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Type SFM Tap Holders
Due to their slender design, the tap holders of type SFM are used primarily on multi-spindle-machines and allow the machining of boreholes with a small spindle distance.
Owing to the various requirements a tap holder is to fulfill, the series SFM is divided up in the 3 following types:
Simple model without length compensation. Relatively short design. Owing to the fact that this tap holder does not have a length compensation, it is necessary to make sure that the thread tapping cycle is cut "synchronically", e. g. over a leading spindle.
The floating tap holder type SFM-NP is in the family of quick-change tap holders utilizing the EM style tap adapters. The holder has no length compensating features, and the feed must therefore be controlled synchronously, i. e. by a lead screw. The new innovative ball-floating system provides an axial parallel floating motion, and allows for tapping in less then ideal conditions, where the floating tap holder type SFM-NP will seek to compensate for:
Type SFM-L (DZ)
The standard equipment of these tap holders contains a spring-loaded axial length compensation on compression. Depending on the tap holder size, the compensation is 0.787, 1.181 and 1.575 inches (20, 30 and 40 mm).
It should be longer than the thread depth to be cut. Tap holders with length compensation on compression are preferably used in connection with overload quick-change adapters. In case of the overload clutch responding, the length compensation is to compensate any difference in movement between tool and feed rate. The length compensation on compression is required, too, when the feed per revolution exceeds the thread pitch.
These tap holders are also available with length compensation on compression and on tension, or only on tension (abbreviation: DZ and Z).
The length compensation on tension is necessary:
Pressure Point Mechanism
In order to guarantee constantly deep cut threads, the tap must cut immediately when touching the work piece. Here, the "pressure point" guarantees that the axial cutting force of the tap does not cause a compression of the length compensation which would result in a wrong thread depth. Only when the actual axial force exceeds the regular cutting force, the pressure point mechanism releases the length compensation movement. This movement is - compared to the pressure point - softly spring-loaded and therefore fulfills its tool protecting function.