Machining vs fabrication is one of the most common points of confusion when buyers source metal parts. Fabrication builds parts and assemblies by cutting, bending, forming and welding sheet, plate and structural shapes. Machining removes material from bar, plate, forgings or castings with CNC lathes and mills to create precise features. A machine shop and a fabrication shop use different equipment, quote differently and hold different tolerances. Knowing which one your part needs saves time and cost.
Machining vs Fabrication: Comparison Table
Figures are typical. Cost is a relative per-part index for a mid-size bracket or mounting assembly, where one machined part at quantity 1 equals 100.
| Factor | CNC machining | Metal fabrication |
|---|---|---|
| Relative cost, qty 1 | 100 | 60 to 90 |
| Relative cost, qty 10 | 40 | 35 to 55 |
| Relative cost, qty 100 | 18 | 20 to 35 |
| Relative cost, qty 1,000 | 10 | 15 to 25 |
| Typical tolerance | ±0.001 to ±0.005 in | ±0.030 to ±0.125 in on welded assemblies; ±0.010 in on cut and formed features |
| Surface finish | Ra 32 to 125 µin | Mill finish, weld beads, grinding marks |
| Materials | Nearly any metal or plastic | Weldable steels, stainless, aluminum |
| Size range | Small to medium precision parts | Small brackets to large frames and structures |
| Lead time | Days to a few weeks | Days to several weeks, depending on assembly size |
| Strength | One-piece wrought material, no welds | Strong structures; weld quality and distortion must be controlled |
| Typical use case | Shafts, housings, fittings, precision plates, manifolds | Frames, skids, guards, enclosures, platforms |
When Fabrication Wins
- Large structures. Frames, skids, guards and platforms are built from plate, tube and structural shapes far more economically than they could be machined.
- Thin, formed parts. Enclosures and brackets bent from sheet use little material and little machine time.
- Loose tolerances. If ±1/16 in is acceptable across the assembly, fabrication is the natural fit.
When Machining Wins
- Tight tolerances. Bores, fits, hole patterns and threads that must hold thousandths come from machining.
- Round parts. Shafts, pins, bushings and fittings are turned on a lathe.
- Precision surfaces. Flatness, parallelism, perpendicularity and surface finish callouts are practical on machined parts.
- One-piece strength. A part machined from solid avoids weld porosity, heat distortion and weld inspection requirements.
Parts That Need Both
Many industrial parts are fabricated and then machined. A welded base may need its mounting pads machined flat and coplanar after welding, because welding heat distorts the structure. Machined components such as bearing housings, shafts and bushings are often bolted or welded into fabricated frames. The practical approach is to keep precision on machined parts and on post-weld machined surfaces, and let fabrication handle size and structure.
Post-Weld Machining
If a weldment has precision features, the drawing should note which surfaces are machined after welding and how much stock the fabricator leaves. Stress relief before machining is often specified on heavier weldments so the part does not move after cutting. The weldment must also fit the machine shop's work envelope and be fixturable.
Common Mistakes
- Sending a precision machined part to a fabrication shop, or a large weldment to a small-part machine shop.
- Putting machining tolerances on welded dimensions without a post-weld machining step.
- Machining a large bracket from solid plate when bent or welded construction would carry the load at a fraction of the cost.
- Not specifying stress relief on weldments that will be machined, which leads to movement and out-of-tolerance features.
How This Applies at Wexmar
Wexmar is a machine shop, not a fabrication shop. We do not weld, bend or cut sheet metal. We turn, mill and Swiss-machine precision parts, and we can machine customer-supplied weldments and fabricated components that fit our horizontal machining center envelopes. Our floor includes 10 CNC lathes, six horizontal machining centers, four Maier Swiss-type machines and two CMMs. See capabilities, parts we make, and the related guide on CNC vs sheet metal.
Getting a Quote
If your project includes precision machined components, send the drawings and we will quote the machined work. You can upload a drawing for an instant estimate, confirmed by a human estimator, or call (315) 400-2654.