Deep Hole Drilling FAQ: the questions buyers ask

Deep Hole Drilling is drilling holes deeper than about ten times the diameter, with guided tools and high pressure coolant. It is used for cooling channels, hydraulic bores and long oil ways that cannot be reached with a twist drill. 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, medical is used as the example: validation evidence that matches the drawing exactly.

The questions buyers ask

What is Deep Hole Drilling used for?

It is used for cooling channels, hydraulic bores and long oil ways that cannot be reached with a twist drill. Drilling holes deeper than about ten times the diameter, with guided tools and high pressure coolant.

What tolerance can be held?

±0.05 mm on diameter, straightness by process is typical, held on the features that carry the function and confirmed by bore gauge and a straightness check.

Which material should be specified?

4140 alloy steel is the usual choice; the certificate requirement is in-house approval with dimensional reports.

What finish comes as standard?

Ra 3.2 µm as drilled. A finer finish is a separate operation and is quoted as one.

How long does it take?

A realistic cycle is 10 to 60 minutes per hole, and the cost driver is set up and coolant filtration, not the cutting time.

What information is needed for a quotation?

A STEP or IGES model and a PDF drawing with tolerances, material and finish called out, plus the quantity and the expected repeat frequency.

Can the same result be guaranteed on a repeat order?

Yes, because the fixtures, tool lists and verified programmes are retained for the life of the part number.

What is the most common mistake on the drawing?

Chip evacuation failing, which packs the flute and breaks the drill.

Applications

Deep Hole Drilling is used for cooling channels, hydraulic bores and long oil ways that cannot be reached with a twist drill, and in practice it appears most often in mould cooling channels, hydraulic cylinder bores, spindle oil ways, heat exchanger plates.

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: set up and coolant filtration, not the cutting time. 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.

Bore gauge and a straightness check 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 Deep Hole Drilling?

±0.05 mm on diameter, straightness by process is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.

Which material is usually used?

4140 alloy steel is the usual choice, supplied against in-house approval with dimensional reports.

How is the result verified?

Bore gauge and a straightness check, with the results recorded so a repeat order can be compared with the first.

What is the most common mistake?

The entry face not square, which walks the drill off position.

How long does it take and what does it cost?

A realistic cycle is 10 to 60 minutes per hole, and the cost driver is set up and coolant filtration, not the cutting time.

Related capability

If you are specifying Deep Hole Drilling 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 Deep Hole Drilling in the encyclopedia: CNC Milling, CNC Turning, 4140 Alloy Steel. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.