Taps and Dies (introduction)

ME 132

1. Taps and Dies

2. Taps and Dies -are used to create screw threads, which is called threading. Many are cutting tools; others are forming tools.

3. Tap - a tap is used to cut or form the female portion of the mating pair. ( e.g. Nut)

4. The three basic types of taps Bottoming tap -used to cut threads in a hole that has already been partially threaded using one of the more tapered types of tap. Intermediate tap or plug tap -it has tapered cutting edges, which assist in aligning and starting the tap into an untapped hole. The number of tapered threads typically ranges from 3-5.

5. Taper tap - is similar to intermediate tap but has more pronounced taper to the cutting edges. The number of tapered threads typically ranges from 8-10. - it is most often used when the material to be tapped is difficult to work.

6. The most common type of power driven tap is the “Spiral point” plug tap, whose cutting edges are angularly displaced relative to the tap centerline.

7. Die Is used to cut or form the male portion. (e.g. bolt )

8. Rethreading dies (die nuts) – are dies made for cleaning up damaged threads, have no split for resizing and are made from a hexagonal bar so that a wrench can be used to turn them. Die nuts cannot be used to cut new threads.

9. Process the process of cutting or forming threads using a tap is called tapping . whereas using a die is called threading. Both tools can be used to clean up a thread which is called chasing.

10. Process of Tapping Begins with forming (drilling) and slightly countersinking a hole to the diameter smaller than the tap’s major diameter. If the hole is to be drilled, the proper diameter is called the tap drill size.

11. The correct tap drill diameter (in inch) computation is as follows: TD= MD - Where TD is the tap drill size, MD is the major diameter and N is the thread pitch.  

12. The correct tap drill diameter for metric sized taps is computed as follows : TD= MD – pitch Where TD is the tap drill size, MD is the major diameter and the pitch is the pitch of the thread.

13. L ubricants Recommended lubricants for some common materials are as follows: