How to specify Turn-Mill Centre on a drawing

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, aerospace is used as the example: traceability and a first article before anything enters the batch.

What belongs on the drawing

A clear drawing for Turn-Mill Centre states the function, the tolerance and the verification, and leaves the route open where the function allows it.

• The feature and its tolerance: ±0.01 mm, applied to the features that locate the part.
• The material and its condition: 17-4PH stainless steel, with the certificate requirement.
• The surface finish: Ra 0.8 µm achievable on both turned and milled faces, called out only where it does something.
• The verification: ISO 13485 or AS9100 depending on the part, and the standard the report is written to.

Mistakes that cost money

• The driven tool working outside its duty cycle, which shortens spindle life, which makes the part more expensive without making it better.
• C axis positioning used as if it were a rotary table, without checking the brake, which makes the part more expensive without making it better.

A workable note

Where a general note is used, say so once in the title block and keep the feature level call outs for the dimensions that matter. Avoid deep pockets that need a holder longer than the Y axis travel allows

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

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: Vertical Machining Centre, Horizontal Machining Centre, Deep Hole Drilling. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.