Taps are common engineer's tools, used in multiple industries. Used to cut the thread inside a hole which when combined with the external threads on a fastener hold workpieces together. Taps create the internal threads also known as female threads, whilst external male threads are created with dies.
How do taps work?
Both hand and machine taps work by cutting into and removing material form a workpiece, one is manually powered by a t-handle, whilst the other is used in a machine. They both operate in the same way being inserted into a pilot hole and turned with the teeth scraping away a spiralling ramp creating the female thread. They can be used to both create new threads and be run in to an already threaded hole to repair a damaged internal thread.
Taps typically cut in a clockwise direction for standard threads, working its way deeper into the hole creating new threads as it is turned, spinning the tap anti-clockwise removes the tap from the hole once the threads are formed.
## Types of taps
There are three main styles of tapping tools, each with their own features and benefits outlined below.
• **Taper tap** - These taps feature a shallow chamfer making the tap easier to align with the pilot hole and the overall process easier. The first few teeth take shallow cuts reducing the force required to turn the tool. Their drawback is that they cannot form threads all the way to the bottom of a blind hole as the first 7-10 threads are not fully formed, making them ideal for first time threading.
• **Plug tap** - These types of taps feature a shallow chamfer which, typically, affects the first 3 or 5 threads. This makes them harder to start the new thread as they require more force to turn along with a more difficult alignment process. However, their advantage lies in their ability to create threads deeper into the pilot hole. They are ideal for thread repair and deeper tapping once the taper tap had been run through. They also make an ideal too for through holes.
• **Bottoming tap** - The lead chamfer of these taps is 2 or less making them the go to tool to cut threads all the way to the bottom of a blind hole after a taper or plug tap has been used to create the initial thread cut.
As well as the different types of taps, the thread or flute design for the tap is suitable for different applications. The main types of flutes appearing on tap tools are:
• **Spiral flute** - These taps function similar to a drill bit, and feature deep flutes cut into the tool to evacuate chips. They are mostly suitable for softer metals that don't chip easily such as cast iron. Their drawback is that they don't feature as wide a cutting web, and this makes them weaker structurally compared to straight flute taps.
• **Straight flute** - These taps feature a larger cross section and straight flutes running down the cutting portion of the tool. This design makes them stronger than spiral flute taps and enables them to cut through hardened metals. Their disadvantage comes with chip evacuation as the operator need to be present to occasionally back the tool out of the hole and manually remove cut material. Failure to do this will lead to a less clean finish and possible breakage.
*What are taps made of?*
Taps, be they hand, or machine taps are typically manufactured from carbon or high-speed steel making them very durable and fit for the purpose of cutting into materials like metals. Some feature oxidised or other such coatings to help improve resistance to wear and heat when working with hardened metals.