Cutting tools

Of Thread Cutting Tools, Taps and Dies

Thread cutting tools, such as taps and dies, are used in the creation of helical turns of threads on bolts. The result: Screwed connections used on virtually all types of equipment, machinery, and electronic devices, among others.

A complete screwed connection has two parts, namely, an internal thread and its matching external thread. Manual thread cutting is still used despite the introduction of machines due to economic and technical reasons. This is true for repair work and single-piece manufacturer of screwed connections.

Tools for Internal Threading

Internal threads on screwed connections are cut using either serial taps or nut taps, the more common thread cutting tools in a workshop.

  • Serial taps

These consist of two or three tools with their distinguishing characteristic being the cutting part. First, the entering tap (i.e., the first pass) consists of a trapeziform cutting edges and long chamfer. For this reason, it performs as much as 60% of the cutting work.

Second, the plug tap (i.e., the second pass) also has trapeziform cutting edges similar to the entering tap but with a difference – the plug tap’s cutting edges are deeper. It also has a short chamfer. It performs about 30% of the threading work necessary for screwed connections.

Third, the finishing tap (i.e., the third pass) has a short chamfer like the plug tap, too. But its cutting edges create the thread groove’s final sharp form. It cuts the thread to its nominal size before finishing the thread flanks.

  • Nut taps

Also called a single-pass hand tap, a nut tap unites the three serial taps’ cutting parts. As such, it has a long chamfer (i.e., approximately 70% of the cutting part’s total length).

It also has a distinctive form to its cutting edges – initially trapeziform before becoming sharper at the end. But this part performs all the cutting operation so be careful about using it properly.

Tools for External Threading

Taps and dies obviously have distinctive uses. Dies or die-stocks are used in the creation of external threads.

First, a threading die has a cutting body with a chamfer on either side. You can then easily apply it both ways.  You should put a threading die into a die holder with two handles.

Second, the die-stock has a handle-equipped holder where two threading dies are positioned – one fixed, the other movable via pressure piece with locking screw. You will find three to five pairs of threading dies in a single die-stock, said threading dies of which are exchangeable for various thread sizes.

Each type is used for specific purposes. A threading die, for example, will cut the thread in single operation, thus, its use in bolt with diameters ranging from 12 to 30mm. A die-stock is mainly used for thread cutting operations on bolt diameters over 30mm.

Thread cutting tools should be used according to the manufacturer’s recommendations. These may be made for heavy-duty purposes but these are also breakable with abuse.


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