CNC milling · Binh Duong, Vietnam
CNC milling in Vietnam: datums and bores, cut to GD&T on castings.
CNC milling here is a second step, not a standalone job shop: it is the CNC machining in Vietnam that turns a raw casting into a part that actually fits its mating hardware. Datum faces, bores, pockets and tapped holes, held to the concentricity you called out, on the machining centers at our lead CNC plant.
- Inches
- ±.001
- Bore tolerance on machined castings
- Inches
- Ø.003
- GD&T concentricity we hold
- RMS
- 125
- Standard as-machined finish
- Hours
- 48
- Quote returned from your drawing
01 — What we actually run
The step between "cast" and "fits."
Almost every milling job we run starts as a casting from the partner foundries we manage. That is a deliberate choice: we are strongest as the second operation in a routing, not as a general billet-machining shop taking in blanks from elsewhere.
Typical work
Datum faces machined flat for downstream assembly, bores bored and reamed to print, tapped holes and ANPT/NPT threads to ANSI/ASME B1.20.1, pockets and mounting features cut into ADC12 aluminum or Zamak 3 zinc castings, and machined bores on sand-cast brass and bronze valve bodies.
We hold concentricity because most of what we machine mates with a turned or pressed part downstream — a bushing, a shaft, a seal — and a bore that is round but off-center fails an assembly just as badly as one that is out of round.
Milled parts by industry: eccentric rings, spindle housings and brackets for machine tool and industrial equipment, and machined housings and valve bodies for gas and water distribution. Moving a machined part out of China? Read how US tariffs and country of origin apply to cast and machined parts.
02 — Process parameters
What we hold, and on what.
If your GD&T call-out is tighter than this table, say so before tooling — not after first samples.
| Parameter | Specification |
|---|---|
| Machined bore tolerance | ±0.001 in. (0.025 mm) |
| GD&T concentricity | To Ø0.003 in |
| Surface finish, as-machined | 125 RMS |
| Thread standard | ANPT and NPT to ANSI/ASME B1.20.1, tapped holes |
| Substrate materials machined | ADC12 aluminum die castings · Zamak 3 zinc die castings · sand-cast brass and bronze |
| Not offered | Simultaneous five-axis machining |
| Machines at the lead CNC plant | 12 machining centers and 9 CNC lathes, with EDM, welding and polishing alongside |
| Volumes we are set up for | Recurring production parts, from a few thousand into the hundreds of thousands a year; not a prototype shop |
| Inspection records you receive | A first-article report against every toleranced dimension, then a dimensional record with each lot |
| Where each step is done | Milling and inspection at our lead CNC plant · castings from partner foundries · finishing at partner plants; the quote names the production site and origin |
03 — Take cost out of the drawing
Where secondary-machining cost actually comes from.
Machining a casting well is mostly about not fighting the casting. These are the drawing choices that keep cycle time down.
1. Pick one datum scheme and use it on both drawings
If the casting drawing and the machining drawing reference different datums, we have to build a second fixture just to reconcile them. One consistent datum scheme keeps it to one setup. For general tolerance notes, NADCA casting grades and roughness conversions, see the ISO 2768 and NADCA tolerance guide.
How to choose those datums on the casting itself is covered in setting datums on castings for machining. Tapped holes in cast aluminum? See form tap vs cut tap and thread inserts vs tapped holes.
2. Reserve Ø0.003 in concentricity for fits that need it
Every GD&T call-out gets measured and logged. Apply the tight concentricity spec only where a bearing, bushing or shaft actually seats — a decorative bore does not need it.
3. Size bores to standard reamer and boring-bar diameters
An odd bore diameter that falls between standard tooling sizes forces a custom tool or a slower interpolated cut. Round to a standard size where the fit tolerance allows it.
4. Keep deep, tight-tolerance holes away from thin cast walls
Core shift during casting means a deep hole positioned near a thin wall can wander off true more than the wall thickness suggests. Position tight-tolerance features in the thicker sections of the casting.
5. Leave non-mating cast surfaces as-cast
A surface finish call-out on a face nobody touches just adds a machining pass for no functional reason. Call out a finer finish only where a gasket, seal or bearing actually lands; everywhere else, 125 RMS as-machined is the standard.
04 — Where this is the wrong process
What CNC milling does not do here.
Not a general billet-machining job shop
We are set up to machine castings efficiently, not to run large monolithic parts cut entirely from billet. If your part has no casting or forging step, a dedicated machining house is likely a better fit than we are.
We do not offer simultaneous five-axis work, on this process or any other. If your part needs it, we will tell you on the first call rather than after tooling.
05 — One supplier, one PO
Milling is the hinge between casting and finishing.
Almost nothing we machine ships unfinished — it goes from the mill at our lead CNC plant to a partner plant for plating or coating.
Die casting
ADC12 aluminum and Zamak 3 zinc housings, cast at partner foundries and machined to print at our lead CNC plant.
See die castingSand casting
Brass and bronze valve bodies, sand cast by a partner foundry and then bored and faced to print at our lead CNC plant.
See sand castingSurface finishing
A machined casting goes to a partner plant for plating, coating or pad printing before it is packed.
See the finish menu
Who is this a good fit for?
Industrial buyers in the United States and Europe who order the same parts from drawings again and again, at annual volumes from a few thousand into the hundreds of thousands. Every quote names the production site and the country of origin, the first article is measured against every toleranced dimension, and each lot ships with a dimensional record. One-off prototypes are a better fit for a prototype shop.
Do you offer five-axis machining?
No. If your part needs simultaneous five-axis motion, we are the wrong shop and would rather tell you now than after tooling is committed.
What is the tightest tolerance you can hold on a bore?
±0.001 in. (0.025 mm) on diameter, with GD&T concentricity to Ø0.003 in against a stated datum. If your print calls for tighter than that, tell us before tooling so we can be honest about whether we can hold it.
Can you machine a casting we already tool elsewhere?
Usually, yes, if the incoming casting passes our inspection for wall thickness and porosity. Send the drawing and a sample and we will quote the machining step on its own.
CNC turning and milling guides
Send a machining drawing. See what comes back.
STEP or PDF. You get a unit price at your volume, the lead time, and a short note on anything in the GD&T we would change to take cost out.