Today, some early computers. The University of Houston's College of Engineering
presents this series about the machines that make our civilization
run, and the people whose ingenuity created them.
1956 found me working for Pacific Car and Foundry
[now renamed as PACCAR] designing equipment for tractors. Of course we used
whatever off-the-shelf parts we could in our designs -- springs, bearings,
pulleys, seals ... One ritual in those days was the infamous three-martini
lunch with parts-manufacturer's representatives. I'd struggle to drink as
little as possible and learn as much as I could.
Those sales people wanted to make it easy for us to select their parts.
And selection is complicated. Example: take the design of a simple spring:
If it's to deflect, say two inches under a one-ton load, we have to chose
workable spring and wire diameters. We need to find a material with the
right stiffness, strength, corrosion resistance, fatigue lifetime. We need
an optimal number of coils per inch. To sell us springs, a salesman helped
us through that selection.
So, when I dug into an old drawer yesterday, I found a special slide rule
made by the Associated Spring Corporation -- a cheap celluloid throw-away
with scales on the front and back. Our regular slide rules were made of
sturdy bamboo or aluminum. They had to survive years of constant daily use,
but this was for rare occasions. How many springs does an engineer design?
Spring selection slide rule. For a large view of both sides, click on this image
Then I dug deeper in that old drawer. More flimsy slide rules emerged.
A cardboard Lufkin Tools circular slide rule. It helped chose threaded
screws and taps. The Standard Pressed Steel Company had one for sizing
socket screws. The fanciest one was from the Lock Joint Pipe Company -- a
10-scale slide rule for sizing pipes and minimizing the pressure loss of
liquid flowing through them.
Those four were all I still have. But we design engineers once collected
them like baseball cards. Mine bear copyright dates from 1938 to '62.
Those dates match the year when John Atanasoff began building the first
digital computer, and the year IBM produced its powerful 7094 computer.
As big computers entered our lives, companies stopped giving us these
useful Cracker Jack prizes.
Now, an odd catch: Surely, over fifty years later, we can just Google
"spring design software". Well I tried and found two things: Vastly
over-simplified routines or very expensive downloadable software.
Maybe I shouldn't be surprised. When I look back at that celluloid slide
rule, my eyes blur over the complexity of it. Our engineering in the late
forties through the early '70s was constantly drenched in calculation and
looking things up in tables. These little band aids provided modest, but
Change usually comes on little cat feet. Digital computation has quietly
taken over our once-crushing load of calculation. As I dig into my musty
old drawer I realize how different engineering now is. And my nostalgia
on finding these quaint old calculators is muted. It's quickly replaced
with a great heaving sigh of relief.
I'm John Lienhard, at the University of Houston, where we are interested in the
way inventive minds work.
The Wikipedia page "Spring (device)"
helps us see the complexity of a seemingly simple machine element.
Lock Joint Pipe Co. Hazen Williams Hydraulic Slide Rule with 10 scales. This one needs an
instruction manual. For a large view, click on this image.
No sooner than this aired, listener John Morreale wrote to recommend
this on-line spring analyzing software.
If you guess a spring design, it will do the stress analysis and allow you to iterate
until you have the spring you want.
This episode was first aired on August 2, 2011
The Engines of Our Ingenuity is
Copyright © 1988-2011 by John H. Lienhard.