CNC Turning vs Deep Hole Drilling: which one fits your part
CNC Turning is a cutting process where the workpiece rotates and a single point tool removes material. It is used for producing diameters, faces, grooves and threads on rotational parts. 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.
The short answer
CNC Turning and Deep Hole Drilling overlap, but they are not interchangeable. Choose CNC Turning when the requirement is producing diameters, faces, grooves and threads on rotational parts; choose Deep Hole Drilling when the requirement is cooling channels, hydraulic bores and long oil ways that cannot be reached with a twist drill.
Side by side
| Point of comparison | CNC Turning | Deep Hole Drilling |
|---|---|---|
| What it is | a cutting process where the workpiece rotates and a single point tool removes material | drilling holes deeper than about ten times the diameter, with guided tools and high pressure coolant |
| Used for | producing diameters, faces, grooves and threads on rotational parts | cooling channels, hydraulic bores and long oil ways that cannot be reached with a twist drill |
| Typical tolerance | ±0.01 mm | ±0.05 mm on diameter, straightness by process |
| Surface finish | Ra 1.6 µm turned | Ra 3.2 µm as drilled |
| Cost driver | cycle time, because turning is fast but repeated often | set up and coolant filtration, not the cutting time |
Which one fits your part
Work from the feature that has to work. If the requirement is producing diameters, faces, grooves and threads on rotational parts, CNC Turning is the safer call; if it is cooling channels, hydraulic bores and long oil ways that cannot be reached with a twist drill, Deep Hole Drilling wins on cost or on lead time. Where the drawing does not make it clear, that is the question to settle before quotation rather than after.
A note on specification
Write the drawing so that either route can be considered where the function allows. That keeps the quotation competitive and stops a process being specified where a result should have been.
Applications
CNC Turning is used for producing diameters, faces, grooves and threads on rotational parts, and in practice it appears most often in shafts, pins, fittings, rollers and pulleys.
How it fits into a machining route
CNC Turning is one operation in a sequence: roughing to leave even stock, any stress relieving the geometry needs, semi finishing, then the finishing operation that holds the tolerance. The order is what keeps the result stable as the machine warms up and the batch runs.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: cycle time, because turning is fast but repeated often. 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 in-house approval with dimensional reports. 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.
Micrometer and bore gauge, roughness gauge on sealing faces 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 CNC Turning?
±0.01 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
303 stainless steel is the usual choice, supplied against in-house approval with dimensional reports.
How is the result verified?
Micrometer and bore gauge, roughness gauge on sealing faces, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
A parting off tool set above centre, which leaves a pip and damages the insert.
How long does it take and what does it cost?
A realistic cycle is 3 to 15 minutes per part, and the cost driver is cycle time, because turning is fast but repeated often.
Related capability
If you are specifying CNC Turning 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 CNC Turning in the encyclopedia: Hard Milling, High Speed Machining, Ti-6Al-4V Titanium. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
