GlossaryKind of term: Manufacturing termHole
What is a hole in machining?
A hole is a round, cylindrical internal feature, through or blind, made by drilling, reaming, boring, milling or turning, among other methods.
A blind hole ends in a flat or conical bottom, depending on the tool used or on what the drawing asks for. On the drawing it appears as ⌀ with a size, a depth for a blind hole, and where needed a tolerance class (⌀12 H7), a position tolerance or a thread callout. Countersinks and counterbores for screw heads are variants with a designation of their own.
Which operation does a hole need?
Which operation a hole needs depends on diameter, depth relative to diameter, tolerance, straightness, roughness, material and location. Drilling alone gives enough size and finish for many uses; for a tolerance class such as H7, reaming, boring or circular milling with a finishing pass come into play. Once the depth exceeds a few diameters, chip evacuation, coolant and drill wander start to count; with a through-coolant drill you can often drill without pecking, without it peck drilling is common. A flat bottom needs a flat-bottom drill or an end mill rather than a twist drill with its point angle.
How does a hole work in practice?
Holes are often the most numerous features on a milled part, and they differ widely in time: clearance holes with one tool, fitted bores with pre-drilling, reaming or boring and measuring, threaded holes with drilling and tapping. So count them by type, not as one item. Holes in a side face or at an angle can need an extra setup, a fourth or fifth axis or an angle head. Deep, narrow holes can call for a special drill or a different machine.
What is a hole often confused with?
A hole is not a thread: the hole is the opening, the thread is made in it. Nor is a hole a pocket: a pocket has a free contour with walls and a floor from a milling cutter, a hole is round. And a hole is not an operation: drilling, reaming and boring are ways of making it.
How do you see a hole in Blake?
Tolerances and threads from the drawing appear on the part in Blake as proposals. The estimate includes drilling and tapping in the machining, per piece and per batch. If you change a time, Blake records who did it, when and why. More on milling.
Frequently asked questions
What makes a deep hole expensive?
The ratio of depth to diameter. A long drill deflects more easily, chips are harder to clear and coolant matters more. Without through-coolant you often drill in steps. A tight tolerance or straightness requirement adds a finishing pass or a different technique on top.
Do I count threaded holes separately?
Yes. A threaded hole is a hole plus a second operation with its own tool. Count by type: clearance holes, fitted bores and threaded holes, each with its depth and material.