When threaded holes for screws and bolts are made, machinists can choose between two main methods – tapping and thread milling. These both have their own strengths and weaknesses that make them better for certain jobs.
Tapping
Tapping uses a tool called a tap that looks like a screw with cutting edges. A machinist drills a hole first and then pushes the tap into the hole while turning it. As the tap turns, it cuts grooves into the walls of the hole which makes the threads. Many workshops use special tapping machines, like the examples seen at cotswold-machinery-sales.co.uk/roscamat-tapping-machines, that can create threads quickly and accurately.
Tapping works best when you need to make many identical threaded holes fast. It’s also good for deeper holes and harder materials like steel. The process is straightforward which makes it easy to learn and use.
However, tapping has some drawbacks. You need a different tap for each thread size which means that you need many tools. Once a hole is tapped, you can’t adjust how tight or loose the threads are. Tapping only works for inside threads but not outside ones and it can be difficult to get perfect threads at the bottom of blind holes that don’t go all the way through the material.
Thread Milling
Thread milling is different, as instead of pushing a tap straight in, it uses a spinning cutter that moves in a spiral path. The machine drills a hole first, then the thread mill enters and follows a circular path while moving deeper.
The biggest advantage of thread milling is how flexible it is. One thread mill can create many different thread sizes simply by changing its path. Machinists can also change how tight the threads will be which means they can be custom fits. Thread mills can make both inside and outside threads, right-hand or left-hand threads and even unusual thread patterns without special tools.
The main disadvantage is that thread milling needs faster, more advanced machines. It’s also slower than tapping when you need to make many identical holes.