Aluminum Brass Iron CNC Machining Service Manufacturers

Aluminum, brass, and iron are grouped together because they are common and machinable, not because they machine the same way. Aluminum 6061 cuts at 3,000 rpm or more with a light depth of cut, while a 4140 or cast iron part often runs below 1,000 rpm with heavier passes and far more attention to heat. Brass machines clean and fast, but C36000 free-cutting brass chips break easily and can grab a small drill. Treating all three with one set of parameters is how you get chatter, torn surfaces, and out-of-round bores.

The alloy within a family matters as much as the family. 7075 aluminum holds a thread far better than 5052, but it is more prone to stress movement after roughing. C27400 brass machines differently from beryllium copper, which needs its own handling rules. Ductile iron and gray cast iron both cut well, yet gray iron makes abrasive dust that wears ways and tooling, so chip control and machine cleaning are not optional.

A shop that cuts all three every week already owns the tooling, fixtures, and coolant for each. That is the practical reason to check material experience before price. A low quote from a shop that mostly runs stainless will usually come back with rework.

• 1
  AluminumHigh spindle speed, light radial engagement, watch thermal growth on thin walls.
• 2
  BrassFast cutting, sharp edges, but gummy alloys need distinct rake angles.
• 3
  IronLower speed, rigid setup, abrasive chips, heat-resistant inserts.

For aluminum, 6061-T6 is the default for brackets, housings, and plates because it welds, anodizes, and machines predictably. 2024 offers higher strength but machines with more residual stress and does not anodize as cleanly. 7075 is the choice when strength matters more than cost, common in aerospace fixtures and lightweight structural parts. 5052 and 5083 are usually sheet and formed parts rather than heavy machined blocks. ADC12 shows up as die cast stock that needs secondary machining.

On the brass side, C36000 is the free-machining grade and produces short chips and good surface finish at high feed. C27400 and C28000 are used when the part needs to be formed or when a specific color and corrosion behavior matter. Beryllium copper is a separate case: it machines well but the dust needs controlled handling, so it belongs with a shop that has a written procedure for it.

Iron covers gray cast iron, ductile iron, and the alloy steels often labeled as iron in drawings. Gray iron is dimensionally stable and damps vibration, which suits machine bases and housings. Ductile iron takes more load and is used for brackets and gears. For steel-side equivalents we stock 1018, 1045, 4130, 4140, 4340, and A36, all of which behave far differently from aluminum on the machine.

If the alloy is still open, bring the load case rather than a grade number. We will tell you where a cheaper alloy works and where it will not.

As-machined finish lands around Ra 1.6–3.2 μm and is fine for most brackets, plates, and internal parts. When a sealing face, bearing seat, or sliding surface is involved, Ra 0.8–1.6 μm is the normal target. Finer than Ra 0.2–0.8 μm is possible on aluminum and brass with a finishing pass and the right insert, but it adds cycle time and should be tied to a real function.

Finishing steps change the part, so plan them before machining. Anodizing adds a few to tens of microns depending on type, and hardcoat changes tight bores. Electroless nickel and zinc plating build thickness evenly but still move a press-fit dimension. Bead blasting hides tool marks and softens gloss; it can also round a sharp edge you need for a seal.

If a drawing calls for a finish and a tolerance on the same face, write the order. Anodize after grinding is not the same part as anodize before grinding, and the shop needs to know which dimension is protected.

Ask for the machine list, not the brochure. The useful questions are how many 5-axis centers are available, what the largest travel is, and whether the shop has a rotary table for parts that need one setup. A shop with a 4,000 mm travel machine solves long aluminum extrusions and iron frames that a 400 mm machine cannot touch.

Ask how inspection is done. A valid answer covers incoming material checks, in-process monitoring, and a final inspection before shipment, with reports available on request. If a shop inspects only the first article and ships the rest, tolerances drift across a 5,000-part run and you find out at assembly.

Ask about the correction path. Free rework for a real quality miss, and a clear refund position if rework still fails, is the minimum. A written NDA matters when your drawings carry geometry you do not want distributed. For aluminum, brass, and iron work in automotive or medical supply chains, the certifications behind the shop are part of the answer: ISO 9001, IATF 16949, ISO 13485, and ISO 27001 each cover a different risk.

One more check: how fast does a quote come back with real DFM notes? A price with no comment on the setup is a guess.

Most of the cost difference between two quotes on the same drawing sits in setup and fixturing, not in the cutting time. An aluminum part that can be held in a vise and cut from three sides is cheap. The same geometry with a thin wall, an undercut, and a true position callout needs soft jaws or a custom fixture, and that work appears in the price.

Five-axis machining is the right answer when a part has features on five faces and you want one setup. It removes the repositioning error that shows up when a part moves between three machines. It is not the right answer for a flat plate with simple holes; a 3-axis machine cuts that faster and cheaper. Mill-turn centers cover round parts with milled flats and cross holes, which is common in brass fittings and iron shafts.

Tolerances follow the same logic. ±0.005 mm is achievable across our equipment, but applying it to every dimension on a part raises inspection time sharply. Put the tight tolerance on the features that mate. Leave the rest at general tolerance and the part gets cheaper without losing function.

For prototypes, no minimum order quantity means you can order one piece to test fit and one revision later. Production runs from the same program scale to 10,000+ parts with the same fixturing.