/ THREADING Tap tolerance 3) Substrate material Tap tolerance Not thread s in all machining operations, the importance of the worked material is clear in tapping. Given the wide range of factors and conditions involved in the characterisation of the material, from a practical point of view it is useful to simplify this as much is possible, provided that it is within rational limits that ensure the required effectiveness levels. tolerance In accordance with the above, we will summarise the topic with three genuinely representative conditions: 6G • Class/nature Within the context of interest, we will focus the topic on 4H 5H 6H commonly used metals in the mechanical manufacturing 4G 5G industry and surrounding fields: • Mechanical construction steels (low and medium alloy) 7G • Alloyed steels for thermal treatment 6H 6G • Stainless/refractory steels preferably austenitic (AISI 304, 316 and similar) Clase 3 Clase 2 4H • Casting, preferably nodular (GGG) • Aluminium and alloys with silicon content ≤ 8% •Mechanical characteristics The standard allows the above mentioned tolerances to be modified for especific cases. Standard; 6 H. • Type of chip This is a factor that is directly associated with the previous For reasons explained in the description of the tap, the type two points, and for practical simplification purposes, we will of hole to be tapped is a determining factor in the tapping summarise it into three reference types: long, typical of operation. Therefore, the proper identification of its materials with low hardness and/or high plasticity in characteristics: form or type and threaded depth or length general, such as low allow and stainless steels and is the second fundamental premise. aluminiums low in Si; intermediate, typical of materials of Even though there are many cases, for practical purposes intermediate hardness and/or medium carbon content they can be grouped into 6 main variants (two types x three >0.50% or easy machining steels, alloyed with the strategic threaded lengths in each one of them). addition of lead or sulphur; and very short/dust, typical of • Blind hole (no exit): with threaded length that is Short (≤ castings. 1xD), Medium (1.5xD) or Long (2.5xD). The tap ddd From the technological point of view, we can distinguish two main types: • Rolling tap, which works by means cold working Blind-ended and Blind-ended Blind-ended tought hole shorts and thought medium and thought deep 2) Characteristics of the hole technology with no chip. Its volumes of use are very much less than the cutting tap in spite of its properties and potential, and its consideration would take up a large section that is strictly speaking outside the scope of this work. 40 / 7H 8H Ø Medio teórico Clase 1 8G 7G Class/nature, Mechanical characteristics and Type of chip. EL=Diferencial fundamental We will focus on tensile strength and/or hardness, with preferential limitation to a maximum of 1000 MPa (350 HB). In a specific section on tapping by cold working - roll forming - with no chip removal, the plasticity or plastic deformation coefficient (not less than 10%) must also be taken into account. • Throughhole(withexit):withthreadedlengththatisShort (≤ 1xD), Medium (1.5xD) or Long (2.5xD).(D= thread nominal diameter). This can be defined as a precision rotating cutting tool specifically designed for machining internal threads. Therefore, the tool par excellence for the purpose in question. t=T D2 (CAL5) 0,1 t 0,3t 0,5t 0,7 t0,9 t