Classification of Thread Manufacturing Methods

Classification of Thread Manufacturing Methods

Classification of Thread Manufacturing Methods - In manufacturing screw threads, the basic problem of course, is how to produce the desired ridge on the workpiece. Various methods are used: cutting, rolling, grinding and casting. Both external and internal threads can be cast, but this process is used primarily in connection with die casting or the molding of plastics, and relatively few threads are made in this manner.

Rolling also can be employed for making both external and internal threads, provided the material is reasonably ductile. Today the majority of threads are formed by rolling. External threads can be made by cutting in the following ways:

I. On an engine lathe.
2. With a die and stock (manual).
3. With an automatic die (turret lathe or screw machine).
4. By milling.
5. By grinding.
6. By rolling.

Internal threads are made by cutting by the following methods:

I. On an engine lathe.
2. With a tap and holder (manual, semiautomatic, or automatic).
3. With an automatic (collapsible) tap (turret lathe, screw machine, or
special threading machine).
4. By milling.

Cutting a thread by using a single point tool on the lathe while indispensable for single and small quantity jobs turned on the lathe, would be too slow for production in large quantities and, moreover, would necessitate long and expensive resetting of work turned on other machines.

For production work, therefore, alternative quicker and simple methods as listed above are employed, the particular method used depending to some extent on the type of work and the methods used in its production.

In earlier years most threads were made by cutting, but at present this method has largely been replaced by thread rolling, because of cost. Cutting is used only for making small quantities or for special threads where standard rolling equipment cannot be applied, for extremely high precision threads, or on material that lacks sufficient ductility to permit rolling to be employed.