GlossaryKind of term: Manufacturing termDrilling and tapping
What is drilling and tapping?
Drilling makes holes in solid material, and tapping cuts or forms an internal thread in them with a cutting tap or a forming tap.
Drilling makes a hole in solid material with a rotating drill, sometimes after spot drilling or pilot drilling. Tapping produces an internal thread in a drilled hole with a tap: a cutting tap removes the profile as chips, a forming tap presses it into the material without chips. A tap makes one thread size; thread milling is the alternative. Reaming, boring and countersinking are separate operations that often follow drilling, for example on a ⌀12 H7 fitted hole.
What decides how a hole and a thread are made?
For a cutting tap in an ISO metric coarse thread, the tap drill is roughly the nominal diameter minus the pitch, for example 5.0 mm for M6; a forming tap needs a larger hole, according to the toolmaker's data. Deep holes need chip evacuation by peck drilling, through-tool coolant or a dedicated drill. A blind thread needs a hole deeper than the usable thread length, because the chamfer of the tap does not produce a full profile and the drill point does not count. Tough or hard material, hole depth and position requirements also shape the approach.
How does drilling and tapping work in practice?
Holes of one size on one side share a tool: the tool change comes once, and each hole adds cutting time and positioning time. An extra size or thread adds a tool change, unless one tool covers several sizes. A rule of thumb per hole can be a fair first estimate, but it goes astray with many holes, deep holes, small threads or tough material such as stainless steel. A tap broken in a blind hole can cost the part; on expensive parts that is a reason to mill the thread. On a 3-axis machine, holes in a side face need another setup, an angle head or a fourth axis.
What is drilling and tapping often confused with?
Drilling and tapping is not the same as the hole: the hole is the feature in the part, drilling and tapping are the operations that make it. And tapping is not the thread: the thread is the requirement on the drawing, such as M6-6H, and tapping is one way to make it, thread milling another.
How do you see drilling and tapping in Blake?
In Blake, drilling and tapping is estimated as a process of its own. The thread from the drawing sits with the part as a proposal you confirm or correct, and its history shows who did so and when. The machining time goes into the estimate, labelled as one. More on estimating.
Frequently asked questions
Why is a blind thread harder than a through thread?
Chips have to come back out, the tap has to stop at depth and reverse, and the hole must be deeper than the usable thread. A tap broken in a blind hole is hard to remove and can turn the part into scrap.
Do I count every hole separately?
Count by size, depth, type and side. Identical holes on one side share a single tool change and each adds cutting and positioning time; a new size means another tool change. That way you can see where the time goes.
When do you mill a thread instead of tapping it?
For large diameters, tough or hard material, expensive parts where a broken tap means scrap, and when one cutter should make several sizes with the same pitch. Per hole, tapping is usually quicker.