InsightsCategory: Know-how
Mill-turn: when does one machine pay off?
Part 2 of 8 in the series From the shop floor
Short answer
Mill-turn pays where setups, fixtures and the position of features relative to the axis make the price. A mill-turn machine costs more per hour, but it saves a second machine, a fixture and the wait in between. In large batches of simple work that flips: the minutes carry the price, and the fastest machine per operation wins.
On this page
What is mill-turn, and what is it not?
Mill-turn is turning and milling on one machine, in one setup. Besides the main spindle, a mill-turn machine carries driven tools on the turret that drill and mill while the C axis holds the workpiece at an angle or turns it under control. A Y axis takes those tools off centre; larger machines add a milling spindle on a B axis for angled holes.
With live tooling and sub-spindle, a part comes off the machine finished: the sub-spindle takes it over at part-off and the back face is done in the same cycle. This is complete machining, and the aim is fewer fresh starts, not faster cutting.
What it is not: a lathe with one driven drill for a single cross hole. The spanner flat still goes to the mill. The process is described under mill-turn, the first choice under milling or turning.
What does the second machine cost on the classic route?
On the classic route the part goes from the lathe to a milling machine for the flat and the cross hole. Each step is simple; the cost sits between them.
The mill needs a second setup, often in a fixture that locates on the turned diameter. That brings a new work origin and a first part to measure. The Lean Enterprise Institute counts changeover time from the last piece of one run to the first good piece of the next. On this route you pay that time twice, once on each machine.
Then a tray of turned parts waits for the mill, and that queue counts towards the lead time. Each re-clamp can also shift the cross hole relative to the axis: the error of the fixture stacks on the error of the turning.
| Criterion | Turn, then mill | Mill-turn |
|---|---|---|
| Setups | Two or more, on two machines | One, sometimes with a sub-spindle transfer |
| Fixture | Often needed for flats and cross holes | Usually not |
| Hourly rate | Two lower rates | One higher rate |
| Position relative to the axis | Depends on re-clamping and the fixture | Fixed in one setup |
| Programming | Two simple programs | One more complex program |
| Throughput time | Waiting between two machines | One place, less waiting |
| Suits | Large batches, little milling | Many small milled features around the axis |
Which features make a part a mill-turn part?
Start with what sits off the axis. Cross holes, spanner flats, eccentric holes, slots and faces on the outside diameter are milled features on a turned part. One of them rarely justifies an expensive machine. A handful around the same axis often does.
Keep features, requirements and operations apart. ‘Six holes, two of them threaded’ says what is on the part. ‘With a position tolerance to the turned axis’ is the requirement. Drilling, tapping and milling are the operations, and only those choose a machine.
The requirement often weighs more than the feature. A tolerance can change whether a part has a feasible route in a given factory at all, as Subduxion Research puts it. How such a requirement appears on the drawing is set out in ISO 1101. What that means for the route is covered in position tolerance and route.
How much does the higher hourly rate weigh?
A mill-turn machine costs more to buy than a plain lathe, and that shows up in the hourly rate. Wikipedia's overview of multiaxis machining names the trade-off: fewer setups and less opportunity for error, at the cost of a more complex and more expensive machine.
So work with a rate per machine, as in machine hour rate, not one average for the shop. On an average the mill-turn machine seems cheaper than it is. A portal that quotes one price per machine group averages away exactly the difference this decision turns on.
The high rate applies to every minute of the cycle time, including turning a lathe would do as well for less. Against that, programming time and setup time fall only once, and the fixture drops out. Which side wins depends on the batch size.
Worked example: a shaft with a flat and a cross hole
A shaft of Ø 30 by 120 mm in 1.4305, 50 parts, with a spanner flat and a cross hole. Hourly rates: lathe € 70, milling machine € 80, mill-turn machine € 120, programming € 80. Setup takes 1 hour on the lathe plus 1.5 hours on the mill, or 1.5 hours on the mill-turn machine; programming 1 or 1.5 hours. One-off lines are divided by 50.
At 50 parts mill-turn wins at € 20.00 against € 22.40 for the classic route: the fixture and the double setup make the difference. The mill-turn machine finishes the part in 7 minutes, quicker than 6 plus 3 on two machines, but each of those minutes costs € 2.00. At 500 parts it flips: the classic route costs € 12.14, mill-turn € 14.60. In this example the break-even sits at about 90 parts.
If the part repeats and you keep its fixture on the shelf as a dedicated fixture, the € 6.00 line drops out. The classic route then costs € 16.40 at 50 parts and is the cheaper one at every batch size in this example.
| Line per part | Turn, then mill | Mill-turn |
|---|---|---|
| Setup | € 3.80 | € 3.60 |
| Fixture for flat and cross hole (€ 300 one-off) | € 6.00 | none |
| Programming | € 1.60 | € 2.40 |
| Turning (6 minutes) | € 7.00 | in one cycle |
| Milling (3 minutes) | € 4.00 | in one cycle |
| Mill-turn (7 minutes) | none | € 14.00 |
| Per part at 50 | € 22.40 | € 20.00 |
When does mill-turn not pay?
Plain turned parts with no milled features pay the high rate for tools that stand idle. Put them on a lathe, with a bar feeder if the batch can run unattended.
Heavy milling belongs on a machining centre. Driven tools on a turret have less power and stiffness than the spindle of a machining centre, so a large pocket or a lot of stock comes off faster there.
When the mill-turn machine is already full, every part that goes on it without need pushes out work only that machine can do. That call belongs to the shop's planning, across every order.
Two shops with the same nominal machine do not necessarily have the same practical capability, Subduxion Research notes: tool libraries, fixtures and programming strategies differ. A route picked from outside the shop is priced for a shop that does not exist.
Rule of thumbMill-turn wins where setups and fixtures make the price. Where cycle time makes the price, the fastest machine per operation wins.
How to choose the route for a mill-turn part
The manufacturing engineer and the cost engineer run through these questions per part, not per machine group. Note the answers in the estimate, so the choice can be traced at the repeat order.
- How many features sit off the axis: flats, cross holes, slots?
- Is there a position tolerance to the turned axis?
- Does the classic route need a fixture, and does one exist already?
- What is the hourly rate of each machine on the route?
- How many parts, and will the part come back as a repeat order?
- Is the mill-turn machine free, or would this part push out work only it can do?
In Blake
In Blake the turning and milling operations of one part sit in one estimate, each as a separate line at the hourly rate of the machine you choose. In the machine registry you record envelope, axes and rate per machine, so lathe, machining centre and mill-turn machine each price with their own figure. Every line shows time, rate and quantity, per part and per quantity break, so you can check where setup, programming and cycle time make the price. Change a line and Blake records who, when and why. Setups proposed by Blake itself will be the next step.
Frequently asked questions
What is the difference between turning and mill-turn?
In turning the workpiece spins and a tool that does not rotate cuts it. Mill-turn adds driven tools that drill and mill on the same machine, so flats and cross holes are finished in the same setup.
When is a mill-turn machine too expensive for a part?
When cycle time makes the price and there is little milling. In large batches of simple turned parts you pay the high hourly rate for every minute, while a lathe turns them for less.
Can you drill cross holes on an ordinary lathe?
Only if the lathe has live tooling. Without it the part goes to a milling or drilling machine, usually in a fixture that locates on the turned diameter.
How do you set the hourly rate for a mill-turn machine?
As for any machine: the yearly cost of depreciation, interest, maintenance, energy, floor space and software, divided by the productive hours. Keep it as its own rate; a shop-wide average hides exactly the difference.
Why does a cross hole drift when you re-clamp?
Because every new setup has its own work origin and its own clamping error. The hole is then placed relative to the fixture, not to the axis the part was turned on. In one setup that reference stays the same.
Sources
- Wikipedia, Multiaxis machining, accessed November 2026 (opens in a new tab)
- NEN, NEN-EN-ISO 1101:2017, Geometrical product specifications (GPS), geometrical tolerancing: tolerances of form, orientation, location and run-out, accessed November 2026 (opens in a new tab)
- Lean Enterprise Institute, Lean lexicon: Changeover, accessed November 2026 (opens in a new tab)
- Subduxion Research, Manufacturability is not a geometry check, September 2026 (opens in a new tab)
- Subduxion Research, Why machine selection is a reasoning problem, not a database lookup, September 2026 (opens in a new tab)