Reaming and Boring specifications: what the numbers mean
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.
What the numbers mean
A data sheet for Reaming and Boring is only useful if the numbers are read against the job. The usual entries, and what they tell you, are these.
- 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.
- Position accuracy – 0.01 mm with a boring head.
- Tool material – carbide or HSS with a straight or helical flute.
- Coolant – emulsion through the flutes.
Comparing offers
Two suppliers can quote the same typical tolerance and mean different things, because the figures are often quoted under the most favourable conditions. Ask what the value is measured over, what the material was, and whether it is a typical or a guaranteed figure.
| Specification | Typical value |
|---|---|
| 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 |
| Position accuracy | 0.01 mm with a boring head |
| Tool material | carbide or HSS with a straight or helical flute |
| Coolant | emulsion through the flutes |
What to check before specifying
Make sure the value you need is the value you have called up. Say H7, not a decimal tolerance, where a standard reamer will do, and the difference between a typical and a worst case figure is where most disputes start.
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
Reaming and Boring 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: 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: CNC Milling, CNC Turning, Duplex 2205 Stainless Steel. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
