Buy Aluminum Brass Iron CNC Machining Service

A single purchase order can cover three metals and still fail at the bench if the shop runs them on one set of parameters. Aluminum cuts fast, brass cuts faster, and iron punishes every weak setup. Each metal pulls a different answer out of the same machine: different spindle speed, different feed, different fixturing, different chip evacuation. The part geometry does not change. The process around it does.

Aluminum is the forgiving one. Grades like 6061-T6 and 7075 machine cleanly, hold tight tolerances, and take anodizing without extra prep. Brass, especially C36000, machines even more freely, but it grabs small taps and deforms thin walls. Iron is the opposite case. It wears tools, throws abrasive chips, and demands rigid workholding before anyone talks about finish.

Buyers usually send all three because the assembly needs all three. A housing in aluminum, a valve body in brass, a bracket in cast iron. That is normal. What matters is that the quote separates them instead of averaging the parameters. When a program moves from one-off samples into a 10,000-part run, we review the fixture, the tool wear pattern, and the inspection plan per metal, not per drawing.

Cost follows the metal, not the hour rate. Aluminum cycle times are short. Brass is shorter still. Iron cycle times run long because you slow down to protect the insert and the surface. If a supplier quotes one blended price for all three, ask how they split it. The answer tells you whether they have actually run these materials.

• 1
  AluminumFast cuts, good tolerance hold, takes anodizing and hardcoat.
• 2
  BrassBest machinability, watch thin walls and small threads.
• 3
  IronTool wear and chip control drive the process, not speed.

Start with the function, then work back to the metal. Aluminum wins when weight matters, when the part needs anodizing, or when thermal conductivity helps. 6061-T6 covers most brackets, plates, and housings. 7075 goes where strength-to-weight is tight, such as aerospace brackets or drone frames. 2024 machines well but corrodes without coating, so plan the finish early.

Brass suits electrical contacts, valve bodies, fittings, and anything that needs tight threads and low friction. C36000 is the free-machining grade and the default for screw machine work. C27400 and C28000 show up in forgings and higher-strength fittings. Beryllium copper is a different animal: it machines like brass but the dust needs controls, so tell the shop before you send the drawing.

Iron covers the structural and wear side. 1018 and 1045 are common for shafts, plates, and brackets that get welded or hardened. 4140 and 4340 handle higher loads. Cast iron, including the fine-chip grades, is chosen for vibration damping and machined faces, but the graphite dust is abrasive and must be evacuated or it grinds the way into every slide.

If two metals can both do the job, pick based on the finish and the assembly, not the metal price. A brass part that needs plating may cost more than the same part in aluminum with anodizing. A cast iron part that needs a ground face may cost more than steel with a tighter machining tolerance. The drawing decides.

GreatLight works to ±0.005 mm (±0.0002 in) on aluminum and brass when the feature supports it. That number is a capability, not a promise on every dimension. A 200 mm long aluminum extrusion with a thin wall will move after clamping, so the tolerance applies to the features you call out and the shop can reach with the setup you approve.

Surface finish follows the same logic. As-machined aluminum sits around Ra 1.6–3.2 μm. Brass polishes easily, so Ra 0.2–0.8 μm is realistic on round features. Iron is harder to bring down because the material tears rather than shears, so Ra 0.8–1.6 μm is the practical target without a secondary grinding step.

Threads are where metal choice bites hardest. Brass threads cut clean but strip if the wall is thin. Aluminum threads need more engagement length. Iron threads are strong but the tapping operation wears taps fast, so we plan tap changes into the run instead of discovering wear at part 300.

If your drawing mixes tight tolerance with a soft metal and a thin wall, expect a conversation. We will tell you which dimensions we can hold in one setup and which need a second operation. That answer rarely changes the design. It changes the price and the lead time, and you should know both before you commit.

• 1
  Aluminum±0.005 mm on stable features, anodizing adds 5–25 μm.
• 2
  BrassHolds tight tolerance, plate thickness affects final size.
• 3
  IronStrong threads, but tap wear drives the inspection plan.

Every part we ship gets inspected before it leaves. That means a raw material check against the mill cert, in-process monitoring during the run, and a final dimensional check against the drawing. Reports are available on request. For medical and automotive programs, the certificate chain matters as much as the part.

Aluminum and brass are easy to measure with standard CMM and optical equipment. Iron adds a wrinkle: cast iron dust settles on fixtures and gauge surfaces, so the inspection area stays separate from the machining area. If a shop measures iron parts on the same granite as aluminum without cleaning, you will see false readings on flatness.

Thread gauges, pin gauges, and surface roughness testers cover most of the dimensional work. For tight-tolerance aluminum and brass, we log the CMM program and the operator so a re-run matches the first article. For iron, we log tool life and replace inserts on a count, not on a hunch.

The certificates behind the paperwork are ISO 9001:2015 for general quality, IATF 16949:2016 for automotive, ISO 13485:2016 for medical devices, and ISO 27001:2022 for information security. If your program needs one of these, say so in the RFQ so the inspection plan is built around it from the first article.

A single supplier usually makes sense. One PO, one inspection plan, one shipping schedule. But there are cases where splitting the work costs less. If the iron parts are large castings and the brass parts are small fittings, the setups have nothing in common and the scheduling conflicts. A shop that runs both may push the small parts to the back of the queue.

Volume matters too. Aluminum parts at 10,000 pieces per year want a dedicated cell. Brass parts at 200 pieces want a flexible mill-turn center. Iron parts at 50 pieces want a rigid horizontal with good chip evacuation. Forcing all three through one cell adds setup time to every batch.

Another split point is finishing. Anodizing, plating, and black oxide run at different vendors, and each has its own lead time. If your assembly needs all three finishes, a supplier who coordinates them saves you three tracking spreadsheets, but only if they actually control the schedule. Ask who owns the finish vendor relationship before you sign.

The honest test is simple. Send the RFQ with all three metals and see whether the reply separates the process, the tolerance, and the finish per metal. If it reads like one generic paragraph copied three times, keep looking. If it tells you which dimensions are tight and which are not, that supplier has run these materials before.

Send one drawing per part, with the material grade named on the drawing, not in the email. If the grade is open, say so, and let the shop propose. Include the finish, the critical dimensions, and the annual volume. Those four items decide the process before anyone opens the CAD file.

Mark the critical dimensions. A drawing with 40 toleranced dimensions and no priority tells the shop nothing. A drawing with 6 marked dimensions and the rest general tells the shop where to spend the inspection time. That single change cuts quote turnaround and prevents disputes at first article.

Send the 3D model in STEP format and the 2D drawing as PDF. If threads, knurls, or surface finishes only appear on the PDF, say so, because the model will not carry them. We return a DFM analysis with the quote, normally within 12 hours, and production can start within 24 hours of approval.

For aluminum, brass, and iron, no minimum order quantity applies. One prototype or a 10,000-piece run are both fine. Parts ship in 3–5 days on standard programs. If your program is confidential, ask for an NDA before you upload. Uploads stay secure either way.