Milling, turning or both: reading your part before you ask for a quote
September 5, 2026
Most parts announce which process they belong to in the first five seconds of looking at the model. The ones that do not are usually round bodies with one awkward feature, and those are where quotes diverge the most.
Turning: the part spins, the tool stays
A lathe rotates the workpiece against a fixed tool. Anything with a dominant axis of revolution belongs here: shafts, pins, bushings, spacers, fittings, threaded bodies, nozzles.
- Typical tolerance: ±0.02 mm on diameters, tighter on ground seats
- What it is good at: concentricity, surface finish on cylindrical faces, removing a lot of material quickly
- Material form: bar stock, which is cheaper to buy and to hold than a block
A pure turned part with no off-axis features is the cheapest thing you can buy from a machine shop at volume. If your design can stay in that category, keep it there.
Milling: the tool spins, the part stays
A mill rotates the cutter and moves it across a clamped part. Anything prismatic belongs here: brackets, plates, housings, manifolds, covers, frames.
- Typical tolerance: ±0.05 mm general, ±0.02 mm on called-out features
- What it is good at: flat faces, pockets, bores in any direction, features that relate to each other on a rectangular datum
- Material form: plate or block, which costs more per kilogram and often becomes chips
The bulk of machined parts bought internationally are milled parts, and the bulk of shop capacity anywhere, Vietnam included, is 3-axis milling capacity.
The middle ground, where the money is
Many parts are round bodies with something that ruins the symmetry. A flat for a spanner. A cross hole. A keyway. A slot. A bolt circle on a flange.
Three ways a shop can make that part:
| Route | What happens | When it wins |
|---|---|---|
| Turn then mill | Turned on a lathe, then moved to a mill for the off-axis features | Low quantity, simple secondary feature |
| Mill-turn with live tooling | One machine turns and mills in a single setup | Repeat orders, several off-axis features, tight relationships between them |
| Mill from bar or block | Everything on a mill, rotary if needed | Very low quantity where lathe setup is not worth it |
The quotes for those three routes can differ by a factor of two on the same drawing. At 20 pieces the second operation on a mill is fine. At 2,000 pieces a shop with mill-turn will win the order and both sides will be better off.
This is why the quantity line in a request changes the answer so much. A shop cannot choose the route without it.
Features that force a decision
Cross holes in a shaft. Live tooling or a second op. Say whether the hole must be on centre within a tolerance, because that decides which.
A flat on a round boss. Cheap on a mill-turn, awkward as a second op if it has to be angularly located to another feature.
Threads. Single point threading on a lathe, tapping on a mill, or thread milling on either. If the thread is critical, call out the standard and the class rather than just the size.
A bolt circle on a flange. Trivial on a mill-turn with a C axis. On a lathe plus mill it means a fixture and an extra datum.
Concentricity between two diameters. Easiest in one turning setup. If you have specified runout between a diameter turned at one end and one turned at the other, say whether it can be done in two chuckings or must be in one.
What this means for your request
You do not need to tell the shop which machine to use. You need to give it the three things that decide:
- The quantity now and the quantity per year
- Which features relate to which datum, and how tightly
- Whether the surface finish on the round faces is functional or cosmetic
A shop that has these picks the cheapest route it owns. A shop that does not have them picks the safest route, which is the slow one, and you pay for the caution.
If your part is a family of similar shafts or fittings rather than a single item, say that too. Shops price a family very differently from a one-off, because the setup can be shared.
What a shop is deciding when it reads your part
Behind the quote there is a routing decision with four parts, and every one of them is affected by what you wrote in the request.
Stock form. Bar for turned parts, plate or block for milled ones. Bar is cheaper and holds better in a collet or chuck.
Number of operations. Turning the front, turning the back, then milling is three operations. A mill-turn with a sub spindle can be one.
Fixturing. A turned part needs jaws or a collet. A milled part may need soft jaws or a plate, and that has to be made for your part.
Inspection. Round features are measured differently from prismatic ones. A part with both needs both, and on tight work that means two instruments and two setups in the inspection room.
Three lines that change the routing
Add these to the description and the shop can pick the right cell straight away:
2,000 pieces per year, released quarterly. The cross hole must be within 0.1 mm of the centre plane. The 12 mm diameter runs in a bearing, everything else is clearance.
Quantity chooses the machine class, the position tolerance decides whether the off-axis feature can be a second operation, and the last sentence tells the shop where to spend its time.
When you are ready, the pre-send checklist covers the rest of what belongs in the message, and you can send the drawing here.
Questions we get on this
Is turning cheaper than milling?
For a round part, almost always. A lathe removes material continuously while the part spins, so metal comes off faster than a milling cutter stepping over a surface. The saving disappears as soon as the part needs a second operation on a mill.
What is mill-turn?
A lathe with driven tools and often a second spindle, so it can turn the part and also drill, mill flats, cut slots and tap holes without moving the part to another machine. It costs more per hour and usually less per part for anything round with off-axis features.
How do I know if my part needs both?
Look for a round body with a feature that is not concentric: a flat, a cross hole, a keyway, a slot or a hole pattern on a flange. Those cannot be made by turning alone.
Have a part like this?
Send the drawing. We shortlist the shop we place it with that run the process and material, and answer within 24 business hours.
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