Hand & Machine Taps
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  1. #1
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    Default Hand & Machine Taps

    I'm not sure if this topic has been discussed earlier, can anyone inform the difference between Hand Taps and Machine Taps, and can they be used vice-versa. Can we use a Third [Bottoming] Hand tap for Machine application.

    Thank you all in advance

    Pali

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    Hand taps have straight flutes with no special geometry to force the chips (in ductile materials) to curl in a controlled direction. Thus, they tend to plug themselves with chips if they are run several turns into the hole.

    Yes, you can tap a hole by hand with a machine tap, but the need for some sort of guidance system is mandatory, because they typically have fewer flutes and are less stable to get started exactly straight into the hole. Mind you, hand taps are also better used with a guidance system too, however, with the long taper of a 'taper' tap, you can usually get the tap started and square it up by pushing this way or that way as you start it, and checking with a square.

    A bottoming tap is really only meant to clean up the last few partial threads left by a plug tap. I cannot imagine using the bottoming tap to tap an entire thread, as the cutting force is very high. If you have to tap that close to the bottom of a blind hole, use a spiral flute tap, as these have maybe only 3 threads of chamfer. Then hand tap to the bottom with a bottoming tap if you must.

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    I stopped using hand taps for anything a long time ago. My new name for hand tap is "broken tap".

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    Quote Originally Posted by PixMan View Post
    I stopped using hand taps for anything a long time ago. My new name for hand tap is "broken tap".
    "Soon to be broken". :-)
    ...lew...

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    Apparently you define a hand tap as a traditional standard 4 flute tap. Period.

    I understand hand taps to have wider lands than machine taps, to help keep them straight. Machine have some relief on the lands, which is no problem since they are held straight, while a hand use of a machine tap can easily tap bellmouthed. Machine tap might be any style otherwise

    But I have taps otherwise identical to standard types (no relief) except that they are spiral point, and eject the chip. Generally two flute in small sizes, but IIRC one or two are 3 flute. Easily usable by hand, no need to turn and back , turn and back all the way through. Also usable by machine, of course.

    A "spiral" tap is my definition of a "soon to break" tap..... and is definitely machine only. Never a problem with spiral *point* taps, though.

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    Would somebody please chime in about the kind of tap that is stronger than the
    rest, and can be used by hand, or under power?

    The two-flute gun tap.

    Sometimes in larger incarnations, the three flute gun tap.

    Only disadvantage is, it cannot be used to bottom tap. Unless you grind the tip
    off of one. Then it's passable.

    AND the chips have to have someplace to go. For this you make every hole a through
    hole. If you can't do that, then drill the tap-drill sized hole, a bit deeper.

    They do make spiral versions of this that eject the chips out the top. As mentioned
    those are the 'damn it snapped off' kind of tap.

  7. #7
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    I've used the spiral point plug (machine) taps for hand tapping for many years now and never made an oversize thread. It's also been a very long time since I broke a spiral flute tap when using them for hand tapping. I think the Starrett tap wrenches I have deserve some credit for having a good feel.

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    I do a fair amount of tapping by hand, with small sizes between 000-96 up to 10-32.

    One trick that practically eliminates tap breakage for small stuff like that, is to omit
    the tap wrench altogether. Simply mount a suitably-sized electronics knob to the
    tap shank, and drive it with that.

    The large the tap, obviously, the larger the knob. 6-32 and below, I use one around
    3/8 inch in diameter. Below 0-80 often the tap shank is large enough depending on the
    material.

  9. #9
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    I thought "gun tap" was Greenfield Tap & Die's trademarked name for what is otherwise referred to as "spiral-point," or "machine," tap (not the spiral-flute, aka "oh shit it broke" tap).

    That's what it says in the tapping handbook I have, published by Greenfield.

    Is this correct?


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