Design for Manufacturability, Not Just Precision
Tolerance ranges, GD&T callouts, and inspection methods that match what shops can hold on the floor, not what looks tight on a drawing. Pull the numbers you need before you quote
CNC Tolerance Guide
Tightening a linear callout from ±0.127 mm to ±0.012 mm on a CNC drawing roughly doubles the per-part price, extra setups, slower feeds, more inspection time. Tag the tight numbers on bores, dowel locations, and bearing seats. Leave cosmetic faces and non-mating walls at ISO 2768-m.
These standards apply to EPOC CRAFTER’s CNC Machining Services → · For design recommendations, see DFM Guidelines →
CNC Practical Tolerance Ranges
| Feature Type | General/Standard | Precision | Critical/Tight | Cost Impact |
|---|---|---|---|---|
| Linear Dimensions | ±0.127 mm | ±0.050 mm | ±0.012 mm | low |
| Hole Diameters | ±0.050 mm | ±0.025 mm | ±0.005 mm | medium |
| Flatness/Straightness | 0.100 mm | 0.050 mm | 0.010 mm | high |
| Surface Roughness (Ra) | 3.2 μm | 1.6 μm | 0.4 μm | medium |
Pro Tip:
A laser-cut blank holds ±0.1 mm on the outline. After MIG-welding two of those blanks into an assembly, expect ±0.5 to ±1.0 mm of distortion on the welded edge, more on long seams, more on thin gauge. Dimension the welded assembly from a post-weld datum, not from the cut edge.
Injection Tolerance Guide
Shrinkage runs 0.4–0.7% for ABS and 0.5–0.8% for PC. PP sits at 1.5–2.5%, PE at 1.5–3.0%. On a 100 mm wall, that gap is the difference between holding ±0.1 mm and fighting ±0.5 mm of part-to-part drift. Pick the resin first, then set the tolerance band, not the other way around.
See Rapid Injection Molding Services →
Molding Tolerance Guidelines
| Feature Type | General (DIN 16742 TG6) | Precision (TG4) | Critical (TG2) | Cost Impact |
|---|---|---|---|---|
| Linear (up to 100 mm) | ±0.200 mm | ±0.100 mm | ±0.050 mm | medium |
| Wall Thickness | ±10% of nominal | ±7% | ±5% | high |
| Draft Angles | 1.0° – 2.0°(standard) | 0.5° (textured needs more) | 0.25°(polished, ejection risk) | low |
Sheet Metal
A press brake leaves an angle within ±0.5° on a well-tuned machine and ±1° on production tooling that’s been running all shift. Material thickness varies too: 10 ga mild steel ships as “0.135 in” but lands anywhere between 0.129 and 0.141 in batch-to-batch. Both errors stack on a multi-bend part, three bends in series can shift the last flange by 1.5 mm even when each bend reads in spec.
Sheet Metal Fabrication Limits
| Feature Type | General/Standard | Precision | Critical/Tight | Cost Impact |
|---|---|---|---|---|
| Bending (Angle) | ±1.0° | ±0.5° | ±0.25° | medium |
| Hole to Edge(laser-cut) | ±0.150 mm | ±0.100 mm | ±0.075 mm | low |
| Hole-to-bend line | ±0.500 mm | ±0.300 mm | ±0.200 mm | medium |
| Flat Pattern(outline) | ±0.250 mm | ±0.150 mm | ±0.100 mm | medium |
ISO / ASME / JIS References
ISO 2768
•Production drawings where 80% of features are non-functional
•Sheet metal and weldments where tight per-feature callouts add cost without function
•Supplier RFQs where you want a baseline before negotiating exceptions
•Hand-written notes like “all dims ±0.1 unless otherwise stated”
•Per-feature tolerance boxes on every linear dimension
ASME Y14.5
•Mating features where ±tolerance alone can’t describe the fit (bearing bore + axis + perpendicularity)
•Anywhere a datum reference matters, bolt patterns, machined faces, gasket grooves
•Suppliers using CMM inspection (Y14.5 maps cleanly to CMM probe data)
•Linear tolerances on hole patterns (gives back the diagonal, true position recovers it)
•Loose “must be flat” or “must be parallel” notes
JIS B 0405
•Drawings supplied to or received from Japanese OEMs (Toyota, Honda, Sony, Panasonic supply chains)
•Tier-2/3 suppliers in Japan and Korea that still default to JIS title blocks
ISO 2768 callouts on drawings routed through a JIS-default supplier (functionally interchangeable, but the title block has to match)
Measurement Methods
| Inspection Tool | Bore Diameter | Flatness | Runout | Hole Position | Thread Pitch | Surface Finish |
|---|---|---|---|---|---|---|
| Caliper | Fair (±0.05 mm) | Poor | N/A | Fair | N/A | N/A |
| Micrometer | Good (bore mic / pin gauge) | N/A | N/A | N/A | N/A | N/A |
| CMM | Excellent | Excellent | Excellent | Excellent | Good (scanning probe) | N/A |
| Dial Indicator | N/A | Good | Excellent | N/A | N/A | N/A |
| Profilometer | N/A | N/A | N/A | N/A | N/A | Excellent (Ra/Rz direct) |
| Thread pitch gauge | N/A | N/A | N/A | N/A | Excellent | N/A |
