GlossaryKind of term: Manufacturing termReaming
What is reaming?
Reaming takes a pre-drilled hole to an accurate diameter with a smooth wall using a reamer, for example for a hole in tolerance class H7.
The reamer is a multi-flute tool that removes only a thin layer from the wall of a pre-drilled or pre-bored hole. Besides an accurate diameter and a smooth wall this gives good roundness; tolerance classes such as H7 follow ISO 286. A machine reamer has a fixed diameter with its own manufacturing tolerance; adjustable reamers exist too. A reamer largely follows the hole that is already there: diameter and finish improve, position and straightness hardly at all.
What decides the size of a reamed hole?
Whether a reamed hole ends up in tolerance depends on the reamer and its tolerance, the stock the pre-drill leaves, the cutting data, coolant, material, wear and the alignment between spindle and hole. Too little stock makes the reamer rub instead of cut; too much overloads it. In some materials the hole comes out slightly larger or smaller than the reamer, for example through built-up edge or spring-back. A floating holder can absorb small misalignment, but does not correct position.
How does reaming work in practice?
A fit hole often needs its own sequence: spot, pre-drill and ream, with an extra tool in the magazine. Common sizes are available from stock; an unusual size may need special tooling, or another route such as single-point boring or helical interpolation. If position is tight too, boring or a more accurate pre-machining step is the more likely route. If a fit on the drawing is overlooked, that step is missing from the estimate. Checking is usually done with a go/no-go plug gauge or a bore gauge.
What is reaming often confused with?
Reaming is not boring: a reamer has a fixed size and follows the pre-drilled hole, while a boring head is adjustable, follows the spindle axis and can therefore correct position. Honing is a process of its own: it uses abrasive stones, usually after reaming or boring, for the tightest form and finish in a bore.
How do you see reaming in Blake?
A tolerance class such as H7 sits in Blake with the other tolerances as a proposal from the drawing, which you confirm or correct; who did so and when stays visible, with a note if you add one. Drilling and tapping have their own line with the machining time as an estimate. If that estimate leaves out a reaming pass, you adjust the line and give the reason. More on estimating.
Frequently asked questions
Why ream a hole after drilling?
Because a drill alone usually does not hold a tolerance class such as H7 or leave a smooth wall reliably. The reamer takes off a thin layer and brings the hole to size. It hardly moves the hole; position comes from the pre-drill.
Do you need a separate reamer for every fit size?
With fixed reamers, yes: a machine reamer has one diameter and one tolerance. Common sizes are available from stock; an unusual size is special tooling with its own price and lead time. Boring or helical interpolation may then be the better route.
How much stock do you leave for reaming?
That depends on diameter, material and reamer; the tool supplier gives guide values. Too little makes the reamer rub and spoils the wall; too much overloads it and costs size accuracy.