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The screw thread is a very important detail in engineering. It is used to hold parts together. (e.g. bolt & nut) and to transmit power (e.g. vice screw). Through the course you will need to learn how to form accurate threads in your parts so that they work properly.
This page talks about external threads, details on internal threads can be found here.
External Threads
External Threads
External threads are cut a metal rod using a tool called a DIE.
Circular Split Die
Circular Split Die
The picture opposite shows a split die, this is the most common type of die used in the school workshop. These are used for cutting external threads. The die is made from high speed steel (HSS).
Die holder or stock
Die holder or stock
The circular split die fits into the die stock with the tapered side of the thread (shown by the writing on the die). The split in the die fits opposite the centre screw to allow the opening and closing of the die. The two screws at the side hold the die in the stock To ensure the die can start to create a thread on the rod the rod must firstly be tapered at the end.
Adjusting the thread
Adjusting the thread
The split die will allow the thread that will be cut to be adjusted. The three screws in the die holder can be used to squeeze the die tighter closed or spread it open. Doing this will change how much material is removed during cutting. As a result if it is opened slightly, by screwing the middle screw into the adjustment split, a shallower cut will be made. Alternatively, if the die is squeezed shut by screwing the outer screw in and squeezing the split closed, then the thread will be cut deeper. Because of this, cutting an internal thread should always be done first since the external thread can be adjusted to ensure the threads work well together.
More details on the process of cutting an external thread can be found in this document.
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