What tolerance can CNC turning hold?

Most job shops hold ±0.01–0.02 mm on turned diameters as standard. Closer limits, around ±0.005 mm, are possible on selected diameters with careful setup; tighter than that usually needs grinding.

Is there a minimum order quantity for CNC turning?

Not as a rule. Workshops do one-offs and prototypes, but the setup cost is the same for one piece or a hundred, so very small quantities cost more per piece.

What is a turn-mill centre?

A CNC lathe with driven (live) tools that can also mill flats, drill cross holes and cut slots while the part stays in the chuck, so the part is finished in one setup.

CNC turning or VMC: which one does my part need?

Round parts made around a centre line are turned. Flat or box-shaped parts with pockets, slots and hole patterns are milled on a VMC. Many parts need both: turned first, then milled.

How long does CNC turning take?

For a batch of simple parts with material in stock, often a few days to two weeks. Special material, heat treatment or plating add time; ask for the lead time with the quotation.

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CNC turning

Also called: CNC lathe work, CNC turning job work, turned parts, turning centre work

CNC turning makes round parts by spinning the workpiece while a computer-controlled cutting tool removes material. It is done on a CNC lathe or turning centre and produces shafts, pins, bushes, flanges and threaded parts, typically to ±0.01–0.02 mm.

Quick facts

Machines: CNC lathe, turning centre (turn-mill), sliding-head (Swiss-type) lathe
Typical tolerance: ±0.01–0.02 mm; ±0.005 mm on selected diameters with care
Typical surface finish: Ra 0.8–3.2 µm
Typical part size: From a few mm up to about Ø300–500 mm in most job shops
Quantities: One-offs to production runs of many thousands
Usually priced: Per piece

How CNC turning works

The bar or blank is held in a chuck or collet and spun by the spindle. Cutting tools mounted on a turret move along the length (Z axis) and across the diameter (X axis), following a program written from the drawing. Because the program repeats exactly, the hundredth part comes out like the first.

A turning centre with live tooling can also mill flats, drill cross holes and cut keyways while the part is still held, which saves a second setup on a milling machine. A bar feeder lets the machine run long batches with little attention.

Facing: cutting the end flat
OD turning: reducing the outside diameter, including steps, tapers and curves
Boring: enlarging and finishing an inside diameter
Grooving and parting: cutting grooves, and cutting the finished part off the bar
Threading: outside and inside threads, metric, inch or pipe
Drilling and reaming on the centre line

Typical parts and industries

Shafts, spindles, axles and pins
Bushes, sleeves, spacers and rollers
Flanges, couplings and pulleys
Hydraulic and pneumatic fittings, nozzles and valve parts
Studs, special bolts and threaded parts
Used by automotive, pump and valve, hydraulics, agricultural machinery, electrical and general engineering companies

Materials commonly turned

Carbon steels: EN8 / C45, EN9, free-cutting steel EN1A
Alloy steels: EN19, EN24, case-hardening EN353 and 20MnCr5
Stainless steels: SS304, SS316, SS410
Aluminium alloys: 6061, 6082, 7075
Brass, bronze and copper
Cast iron blanks and castings
Engineering plastics: nylon, acetal (Delrin), PTFE

What decides the price

Material: the grade, and the bar size it must be cut from
Cycle time: how much material comes off and how many operations the part needs
Setups: parts that must be turned around, or sent to a milling machine afterwards, cost more
Tolerance and finish: tighter limits mean slower cutting and more inspection
Quantity: setup and programming are shared across the batch, so larger batches cost less per piece
Extras: heat treatment, grinding, plating or coating, and inspection reports

Design tips that save money

Choose diameters close to standard bar sizes to reduce waste
Put tight tolerances only on the diameters that really fit with something
Use standard thread sizes, and leave a thread relief (undercut) where the thread ends
Avoid sharp inside corners; a small radius is cheaper and stronger
Long, thin parts (length more than about 4 times the diameter) need support and cost more; say if a slightly larger diameter is acceptable
If the part will be hardened and then ground, leave a grinding allowance on those diameters and mark it on the drawing

What to send a workshop for a quotation

Drawing (PDF), and a 3D model (STEP) if you have one
Material grade, and its condition if it matters (for example hardened and tempered)
Quantity, and how often you will reorder
Critical diameters, tolerances and surface finish
Heat treatment, coating or plating needed
Inspection requirements and the delivery date

CNC turning or conventional turning?

	CNC turning	Conventional (manual) turning
Best for	Repeat batches, complex profiles, tight tolerances	One-offs, repairs, simple parts
Repeatability	Very high: the program repeats exactly	Depends on the operator
Setup	Programming and setup time per job	Little setup
Typical tolerance	±0.01–0.02 mm	±0.02–0.05 mm

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Questions

What tolerance can CNC turning hold?: Most job shops hold ±0.01–0.02 mm on turned diameters as standard. Closer limits, around ±0.005 mm, are possible on selected diameters with careful setup; tighter than that usually needs grinding.
Is there a minimum order quantity for CNC turning?: Not as a rule. Workshops do one-offs and prototypes, but the setup cost is the same for one piece or a hundred, so very small quantities cost more per piece.
What is a turn-mill centre?: A CNC lathe with driven (live) tools that can also mill flats, drill cross holes and cut slots while the part stays in the chuck, so the part is finished in one setup.
CNC turning or VMC: which one does my part need?: Round parts made around a centre line are turned. Flat or box-shaped parts with pockets, slots and hole patterns are milled on a VMC. Many parts need both: turned first, then milled.
How long does CNC turning take?: For a batch of simple parts with material in stock, often a few days to two weeks. Special material, heat treatment or plating add time; ask for the lead time with the quotation.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 8 October 2026.