BS 426:1969

1.1 This British Standard relates to fixed centres for use on machine tools and their auxiliary equipment, and in any other suitable circumstances such as on inspection or gauging equipment, etc.

1.2 The fixed centres specified in this standard fall into the following three series:

• Type 1. Fixed centre, long series, standard Morse taper shank. This type utilizes the Morse taper shank details, and conforms to relevant dimensions contained in ISO/R 296¹⁾, ISO/R 298²⁾ and BS 1660-1³⁾. The section forward of the gauge plane includes a parallel cylindrical portion (see Figure 1). When this type is fitted with a tungsten carbide tipped nose cone the amount of regrinding of the tip is strictly limited. Details showing the extent of regrinding are given in Figure 5.
• Type 2. Fixed centre, short series, standard Morse taper shank. This type conforms to Type 1 in respect of the dimensions rearward of the gauge plane. The section forward of the gauge plane conforms in part to Type 1, but it is arbitrary whether a parallel cylindrical portion is included forward of the gauge plane or whether the Morse taper is extended (see Figure 2).
• Type 3. Half centre, long series, standard Morse taper shank. This type utilizes the same basic dimensions as Type 1 with the exception that a portion of the centre forward of the gauge plane is cut away parallel to the axis of the centre (see Figure 3).

NOTE The dimensions of the cutaway area align with those of DIN 806, “Lathe centres (60°)”.

¹⁾ ISO/R 296, “Self-holding tapers for tool shanks”.

²⁾ ISO/R 298, “Lathe centres. Sizes for interchangeability”.

³⁾ BS 1660, “Machine tapers”, Part 1, “Self-holding tapers and gauges for self-holding tapers”.

Materials, dimensions, tolerances, finish, etc., for three types of fixed centre for machine tools and auxiliary equipment, and for other suitable circumstances such as inspection or gauging equipment.