What is BS 11570 - Fluted taps about?
BS 1157 provides recommendations for tapping drill sizes for use with fluted taps.
These recommendations give drill sizes, covered by BS 328-1, for use before tapping the indicated threads. BS 1157 covers preferred thread forms and non-preferred forms.
BS 1157 also covers alternative tapping drill sizes.
Who is BS 1157 - Fluted taps for?
BS 1157 on recommendations for tapping drill sizes for use with fluted taps is useful for:
- Manufacturers of drill bits
- Drill bit designers
- Testing and inspection personnel
Why should you use BS 1157 - Fluted taps?
The diameter of a hole produced by a drill depends to some extent upon the degree of accuracy to which the drill point is ground, the material being drilled, the lubricant used, and the alignment, feed and speed of the operation. When tapping relatively soft material, there is a tendency for the material to be squeezed down towards the root of the tap threads and in such cases, the minor diameter of the tapped hole may become smaller than the diameter of the drill used. The tendency is very much less with harder materials, and in some cases is absent.
The guidance of BS 1157 on tapping drill sizes helps you to drill appropriately sized drills for some of the common scenarios and also makes tapping more economical. BS 1157 comparable figures of the theoretical extent of engagement of the nut and bolt threads resulting from the use of the stipulated drill size.
Overall, the recommendations of BS 1157 help you to design high-quality fluted taps.