The short answer
A precision lathe can hold far better tolerances than a general commercial turning job, but price rises fast once you push into tenths, thin walls, long reach, or hard materials.
What is realistic on a turned part
For general commercial turning, a shop will often quote around ±0.005 in on non-critical features. Precision turned diameters often land around ±0.001 in. Tighter than that is possible, but not free. Once you ask for ±0.0005 in or tighter, the shop starts managing machine condition, thermal growth, insert wear, in-process gaging, and lot size much more aggressively.
The print matters. A single ±0.0005 in diameter on a short, rigid feature is not the same as the same tolerance on a thin-wall tube, a long shaft between centers, or a part that needs post-heat-treat finish. The number alone does not define difficulty.
What drives cost
Material, part rigidity, L/D ratio, interrupted cuts, thread class, and surface finish all push cost. So does quantity. Tight tolerance on 5 parts often needs the same process discipline as tight tolerance on 500 parts, but setup is spread over far fewer pieces.
Secondary operations also matter. Grinding, lapping, honing, and post-process inspection can be the right answer when the lathe alone is no longer the cheapest way to guarantee the result.
How to avoid over-tolerancing
Put tight tolerances only on features tied to fit, sealing, bearing performance, or balance. Leave non-functional diameters and lengths on title-block tolerances. Buyers pay a hidden tax when every feature is made 'precision' by default.
A good supplier will challenge broad tolerance stacking and suggest datum-driven dimensions or selective grinding. That is not pushback. That is how experienced shops stop scrap before it starts.
Where drawings go wrong
Common failures are missing datum strategy, no note on stock allowance for grind, vague runout requirements, and thread callouts with no class or inspection method. Another classic error is mixing inch dimensions with metric gages and not telling the supplier which controls.
If cylindricity, roundness, or total runout matter, state those explicitly. A simple diameter tolerance does not communicate the full functional requirement.
What an experienced buyer does next
Related reading: Mill-turn machining: combining milling and turning in one setup and How to choose between 3-axis and 5-axis milling for your part.
The right move is usually to define the real functional requirement, remove the decorative requirements, and let the supplier build a route around what actually matters.
Comparison table where relevant
| Tolerance level | Typical range | What changes |
|---|---|---|
| General commercial | Around ±0.005 in | Standard process, limited in-process correction |
| Precision turning | Around ±0.001 in | Better workholding, wear control, more inspection |
| Very tight turning | ±0.0005 in and tighter | Thermal control, gaging, smaller process window |
| Best finish option | Grinding or honing post-turn | Higher cost, lower geometric risk |
How to specify this in your RFQ
Mark the few diameters that drive fit and performance. State whether tolerances apply before or after heat treat and finish. If runout matters, reference the datums. If grinding stock is needed, add it on the print instead of hoping the shop guesses correctly.
A clean RFQ does not just list requirements. It separates must-haves from preferences so the supplier can optimize where it is safe.
Have a part that needs quoting? Email your drawings to rfq@precisionmachining.co -
we return a competitive quote within 24 hours. Phone: +1 312-579-0808.