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Hi John,
This query immediately brought to mind an interesting aside from the
autobiography of Neville Norman, who wrote novels under the pen-name of Neville
Shute, as he did not wish to trivialize his main profession as an aeronautical
engineer. Working in the team of Dr. Barnes Wallis designing the airship R100,
(the successful commercial opponent of the fatal government-controlled R101),
he was given the job of stressing its 16-sided lightweight polyagonal frames,
held rigid by wires.
Working in pairs, to avoid careless inputs to their mechanical calculators,
they would take many weeks to assess the stress pattern of each assembly of
girders and wires based on an initial assumption. When, after much tedious
labour, they found that one of the wires based on their first proposal was 'in
compression' (have you ever tried pushing a chain?) he said "We would moisten
our lips and begin all over again". Electronic computers would have achieved
the ultimate solution to this problem in microseconds both almost within my
lifetime.
http://www.century-of-flight.net/Aviation%20history/coming%20of%20age/R101%20disaster.htm
----Original Message----
From: john.pick...@bigpond.com
Date: 07/09/2016 0:14
To: "Sundial List"<sundial@uni-koeln.de>
Subj: Using linkages to draw curves on sundials
Good morning,
While researching mechanisms of wire strainers used to tighten wires in
fences, and trying to find the theoretical mechanical advantages of the
different mechanisms, the first thing I learned was that "linkages" are the
key to many of them. There's a whole branch of mechanics devoted to the
theory of these things which involve a zillion combinations of pivots and
links to achieve various purposes, usually to transmit motion in a specific
manner.
The best explanation I found was Slocum, A. (2008). Fundamentals of design.
Topic 4. Linkages
(http://web.mit.edu/2.75/fundamentals/FUNdaMENTALs%20Book%20pdf/FUNdaMENTALs%20Topic%204.PDF).
3.3 MB
But my curiosity lead me further, to a more mathematical treatment.
Unfortunately and for unknown reasons, the Jefferson Lab Library has removed
the title page.
Bizarre! I contacted the library and they gave me the full title etc.
Svoboda, A. (1948). Computing mechanisms and linkages. MIT Radiation
Laboratory Series, Volume 27. New York, McGraw-Hill.
(https://www.jlab.org/ir/MITSeries/V27.PDF) (CAREFUL: 40.8 MB)
Among other things, this book shows how you can use mechanical linkages of
various forms to draw the curves of mathematical functions. And seeing that
the curves on sundials are all defined by equations, I was wondering if
anyone knows of any attempts to make a mechanical device of links and pivots
specifically for generating sundial equations, and thus drawing sundials? It
seems to be a feasible but complicated way of doing it, with some serious
mathematics behind the linkages.
I don't include sundial rulers in this, as they are not physically linked
and pivotted. Similarly, I don't include CNC machining as this involves
moving the tool / work using a pre-programmed series of x, y and z
coordinates. And of course, 3-D printing is out.
(And I still haven't figured out what sort of linkages are used in the wire
strainers I'm studying!)
Cheers, John
John Pickard
john.pick...@bigpond.com
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