structural applications.
• Stainless 304/316: Machinable with appropriate tooling and speeds; weldable with TIG using correct filler and shielding procedures. Higher material and machining cost. Required for corrosion-critical environments.
• Titanium Grade 5 (Ti-6Al-4V): Machinable but demanding, requires sharp tooling, low speeds, high feed rates, and aggressive coolant. Very difficult to weld in standard shop environments. Primarily a machined material for structural applications.

Fabrication vs. Machining Cost Comparison

Neither process is universally cheaper. Cost depends on part geometry, material, quantity, and required tolerances.

• Fabrication cost drivers: material type, weld count, weld joint complexity, fixturing requirements, finishing specification
• Machining cost drivers: material removal volume, feature complexity, required tolerances, number of setups, tool changes
• Combination approach cost: fabrication for the structural body reduces material cost vs. solid billet; machining for precision features avoids fabrication tolerance limitations

For prototype quantities, fabrication is typically faster and less expensive for structural assemblies. For high-precision components, machining is required regardless of quantity. For production volumes where stamping or casting tooling amortizes over quantity, fabrication may not be the most economical choice, but for low to medium volumes, fabrication avoids the tooling investment entirely.

Frequently Asked Questions: Fabrication vs. Machining

What is the difference between fabrication and machining?

Fabrication shapes metal by cutting, forming, and joining stock material, sheet, plate, tube, structural sections, into assemblies. Machining subtracts material from solid stock using CNC mills and lathes to create precise features. Fabrication produces structural assemblies and complex thin-walled shapes economically; machining produces tight-tolerance features and complex 3D geometry that forming cannot achieve.

Is a fabricator a machinist?

Not necessarily. A fabricator manages the full production workflow, reading drawings, procuring material, cutting, forming, welding, and coordinating finishing. A machinist operates CNC mills and lathes to cut precise features from solid stock. Many experienced fabricators also have machining skills, and shops that run both processes have staff who span both disciplines.

When should you use fabrication instead of machining?

Use fabrication when the part is a large structural assembly, requires thin-walled geometry, involves joining dissimilar sections, or when volume is too low to justify casting or stamping tooling. Use machining when tight tolerances are required, when complex 3D features must be cut from solid stock, or when surface finish requirements exceed what fabrication processes can achieve. Use both when the part has both structural and precision requirements.

What is the difference between a metal fabricator and a machinist?

A metal fabricator works with sheet, plate, tube, and structural stock, shaping it through cutting, bending, and welding into assemblies. A machinist uses CNC mills and lathes to subtract material from solid stock and produce precise features. Most complex assemblies require the work of both, and the best outcomes come when fabricators and machinists collaborate during the design stage, not just during production.

Process Economics at Different Production Quantities

The fabrication vs. machining decision changes with quantity. What is economical at prototype volume may not be at production volume, and vice versa.

• 1–10 units (prototype): Fabrication and machining both viable. No tooling amortization required. Design flexibility is high, changes are inexpensive. Fabrication favored for structural assemblies; machining for precision components.
• 10–500 units (low volume production): CNC machining remains viable without tooling. Fabrication economics hold for structural parts. Consider fixturing investment for welded assemblies to improve repeatability and reduce per-part setup time.
• 500–5,000 units (medium volume): Stamping, progressive die tooling, and casting begin to compete with machining and fabrication on cost per part. Tooling investment amortizes over volume. Fabrication remains competitive for large structural parts where tooling is not practical.
• 5,000+ units (high volume): Stamping, casting, and injection molding dominate for small parts. Machining with dedicated fixtures and automation is optimized for high throughput. Custom fabrication is rarely the right process at this volume except for large one-of-a-kind assemblies.

How to Specify Parts for Mixed Fabrication-Machining Designs

Drawing packages for assemblies that require both fabrication and machining need to communicate which features belong to which process, and in what sequence. Ambiguous drawings produce ambiguous results.

• Mark fabricated features with standard weld symbols and forming notes. Mark machined features with standard tolerance callouts and surface finish symbols.
• Specify sequence where it matters: “Machine after welding” or “Weld after machining” on the drawing prevents the shop from making assumptions that conflict with the design intent.
• Reference surfaces for machined features should be defined off a welded datum that is accessible after assembly, not off a feature that gets buried during fabrication.
• Post-weld machining callouts should include notes on allowable distortion of the weld assembly before machining, so the shop knows when a welded sub-assembly needs corrective action before it goes to the mill.

Drawings that specify mixed-process assemblies clearly are drawings that come back right the first time. The investment in clear documentation is always recovered in reduced first-article iterations.

Fabrication vs. Machining: Summary Decision Framework

Use this framework to choose the right process for a given part or feature:

• Use fabrication when: The part is structural, thin-walled, or an assembly of multiple sections. Volume is too low for hard tooling. Design is still evolving. Lead time is the priority and structural tolerances are acceptable.
• Use machining when: Tight tolerances are required (+/- 0.005″ or tighter). Complex 3D features must be cut from solid. High surface finish is specified. The part is a precision component rather than a structural assembly.
• Use both when: The assembly has a structural body and precision interfaces. Post-weld machining is required to bring critical features to tolerance. Machined components are integrated into a fabricated structure.
• Revisit your design when: You are calling out machining tolerances on welded features, or designing machined parts from solid that could be fabricated from sheet or plate at a fraction of the material cost.

For more on how process selection integrates with design review, see our guide on design for manufacturability decisions and our complete guide to custom metal fabrication.

When Fabrication and Machining Are Specified on the Same Drawing

Drawings that call out both fabrication and machining operations on a single part or assembly require a shop capable of running both processes in sequence without partner handoffs. The alternative, sending a weld-fabricated assembly to a separate machine shop for secondary operations, introduces scheduling friction, communication gaps, and quality risk at the handoff.

In-house fabrication and machining under the same roof eliminates that handoff entirely. The fabrication team and the machine shop team review the drawing together before anything is cut, agree on the sequence, and execute the job without a gap between processes. That is the operational advantage Bravo Team’s integrated shop provides. For more, see our guide to custom metal fabrication.

Engineering-Integrated Fabrication and Machining, Under One Roof

Bravo Team runs fabrication and machining in the same 4,200 SF in-house shop, alongside our engineering team. When your design requires both processes, structural fabrication for the frame and precision machining for the critical interfaces, both disciplines review the drawing before anything is cut. That collaboration catches process conflicts at the design stage.

Ready to discuss fabrication, machining, or a combination approach for your project? Talk to an engineer today.