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

[partzpicker at yahoo.com]

A chain is 66 feet long and is subdivided into 100 links or 4 rods. A rod is 16 2/2 feet.   There are 10 chains in a furlong and 80 chains in one statute mile.

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  On Sat, May 4, 2019 at 8:42 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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