A useful manufacturing tolerances comparison begins with an uncomfortable fact: the tolerance on your drawing is a cost driver, not a wish. Ask for ±0.01 mm where ±0.1 mm would do, and you can quadruple the price of a part that fits perfectly either way. At Layer X in Satellite, Ahmedabad, we quote the same geometry across FDM, SLA, SLS, DMLS metal printing, fibre laser cutting, press-brake bending and injection tooling, so we watch identical features priced six different ways every week. This is the manufacturing tolerances comparison our applications engineers use on the shop floor — grounded in ISO 2768, ISO 286, ASME Y14.5 and ISO 8062 rather than marketing round numbers. Below you will see what each process holds as-built, what it reaches after finishing, and how to choose the loosest, cheapest route that still passes a CMM-verified dimensional report.
Key Takeaways
- CNC machining and finished DMLS hold the tightest tolerances — down to ±0.005 mm and ±0.05 mm — while sand casting is loosest at ±0.5–1.5 mm.
- Never quote a bare ± number; cite a standard such as ISO 2768-m, an ISO 286 IT grade, or an ASME Y14.5 feature control frame.
- 3D printing tolerances scale with part size and material — budget roughly ±0.3% on large SLS and DMLS parts, not a fixed figure.
- Layer X CMM-verifies critical dimensions and issues FAIR under AS9100, so tolerances are proven on paper, not just promised.
- The cheapest correct process is the loosest one that still meets fit and function — that gap is where real savings live.
What a tolerance actually means on the drawing
Before any manufacturing tolerances comparison is meaningful, the tolerance itself has to be defined properly. A ±0.1 mm scribbled beside a dimension tells a machinist almost nothing about datums, form or fit. Three standards do the real work:
- ISO 2768 sets general, unmarked linear and angular tolerances in four classes — f, m, c and v — so a title-block note like "ISO 2768-mK" covers every dimension you did not individually tolerance.
- ISO 286 defines the limits-and-fits system (IT01–IT18, plus H7, g6 and friends) for holes and shafts that must mate.
- ASME Y14.5 adds geometric dimensioning and tolerancing — flatness, position and true datums — controlling how a part functions, not merely how big it is.
| Nominal size | Fine (f) | Medium (m) | Coarse (c) |
|---|---|---|---|
| 0.5–3 mm | ±0.05 mm | ±0.1 mm | ±0.2 mm |
| 6–30 mm | ±0.1 mm | ±0.2 mm | ±0.5 mm |
| 30–120 mm | ±0.15 mm | ±0.3 mm | ±0.8 mm |
| 120–400 mm | ±0.2 mm | ±0.5 mm | ±1.2 mm |
Under ISO 2768-1, a "medium" (m) general tolerance permits ±0.3 mm on any unmarked dimension between 30 mm and 120 mm — a band most shops meet without inspection, and the sensible default for non-critical features.
3D printing tolerances: FDM, SLA, SLS and DMLS
Additive processes are the widest band in any manufacturing tolerances comparison, because each one melts, cures or sinters differently. Layer height, thermal shrinkage and raw part size all move the number, so a single fixed ± figure is misleading above roughly 100 mm.
- FDM — ±0.3–0.5 mm; fine for jigs, fixtures and form-study models.
- SLA — ±0.1–0.2 mm with crisp detail; ideal for master patterns and housings.
- SLS nylon — ±0.3 mm or ±0.3% of the dimension, whichever is larger.
- DMLS metal — ±0.1 mm as-built, tightening to ±0.05 mm on controlled features.
On a recent titanium bracket for an aerospace customer, our team held ±0.05 mm on the datum bosses as-built, then finish-machined the bearing bore to an H7 fit. That hybrid route — print near-net, machine what matters — is the core of our DMLS metal 3D printing service, and the reason additive now meets drawings that once demanded solid billet.
ASTM F3091, the standard specification for powder-bed fusion of polymers, formalises SLS dimensional and mechanical expectations — proof that additive tolerances are now standardised, not improvised.
CNC machining tolerances: the benchmark
CNC milling and turning set the reference point everyone else is measured against in a manufacturing tolerances comparison. A well-maintained 3-axis mill holds ±0.025 mm (±0.001") comfortably; precision setups reach ±0.005 mm. Four things decide where you land:
- Machine rigidity and spindle runout.
- Fixturing — every re-clamp of the part adds error.
- Tool wear and thermal growth across a long cycle.
- Material behaviour — aluminium 6061 is stable; annealed stainless moves.
| Feature | ISO 286 grade | Tolerance at 25 mm |
|---|---|---|
| Reamed / bored hole | IT7 | ±0.011 mm |
| General machining | IT9 | ±0.031 mm |
| Rough milling | IT11 | ±0.075 mm |
We lean on this precision to finish our own DMLS parts and press-brake tooling, closing a printed bore from ±0.1 mm to a ±0.011 mm reamed fit wherever a bearing demands it.
ISO 286 defines IT7 as the workhorse grade for machined fits — the tolerance class behind almost every H7 bore in a gearbox or bearing housing.
Sheet metal tolerances: laser cutting and bending
Sheet metal splits into two tolerance conversations — the flat cut and the formed bend — and conflating them causes most rejects in this corner of a manufacturing tolerances comparison. The cut is precise; the bend accumulates error.
- Fibre laser cutting — ±0.1 mm on profile, kerf 0.1–0.2 mm, edge quality graded by ISO 9013.
- Press-brake bending — ±0.2 mm on bend position, ±0.5° on angle for a single bend.
- Stack-up — each additional bend adds roughly ±0.1–0.2 mm as errors compound.
| Operation | Position tolerance | Angular tolerance | Standard |
|---|---|---|---|
| Laser profile cut | ±0.1 mm | — | ISO 9013 |
| Single press-brake bend | ±0.2 mm | ±0.5° | ISO 2768-m |
| Four-bend part | ±0.5 mm | ±1° | ISO 2768-c |
For a control-cabinet chassis we recently laser-cut and folded, we called ISO 2768-m on the flat pattern and tightened only the two mounting-hole datums — a pragmatic split you can specify through our CNC sheet metal fabrication service.
ISO 9013 grades thermally cut edges by tolerance range and perpendicularity; a fibre laser routinely achieves its highest quality class on mild steel up to 6 mm.
Casting tolerances: why they run loose
Casting anchors the loose end of every manufacturing tolerances comparison. Molten metal shrinks as it solidifies, moulds shift and cores drift, so as-cast tolerances follow ISO 8062 and its Dimensional Casting Tolerance Grades (DCTG) rather than the tight bands of machining.
- Sand casting — ±0.5–1.5 mm, roughly DCTG 9–11.
- Investment casting — ±0.1–0.5 mm, about DCTG 4–6.
- Die casting — ±0.05–0.1 mm on small features, DCTG 4–5.
We rarely pour metal in-house, but when a customer arrives with an as-cast housing, we treat the casting as a rough blank and machine every mating face — the same near-net logic we apply to DMLS parts.
ISO 8062-3 typically assigns sand casting grade DCTG 9–11, which on a 100 mm dimension permits a band of ±1 mm or more — an order of magnitude looser than CNC machining.
Manufacturing tolerances comparison: choosing the right process
Put side by side, the manufacturing tolerances comparison below turns process selection into a two-minute decision. Match the tightest critical dimension to the loosest process that clears it — then finish only the features that truly need it.
| Process | Typical tolerance | Best achievable | Standard reference |
|---|---|---|---|
| FDM | ±0.3–0.5 mm | ±0.2 mm | ISO 2768-c |
| SLA | ±0.1–0.2 mm | ±0.05 mm | — |
| SLS nylon | ±0.3 mm / ±0.3% | ±0.2 mm | ASTM F3091 |
| DMLS metal | ±0.1 mm | ±0.05 mm | ISO 2768-f |
| CNC machining | ±0.025 mm | ±0.005 mm | ISO 286 IT7 |
| Fibre laser cutting | ±0.1 mm | ±0.05 mm | ISO 9013 |
| Press-brake bend | ±0.2 mm / ±0.5° | ±0.1 mm | ISO 2768-f |
| Investment casting | ±0.3–0.5 mm | ±0.1 mm | ISO 8062 DCTG 5 |
| Sand casting | ±0.5–1.5 mm | ±0.5 mm | ISO 8062 DCTG 9 |
- Fix fit and function first — which two or three dimensions actually matter?
- Assign the loosest standard that still works, starting at ISO 2768-m.
- Choose the cheapest process that clears those critical dimensions, not the whole part.
- Add finishing — reaming, machining, grinding — only where the drawing demands it.
Every Layer X job that carries a tight callout leaves with a CMM report and, on request, a full AS9102 FAIR, so the tolerance you specified is the tolerance we prove — the evidence layer that makes any manufacturing tolerances comparison real rather than theoretical.
Frequently Asked Questions
Which process has the tightest manufacturing tolerances?
CNC machining leads at ±0.005 mm on precision features, followed by finished DMLS metal parts at ±0.05 mm. For a like-for-like manufacturing tolerances comparison, remember that any additive or cast part can be machined afterwards to reach machining-grade fits where they count.
Can 3D printing replace CNC for tight-tolerance parts?
Partly. DMLS holds ±0.1 mm as-built and ±0.05 mm on controlled features, but for H7 bores and sealing faces we finish-machine the printed blank. The hybrid approach gives additive geometry with machined accuracy.
What tolerance should I put on a non-critical dimension?
Default to ISO 2768-m and tighten only the handful of dimensions that affect fit or function. Over-tolerancing every feature is the single most common cause of an inflated quote.
Do you supply inspection data with parts?
Yes. Under our AS9100 system we provide CMM-verified dimensional reports and, on request, full AS9102 first-article inspection, with material traceability on every order.
Send us your drawing and we will return a process-by-process manufacturing tolerances comparison with pricing and inspection level for each route. Request a 24-hour quote.