A beginner's guide to Reaming and Boring

Reaming and Boring is finishing a hole to size with a multi tooth reamer or an adjustable single point boring head. It is used for holding hole size and position more closely than drilling can. 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.

In plain terms

Reaming and Boring is finishing a hole to size with a multi tooth reamer or an adjustable single point boring head. If you have not met the term before, the useful way to think about it is this: it is chosen when a part needs holding hole size and position more closely than drilling can.

The terms you will hear

• Typical tolerance – H7 by reaming, H6 by fine boring.
• Surface finish – Ra 0.8 to 1.6 µm.
• Stock left by the drill – 0.2 to 0.5 mm.

What it costs and how long it takes

The number of size adjustments and the gauge check, and a realistic cycle is 2 to 10 minutes per hole. Those two numbers, not the headline hourly rate, decide the price of the part.

What to ask a supplier

• What tolerance will you hold in production, not just on the first part?
• What does the dimensional report cover, and which standard is it written to?
• What happens to the fixtures and programmes if we reorder in a year?

Applications

Reaming and Boring is used for holding hole size and position more closely than drilling can, and in practice it appears most often in bearing seats, dowel holes, pin bores, pump and valve bodies.

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: the number of size adjustments and the gauge check. 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.

Plug gauge and an air gauge for production 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 Reaming and Boring?

H7 is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.

Which material is usually used?

6082-T6 aluminium is the usual choice, supplied against in-house approval with dimensional reports.

How is the result verified?

Plug gauge and an air gauge for production, with the results recorded so a repeat order can be compared with the first.

What is the most common mistake?

A boring head adjusted by guesswork rather than by measuring the cut.

How long does it take and what does it cost?

A realistic cycle is 2 to 10 minutes per hole, and the cost driver is the number of size adjustments and the gauge check.

Related capability

If you are specifying Reaming and Boring 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 Reaming and Boring in the encyclopedia: Honing, Lapping, Duplex 2205 Stainless Steel. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.