Tool Talk
What's-It Forum => What's-It Forum => Topic started by: thiggy on December 02, 2013, 09:48:56 PM
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Last week while going through a box of old drill bits and pipe taps in the attic of my great grandfather’s (now my) farm house, I came upon these three taps. I have never seen this particular type. They appear to have straight tapers. The longest is 5.25”, the next is 2.125” with a broken tip and the smallest is 3.125”. Each have a number stamped on the wrench end, 10,14, and 16, respectively. The numbers represent the threads per inch for each. My grandfather was the local blacksmith in the area, but not a machinist by any account. My question is what kind of taps are these and what purpose did they serve?
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Possibly for cast iron repair, tapered iron plugs
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Not surprisingly, given your grandfather's occupation, they're blacksmith's taps. There have been a few posts here in the past about them. From the earlier posts, you ran them in from one side, then the other until whatever you were tapping was a snug fit on the corresponding threaded piece. I have a handful of these as well, and was mystified as to how they were used and why they were tapered until I found the answer here.
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They are indeed blacksmith's taps, and the explanation of how they were used is generally correct. I don't remember the episode number, but Roy Underhill ("The Woodwright") visited a blacksmith, who used such a tap to make nuts. He went in from one side until the male thread would go partway in; then he finished from the opposite side, so the nut had a fairly tight fit at its center, with a taper going in from each side. The die he had more or less swaged the threads, rather than cutting like modern dies do. It was a two-piece, with some adjustment. The number of threads per inch was the same for tap & die, but diameter wasn't precise at all. When the smith made a part, the diameter of his raw part was whatever it happened to be; he needed to adjust the die to match. It might take several passes before he got decent threads full length. By that time, the diameter was fairly uniform, but its size was luck-of-the-draw. The tapered tap let him make the nut to match.
Be on the lookout for dies (or diestocks) to match these!
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> Each have a number stamped on the wrench end, 10,14, and 16,
Nearly every thread pitch from 8 to 24 was available for these taps.
There are quite a few tap wrenches to choose from, more than there were die holders...