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The Plansee Tizit external and internal threading tool tips are designed to cut threads with pitches in the range 0.5 to 1.5mm. This covers the coarse ISO threads M3 to M10 and the fine ISO threads M8 to M20. With an appropriate tool, threads with larger pitches can be cut provided the spindle speed and necessary matching feed rate are achievable.

Tips which cut threads over a range of pitches do not form the crest and root of a thread to the ISO profile. For most purposes this does not matter. However, there is a problem with the depth of a thread when it is cut with a multi-pitch tip.

In the ISO standard, the larger the thread pitch, the larger its root radius. However, a multi-pitch cutting tip has a small fixed radius, say 0.04mm. Therefore, to form a thread so that the groove is the correct width, the tip must cut the root of the thread more deeply than is specified by the ISO standard.

For example, the M10 coarse thread has a pitch of 1.5mm. The ISO depth of the thread is 0.9202mm. Therefore the root diameter is 10 - (0.9202 x 2) = 8.1596mm. A multi-pitch tip with a radius of 0.04mm must cut the thread to the greater depth of 1.1mm, a root diameter of 7.8mm, for the groove to be the correct width. Proportional adjustments must be made for the depths of threads of other pitches.

The table below gives the depths and root diameters for threads cut with a multi-pitch tip with a tip radius of 0.04mm.

                                        

There is no need to screw cut at the lowest spindle speed. The table below illustrates the spindle speed and feed rate options for threads of various pitches. WELturn calculates a feed rate to match the spindle speed. The table was prepared with a maximum feed rate of 500mm/min in mind.

                              

G78 Threading Cycle
Spindle Speeds