Aluminum CNC Machining Service | ±0.005mm Frame Parts

Frame parts are not decorative — they are the datum everything else is measured from. A bracket drilled 0.05 mm off does not fail on its own; it pushes the error into the linear rail, and the machine loses repeatability three assemblies later. That is why this page is built around two numbers rather than a parts list: ±0.005 mm on location and Ra 0.4 on the faces that matter. Everything else — the material choice, the setup sequence, the way we stress-relieve a plate before the finishing pass — exists to protect those two numbers at volume.

What We Machine

The photo set spans the full range a machine builder actually orders: a bolt-circle flange ring, a toothed pulley, a threaded adapter, an L-bracket with gusset ribs, tapered seats, a dome cover, socket head screws and a perforated fixture plate — nine part families, one supplier. That matters more than it sounds. When brackets, plates and pulleys all come from the same shop, the hole patterns are generated from the same datum convention, so a sub-assembly built from them stacks up with far less shimming. These are the cnc machining aluminum parts that hold an automation cell together.

Capability & Specifications

Read the gap between the two columns as money. Moving from ±0.01 mm to ±0.005 mm on a frame part usually means an extra finishing pass, an extra flip, and a CMM check that did not exist before — that is where the cnc machining cost for custom parts actually comes from, not from the aluminium itself. Our advice to most buyers is to mark only the datum faces and the mating bores at ±0.005 mm, and leave clearance holes at ±0.05 mm. A drawing where every dimension carries the same tight tolerance is a drawing that pays for precision it never uses.

Material & Finishing

Material choice on a frame part is a stiffness decision, not a cost decision. 6061-T6 covers most brackets and plates; step up to 7075-T6 only where the section is thin and the load is real, because it machines slower and the price jump is not small. Anodizing is the other half of the story and the half buyers forget: hard anodizing grows into the surface and out of it, so a bore that was ±0.005 mm before the bath is not ±0.005 mm after it. We mask critical bores and threads, and state the masking plan on the drawing before production rather than discovering it at assembly.

How ±0.005 mm and Ra 0.4 Are Held

Anyone can hit ±0.005 mm on one part. The difficulty is holding it on the five-hundredth, after the tools have worn and the operator has changed shift. That is why our precision cnc machining services are built as a frozen sequence rather than a set of skills: the stress-relief step sits between roughing and finishing and is never skipped on a plate, the finishing pass uses the same tool path and the same parameters every run, and the CMM program is written from the drawing's datum scheme rather than from whatever the operator finds convenient. Repeatability is a process property, not an operator property.

Distortion Control on Plates and Thin Walls

A 500 × 400 mm plate with a dense hole pattern is the classic distortion trap: you remove 40% of the material from one face, the plate bows, and every hole you drill afterwards is drilled into a warped surface. We rough both faces in alternating passes, stress-relieve, then finish — and we check flatness on the surface plate before drilling, not after. If a design puts a thin wall next to a deep pocket, expect a DFM note asking whether that wall can be 1.5 mm instead of 1.0 mm; the answer usually decides whether the part is affordable.

Inspection & Traceability

Our cnc precision machining services end at a CMM report, not at a visual check. Position tolerance on a hole pattern is verified against the datum scheme stated on the drawing, flatness is measured on a granite plate, and Ra is measured with a profilometer rather than judged by eye under a lamp. If your assembly has an interface you care about, tell us which one — we will add it to the first-article report so the number you argue about later is already on paper.

Applications

How a Custom Order Runs

Custom cnc machined parts are quoted fastest when the drawing states the datum, the critical interface and the finish on specific faces rather than globally. As a custom cnc machining parts factory that runs both prototype and production quantities, we keep the same program and the same fixture between the sample and the batch, so approval of the sample actually predicts the batch instead of starting a second argument.

Packing, Lead Time and Shipping

FAQ

Is ±0.005 mm realistic on a part this size, or is it a catalogue number? It is realistic on the features that are marked as datums and mating bores, on parts up to roughly 400 mm, in a temperature-controlled shop. It is not realistic across a 1,200 mm plate on every dimension — thermal expansion alone moves aluminium about 0.023 mm per metre per °C. A good drawing marks where the tight tolerance is needed and lets the rest breathe.

Can you hold Ra 0.4 on a large milled face? Yes, with a fly-cutting pass or a subsequent lapping step, but Ra 0.4 across a whole 500 × 400 mm face is a cost decision, not a capability limit. Most frame parts only need Ra 0.4 on a sealing land or a slideway, typically 10–20% of the surface. Specify it there and save the rest.

Does anodizing change my dimensions? Yes. Hard anodizing builds both into and out of the surface, so a bore can close by a few hundredths of a millimetre. We mask critical bores and threads, and if a fit is tight we will ask whether the part should be machined undersize before the bath. This is decided at quotation, not after plating.

Do you make one-off frame parts, or only batches? One piece is fine, and most frame-part projects start that way — a prototype bracket, then a fixture plate, then a small batch. The catch is that at one piece the per-part price is dominated by programming and setup, so a single bracket can cost more than ten of the same bracket. If you know the eventual quantity, tell us at the quotation stage; it changes how we build the fixture.

What is actually driving the price of my custom part? In order: tolerance class, surface finish, material removal volume, then material cost. A part with three tight tolerances and Ra 0.4 on two faces is usually cheaper than the same part with every dimension at ±0.005 mm, even though it looks more complex on paper. Send the drawing and we will show which callouts are costing you the most.

Which files do you need? A STEP or IGES for the geometry, plus a 2D PDF carrying tolerances, datums, thread callouts and surface finish. A 3D model alone does not define tolerance, and a 2D drawing alone makes us guess the geometry. Both, and the quotation comes back within one working day.

Request a Quote

Send the drawing for the part that is currently causing you trouble — the bracket that never sits flat, the plate whose holes will not line up, the adapter that leaks. We will tell you whether the problem is the design, the tolerance callout or the previous supplier, and quote accordingly. Our aluminum CNC machining services are built for equipment builders who measure success in assembled machines, not in shipped boxes.