Design guide: tolerances, finishes and how we read your drawings
This is the reference behind every Zedaxis quote. Unless your drawing says otherwise, these are the tolerances we hold and the finishes we apply — so you can design to them, call out only what genuinely matters, and get a sharper price for it.
1. General tolerances — ISO 2768-mK
Every machined, laser-cut and folded part we make is held to ISO 2768-mK unless your drawing specifies something tighter: class m (medium) for linear and angular dimensions, class K for geometric tolerances. You don't need to write these on your drawing — they apply automatically. Write a tolerance only where a feature needs better than this.
Linear dimensions (ISO 2768-1, class m)
| Nominal size range (mm) | Permissible deviation |
|---|
| 0.5 up to 3 | ± 0.10 |
| over 3 up to 6 | ± 0.10 |
| over 6 up to 30 | ± 0.20 |
| over 30 up to 120 | ± 0.30 |
| over 120 up to 400 | ± 0.50 |
| over 400 up to 1000 | ± 0.80 |
| over 1000 up to 2000 | ± 1.20 |
| over 2000 up to 4000 | ± 2.00 |
External radii and chamfer heights (class m)
| Nominal size range (mm) | Permissible deviation |
|---|
| 0.5 up to 3 | ± 0.2 |
| over 3 up to 6 | ± 0.5 |
| over 6 | ± 1.0 |
Angular dimensions (class m)
| Length of shorter side (mm) | Permissible deviation |
|---|
| up to 10 | ± 1° |
| over 10 up to 50 | ± 0° 30′ |
| over 50 up to 120 | ± 0° 20′ |
| over 120 up to 400 | ± 0° 10′ |
| over 400 | ± 0° 5′ |
Geometric tolerances (ISO 2768-2, class K)
| Characteristic | Range (mm) | Tolerance (mm) |
|---|
Straightness and flatness
range = length of the line or longer side of the surface | up to 10 | 0.05 |
| over 10 up to 30 | 0.10 |
| over 30 up to 100 | 0.20 |
| over 100 up to 300 | 0.40 |
| over 300 up to 1000 | 0.60 |
| over 1000 up to 3000 | 0.80 |
Perpendicularity
range = length of the shorter side | up to 100 | 0.40 |
| over 100 up to 300 | 0.60 |
| over 300 up to 1000 | 0.80 |
| over 1000 up to 3000 | 1.00 |
| Symmetry | up to 300 | 0.60 |
| over 300 up to 1000 | 0.80 |
| over 1000 up to 3000 | 1.00 |
| Circular run-out | all | 0.20 |
What to put on your drawing. Leave general dimensions untoleranced — ISO 2768-mK covers them. Call out only the features that matter: a bearing bore as Ø30 H7, a critical spacing as 120 ± 0.05, a sealing face as Ra 0.8. Our quoting tool reads ISO fits, ± values and Ra callouts straight from your PDF and prices them at review, so the more precisely you say what matters, the less you pay for what doesn't.
Need the full ISO 286 limits & fits tables, a fit calculator, the RAL chart or our stocked grades? They live on our free reference site:
reference.zed-axis.co.uk.
2. Welded and fabricated assemblies — ISO 13920 class B
Welded constructions can't hold machined tolerances across a weld: heat moves metal. Fabricated and welded assemblies are therefore held to ISO 13920, class B (lengths and angles) unless your drawing says otherwise — and where a face or bore must be precise after welding, we machine it afterwards and tell you so on the quote. We are certified to EN 1090-2 EXC2 for structural steelwork.
| Nominal length range (mm) | Permissible deviation (class B) |
|---|
| 2 up to 30 | ± 1 |
| over 30 up to 120 | ± 1 |
| over 120 up to 400 | ± 2 |
| over 400 up to 1000 | ± 3 |
| over 1000 up to 2000 | ± 4 |
| over 2000 up to 4000 | ± 6 |
| over 4000 up to 8000 | ± 8 |
| Angular — length of shorter leg (mm) | Permissible deviation (class B) |
|---|
| up to 400 | ± 0° 45′ |
| over 400 up to 1000 | ± 0° 30′ |
| over 1000 | ± 0° 20′ |
Designing a weldment that needs precision? Add machining stock (typically 2–3 mm) on the faces or bores that matter and note “machine after welding” — we'll quote the extra operation and hold those features to ISO 2768-mK.
3. Sheet metal and laser cutting
- Cut profile: ISO 2768-m on the cut dimensions. Laser kerf is compensated in our programming — design to nominal.
- Minimum hole diameter: at least the material thickness (1 × t); for punched-quality round holes prefer 1.5 × t. Smaller holes are better drilled afterwards — say so and we'll quote it.
- Minimum slot width: 1 × t. Minimum web between features: 1.5 × t to avoid heat distortion.
- Folds: inside bend radius ≈ material thickness (tighter on request); bend angle ± 1°; flange length measured to the outside of the fold. Keep holes at least 2 × t + bend radius from a bend line or they will distort.
- Edge quality: laser-cut edges carry fine striations and a slight taper (roughly 0.1 mm per 10 mm of thickness); edges are deburred as standard. Mild steel up to 20 mm, stainless up to 15 mm, aluminium up to 12 mm.
- Countersinks and tapped holes in sheet: add the callout (e.g. “8× M6 tapped”, “4× CSK for M5”) to the drawing — the quoting tool reads these and includes them.
4. Surface finish by process
Roughness values are what you receive as standard from each process. If a face needs better, call out the Ra on the drawing and we'll add the finishing operation.
| Process | Typical as-produced Ra | Achievable on request | Notes |
|---|
| Laser-cut edge (steel, 1–10 mm) | 3.2 – 12.5 µm | — | Fine vertical striations; deburred both sides |
| CNC milled face | 1.6 – 3.2 µm | 0.8 µm | Visible tool path on large faces; finishing pass on request |
| CNC turned | 1.6 – 3.2 µm | 0.4 – 0.8 µm | Fine turning for seal and bearing diameters |
| Surface / cylindrical ground | 0.4 – 0.8 µm | 0.2 µm | Specify when fits, flatness or sealing demand it |
| Bead blasted | 1.6 – 3.2 µm (uniform matte) | — | Hides tool marks; standard under anodising |
| Cold-reduced sheet (CR4 / DC01), as supplied | 0.5 – 1.6 µm | — | Smooth mill finish, light oil |
| Hot-rolled plate (S275 / S355), as supplied | mill scale | — | Blast-cleaned before coating (Sa 2½) |
5. Finishes and coatings we apply
All of these are selectable on the instant-quote tool. Coating thickness adds to the part's dimensions — see the note under the table before you toleranced a plated thread or a powder-coated fit.
| Finish | Standard | Typical thickness | Good for | Design notes |
|---|
| Powder coating (RAL colours) | BS EN 13438 | 60 – 120 µm | Enclosures, brackets, frames — tough, uniform colour | Masking for threads and mating faces; radius sharp edges ≥ 0.5 mm for coverage; cured at ~200 °C |
| Wet paint | — | 30 – 60 µm per coat | Large fabrications, touch-up-able finishes | Primer + topcoat; colour to RAL |
| Zinc plating (clear or yellow passivate) | BS EN ISO 2081 | 5 – 12 µm | Fasteners, small brackets, indoor corrosion protection | Threads usually plated after tapping — fine for standard 6g/6H fits |
| Hot-dip galvanising | BS EN ISO 1461 | 45 – 85 µm (by steel thickness) | Outdoor and structural steelwork | Vent and drain holes in hollow sections are mandatory; thin sheet may distort; threads tapped after galvanising or oversize |
| Anodising — clear, black, colour | BS EN ISO 7599 | 10 – 25 µm | Aluminium parts needing wear and corrosion resistance with colour | Roughly half the film grows outward — allow ~10 µm per surface on fits; bead blast first for a matte look |
| Hard anodising — natural or black | BS ISO 10074 | 25 – 50 µm | Sliding and wear faces on aluminium | ~50 % outward growth; mask threads and precision bores |
| Black oxide / chemical blackening | — | ≈ 1 – 2 µm | Steel tooling, fixtures, fasteners — cosmetic, light corrosion resistance when oiled | No dimensional change; not for outdoor use |
Plating and fits. State whether a dimension applies before or after coating. Our default: tapped holes are tapped before plating/anodising and gauged after; turned fits are toleranced after coating. Tell us if your drawing assumes otherwise.
6. Heat treatment
| Option | Typical use | Design notes |
|---|
| Through hardening (harden & temper to HRC) | Shafts, dies, wear parts in EN8 / EN19 / EN24 | Specify the hardness range (e.g. 40–45 HRC); finish-grind after hardening for tight fits |
| Case hardening (carburise and harden) | Gears, pins, cams — hard skin, tough core | Specify case depth (e.g. 0.6–0.8 mm) and surface hardness; mask areas that must stay soft for machining |
| T condition (EN24T, EN19T as supplied) | General engineering strength without post-machining heat treatment | Ordered in the T condition — no further treatment needed |
| Stress relieving | Welded frames and large machined plates before final machining | Recommended when flatness after welding matters |
7. Material certification
A certificate of conformity (CoC) or mill certificate (EN 10204 3.1) can be supplied with any order — tick “Material cert required” on the part in the quote tool. Structural steelwork under EN 1090 is supplied with full traceability as standard.
8. Checklist before you upload
- STEP file for the 3D shape, plus a PDF drawing for tolerances, threads, finish and material — the tool reads both.
- Material grade written on the drawing (we map BS, EN and ASTM designations — e.g. S275JR / 1.0044, EN24T / 817M40, 304 / 1.4301).
- Only the critical dimensions toleranced; everything else rides on ISO 2768-mK.
- Thread callouts with count (“6× M8”), countersinks with the screw size, finish and colour (RAL) named.
- Quantity on the drawing matches the quantity you enter — price breaks start at 2, 10, 25 and 100 off.
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