Custom Metal Parts: When to Use Laser, Waterjet, Bending or Machining
Asking for the wrong process is the most common way to lose two weeks on a sheet metal part. This guide decides between laser, waterjet, plasma and machining based on thickness, material, tolerance and edge quality, and explains which files to send.
You have a sheet or plate part and three ways to order it: laser cutting, waterjet, or machining from plate. The decision looks technical and minor, and it is the one that most often sets a project back two weeks, because a badly chosen process gets discovered once the part is already cut and the critical callout does not conform.
The rule that organizes everything is short: cutting solves contours, machining solves surfaces. From there, the choice is decided by four data points already on your drawing: thickness, material, the tightest tolerance, and what edge quality you need.
In Summary
- Cutting solves the perimeter; machining solves a functional surface. If your critical callout is a seat, a perpendicularity or a fit, it is not a flat-cut part.
- Laser for thin and medium sheet with a clean edge and good contour precision, especially at volume.
- Waterjet when heat is the problem or the material is not laser-friendly: it cuts cold, with no heat-affected zone.
- Plasma for thick conductive plate when cost rules and a fine edge is not a requirement.
- Bending is where variation accumulates. Tolerance generously across bends. At Radii the scope covers laser and waterjet cutting, bending and assembly, plus machining when the part calls for it.
1. The four data points that decide the process
Before ordering anything, have these at hand:
- Thickness. The first filter, and the one that rules out processes on its own.
- Material. Conductive or not, low melting point or not, heat-sensitive or not.
- The tightest tolerance and where it sits. On the contour, in a hole, between two bent faces, or on a surface.
- The edge quality you need. Whether the part gets welded, painted, hand-assembled, or stays visible.
With those four, the next decision almost makes itself.
2. Decision table
| Process | Where it wins | Limits |
|---|---|---|
| Laser cutting | Thin and medium sheet, good contour precision, clean edge, volume | Stops being efficient at high thickness; adds heat to the material |
| Waterjet | Cuts cold, no heat-affected zone; almost any material, composites and low melting point materials included; thick plate | Slower than laser on thin sheet |
| Plasma | Thick conductive plate with contained cost | Lower edge quality and precision than laser and waterjet |
| Machining | Functional surfaces, holes with fits, depths and perpendicularity | Not the route for cutting a large contour in thin sheet |
The comparison between thermal and cold cutting, with the cases where waterjet is the only sensible option, is developed in high-precision waterjet cutting, and the general criteria for choosing a process on a new part in prototype process selection.
3. Bending is where variation accumulates
On a cut and bent part, the contour is the precise portion and the bend is what introduces uncertainty. Three reasons, all physics rather than shop quality:
- The inner radius the tooling can produce depends on thickness and material, not on the drawing.
- Springback makes the material open slightly after bending, and the compensation depends on the material lot.
- Developed length changes with radius and stretch factor, so the actual position of a hole relative to a bent face accumulates variation.
Design consequences that save money:
- Tolerance generously on dimensions that cross a bend; tighten only within a single face.
- Keep holes a reasonable distance from the bend: too close and they deform.
- If a dimension between two bent faces has to be tight, consider a welded assembly with a fixture, or move that dimension to machining after bending.
4. When the part is not really a cutting job
Signs that you are asking for the wrong process:
- The critical callout is a bearing surface or a seat, not a contour.
- There is a hole with a fit tolerance for a bearing, bushing or precision pin.
- The drawing specifies perpendicularity or flatness with a geometric tolerance.
- There are controlled depths, pockets or steps.
- Thickness is high enough that the part is no longer sheet, it is machined plate.
In those cases there are two healthy routes: cut the contour and machine the surface afterward, usually cheapest on large parts; or machine everything from plate, which wins on small parts with several functional surfaces. The precision route, with what can be held and what needs a secondary operation, is on the CNC machining service page.
5. Which files to send
- Flat part: DXF of the contour and holes, plus the drawing with thickness, material, finish and quantity. Without thickness and material, the quote is not valid.
- Bent part: STEP of the 3D model, plus the flat pattern drawing if you already have it. If you send only the flat pattern, tell the shop which inner radius you assumed.
- Welded assembly: STEP of the assembly and the individual parts, drawing with welding symbols and notes on post-weld finishing.
- Any of the three: mark on the drawing which dimensions are functional. That is what decides whether the part can be solved by cutting or needs machining.
6. How to read a metal fabrication quote
The line items that should appear, for the same reason as in machining: with no breakdown there is no comparison.
| Line item | What to check |
|---|---|
| Material | Thickness, grade, mill finish, and whether the price includes nesting scrap |
| Cutting | Process used and cut length or time, with the declared edge quality |
| Bending | Number of bends and whether special tooling is required |
| Welding and assembly | Weld type, whether a fixture is required and who pays for it |
| Finishing | Deburring, paint, galvanizing, anodizing, each with its own lead time |
| Inspection | What gets measured and which document ships with the delivery |
Two questions that separate suppliers fast: whether deburring is included, because on cut sheet it is almost never optional and often not quoted; and whether finishing is applied after welding, because the order changes both the result and the price.
7. Small lots, prototypes and assemblies
For one or two parts, cost is dominated by preparation: programming the nest, loading the sheet, changing bend tooling. There it pays to:
- Design for fewer operations. One less bend is usually worth more than one less gram of material.
- Consolidate parts of the same material and thickness into one run, even across different projects.
- Accept a standard inner radius instead of specifying one that requires dedicated tooling.
- Avoid fixtures on the prototype: if the assembly can locate itself with tabs and slots cut into the parts, the prototype ships with no tooling.
That last point is the most often forgotten and the one that speeds a prototype up the most: self-locating geometry is cut for free in the same operation.
Frequently Asked Questions
When is laser cutting the right call, and when is waterjet?
Laser is the option for thin and medium sheet where speed, a clean edge and contour precision matter. Waterjet comes in when heat is a problem, because it cuts cold and creates no heat-affected zone, and when the material is not suited to laser: low melting point materials, composites, stone, glass, or thick plate where laser stops being efficient.
What about plasma?
Plasma dominates on thick conductive plate when cost rules and the edge does not need to be fine: it is the cheapest process to install and operate at those thicknesses. Its drawback is edge quality and precision compared with laser and waterjet, so it is not the choice for a contour with a tight tolerance.
When does a sheet metal part actually need machining?
When the critical callout is defined by a surface rather than a contour: a flat seat, a hole with a fit tolerance, a perpendicular face or a controlled depth. Flat cutting solves the perimeter; it does not solve a functional surface. In those cases you cut first and machine the surface afterward, or the part comes straight out of machined plate.
What files does a metal fabrication shop need?
For a flat part, a DXF with the contour and hole geometry, plus the drawing with thickness, material and finish. If the part has bends, assembly or welding, also send a STEP of the 3D model and the flat pattern or assembly drawing. With no thickness and material declared, no cutting quote is valid.
What tolerance should I expect on a cut and bent part?
The cut contour is the precise part; bending is where variation accumulates, because inner radius, material and springback change where the faces actually end up. As a design practice, tolerance generously on dimensions that cross a bend and tightly only on those defined within the same face, or move those dimensions to a later machining operation.
Conclusion: cutting defines the contour, not the function
Almost all rework on custom metal parts comes from the same place: cutting was ordered for a callout only a machined surface could hold. Reviewing the drawing with that one question, which dimension is functional and what produces it, takes five minutes and saves the lost run.
If you would rather have the process proposed by whoever manufactures, upload the DXF or STEP at app.radii.com.mx: the quote arrives with the process, finish and inspection written down, and with machining included when the part needs it.