Face milling
Best for: Generating a flat reference face and controlling flatness
Indicative
Milling
Milling for steel: tolerances, flatness, surface finish and what a quote needs
Milling is machining steel with a rotating cutter to hit a dimension, a flat face or a pocket a saw cannot produce. This page covers what a milling quote actually turns on: the ISO 2768 tolerance and flatness class you can realistically call out, the surface finish a face mill leaves behind, and what a provider needs from you before they can price the job. It covers face milling, pocketing and milling plate to a tighter size than as-rolled — not turning or general CNC work, which is its own service.
What drives the price
- Material thickness and how much stock has to come off
- Steel grade and machinability
- Tolerance class (ISO 2768)
- Surface finish requirement
- Feature complexity — pockets versus a flat face
- Total volume
- Fixturing requirement
What to send for a quote
- A drawing with dimensions
- Grade or material number
- Tolerance class (ISO 2768) or individual tolerances
- Required surface finish (Ra)
- Quantity
- Whether you need an inspection certificate
- Delivery address and required date
Traceability and EN 10204 certificates
- 2.1
- 2.2
- 3.1
- 3.2
Standard for steel purchases: 3.1
The certificate belongs to the material, not to the milling operation. Milling does not create an EN 10204 certificate — the real question is whether the material's traceability survives being cut into smaller milled pieces, and how each piece is marked so that it does.
Standard-defined
Source: EN 10204 defines inspection-document types; confirmed offered as 'Werkszeugnis 2.2 or Abnahmeprüfzeugnis 3.1' by holter-eisenhandel.de/anarbeitung/werkszeugnisse.
Achievable dimensional tolerances — ISO 2768-1
ISO 2768-1
| 0.5 – 3 mm | f — fine: 0.05 mm · m — medium: 0.1 mm · c — coarse: 0.2 mm | ||
|---|---|---|---|
| 3 – 6 mm | f — fine: 0.05 mm · m — medium: 0.1 mm · c — coarse: 0.3 mm · v — very coarse: 0.5 mm | ||
| 6 – 30 mm | f — fine: 0.1 mm · m — medium: 0.2 mm · c — coarse: 0.5 mm · v — very coarse: 1 mm | ||
| 30 – 120 mm | f — fine: 0.15 mm · m — medium: 0.3 mm · c — coarse: 0.8 mm · v — very coarse: 1.5 mm | ||
| 120 – 400 mm | f — fine: 0.2 mm · m — medium: 0.5 mm · c — coarse: 1.2 mm · v — very coarse: 2.5 mm | ||
| 400 – 1000 mm | f — fine: 0.3 mm · m — medium: 0.8 mm · c — coarse: 2 mm · v — very coarse: 4 mm | ||
| 1000 – 2000 mm | f — fine: 0.5 mm · m — medium: 1.2 mm · c — coarse: 3 mm · v — very coarse: 6 mm | ||
| 2000 – 4000 mm | m — medium: 2 mm · c — coarse: 4 mm · v — very coarse: 8 mm |
Indicative figures. Confirm the achievable tolerance, flatness and finish with the provider for your grade, section and quantity.
Supplier-published
Achievable flatness and straightness — ISO 2768-2
ISO 2768-2
| 10 mm | H: 0.02 mm · K: 0.05 mm · L: 0.1 mm | ||
|---|---|---|---|
| 10 – 30 mm | H: 0.05 mm · K: 0.1 mm · L: 0.2 mm | ||
| 30 – 100 mm | H: 0.1 mm · K: 0.2 mm · L: 0.4 mm | ||
| 100 – 300 mm | H: 0.2 mm · K: 0.4 mm · L: 0.8 mm | ||
| 300 – 1000 mm | H: 0.3 mm · K: 0.6 mm · L: 1.2 mm | ||
| 1000 – 3000 mm | H: 0.4 mm · K: 0.8 mm · L: 1.6 mm |
Supplier-published
Surface finish by pass
| Rough milling pass | 3.2 – 6.3 µm · 3.2 µm | Supplier-published | Source: Precision Smith surface-roughness guide — rough face/end milling Ra range |
|---|---|---|---|
| Finish milling pass | 1.6 µm · 0.8 µm | Supplier-published |
Not achievable by milling alone on most materials — needs grinding, lapping, polishing or electropolishing as a follow-on step.
What milling covers
Pocketing
Best for: Enclosed cavities, slots and recessed features
Indicative
Milled-to-size plate
Best for: Plate that needs a tighter thickness or flatness than as-rolled stock provides
Indicative
Services
What tolerance can milling achieve?
ISO 2768-1 sets four general tolerance classes for linear dimensions: f (fine), m (medium), c (coarse) and v (very coarse). On a dimension from 30 to 120 mm, for example, published engineering-reference tables restating the standard give ±0.15 mm in class f, ±0.3 mm in class m, ±0.8 mm in class c or ±1.5 mm in class v. Tolerance widens with size rather than staying fixed — on a larger dimension, say 1000 to 2000 mm, the same table gives ±0.5 mm in class f, ±1.2 mm in class m, ±3 mm in class c or ±6 mm in class v. Check the full table for your dimension. Milling shops most commonly quote class m or class f. Confirm the achievable tolerance for your grade, section and quantity with the provider.
What flatness can a milled surface hold?
Flatness and straightness are covered by ISO 2768-2, in classes H, K and L, and the applicable row depends on the larger side length of the surface (or the diameter, for a round one). On a 100 to 300 mm face, published engineering-reference tables restating the standard give 0.2 mm in class H, 0.4 mm in class K or 0.8 mm in class L. A face-milling call-out for 'flat' is not a complete specification without a length and a class letter — put both on the drawing.
What surface finish does milling leave?
A rough milling pass typically leaves Ra 3.2 to 6.3 µm, with 3.2 µm the best case. A finish pass typically reaches Ra 1.6 µm and can get to Ra 0.8 µm on steel with a sharp tool and the right feed and stepover. Getting below Ra 0.4 µm needs a follow-on step — grinding, lapping, polishing or electropolishing — milling alone will not get you there on most materials.
Which ISO 2768 class should I specify — f, m, c or v?
It comes down to what the part actually needs and what it costs to hold. Class f (fine) and class m (medium) are the two milling shops quote most often; c (coarse) and v (very coarse) exist for parts where dimensional accuracy genuinely does not matter, such as some fabrication blanks. Tighter classes cost more to hold in machining time and inspection, so specify the loosest class the part's function allows rather than defaulting to the tightest one.
What information do you need for a milling quote?
Send a drawing with dimensions, the grade or material number, the tolerance class (ISO 2768) or your individual tolerances, the surface finish you need, quantity, whether you require an inspection certificate, and the delivery address and date. Those seven things are what turn an enquiry into a firm price rather than a range.
Do I get an EN 10204 3.1 certificate?
EN 10204 defines inspection document types 2.1, 2.2, 3.1 and 3.2, and 3.1 is the usual buyer default in steel procurement — one supplier we checked offers exactly 'Werkszeugnis 2.2 or Abnahmeprüfzeugnis 3.1'. But milling does not create the certificate — the certificate belongs to the material. What matters is whether traceability survives the material being cut into smaller milled pieces, and how each piece is marked so it stays linked to its heat. Ask the provider that directly.
Which steel grades can be milled?
Milling works across the common structural and engineering steel grades, but machinability differs by grade — it is one of the things that drives the price and the achievable finish. We have no sourced list of which grades a given provider mills, so ask directly rather than assuming a grade is covered.
Can I send my own material to be milled?
Milling customer-supplied material is common practice, but whether a given shop accepts it — and on what terms regarding liability, remnants and traceability — varies by provider. Ask before shipping. If the material carries an inspection certificate, ask in the same message how they will mark the milled pieces so that traceability survives.
Is there a minimum order quantity?
There is no industry-wide minimum order quantity for milling; it varies by provider. Some will mill a single piece, others price small quantities in a way that makes them impractical. Ask as part of your enquiry rather than assuming.
What is the lead time?
No general lead time can be stated honestly for milling — it varies by provider, and with feature complexity, tolerance class, quantity and their current load. Ask for a committed date with your quote rather than assuming a standard turnaround.
What is the difference between milling and CNC turning?
Milling removes material with a rotating cutter against a stationary (or fixtured) workpiece, which is what generates flat faces, pockets and slots. Turning rotates the workpiece against a stationary cutting tool, which is what produces round, symmetric features — shafts, bores, threads. If your part is a flat plate, a bracket or anything with pockets, that's milling; if it's a cylindrical part, that's turning, which sits under our CNC machining service rather than this one.
What does milling steel cost?
Milling is not priced from a single rate, so any figure quoted here would mislead. What drives it is material thickness and how much stock has to come off, steel grade and machinability, the tolerance class you require, the surface finish, feature complexity — pockets cost more than a flat face — total volume, and any fixturing the job needs. Send the seven items in the quote checklist and you will get a firm price instead of a range.
