[AT] OT: the inch is somewhat metric Cast iron work on a replica cannon

[Jim Becker]

For some more of the Jo Block story, take a look at the 1908 Dewar Trophy story here: https://en.wikipedia.org/wiki/Dewar_Trophy
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.

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.

Jim Becker

From: Stephen Offiler 
Sent: Sunday, May 05, 2019 5:56 AM
To: Antique Tractor Email Discussion Group 
Subject: Re: [AT] OT: the inch is somewhat metric Cast iron work on a replica cannon

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:

https://youtu.be/gNRnrn5DE58


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.

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.


SO


On Sat, May 4, 2019 at 9:42 PM James Peck <jamesgpeck at hotmail.com> wrote:

  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. 

  This made it possible for CNC machines to switch from inch to metric on the displays. 

  Some university courses would have test problems using either system or both. That is the real world.

  [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.  

  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.

  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.


  [ 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.

  [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.
  .
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