1] External Threading Tools:
These tools are used to cut screw threads on the outside diameter of components/parts such as bolts, shafts, pipes, castings and forgings made from ferrous and non ferrous materials.
These tools can be used to cut screw threads in Metric, British, Acme and other standards.
2] Internal Threading Tools:
These tools are used to cut screw threads on the internal diameters of components/parts such as nuts, pipes, collars, castings and forgings made from ferrous and non ferrous materials.
These tools like aluminium end mill can cut screw threads in Metric, British, Acme and other standards.
The major diameter of the thread has to be machined prior to external threading and the root diameter of the thread has to be machined prior to internal threading.
It is very important to provide an undercut on the outside or inside diameters before carrying out thread cutting as this allows the threading tool to pass into the undercut just after carrying out threading to the required length and before it returns to the starting point.
While cutting threads it is essential to use a cooling medium such as straight oils or oil in an emulsion with water.
Thread cutting is always done in multiple passes of depths of about 0.1 mm or 0.004 inch to reduce load on the lathe as both cutting edges are working together, maximise tool life and achieve proper thread form to meet gauging requirements.
Overhang of the threading tools is a major factor that contributes to vibration, poor cutting conditions and poor thread form.
As the pitch of threads vary from 0.5 mm to 5.0 mm the rotational speed on conventional lathes are kept low. However, higher speeds can be used in CNC Lathes as the tool return is preset on the machine and controlled.
Care should be taken while setting up for threading so that over run of the threading tool is avoided as it may cause major accidents and damage to the tools and the machine.