Manufacturing services · Chapter C · Method 16

Drilling & tapping

Holes are drilled, reamed or bored and then threaded with taps or thread mills, either on a CNC machine or as a dedicated operation.

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High-speed drilling with coolant on a machining centre. Representative process photo · Daniel Smyth · Pexels

Hand tapping a thread with a tap wrench. Representative process photo · Ash Crow · CC BY-SA 4.0 · Wikimedia Commons

How it works

Drilling & tapping, step by step.

A labelled schematic of the process (not to scale), and the four steps every job goes through.

Labelled diagram showing how drilling & tapping works — Schematic · not to scale. Drawn by TCI Group.

STEP 01

Spot

Spot drill to locate the hole accurately.

STEP 02

Drill

Drill to tapping size, or ream for precision.

STEP 03

Tap

Tap or thread-mill to the specified class.

STEP 04

Check

Gauge threads with go/no-go gauges.

Reference figures

What to expect.

Typical industry values to help you plan. We agree the figures for your part on the drawing.

Hole Tolerance±0.13 mmStandard machined

ThreadsFully formedTo size and class

Precision HolesReamedH7 fits by request

DepthUp to ~3× dia. tappedTypical guidance

Materials	All machinable metals and plastics; inserts (helical or threaded) for soft materials.
Finishes	Countersunk or counterbored; deburred as standard.
Design guidance	Use standard thread sizes (M, UNC/UNF, BSP). Tapped depth beyond 3× diameter rarely adds strength. Add threaded inserts in plastics that see repeated assembly.
Best suited to	Fixing points, manifolds, mould tools and assemblies.
Watch-outs	Small, deep tapped holes risk tap breakage and cost more.

Other methods in CNC machining

Previous: 3, 4 & 5-axis machining Next: Wire EDM

Next step

Not sure this is the right route?

Send a sketch, photo, sample or CAD file with your quantity and target date. We will recommend the most sensible route and explain the trade-offs before quoting.

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Reference figures are typical published industry values for planning, not a guarantee; final tolerances, materials and finishes are agreed in writing for each project.