• Cuttingtap,whichworksusingcuttingtechnologyorchip removal. This is the predominant type overall and within Important notes / THREADING it is the outstanding exponent, the multi-metal tap which we are considering in this article. In practice, the obtaining a precise and continuous coordination between both synchronisms - that of the tap and that of the feed system - in all tapping phases (feed, stop, reversal, withdraw) can be complicated in certain situations and/or circumstances, even with advanced CNC systems. Only the known mechanical n fact is used with optimal alised tapping machines, nisation errors is resolved For clarification, in case of possible misunderstanding, we system using a master spindle offers full assurances, and i results by several prestigious manufacturers of speci without hindering their combination with CNC systems. In practice, the problem associated with possible synchro with the use of a tap fastening element or tap holder with axial flotation (elastic think it necessary to put a special emphasis on this important topic. When machining holes in general (drilling, retractable displacement mainly to tension (25% minimum of the length to tap field) reaming and tapping), the effective speed is determined by and compression (approximately 20% of tension field). The axial flotation acts by the axial feedrate. The rotational or tangential speed is a continuously compensating for possible synchronisation errors. Moreover, we can complementary factor. Under this premise, it is evident that the tap is, per se, a high-speed tool because of the high feedrate due to its particular working mechanism. Consequently, rarely does tapping constitute a bottleneck from the cycle time perspective. affirm that this device does not pose risks of negative effects in any case. In addition to the above, the use of systems equipped with limiters or clutches can appear beneficial in theory, but in practice they entail significant complications that question their usefulness. In comparison with high-speed drilling with hard metal bits, the feed ratios x 1 rpm of the tap are up to 10x greater, therefore rarely does the axial feedrate of the bit reach 75% of the axial feedrate of the tap, in spite of the difference in tangential or rotation (rpm) speed favourable to the bit (by • Fundamental characteristics of the tool 6x). From the functional point of view, the overall quality of the tap is the result of the sum of 4 partial interactive qualities: • Tap working mechanisms Substrate material quality and appropriate thermal The basic actuation mechanism of the tap is characterised treatment + Geometrical - dimensional quality + Grinding by a single and determining condition which is the linking of quality + Finish/surface treatment quality. rotation to a single value or feed ratio, that is the feed value For reference purposes, the following is a brief summary: Tapping work speed x 1 rpm must be exactly equal to the thread pitch value. This is known as synchronisation. • Substrate material From this fact, there are two main consequences: High speed steel or super high speed steel are the only • 1) Any possible error, up or down, in the exactness of this options in practice, with a small use of tungsten carbide synchronisation brings inevitable negative consequences, (WC) hard metal. The reasons are technical and lie either in the quality of the thread cut (measurement and especially in the undeniable greater toughness finish) and/or in the lifetime of the tool. (minimisation of breakage risks) of high speed steels with • 2) All partial turns of the tap mean that an axial movement respect to carbon steels, in spite of the significant progress is essential with a magnitude proportional to the rotation made with the latter. value. Within the high speed steels, there are two main specific The final consequence is that success in tapping is very qualities: M 2 (1.3343, S 6-5-2) which is an excellent high closely linked to the factors associated with rotation-feed speed steel up to the point that its true capabilities can be synchronism. insufficiently appreciated in some cases. And M35 (1.3243, S6-5-2-5) quality, which incorporates cobalt over a base of M2 in its alloy content, which provides it with an appreciable improvement in thermal resistance (hot hardness) for working at very high cutting speeds. The downside is that its fragility increases slightly. Both materials are used for multi-metal taps. / 41