Types of Turn-Mill Centre and how to choose between them
Turn-Mill Centre is a lathe with driven tooling and a Y axis, so milling and turning are completed in one machine. It is used for complex parts that would otherwise move between a lathe and a machining centre. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, robotics is used as the example: repeatability across a family of near identical parts.
The main types
Turn-Mill Centre is not one thing. The variants below differ in what they suit, and the choice is usually made on the part rather than on preference.
- Single turret with driven tools – suited to medical device bodies.
- Twin turret – suited to aerospace fittings.
- With a lower turret and a sub spindle – suited to hydraulic components.
- With a B axis milling head – suited to instrument housings.
How to choose
Start from the feature that has to work, then from the quantity. A robotics run suits one arrangement, a repeat run suits another, and the wrong choice shows up as cost rather than as failure.
The second question is what has to be measured. Where ISO 13485 or AS9100 depending on the part applies, the inspection requirement usually decides the route before the machine does.
Comparison at a glance
| Parameter | Value |
|---|---|
| Turning length | up to 1,000 mm |
| Live tool speed | 6,000 to 12,000 rpm |
| Y axis travel | ±60 mm |
| C axis resolution | 0.001 degree |
| Positioning accuracy | ±0.005 mm |
| Tool positions | 24 to 48 |
Applications
Turn-Mill Centre is used for complex parts that would otherwise move between a lathe and a machining centre, and in practice it appears most often in medical device bodies, aerospace fittings, hydraulic components, instrument housings.
How it fits into a machining route
Turn-Mill Centre is one station in a route rather than the whole of it. The part arrives with the previous operation finished and leaves with the features it is responsible for completed, so the datum and the clamping method are agreed before the first part rather than discovered on it.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: one setup replaces two machines, which is where the saving is. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is ISO 13485 or AS9100 depending on the part. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
CMM for the milled features, micrometer for the diameters is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for Turn-Mill Centre?
±0.01 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
17-4PH stainless steel is the usual choice, supplied against ISO 13485 or AS9100 depending on the part.
How is the result verified?
CMM for the milled features, micrometer for the diameters, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
C axis positioning used as if it were a rotary table, without checking the brake.
How long does it take and what does it cost?
A realistic cycle is 15 to 45 minutes for a complete part, and the cost driver is one setup replaces two machines, which is where the saving is.
Related capability
If you are specifying Turn-Mill Centre on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to Turn-Mill Centre in the encyclopedia: Horizontal Machining Centre, 5-Axis Machining Centre, High Speed Machining. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
