Threading Techniques: Machining and Handcrafting

A thread is a hollow helix built on a cylindrical surface with a certain profile, continuous and uniform. This type of machining is characteristic of restraint devices such as screws, studs, anchor bolts, and nuts. The threading process can be done with a machine or by hand.

Hand Threading

• Taps: Used to make internal threads, a tap is a tempered tool with longitudinal slots, having the required shape and dimensions.
• Dies: Dies are like tempered steel nuts with longitudinal grooves of the appropriate shape and size. They cut metal by removing material to create a thread on a cylindrical body, thereby obtaining a screw or threaded rod.

Threading on a Lathe

Lathe threading involves giving the part a rotational motion about its axis, and a synchronized translational movement of the tool parallel to the generatrix of the thread.

• Tapping: A tap is placed on the tailstock. This is used for small-diameter internal threads.
• Threading with a Die: A die is placed in the tailstock carriage or attached to the tool holder. This process is used for small-diameter external threads.
• Threading with a Die Head: This is similar to using a die, but the die head opens at the end to allow for quick removal of the part or backward movement. In this case, the threads are obtained in a single pass.
• Single-Point Threading: Tool holders are available with a blade of the dimensions required to create the thread. The thread is obtained after several passes, allowing for both internal and external threads.
• Thread Rolling: A thread rolling die is placed in the tailstock, creating the thread by deforming the material. This process does not produce chips.

Milling Threads

• Disc Milling: The milling cutter is mounted on a swivel head, which is tilted to the required thread angle. This process is especially suitable for very long threads.
• Thread Milling with a Master Hob: The thread is obtained in a single pass using a drill of the required size. The teeth of the hob produce the openings between the thread fillets. This procedure is used for internal and external threads of small length at the ends of a piece.

Thread Rolling

In this process, no chips are produced as the thread form is achieved by deforming the workpiece. This results in a highly resistant thread because the material takes the shape of the fillet.

• Thread Rolling with Rollers: Two identical profiled cylinders with parallel shafts rotate in the same direction and at the same speed. They compress the part, which rotates between them without advancing.
• Thread Rolling with Flat Dies: This involves two distorting prismatic machined and ground pieces, called flat dies, one fixed and one mobile, between which the part to be threaded rotates.