
Wringing - leetbulb
https://en.wikipedia.org/wiki/Gauge_block#Wringing
======
Bizarro
Great stuff. We need more of these types of science tidbits on HN. And good
links by the commenters too.

I love Feynman's classic style of "explaining to a 5 year old" on Cold
Welding.

 _The reason for this unexpected behavior is that when the atoms in contact
are all of the same kind, there is no way for the atoms to “know” that they
are in different pieces of copper. When there are other atoms, in the oxides
and greases and more complicated thin surface layers of contaminants in
between, the atoms “know” when they are not on the same part.

— Richard Feynman, The Feynman Lectures, 12–2 Friction_

~~~
hwillis
Note that this is a big oversimplification- it doesn't apply to gage blocks.
Cold welding and similar phenomenon can only truly happen with metallic bonds
and very large grain sizes. Non-metallic bonds are structured and require
precise orientations and conditions to reform. Metals are still structured
-metals have crystal grains- and the microscale structure needs to line up in
order to reform. In cold welding, you force that to happen with high
pressures.

This doesn't really apply to gage blocks because tool steel has passivated
surface oxides and complex crystal structures. There are very few metallic
bonds exposed on its surface. It also has very nasty, often needle-like
grains. There's no chance that the metal atoms are being attracted to each
other. Not to mention that wringing works with ceramic gage blocks as well.

It is probably a complicated combination of effects. Adhesion (intermolecular
forces) probably plays a minor effect at small regions where the surfaces are
_extremely_ close together. Casimir forces probably have an effect on most of
the surface. Small amounts of grease probably form much stronger adhesions by
"carrying" the forces between the surface oxides. Vacuum being trapped by
grease probably plays a fairly large part in rougher blocks wringing in an
atmosphere. Adhesion and Casimir forces are not well understood.

~~~
nabilhat
There's something at play that causes precision ground surfaces to stick
together. Oil certainly plays a part, but there's a point that when two
surfaces are flat enough, they'll stick hard in place, and there's a "crack"
moment when twisting them apart.

Around a decade ago, I worked in a machine shop. Mill table surfaces are
ground flat. Not precision surface flat, but good enough to be a reference for
cutting tools. Mill vise clamping surfaces are ground flat. It's normal for an
object that's at least cut (not even ground) flat on one side to get
hydraulically suctioned via cutting oil to either of these. It's usually easy
to slide the part off to the edge of the surface.

Very flat surfaces do this as well, but with a little more encouragement to
work out oil from between parts, they'll start to stick in place. The more
finely ground and flat each side is, the more pronounced the sticking moment
will be. Extremely finely surfaced blocks being wrung together will frustrate
you by sticking before you have them lined up the way you want them.

This made me suspicious of the role that surface tension and vacuum played.
Hydraulically stuck things are easily separated by a quick blast of compressed
air. Wrung blocks aren't as easily separated by a blast of air. I tried to
clean blocks as devoid of liquid as possible and wrung them together. They
still stick, but it's not as secure, and they come straight apart the moment
they're twisted apart.

After this, it seemed that wringing blocks together worked best with a trace
of oil. Brief cleaning with a dry rag does leave a trace, and if the surfaces
are flat enough, perhaps that trace is enough to fill some microscopic voids
between flat-ground surfaces. Twisting blocks together encourages entrapped
air to escape, and can shuffle trace oil into voids. The solution I came up
with is that the metal of the two blocks does stick together somehow once it's
in contact, and the surface tension provided by a trace of oil contributes
additional sticking force where the surfaces don't meet.

We didn't have ceramic blocks, though. It might be an interesting additional
experiment to try this with mixed materials. Does wringing together ceramic
and steel precision surfaces work the same way? Should it? What would that
mean?

~~~
hwillis
> Mill vise clamping surfaces are ground flat. It's normal for an object
> that's at least cut (not even ground) flat on one side to get hydraulically
> suctioned via cutting oil to either of these. It's usually easy to slide the
> part off to the edge of the surface.

Like you say, this is a hydraulic/air pressure effect- it's related to why you
can float things on a reference plane:
[https://www.youtube.com/watch?v=Kj6jmQxZe8s](https://www.youtube.com/watch?v=Kj6jmQxZe8s)

> Twisting blocks together encourages entrapped air to escape, and can shuffle
> trace oil into voids. The solution I came up with is that the metal of the
> two blocks does stick together somehow once it's in contact, and the surface
> tension provided by a trace of oil contributes additional sticking force
> where the surfaces don't meet.

Basically right, but the dominant theory is that the twisting/sliding motion
creates vacuums. First a sealed pocket forms by bringing asperities close
together so that they are attracted by stronger forces. Then as the blocks
slide, they stretch out the voids and cause the pressure inside to go below
atmospheric. I'm kind of skeptical of it, but the sliding does definitely
prevent anything additional from being trapped between, and makes the oil film
as thin as possible.

Additionally, there is an oil film on literally everything. It takes really
serious equipment, like plasma chambers, to actually remove the thinnest layer
of oil from a material. Oil just floats around the air constantly, and bonds
like glue to basically everything:
[https://youtu.be/atVSxvbiPg0?t=39](https://youtu.be/atVSxvbiPg0?t=39)

> We didn't have ceramic blocks, though. It might be an interesting additional
> experiment to try this with mixed materials. Does wringing together ceramic
> and steel precision surfaces work the same way? Should it? What would that
> mean?

Indeed they do:
[https://youtu.be/_YVWdxr0E_g?t=155](https://youtu.be/_YVWdxr0E_g?t=155)

It mostly just indicates that intermolecular forces don't have much to do with
it. There's no real reason they'd want to stick together- the bonds in the
ceramic are extremely tight and ordered. Ceramic blocks also wring more
tightly than steel blocks, but shouldn't experience high intermolecular forces
between each other.

~~~
sirsar
> the dominant theory is that the twisting/sliding motion creates vacuums.

Unfortunately for this theory, gauge blocks will remain wrung together even in
a vacuum!

------
lqet
If you (like me) read the entire article without really getting an intuition
for these "gauge blocks", here they are in action:

[https://www.youtube.com/watch?v=gbsd2OpPOMw](https://www.youtube.com/watch?v=gbsd2OpPOMw)

[https://www.youtube.com/watch?v=2lOOl3VxOtE](https://www.youtube.com/watch?v=2lOOl3VxOtE)

~~~
nas
This is a really nice video if you are interested in measurement precision for
manufacturing:

Machine Thinking: Origins of Precision and first project introduction
[https://youtu.be/gNRnrn5DE58](https://youtu.be/gNRnrn5DE58)

------
idlewords
This reminds me of a phenomenon called cold welding, where if the surfaces are
flat and clean enough, the blocks of metal will fuse. Just touching two
sufficienly thin gold wires will weld them.

[https://en.wikipedia.org/wiki/Cold_welding](https://en.wikipedia.org/wiki/Cold_welding)

------
sgnelson
Almost all you'll ever need to know about gauge blocks [1]. It's also a fairly
decent introduction to the uncertainties of measurements, and other factors of
taking measurements of objects. Of course it also includes a section on
wringing. (and other sources on papers about the wringing phenomenon)

[1]
[https://www.nist.gov/sites/default/files/documents/calibrati...](https://www.nist.gov/sites/default/files/documents/calibrations/mono180.pdf)

Further more, if you're really interested in how modern precision
engineering/industrial manufacturing came to be; I highly highly recommend you
look into Foundations of Mechanical Accuracy by Moore. (it's a $150 book, pdf
easily found by googling.)

(I'm a flatness/metrology nerd. I recently lapped three cast iron plates
together just because I wanted to create as flat a surface as I could. Just
because. )

~~~
ChainOfFools
what would you consider to be the flattest off the shelf metal commodity
component available today, would it be a typical hard drive platter or
something else?

------
robocat
To play with this effect yourself:

1\. pull apart an old multi-platter hard drive

2\. Take the platters out

The platters are _very_ flat, and they stick together remarkably well without
any liquid between the surfaces. Specks of dust will stop them sticking
together so well.

Be careful not to breath in any dust (or eat anything!) from the drive, as
they do contain some exciting elements.

~~~
mietek
_> Be careful not to breath in any dust (or eat anything!) from the drive, as
they do contain some exciting elements._

Can you expand on this? Which elements?

------
ndespres
If you're interested in how gauge blocks fit into the history of precision
engineering, a new book called "The Perfectionists: How Precision Engineers
Created the Modern World" puts them into context, and presents a very
interesting perspective on the events and developments that brought us into
modernity. These blocks feature strongly into the industrial revolution. I
strongly recommend the book!

[https://books.google.com/books?isbn=0062652575](https://books.google.com/books?isbn=0062652575)

~~~
russdill
Or for the lazy, here's Destin
[https://www.youtube.com/watch?v=T-xMCFOwllE](https://www.youtube.com/watch?v=T-xMCFOwllE)

------
Waterluvian
This got me wondering, (and I know it's probably not a physics question). If I
scrape two fingers and press them together for a week. How do the skin cells
know which other cells to attach to when healing? Or will I have one super
finger?

~~~
hanniabu
They can grow together but will take longer than a week. There's a man the had
his hand degloved and they sewed it into his stomach to heal, after which they
cut his hand back out and used his stomach skin to wrap around and reshape
some resemblance of a hand.

Example 1: [https://www.thesun.co.uk/news/4303135/surgeons-save-hand-
sew...](https://www.thesun.co.uk/news/4303135/surgeons-save-hand-sewing-into-
stomach/)

Example 2: [https://www.menshealth.com/health/a19517212/carlos-
mariotti-...](https://www.menshealth.com/health/a19517212/carlos-mariotti-
mitten-hand-surgery-mangled/)

~~~
winrid
Wow. Can you imagine how that would feel, to have your hand inside of you? I'd
worry about accidentally breaking something inside me. Amazing though.

------
emmelaich
At our physics school we had some super flat metal blocks. Much flatter than
gage blocks. We were warned never to put them together or we'd never get them
apart.

These blocks were used for measurement, but I can't remember exactly how.

~~~
mveety
They’re probably surface plates. They’re used as a flat reference for
measurement.

------
nateburke
This is part of the reason why you commonly see cymbal players in orchestras
use an oblique motion for a crash rather than a head-on direct motion.

Bringing two symbols together directly along their axis of rotation risks
getting them stuck together like suction cups--the crazy part is that even
when holes are drilled to release the near vaccum between two stuck cymbals,
they remain glued together by the forces described in this article.

~~~
mrob
Are you sure that's not just the air pressure difference? Cymbals often have a
shape with many concentric ripples, so you might need multiple holes to
equalize the air pressure between each ripple. Wringing only works with
extremely flat surfaces, and it works even in vacuum.

~~~
defterGoose
Yep, admit I was a little taken aback after the drilled holes explanation.
This seems correct, as no practically priced cymbal could be so precisely
made.

~~~
emmelaich
I don't think they need to be precise; any reduction in the natural vibration
can be detrimental to the sound.

They never get "stuck" together, however, imnsho.

~~~
defterGoose
Yeah, I was saying that getting the surfaces to adhere sans vacuum seems
unlikely for such an imprecise object

------
pard68
I grew up next to an abandoned granite quarry. You could, and still can
--though they are beginning rarer as the quarry is a bit of a tourist
attraction, find super smooth, polished rocks. We would do this wringing with
them all the time as kids. Never over until now did I wonder if anyone else
had ever done this or if it had a proper name.

~~~
defterGoose
Really? It seems unlikely to find ones flat enough in such a non-precision
environment to exhibit the same behavior. Maybe they were flat enough and
cupped so that you could create a slight vacuum like you can with the palms of
your hands? Would love a picture if you could get one.

~~~
pard68
I believe that the difference is our stones were wet. But also, very smooth.
The blocks ship with one side polished smooth. Still being wet probabny
helped.

------
someexgamedev
Is this what makes clear plastic card sleeves stick together? I always figured
it was static electricity but maybe it's this?

------
microcolonel
I suspect OP was brought here by this excellent video which enjoyed some
success over the past couple days on the topic of _flatness_.

[https://youtu.be/OWa3F4bKJsE](https://youtu.be/OWa3F4bKJsE)

------
userbinator
You can see a similar effect with ordinary glass plates --- the production
process[1] is such that it normally has a flat enough surface that two pieces
will naturally "stick" together if placed upon each other and there's nothing
else between.

[1]
[https://en.wikipedia.org/wiki/Float_glass](https://en.wikipedia.org/wiki/Float_glass)

~~~
dredmorbius
The manufacture process is fascinating:

[https://youtube.com/watch?v=ig4G5WbOMLc](https://youtube.com/watch?v=ig4G5WbOMLc)

------
JackFr
This takes me back to a summer job I had 35 years ago, calibrating a set of
gauge pins. I think it was a couple hundred of them. Visually inspect them for
corrosion or scratches, wipe them down with WD-40, measure each end and the
middle with digital calipers, and log the measurements and any comment on
their appearance. Honestly it probably to0k 2.5 days but it felt like forever.

------
leetbulb
Also:

[https://en.wikipedia.org/wiki/Cold_welding](https://en.wikipedia.org/wiki/Cold_welding)

[https://en.wikipedia.org/wiki/Optical_contact_bonding](https://en.wikipedia.org/wiki/Optical_contact_bonding)

Super interesting stuff.

------
TeMPOraL
I wonder how stable is such a "wring joint" over time and over mechanical
stresses like temperature change and vibrations. Could you use this feature to
e.g. attach stuff as a product assembly technique, as a temporary/non-
destructively modifiable alternative to gluing or welding?

~~~
greenyoda
The joined blocks can be pulled apart with you hands. See the first video
posted in this comment:

[https://news.ycombinator.com/item?id=20366089](https://news.ycombinator.com/item?id=20366089)

So the bond is not comparable in strength to gluing or welding.

~~~
TeMPOraL
I watched both. I know it's not comparable, but it seems plenty strong. In the
case of the video, I'd guess if you'd double the contact surface, you could
easily hang a coat on it. My question is, how long would the join last.

~~~
jcims
FWIW the Starret tips on maintaining gauge blocks says not to leave them wrung
overnight.

------
kohtatsu
I feel like the article is missing a section on uses. Is it strictly
measurement?

~~~
jcims
You can use them in concert with a Sine bar to create precise angles

[https://en.wikipedia.org/wiki/Sine_bar](https://en.wikipedia.org/wiki/Sine_bar)

~~~
lightbulbjim
Sine bar in action: [https://www.youtube.com/watch?v=PO-
Ab7YfBzY](https://www.youtube.com/watch?v=PO-Ab7YfBzY)

~~~
jacobolus
Check out this alternative version of a sine bar
[https://observablehq.com/@jrus/sinebar](https://observablehq.com/@jrus/sinebar)

Also includes some nice youtube videos inline for context.

------
nmstoker
Edit: Oops - somehow missed the other post mentioning this book. Sorry!

These are covered with a charming personal story by Simon Winchester in his
book The Perfectionists: How Precision Engineers Created the Modern World

It's reviewed here: [https://bookmarks.reviews/reviews/the-perfectionists-how-
pre...](https://bookmarks.reviews/reviews/the-perfectionists-how-precision-
engineers-created-the-modern-world/)

and the audiobook as pretty good too.

------
narrator
Is this the Casimir effect?

[https://en.wikipedia.org/wiki/Casimir_effect](https://en.wikipedia.org/wiki/Casimir_effect)

~~~
hwillis
Casimir forces are probably involved- gage blocks work with
flatness/separation (tens of nanometers) that is too high for intermolecular
attraction (hundreds of picometers). Casimir attraction works at longer
distances, but it's far from well understood. It's most likely a combination
of all the common guesses, although the air pressure one is pretty weak.

------
kashishhora
There's a great Sixty Symbols video about gauge blocks and how they work:
[https://www.youtube.com/watch?v=mgL_qH70KAU](https://www.youtube.com/watch?v=mgL_qH70KAU)

------
ryansmccoy
[https://www.youtube.com/watch?v=2lOOl3VxOtE](https://www.youtube.com/watch?v=2lOOl3VxOtE)
<\- Video Explanation

------
AnthonBerg
This is such a beautiful HN post :) thanks!!

------
superjan
Isn’t this the same effect as the screen protectors we all have on our phones?

------
applecrazy
Who knew intermolecular forces could be so strong? This blew my mind.

~~~
cryptonector
Johannes Diderik van der Waals!

------
DonHopkins
Flat suction cups.

~~~
newnewpdro
Yep, that's what I always thought was the mechanism behind this action.
Separating such precisely contacting surfaces creates vacuum, resisting the
separating force.

~~~
NickNameNick
The Cody's lab video linked above demonstrates that they don't fall apart in a
vacuum.

