Please Help I.D these taps
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  1. #1
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    Default Please Help I.D these taps

    I stumbled on these taps in a set of vintage taps. GTD 7/8-32 5-p LH Fin. It has a tapered rod with an adjusting nut (I assume to be variable over-sizing)
    SW Card 7/8-32 USF L20191211_012413.jpg20191211_012426.jpg20191211_012511.jpg20191211_012637.jpg

    In what application would 7/8-32 LH be used? Is the finishing tap for adjusting specific over-sizing? Are these "off the shelf" or completely custom? I don't think these have ever been used as they were covered in protective grease. The full size cards even had old cloth wrapper. The GTD is easily the coolest tap I have seen, I just don't know what the hell they're for, fine adjusting mechanism.

    Thanks in advance, Rick

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    A 7/8-32 thread is a "standard" size--listed in Machinery's Handbook. The fact that the tap is adjustable makes
    it quite unique. As to usage, could be almost anything...

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    I have been able to find hat thread in "some" charts, but never left hand. Hell, I can't find any "adjustable" taps anywhere. As for applications, can you give me some/any examples? I'm not asking for an exhaustive list by any means. The only thing I can think of is some sort of fine adjusting mechanism for some kind of machinery. It really doesn't look like it would be a strong attachment. I just happened upon them, there are 3 of the Card, and my curiosity is in high gear.

    Thanks for the quick response.

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    Stating the obvious here, they are to tap a 7/8"-32 left hand hole, though goodness knows what in. I reckon they are adjustable as the part being made is hardened and may shrink in that process. Maybe it is a "trial and error" process to get the final result in the initial stages of production?

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    Or adjustable for sharpening like a reamer???

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    i made some tie rod ends for a fella, 7/8s R.H&7/8s L.H.,so maybe......
    and adj., to cover the split in some tie rods???
    Gw

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    I may have heard of "repair taps." Collapse, insert, expand, back out.

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    Judging from my collection of United Shoe Machine special taps, large companies would design in odd threads so you had to buy parts from them

    I mean, I have something to the effect of a 14mm 22tpi whitworth tap. I mean, why?

    A thread that fine would seem to be thinwall tubing, were it a 40 pitch it might be adjustment. Maybe the adjustment is for field repair

    Unless someone has familiarity with that thread...

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  12. #9
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    Look closely. That is a 5 start thread. The lead in the last picture is way too fast for 32 tpi single thread.

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    Before threads became "standard," machinists and engineers made whatever thread they thought worked best for their application. For many years AFTER threads became standard, many shops were still doing the same (ours is one of them). You had companies that were still servicing the old machinery with old threads who saw no reason to change over. Keep in mind too that this was a time when using "off the shelf" tooling was a moot point because everyone ground their own cutters, or knew a guy next door that would do it for a cup of coffee. Sometimes they would but they would keep an odd thread here and there because their lead engineer swore an extra thread per inch was necessary. Sometimes the idea was to keep threads special so that you the OEM were the only source of parts for said machine. It was a slow transition that still isn't 100% done even today.

    We have a few parts we make that use a 7/16-30 Modified 'V' thread, that is an odd thread already, but what you find in the Machinery Handbook doesn't apply because the major/minor diameters are a few thousandths too large. We have some old plug gauges and prints that are "the standard," and we need to stick with them because we have a few thousand machines out there that use the same old thread and it's not worth the hassle to have to keep track of what's old and what's new. We're tried making changes in other instances and Jack-old-timer in Montana get's really pissed when you send him parts that were "made wrong." In situations like this, the only way to handle it IMO is to group enough changes together that you can make a new style machine that is easy to differentiate from the old ones.

    It's why I roll my eyes at the guys wining about everyone needing to change over to the Metric system. It's the same story with a different ruler that is less about "choice" and more about dealing with variables that are not always in your stewardship to change. Contrary to what our kindergarten teachers said, we can change our own worlds, but we can't (or shouldn't) change everyone else's world (IMO).

  14. #11
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    My first reaction was the same as Greg White. Tie rod end.


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