Material selection guides written for people who set up the job. Compare stainless grades, aluminum alloys and plastics by machinability, density and finish, then send the file for a DFM check.
Most scrap on a first article traces back to one of these four decisions.
Specifying 304 for a part that sees chlorides leads to pitting in service. Choosing 4140 in the annealed state when you needed the heat-treated properties means the part fails a hardness check after machining is already paid for. Grade selection should start from the service environment, not from what is on the shelf.
Young's modulus drives deflection, and deflection drives whether a thin wall holds tolerance. A 2 mm rib in 6061 will move more than the same rib in 17-4 under the same cut. If the calculation is skipped, the first article comes back out of tolerance and the fix is a design change, not a re-cut.
Polycarbonate and acrylic machine differently. Acrylic crazes around a drilled hole and cracks at the edge. Polycarbonate smears when the feed is too light. Applying aluminum speeds and feeds to either one gives you a melted edge or a chipped corner, and both show up on the cosmetic surface.
A part with a 0.5 mm floor, a deep pocket or a thread too close to a wall will machine, but not at the price on the first quote. Catching it in DFM costs nothing. Catching it after the first article means a redesign, a new setup and a second run.
A number on a data sheet only helps if you know how the material behaves at the spindle.
The comparison tables below put stainless, aluminum, steel and plastic side by side on the values that change a program: density, machinability, typical hardness and what surface finish you can realistically hold. 304L and 316L sit close on tensile strength but behave differently under a tap. 7075 machines clean and holds a thread, but it costs more than 6061 and will not take a weld.
We keep 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12 on the aluminum list, and 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH on the stainless side. If your drawing names a grade we do not stock, the question is usually whether the substitute matches the service condition, not whether it looks the same.
Young's modulus tells you how far a part moves under a known load. For a simple cantilever, deflection is F L³ divided by 3 E I, so the modulus and the second moment of area do all the work. Doubling the wall thickness cuts deflection by roughly eight times; changing from aluminum at 69 GPa to stainless at 193 GPa cuts it by close to three times. Both are cheaper than adding a support rib after the fact.
The same arithmetic applies to thin floors, long bores and any part that gets clamped during assembly. If the calculated deflection is larger than the tolerance band, the drawing needs a change. We run this check during the free DFM review and flag it before the job is scheduled.
Values are typical for the grades we run most often.
| Material | Density (g/cm³) | Machinability | Notes |
|---|---|---|---|
| 6061-T6 aluminum | 2.70 | Excellent | General parts, good finish |
| 7075 aluminum | 2.81 | Good | High strength, no welding |
| 5083 aluminum | 2.66 | Fair | Marine, weldable, gummy |
| 303 stainless | 8.00 | Excellent | Free-cutting, lower corrosion |
| 304 / 304L stainless | 8.00 | Fair | General corrosion resistance |
| 316 / 316L stainless | 8.00 | Fair | Chlorides, medical, marine |
| 17-4PH stainless | 7.80 | Fair | Heat treatable, high strength |
| 4140 steel | 7.85 | Good | Shafts, gears, heat treatable |
| C36000 brass | 8.50 | Excellent | Fittings, fast turnaround |
| Polycarbonate (PC) | 1.20 | Good | Tough, transparent, smears |
| Acrylic (PMMA) | 1.18 | Good | Clear, brittle at edges |
| POM (Delrin) | 1.41 | Excellent | Bushings, tight tolerance |
The same shop that writes the notes cuts the parts.
Complex geometry in one setup. 16 simultaneous 5-axis centers handle contoured surfaces, deep pockets and parts that would need four fixtures on a 3-axis machine.
3-axis, 4-axis and mill-turn capacity for prismatic parts and turned diameters. 27 three-axis machines and 12 four-axis mills cover the straightforward work at volume.
First articles for fit checks before tooling is committed. Useful when the material call is still open and you want to test the geometry.
Bent and formed parts for enclosures and brackets, where the modulus question becomes a bend radius question.
Polymer parts for early ergonomic or packaging checks, before the design moves to a machined alloy.
Anodizing, plating, powder coating, bead blasting and laser marking. Finish choice often decides the alloy, not the other way around.
| Item | Range | Notes |
|---|---|---|
| Maximum part size | 4,000 mm | Largest travel 4,000 × 400 × 150 mm |
| Standard tolerance | ±0.005 mm | ±0.0002 in on request |
| Fine finish | Ra 0.2–0.8 μm | Grade and finishing pass dependent |
| As-machined finish | Ra 1.6–3.2 μm | Default for most parts |
| Rotary table | Ø400 mm | For turned and indexed features |
| Run size | 1 to 10,000+ | No minimum order quantity |
| Inspection | 100% before shipment | Reports on request |
| Certifications | ISO 9001, IATF 16949 | Also ISO 13485, ISO 27001 |
Fifteen years of production work across three wholly-owned plants, with 150 technicians on the floor.
5-axis, 4-axis, 3-axis and mill-turn capacity under one roof, so the process follows the part instead of the other way around.
Held on production parts, not just on a sample. Tighter bands are quoted after a DFM review.
Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours after approval.
Machining, finishing and inspection in the same facility, which shortens the loop when a dimension needs a second look.
Raw material check, in-process monitoring and final inspection on every order. Reports available on request.
7075 and 17-4PH where strength-to-weight and heat treatment both matter.
316L and PEEK for cleanability and dimensional repeatability across lots.
4140 and 6061 for wear surfaces and light structural plates in the same assembly.
5083 and PC where weldability and impact resistance set the grade choice.
Start from the service environment. 304 handles general indoor and mildly corrosive conditions at lower cost. 316 and 316L add molybdenum, which is what resists chlorides, so they are the right call for marine, medical and food-contact parts.
On the machine, both cut similarly and both can work-harden under a light feed. If the part is mostly about cost and the environment is dry, 304 is enough. If you are unsure, tell us the fluid or cleaning agent the part will see and we will make the call with you.
It is worth it when strength-to-weight drives the design or when the part needs a hard, wear-resistant surface after anodizing. 7075 machines cleanly and holds a good thread.
It is not worth it when the part will be welded, when corrosion resistance matters more than strength, or when the geometry is simple and 6061 already passes the stress check. For most brackets and housings, 6061-T6 is the cheaper answer.
It sets stiffness. Deflection under load scales with 1/E, so a material with three times the modulus moves one third as far for the same geometry and load. Yield strength does not enter that calculation until the part starts to bend permanently.
In practice this decides thin walls, long unsupported bores and any part that gets clamped during assembly. If the calculated deflection exceeds the tolerance band, change the geometry first.
Acrylic is more brittle and has a lower impact resistance, so stress at the hole edge finds a crack instead of deforming. Polycarbonate absorbs that stress and stays intact.
Tooling matters too. A sharp, polished drill with a slow feed and a backing plate reduces the risk. If the part needs a clear window with a fastener through it, polycarbonate is usually the safer grade even at higher cost.
4140 is a chromium-molybdenum steel that responds well to heat treatment, so it suits shafts, gears, pins and any part where you need through-hardness rather than corrosion resistance. It machines well in the annealed condition.
Choose stainless instead when the part will see moisture, washdown or chemicals. Choose 4140 when the load and the wear surface matter more than the environment, and plan the heat treatment before the finishing step.
Often yes. The question is whether the substitute meets the service condition, since a different alloy number can change corrosion resistance, weldability or heat-treatment response even when the tensile values look close.
Send the drawing with the grade and the application. We will tell you whether to source the exact grade or whether a stocked equivalent does the job without changing the design.
±0.005 mm is our standard production tolerance. Achieving it depends on the feature, the material and the setup, not on the number alone. A short bore in brass is easier than a deep pocket in 316L.
Features that need a tighter band are quoted after a DFM review, so the process and the inspection method are agreed before cutting starts. Final inspection reports are available on request.
Uploads are secure and confidential. We do not share drawings outside the project team, and we can sign a non-disclosure agreement before the files move.
The DFM review, the quotation and any questions about the material call all stay inside that boundary. Ask for the NDA on the contact page and we will return it before you upload.
Tell us the grade you have in mind and the environment the part sees. We will come back with a quotation, a DFM note and a clear answer on whether the grade holds up.
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Upload your 3D model or 2D drawing and get a quotation with a free DFM analysis. Maximum processing size 4,000 mm.
CNC Metals 13 grades
CNC Plastics 10 grades
Machines & processes 12 options
Surface & post-processing 10 options
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