Resources · Tolerances
Aluminum extrusion & CNC tolerances
What tolerance you can expect, and where to spend effort: extrusion per EN 755-9, machining per ISO 2768, with notes on when to machine critical features.
Extrusion tolerances (EN 755-9)
Extruded profiles are held to EN 755-9 general tolerances — typically fractions of a millimeter on dimensions, with straightness and twist also specified. Tighter bands are possible with post-extrusion machining.
| Feature | Typical (EN 755-9) |
|---|---|
| Cross-section dimension | ±0.1 to ±0.3 mm (size-dependent) |
| Wall thickness | ±0.1 to ±0.2 mm |
| Straightness | per standard length class |
| Twist | per standard length class |
CNC machining tolerances (ISO 2768)
Machined features follow ISO 2768 (medium, or fine on request). Positioning can reach ±0.01 mm on our centers.
| Feature | Typical |
|---|---|
| Linear machined dim | ±0.05 to ±0.1 mm (ISO 2768-m) |
| Positioning | ±0.01 mm |
| Hole / thread | H7 / 6H typical |
| Surface (Ra) | 0.8 achievable |
Tube bending tolerances
Bent sections are held to the bend angle and the centerline radius; wall thinning on the inside of the bend depends on the R/D ratio. We specify mandrel bending to protect the inside wall on thin tubes.
| Feature | Typical |
|---|---|
| Bend angle | ±1–2° typical |
| Centerline radius (R/D) | ≥ 1.5 typical; smaller with mandrel support |
| Wall thinning | ~5–15% depending on R/D and wall |
| Ovality | kept within spec by mandrel / wiper tooling |
Welding & assembly tolerances
Welding holds fit to the prepared joint; the main risk is distortion, controlled by joint prep, sequencing and fixturing. Final dimensions are confirmed by gauge or CMM after weld.
| Feature | Typical |
|---|---|
| Joint fit (prep) | ±0.1–0.2 mm typical |
| Weld distortion | controlled by sequence & fixture; verify after |
| Leak (cold plate / sealed) | ≤1×10⁻⁹ mbar·L/s helium, hydrostatic above WP |
| Final dim check | gauge / CMM to drawing |
How to specify
- Let extrusion hold general shape; machine only critical faces, holes and threads.
- Mark true datums so inspection is unambiguous.
- Ask for fine class (ISO 2768-f) only where needed — it costs more.
Questions buyers ask first
On tolerances and where to spend the effort.
What tolerance can aluminum extrusion hold?
Extruded profiles follow EN 755-9 general tolerances — typically ±0.1 to ±0.3 mm on cross-section dimensions and ±0.1 to ±0.2 mm on wall, with straightness and twist set by length class. Tighter values come from post-extrusion machining referenced to true datums. The exact band depends on section size and alloy, confirmed against your print.
When should I machine instead of extrude to tolerance?
Machine any feature that must vary along the length, any hole, thread, or seat that needs a tight fit, and any face used as a datum. Extrusion is for the constant shape; machining is for the precise features. Marking true datums lets us machine from the same reference the profile was extruded to, so the part inspects cleanly.
What CNC tolerance can you hold?
Machined features follow ISO 2768 (medium, or fine on request); positioning can reach ±0.01 mm on our centers, holes to H7 / threads to 6H, and surface finish Ra 0.8 is achievable. These are typical ranges — your drawing and acceptance plan set the final call.
What tolerance can tube bending and welding hold?
Bends hold angle to about ±1–2° and centerline radius to an R/D of 1.5 or more (smaller with mandrel support); wall thinning runs ~5–15% depending on R/D. Welding holds fit to the prepared joint (±0.1–0.2 mm) and controls distortion by sequencing and fixturing, with final dims confirmed by gauge or CMM. Sealed welds and cold plates are helium leak-tested to ≤1×10⁻⁹ mbar·L/s. Full bands are above.
Unsure what to call out?
Send the drawing — we flag which dims need machining vs extrusion tolerance.