A typical CNC machine shop holds plus or minus 0.005 in as a standard tolerance and plus or minus 0.001 in on precision features, with tighter limits possible on turned diameters and ground surfaces. What a machine shop can actually hold on your part depends on the feature, material, part size, and how the tolerance is measured.
Engineers often ask for a single number, but machining tolerances vary by process and feature type. This page gives typical tolerance ranges for CNC turning, milling, Swiss machining, and grinding, and explains what makes tight tolerances expensive.
Typical CNC machining tolerances by class
The values below are typical for a well-equipped precision CNC shop working in stable materials. They are guidelines, not guarantees for every geometry.
| Tolerance class | Typical value (in) | Typical value (mm) | How it is produced |
|---|---|---|---|
| Standard | +/- 0.005 | +/- 0.13 | Normal CNC turning and milling |
| Precision | +/- 0.001 | +/- 0.025 | Finish passes, controlled tooling, in-process checks |
| Tight | +/- 0.0005 | +/- 0.013 | Turned diameters and bores with temperature and tool wear control |
| Ground | +/- 0.0002 | +/- 0.005 | Centerless or surface grinding |
What affects the tolerance a machine shop can hold
Feature type
Turned outside diameters are usually the easiest features to hold tight because the lathe cuts around a single axis. Bored holes, milled pocket widths, and hole positions across a large part are harder. True position between features on different faces depends on how many setups are needed.
Material
Aluminum moves with temperature. Stainless steels and high-nickel alloys such as Inconel work harden and are harder on tools. Plastics can move after machining as stress relieves. Each affects the practical tolerance.
Part size and wall thickness
Long, thin, or slender parts deflect under cutting force. Swiss-type machining supports slender parts close to the tool, which helps hold diameters on small shafts.
Number of setups
Every time a part is re-clamped, some error enters. Lathes with live tooling and Y-axis, and horizontal machining centers with a rotary axis, reduce setups and hold feature relationships more consistently.
Measurement method
A tolerance is only as good as the ability to measure it. Tight tolerances need a CMM, calibrated gages, or an optical comparator, and a measurement uncertainty well below the tolerance band.
Typical tolerances by process
| Process | Typical feature | Typical achievable tolerance (in) |
|---|---|---|
| CNC turning | Outside diameter | +/- 0.0005 to 0.001 |
| CNC turning | Bore | +/- 0.0005 to 0.001 |
| Swiss turning | Small diameter on a slender part | +/- 0.0005 |
| Horizontal milling | Hole position, same setup | 0.001 to 0.002 true position |
| Horizontal milling | Milled face or pocket depth | +/- 0.001 |
| Centerless grinding | Outside diameter | +/- 0.0002 |
| Surface grinding | Thickness and flatness | +/- 0.0002 |
These are typical values under good conditions, not guarantees. Hole position across multiple setups, thin-wall parts, and difficult alloys typically need more allowance. Tolerance also interacts with finishing. Plating and anodizing add thickness, and heat treatment can distort parts, so pre-finish dimensions must account for both. If a tolerance applies after coating, state it on the drawing.
Why tight tolerances cost more
- Additional finish passes and slower feeds increase cycle time.
- More frequent tool changes and offset adjustments.
- Possible grinding as a separate operation.
- Longer inspection, sometimes 100 percent inspection of a feature.
- Higher scrap risk, which is priced into the quote.
The practical advice is to apply tight tolerances only where the part mates, seals, or locates, and leave everything else at the standard title block tolerance.
Tolerances at Wexmar
Wexmar turns parts on Mazak and Doosan CNC lathes, mills on Mazak horizontal machining centers, and runs small-diameter parts on Maier Swiss-type machines. For ground diameters and flats, the shop has a centerless grinder and a surface grinder. Dimensions are verified on Brown & Sharpe CMMs that are NIST-traceable and an optical comparator. See inspection and quality and our machine list.
Tolerance checklist for your drawing
- Title block tolerance set to a realistic default, such as plus or minus 0.005 in.
- Tight tolerances applied only to functional features.
- GD&T datums reflect how the part is used.
- Critical characteristics flagged for inspection reporting.
- Material and heat treat condition stated, since both affect achievable tolerance.
Getting a quote
If you are unsure whether a tolerance is realistic, send the drawing and ask. A Wexmar estimator will flag any feature that drives cost or risk. You can upload a drawing for an instant estimate or call (315) 400-2654.