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Custom tap

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Lew_Merrick_PE:
Chuck,

Stop and think about this for a minute.  The purpose of flutes on a tap is to clear the chips axially down the length of the tap.  Because of fracturing and curling, a chip will take up as much as 50% more volume than it required as solid material.  Depending on the type of tap being used (i.e. plug vs. taper vs. bottoming) up to 6 threads (taper) or 4 threads (plug) do the cutting.  If you allow for the cross-sectional area of the thread being cut X the number of threads doing the cutting X the "expansion factor", you should have enough area (reduced by the number of flutes in use) for your fluting.

The fact is that the thread is being cut in "stages" such that you are really only disposing of (about) 2X the cross-sectional area of a thread.  The excess allowed in the previous paragraph merely provides a safety margin on the cut.

The square corner of the flute is going to create a stress riser that may well cause the tap to break prematurely.  Except in the case of spiral-fluted taps, the radius only has a small effect on the ejection of chips -- it is more to do with preventing stress risers.  The main thing in the design of flutes is to get the rake angle right for the cutting.

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