
Lifting a Million Pounds of Stainless Steel - state_machine
http://www.npr.org/sections/thetwo-way/2016/05/20/477926381/how-do-you-lift-a-million-pounds-of-stainless-steel-very-carefully?
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cmsmith
I work at NIST and took a tour of this machine a few months ago. A few bonus
facts:

\- The spatial distribution of the local gravity field is a significant part
of the uncertainty of these measurements. The weights extend into the basement
of the lab, and the gravity in the basement is less than that above the
surface. They produce gravity maps by dropping things in a vacuum to get a
handle on it.

\- The drift in the dead weight standard was mostly caused by the individual
masses welding themselves together under the immense pressure of the weight
stack. The interface has been designed to reduce this effect.

\- The same group is also working to count the number of atoms in the
kilogram, so that the mass of the dead weight stack will not be 500,000 times
the mass of a piece of platinum in Paris, but will be 500,000 times the mass
of 6.XX E23 silicon atoms.

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elbrownos
Those sound like great reasons to use something sensible like a hydraulic ram
to apply 1,000,000 lbf. Force = pressure x area, and neither pressure nor area
is difficult to measure precisely. I can't see the upside of using 1,000,000
lbm of stainless steel.

~~~
kabouseng
It's much simpler to compensate for dead weight to get as exact as possible
measurement. With a hydraulic press you need to compensate for the compression
and heat buildup of the liquid etc.

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teh_klev
There's some reasonable sized photo's of this monster here:

[http://www.nist.gov/pml/div684/grp07/million-pound-
deadweigh...](http://www.nist.gov/pml/div684/grp07/million-pound-deadweight-
restoration-continues-06262015.cfm)

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Tim61
This would sound much less impressive if they just said 500 tons. Also, why
the dead weight? 500 tons is easily doable with a (smallish) hydraulic press.

The actual title of the article is "How Do You Lift A Million Pounds Of
Stainless Steel?" I feel like they didn't answer that question either. It
turns out that the weights are in fact lifted by hydraulics.

~~~
Retric
It's a question of accuracy not maximum force. At some point you want to
calibrate the things you use to calibrate the hydraulic presses.
[http://www.nist.gov/calibrations/index.cfm](http://www.nist.gov/calibrations/index.cfm)

~~~
Animats
Right. Something the parent article completely fails to mention. This is
NIST's force standard for large forces, the place you send load cells to be
calibrated.[1] If they have to use the whole million pound stack, the fee is
$16,489.

[1]
[http://www.nist.gov/calibrations/force.cfm](http://www.nist.gov/calibrations/force.cfm)

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gadders
Now they just need to try folding some paper 7 times, squash some playdoh
animals and set up a YouTube channel and the thing will pay for itself:

[https://news.ycombinator.com/item?id=11694819](https://news.ycombinator.com/item?id=11694819)

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jaseemabid
Why they don't use SI _even_ for scientific measurements?

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venning
Considering the machine was built in the US in 1965, it's not surprising that
the machine used imperial units. Based on Wikipedia's table [1], it looks like
_metrication_ had not yet begun in a large number of countries by 1965.

Also, if your goal is to build a device that calibrates other machines, and
most of the machines in your country (and, likely, most of the machines
belonging to the majority of your trading partners) use one system of
measurement, then that's probably the system of measurement you build the
machine to calibrate against.

[1]
[https://en.wikipedia.org/wiki/Metrication#Conversion_process](https://en.wikipedia.org/wiki/Metrication#Conversion_process)

~~~
jrapdx3
That's an excellent way to express the situation back then. Given the ease of
converting results with modern technologies, it's hardly a handicap to use the
Imperial units, besides doing so preserves the "feel" of the era it came from.
I think that's not a shabby or minor aspect of the machine being brought back
to useful life.

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dsfyu404ed
Did they put the tools back in the cabinet when they were done?

That's a serious question.

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yuubi
> why the dead weight?

I assume it's because masses are more stable and easier to calibrate than the
gauge on a hydraulic press.

