In engineering, the most common connection is threaded. If it is of high quality, the entire structure is reliable and durable.
Thread cutting is the process of removing chips on a rod or in a hole using a special tool or the method of plastic deformation (knurling).
There are single and multiple threads, right-handed or left-handed. Another parameter is the step, the distance between the two ridges. There are several thread profiles: universal - regular triangular; trapezoidal - its profile is made in the form of a trapezoid; resistant - for devices operating under high pressure, and pipe, which is used to connect pipes. There are standard diameters for threaded connections.
Thread cutting can be done manually when the cutting tool is inserted into a hand-held screwdriver or drill, or mechanically, when cutting is performed on a machine - drilling or turning.
Before this, it is necessary to perform an additional operation on the part - to make the desired diameter of the hole or rod. If you need to make internal cutting, a drill is selected so that the tap smoothly enters the hole, but at the same time captures the volume of metal necessary for removing the chips. Otherwise, the tool may break and the thread will become loose. Typically, the diameter of the desired workpiece is selected according to existing tables.
Thread cutting inside the hole is done with a special cutting tool called a tap. It has a working part, which performs the cutting process itself, and a shank designed to secure the tool in the chuck of a drilling machine, lathe, in a hand drill or screwdriver. The working part of the tool is made of high speed steel or sometimes hard alloy.
Tapping is a rather time-consuming and complicated job requiring utmost care. First you need to expose the product so that the tap is located exactly in the center, otherwise marriage cannot be avoided. When working with a tap, it is difficult to remove chips, as access to the hole in which threading is performed is difficult. The taps themselves can often break due to their low stiffness.
However, tapping has advantages as well:
- simplicity of design and manufacturability;
- cutting occurs due to self-feeding;
- the accuracy of the thread depends on the correct tap.
External threading is done with a special cutting tool called a die.
The die for threading is made in the form of a nut of high-speed or tool steel. The sharp edges of the working profile of the tool allow you to freely remove chips from the rod, and the chips themselves freely enter the hole. Before threading, the part is machined to the required diameter, the bevel is removed at the end of the bar to facilitate the part entering the die and to center it more correctly in the part. The die is mounted in a die holder. When threading, it is advisable to apply lubricant to the part. This makes the process easier.