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<DIV>For some more of the Jo Block story, take a look at the 1908 Dewar Trophy
story here: <A title=https://en.wikipedia.org/wiki/Dewar_Trophy
href="https://en.wikipedia.org/wiki/Dewar_Trophy">https://en.wikipedia.org/wiki/Dewar_Trophy</A></DIV>
<DIV>Although not explained in this article, a main reason Cadillac was able to
accomplish this was the early purchase and use of a set of Jo Blocks. This
was the genesis of Cadillac’s “Standard of the World” slogan.</DIV>
<DIV> </DIV>
<DIV>On the subject of paper tape. Ask almost any programmer how big a
program is, he will give you an answer in bytes, kilobytes, or these days
megabytes. Ask an NC programmer about the size of a program, he will
answer in feet, as in how long the paper tape would be if you punched it
out. I found that even in the ‘90s, long after paper (or mylar) tape had
disappeared from the shops, that was still the way they answered.</DIV>
<DIV> </DIV>
<DIV>Jim Becker</DIV>
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<DIV style="font-color: black"><B>From:</B> <A title=soffiler@gmail.com>Stephen
Offiler</A> </DIV>
<DIV><B>Sent:</B> Sunday, May 05, 2019 5:56 AM</DIV>
<DIV><B>To:</B> <A title=at@lists.antique-tractor.com>Antique Tractor Email
Discussion Group</A> </DIV>
<DIV><B>Subject:</B> Re: [AT] OT: the inch is somewhat metric Cast iron work on
a replica cannon</DIV></DIV></DIV>
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<DIV>There is a fairly complex history leading to the definition of 1 inch =
25.4mm exactly. There were some troubles with parts interchangeability in
WW2 because different definitions were used in different countries. But
the man who invented extreme precision, Carl Johannson - inventory of the gage
block - arrived upon this definition while working with Ford Motor Co. in the
1920's. It took a while for this definition to become universal. If
you find this subject of interest, I suggest:</DIV>
<DIV> </DIV>
<DIV><A
href="https://youtu.be/gNRnrn5DE58">https://youtu.be/gNRnrn5DE58</A><BR></DIV>
<DIV> </DIV>
<DIV>The very earliest numerical-control (NC) machines had no computer, but
rather read instructions from a punched paper tape, and these were in the
research stage in the 1940's and began to appear in practice in the
1950's. It was not until the 1970's that computers and digital displays
began to appear on the shop floor. Conversion from metric to inch in
the displays was not an issue. Even if it was, the conversion could have
been accomplished regardless of the definition, because even prior to the
universal adoption of 1" = 25.4mm exactly, the errors were on the order of
25.39993 to 25.40005 which is well beyond the precision of the machines in those
days.</DIV>
<DIV> </DIV>
<DIV>And finally, it is a rare engineering course anywhere in the USA that does
not present problems to students using both metric and inch systems.<BR></DIV>
<DIV> </DIV>
<DIV>SO</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV class=gmail_quote>
<DIV class=gmail_attr dir=ltr>On Sat, May 4, 2019 at 9:42 PM James Peck
<<A>jamesgpeck@hotmail.com</A>> wrote:<BR></DIV>
<BLOCKQUOTE class=gmail_quote
style="PADDING-LEFT: 1ex; BORDER-LEFT: rgb(204,204,204) 1px solid; MARGIN: 0px 0px 0px 0.8ex">Early
in WW2, the US, UK, and Canada all had a different length inch. To ensure
parts made in the US fit into machines made in the UK, etc., they needed a
common inch. They solved it by defining the inch as 25.4 MM. I bet one heck of
a lot of calipers and micrometers had to be recalibrated. <BR><BR>This made it
possible for CNC machines to switch from inch to metric on the displays.
<BR><BR>Some university courses would have test problems using either system
or both. That is the real world.<BR><BR>[Rena Glover Goss] It has been too
long since I did this, Stephen. I used to teach this material to
engineering and engineering technology students, but have been retired for 18
years, and gave all my metric taps, dies, drills, and wrenches to one of my
grandsons when I downsized. <BR><BR>I used to get criticized by faculty
colleagues because I taught my drafting and graphics courses only in metric
units. I told them the students really didn't know how to use any of the
four systems of measurement, and that they would develop a decent sense of at
least one of them if they didn't have to be confused by dealing with the
others. I don't think my colleagues necessarily "bought" my argument,
but I did find that things were much simpler when students only had to deal
with a single measurement device. I think I still have metric,
architectural, mechanical engineering, and civil engineering scales laying
around--but not nearly as many of them as I used to.<BR><BR>So tell me-- How
long is a surveyor's chain, and what are the units in it? This is not an
esoteric question. Our family is currently dealing with a real estate
transfer that dates to the original survey for the Wabash-Erie canal.
The concepts of Range and Township were still reasonably new at that time, and
the units of measure corresponded to the most current technology.<BR><BR><BR>[
Stephen Offiler] Larry: yes, with metric threads, you find the tap drill
simply by subtracting the pitch from the major diameter. M15 x 1.0
gives a 14mm tap drill. Using this formula, you always end up with
77% thread engagement for any thread, any pitch. I'm not quite
following your comment about the reduction you use.<BR><BR>[Rena Glover
Goss] THAT'S NO FAIR, SPENCER. You were not supposed to
figure out how simple those relationships are in the metric system
when compared to any other system of threading. I used a
reduction by 1.5 millimeters so the thread engagement came closer
to 75%, as is used in the SAE system. There are no charts
for pilot drills in the metric system--they simply aren't
needed.<BR>.<BR>_______________________________________________<BR>AT mailing
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rel=noreferrer
target=_blank>http://lists.antique-tractor.com/listinfo.cgi/at-antique-tractor.com</A><BR></BLOCKQUOTE></DIV></DIV></DIV>
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