China Machining Services Parts

You are not limited to one alloy family. We machine the materials buyers actually specify on drawings, and every incoming lot is checked by XRF against its mill certificate before it reaches a machine, so the material you ask for is the material you get.

What tolerances can this shop actually hold?

A tolerance on paper means nothing without the measurement to back it. Our tolerances are tied to the process, and every critical dimension is checked on a CMM rather than taken on faith.

We hold these to process capability, not to a best-case claim. On a representative length characteristic (76.1–76.5 mm) our SPC shows Cpk = 1.851 (one characteristic on one part, not a blanket capability claim) against an initial-study target of Ppk ≥ 1.67. If your print calls out a dimension we cannot reliably hit, we tell you during the design review — before cutting, not after.

Read the tolerance band before you read the index. Cpk is a ratio of the tolerance band to the process spread, not an absolute measure of accuracy. The figure above was recorded on a length characteristic with a 0.4 mm band (76.1–76.5 mm) — wide by design. Hold the same process spread against a ±0.005 mm feature and it fails outright. Ask for the band, the subgroup count and the sampling window on every capability number a supplier quotes.

Tolerances on single parts become fits when two parts meet, and the fit class is what the tolerance is really for. A clearance fit keeps a gap so a shaft turns freely in a bore; a transition fit allows a slight gap or a slight interference, for parts that locate but do not lock; an interference fit (a press fit) forces the parts together and holds them by friction. Each fit lives in a narrow band of the tolerance ladder, and the difference between them is often a few thousandths of a millimetre. That is why a mating pair should never carry blanket tolerances: the bore and the shaft need coordinated, not identical, bands, and a DFM review checks that the two halves of the fit actually agree before anyone machines either one.

How does the DFM review change the part before it is quoted?

The review is the part of the process where a buyer actually saves money. Before quoting, we look at the geometry the way a machinist does: where the part must be fixtured, how many orientations it needs, and which features will fight the cutter.

• Internal corners. An end mill is round, so a square corner needs EDM or a second operation. A radius matching a standard tool removes that cost.
• Deep pockets and thin walls. Long-reach tooling and vibration slow the process and risk scrap; a draft angle or added wall thickness stabilizes the part.
• Tolerance creep. A single over-tight dimension forces slow feeds and extra measurement across the whole part; relaxing the non-functional ones is free.

Which processes run in-house for parts?

Having the process in-house means shorter lead time and one accountable supplier. Our floor spans the full metal-cutting range, so most parts stay under one roof between operations.

How are parts verified before they ship?

Machined parts are useless if they measure wrong. Our inspection bench is the same class of equipment a buyer would use to audit us, and we document the results, not just the pass/fail.

• Hexagon GLOBAL S CMMs (2) for dimensional verification, plus vision measuring machines and a gear measuring center.
• KEYENCE VK-X3000 laser microscope and SURFCOM 1800D for surface finish and profile.
• XRF (iCHEQ) spectrometer for incoming material composition checks against the mill certificate.
• SPC: control charts on key characteristics, with Ppk ≥ 1.67 at the initial study on critical characteristics and Cpk ≥ 1.33 in production on general characteristics.

Which secondary operations can be bundled with the parts?

We ship finished parts, not just machined blanks. Secondary operations run in parallel or through qualified partners, so you get one invoice and one accountable supplier.

• Surface finishing: standard and hard anodizing, zinc / nickel / silver / gold / chrome plating, powder coating, painting, brushing, mirror polishing.
• Heat treatment: vacuum, bright, carburizing, nitriding, and stress-relief aging. In-house ovens reach 500 °C (fine for aluminum and low-temperature steel stress relief); titanium stress relief above that is outsourced to a qualified partner.
• Deburring, tapping, laser marking, assembly: included as your print requires.

What should you check before ordering parts?

Whether you buy from us or someone else, these are the questions that separate a real manufacturer from a trading desk. Ask them of any shop — including this one.

Send a drawing and we will run all five checks on ourselves for you, in writing, before you commit.

How does the DFM review treat a housing differently from a shaft?

The same review asks different questions of different part shapes, and seeing the two extremes makes the method clear. A housing is a prismatic part, so the review hunts for what a milling cutter cannot reach. A shaft is a round part, so the review hunts for what a rotating workpiece cannot hold still. The table lays the two side by side.

The point of the comparison is that "DFM" is not one set of rules applied uniformly — it is a set of questions chosen by the geometry. If you know which column your part falls in, you can predict the flags before the quote arrives, and that prediction is the difference between being surprised by the review and using it.

How do you read the dimensional report that ships with your parts?

A CMM report is only as useful as your ability to read it, and the skill is a few simple checks. The report lists dimensions against their tolerance bands, and each line tells you three things: what was measured, what the print allowed, and what the part actually measured. Your job is to look at the third column, not just the second.

• Match the critical dimensions first. The dimensions that control function are the ones that must sit comfortably inside their band — check those before the cosmetic ones.
• Watch the margin, not just the pass. A dimension that passed but sits at the very edge of its band is a dimension with no margin for the next part. Ask about the Cpk, not just the pass/fail.
• Confirm the report is for your part. The part number, revision, and date should match your PO; a generic report proves nothing about your order.
• Pair the report with the material certificate. The part can measure perfectly and still be the wrong alloy — the dimensional report and the material certificate are two halves of the same evidence.

Reading the report this way turns a piece of paperwork into an audit tool. It is the same discipline we apply before shipping — we check the margin, not just the pass — and if you do the same, you never accept a part that only barely made it.

How does material condition — temper and heat treatment — change the finished part?

The alloy name is only half the material specification; the condition is the other half, and it changes everything you care about. 6061 aluminum in the annealed O condition is soft and easy to machine but weak; the same 6061 in the T6 temper is age-hardened to roughly three times the strength and machines with a different feel. 4140 steel in the annealed state cuts easily; the same 4140 quenched and tempered to a high hardness is a grinding job, not a milling job.

The condition matters twice: once before cutting, once after. Before cutting, the condition sets the machinability — annealed stock cuts faster and wears tools less, which is why roughing is often done in the softer condition. After cutting, heat treatment changes the final properties — quenching and tempering raise strength, aging precipitates hardness in aluminum, carburizing and nitriding harden a surface for wear. The finished part's performance is decided by the condition it ends in, not the condition it started in.

The DFM sequence follows from that split. For a hardened part, the economical route is to rough-machine in the soft, machinable condition, send it to heat treatment, then finish-machine — usually grind — the critical surfaces that heat treatment may have moved. Machining the part entirely to final size and then heat-treating it risks discovering the part has warped past tolerance after the last operation.

your rule is to write the condition onto the drawing, not just the alloy. "6061" without a temper leaves the supplier to guess whether you want the machinable soft stock or the hardened final state, and the guess is rarely the one you meant. The full callout — alloy, temper, and any post-machining heat treatment — is what turns a material name into a material specification.