1/2 - 12 tap

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LIALLEGHENY
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Re: 1/2 - 12 tap

Post by LIALLEGHENY »

I have a 1935 Machinery handbook that explains the 1/32 number on the tap.....except that I don't know if I am understanding it.

There is a chart ( First page in the tap section of the handbook) for pitch diameters of US screw threads 1/32 is top of one of the columns. Follow the column down to 12 threads per inch and .9771 is given. ( this number is located below a heavy line)

According to the chart" When the outside diameter and the number of threads per inch are known, the pitch diameter is found in the chart above. Decimals only are given, so that whatever the whole number is that precedes the fraction at the head of the columns, giving the outside diameter, if the same number is placed before the decimal, the correct pitch diameter is obtained, except in the portion of the table below the heavy line. where the whole number preceding the decimal should be one less than the whole number preceding the fraction at the top of the column"

What I am getting is 1/2" (.500) (tap diameter) minus 1.000 ( # falls below the line) = -.500 + .9771 ( # on chart) = .4771 which should be the pitch diameter Maybe???
Nyle
whateg0
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Re: 1/2 - 12 tap

Post by whateg0 »

Wow! I'm going to have to have somebody from legal translate that for me. My 17th edition is from 1964 and I find no such chart in it. I'll have to try to reread that a few times and maybe it will make sense to me. Did that sort of thing exist before thread classes maybe?

Dave
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Steggy
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Re: 1/2 - 12 tap

Post by Steggy »

LIALLEGHENY wrote: Tue Jun 26, 2018 11:41 pm...When the outside diameter and the number of threads per inch are known, the pitch diameter is found in the chart above. Decimals only are given, so that whatever the whole number is that precedes the fraction at the head of the columns, giving the outside diameter, if the same number is placed before the decimal, the correct pitch diameter is obtained, except in the portion of the table below the heavy line. where the whole number preceding the decimal should be one less than the whole number preceding the fraction at the top of the column...
That makes almost as much sense as some of the "instructions" the IRS publishes for filing your tax returns. :D
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Harold_V
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Re: 1/2 - 12 tap

Post by Harold_V »

If you hope to gain a good understanding of threads, I highly recommend the H28 handbooks published by the US government. Don't know if they're still available, but they used to cost just a couple dollars each. There's four of them (or there used to be---don't have a clue about what's happening today).

H
Wise people talk because they have something to say. Fools talk because they have to say something.
SteveM
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Re: 1/2 - 12 tap

Post by SteveM »

Harold_V wrote: Wed Jun 27, 2018 3:03 am If you hope to gain a good understanding of threads, I highly recommend the H28 handbooks published by the US government. Don't know if they're still available, but they used to cost just a couple dollars each. There's four of them (or there used to be---don't have a clue about what's happening today).
Available here:
https://publicaccess.dtic.mil/psm/api/s ... rvices+h28#
John Hasler
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Re: 1/2 - 12 tap

Post by John Hasler »

Harold_V wrote: Wed Jun 27, 2018 3:03 am If you hope to gain a good understanding of threads, I highly recommend the H28 handbooks published by the US government. Don't know if they're still available, but they used to cost just a couple dollars each. There's four of them (or there used to be---don't have a clue about what's happening today).

H
Since all works of the US government are in the public domain all those documents that we used to buy from the GPO for a couple of bucks are now available free on the Web (along with thousands of others that the GPO didn't publish).
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tornitore45
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Re: 1/2 - 12 tap

Post by tornitore45 »

The 12 TPI tapered taps I mentioned were described as 3/4" and 1-1/4" .taper per foot, so I didn't see any obvious correlation between that and the "1/32".
12/32 = 3/8 could be the 1/2 taper (measured on the radius)?????
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earlgo
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Re: 1/2 - 12 tap

Post by earlgo »

I couldn't find the 1/2-14 tap but I found this one. May be time to upgrade some of my tooling. :roll:
11/16-11 tap
11/16-11 tap
NYT&D Patent date
NYT&D Patent date
--earlgo
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duckman903
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Re: 1/2 - 12 tap

Post by duckman903 »

I've found that stuff made in India uses 1/2-12 if you only need to thread on less than 3/8" it'll go.
Downwindtracker2
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Re: 1/2 - 12 tap

Post by Downwindtracker2 »

We had some old Japanese wire drawing machines from the '60s, they were Whitworth. Well not all millwrights find thread design interesting. . So when the cap of the capstan block were replaced, the securing allen head cap screws could go missing, The less than bright would find 1/2x13 wouldn't fit so would use a 12mm. They would impact in . With less meat in cast iron, the cap could get pulled off and injure an operator. The caps were heavy enough to be a two man lift.
A man of foolish pursuits, '91 BusyBee DF1224g lathe,'01 Advance RF-45 mill/drill,'68 Delta Toolmaker surface grinder,Miller250 mig,'83 8" Baldor grinder, plus sawdustmakers
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