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Thread: Can you make bottoming taps?

  1. #11
    hdrideblue's Avatar
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    yes I have done it many times slowly repeat slowly grind the bottom down till you get to the last thread or 2 that has a slight taper if you grind the end to fast and it turns blue than it is junk and it could break in the hole. when threading drill the hole to the correct size compare it to a chart then start it with a standard tap finish it with a bottom you made

  2. #12

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    I didn't recall reading anything about only using a HSS (High Speed Tool Steel) tap for this type operation. I would never use a HF tap because it's probably carbon steel which is brittle and or sub par quality. I've done this for forty years and it can be done but I don't remember what you said you were tapping into. Or were you hand tapping or machine, single job or multiple? Anyway, if it is mild steel, aluminum, cast iron or other softer metals you can do it but obviously tap with a good HSS spiral pointed gun tap first. Then clean out hole 100% and hand tap (with oil/ coolant) the hole so you can feel the tap cut or not. If not cutting try something else. Tapping into a blind hole is problematic for the untrained. It's easy to break one off if you don't do everything correctly.

  3. #13
    Supporting Member bobs409's Avatar
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    Well I had success! I used a thin cut off wheel and trimmed it in seconds. I'm only using this in aluminum and it worked great! Just use a regular tapered tap to start and finish off with the modified one.

  4. #14

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    Taps are so inexpensive that I almost always just buy one. But I have threw it in the grinder with a water cup near by so I don't change the color any by keeping it cool and have successfully done this 3 or 4 times. I bought a lot on eBay that has everything I ever need now 3 times over and it was very cheap! (All USA taps)

  5. #15
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    Frank S's Tools
    I generally buy my taps in a 3 tap set which comes with a taper or starting tap a plug tap which has a couple of the end threads tapered and the bottoming tap which will have only the last thread slightly tapered
    . Cutting a plug or a taper tap has never been a problem for me I just use a thin cut off wheel and coolant then grind the end thread to look like a regular bottoming tap would.
    making taps from annealed drill rod o1 tool steel or just about any harden able steel can be accomplished with good results but you need a lathe and a way to cut the flutes or a die that can be spread out about .001" of an inch per tenth of an inch in diameter. In some emergency repair situations I have even ground flutes in hardened bolts then heated them to a dull red then quenched them in water to use for cleaning out threaded holes when I found myself without the proper tap
    Never try to tell me it can't be done
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  7. #16
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    Peter Sanders's Tools
    Of course people buy bottoming taps! Obviously they're no a requirement for thin stock with through holes, but there is a need for them. I have used my bottoming taps quite regularly.

  8. #17
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    Peter Sanders's Tools
    Hi While you can make a bottoming tap out of either of the other two taps, you do lose a substantial number of threads. This may not be a problem for shallow holes. Personally, I would buy a bottoming tap. You never know when it could be useful again. If you are stuck in an "emergency" situation and cannot obtain a bottoming tap then by all means "convert away". As others have already stated be careful not to overheat the tap during the grinding/cutting process.

    When I have a need to tap a thread into a blind hole, if I don't already have that particular thread size, I normally buy the set of three.

  9. #18

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    Lots of taper and plug taps have been ground into sorta bottom hole taps. I've even been a guilty party when in a bind. But when it's all said and done the shape of the end teeth can't be right if you just cut off a taper or a plug. The homemade ones always turn a little harder and break more often because the end two teeth are shaped wrong. If you have the time and money get a real bottom hole tap.
    Dusty

  10. #19

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    I never throw away a broken tap.

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  12. #20

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    If you are using a high speed steel tap you don't need to worry about getting it too hot when you grind it. They are not carbon steel and do not respond to heat like a carbon steel does. It was made to replace carbon steel cutters so that turning speeds and drilling speeds could be increased to the point that a carbon steel tool would lose it's temper. I seem to remember an article about HSS wherein they claimed it would continue to cut at a red heat. GP

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