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Absolute limit of precision and myths...

Nathanhamler

Plastic
Joined
Oct 7, 2015
First post here, and I just had a quick question...I have a bench top mill and lathe, and I'm learning more as I go, but absolute precision isn't really on my radar for what I do...my tolerances are generally around .003" to .005, and I'm totally fine with that for my purposes....

But I've heard myths and urban legends that speak of people creating surfaces so perfect, that parts can actually "fuse" together....of course I can't believe these claims, as I've found no evidence beyond legend.....but, that being said, What is the absolute limit of precision with automated machinery, and hypothetically, how precise WOULD two surfaces have to be to "fuse" together at a molecular level lol....I feel it would take more than machining, there would have to be endless polishing involved as well...

Thoughts?
 
First post here, and I just had a quick question...I have a bench top mill and lathe, and I'm learning more as I go, but absolute precision isn't really on my radar for what I do...my tolerances are generally around .003" to .005, and I'm totally fine with that for my purposes....

But I've heard myths and urban legends that speak of people creating surfaces so perfect, that parts can actually "fuse" together....of course I can't believe these claims, as I've found no evidence beyond legend.....but, that being said, What is the absolute limit of precision with automated machinery, and hypothetically, how precise WOULD two surfaces have to be to "fuse" together at a molecular level lol....I feel it would take more than machining, there would have to be endless polishing involved as well...

Thoughts?
.
clean gage blocks will stick together but i have never had problems separating them before.
.
a screw can rust in a thread hole and be impossible to unscrew sometimes. rust can swell bigger and cause things to be tighter than before
 
Gage blocks wring together almost as if they were magnetic. But,pure gold is the only metal I know of that will actually fuse together when hammered or rubbed. An example of this is gilding. Overlapping sheets of gold are easily fused together when rubbed with a burnisher usually made of agate. I have done this many times.
 
Permanently fusing together is only a problem in space, where things gall easily. The closest you'll come here is two gage blocks wrung together and held quite powerfully because of a very thin film of oil.

As for automated machinery, a planetary lapping machine will get you within a fraction of a wavelength of light very quickly if used properly.
 
When I was a lot younger, I had a friend that worked in a shop making medical somethings....

He made two blocks one with a male dove tail and one with a female dovetail.

When together the blocks were about 2" x 2" x .75" thick, he use to carry it with him showing his work. When the parts were slid together you could not see any line or separation, you could not at all tell there were two parts.

I made the mistake of sliding them completely apart. It took a long time to get them lined back up so they would slid together.

That part is what got me interested in machining.
 
The "fusing" of two pcs can and is done.

Place I worked at worked on some discs that were SS on one side and Ti on the other.

We were told the process involved a lot of lapping and dynamite ...

More impressive to me is the tale of how "we" (insert your country/company name here) drilled a hole(s) in a microscopic sized drill from "there" (insert rival country/company name here).
 
it is common on structural steel bolted connections outside in the rain and if not painted to see rust forming between connection pieces and pushing apart or causing it to swell apart
.
seeing a 1/8" or 1/4" of rust and steel angle bracket bending back from the force is impressive or for me a pain as i would have to repair structural steel connections if too badly damaged from rust
.
rust does not require a perfect surface finish it will fill gaps over time. thus why some bolted connections refuse to come apart.
 
First post here, and I just had a quick question...I have a bench top mill and lathe, and I'm learning more as I go, but absolute precision isn't really on my radar for what I do...my tolerances are generally around .003" to .005, and I'm totally fine with that for my purposes....

But I've heard myths and urban legends that speak of people creating surfaces so perfect, that parts can actually "fuse" together....of course I can't believe these claims, as I've found no evidence beyond legend.....but, that being said, What is the absolute limit of precision with automated machinery, and hypothetically, how precise WOULD two surfaces have to be to "fuse" together at a molecular level lol....I feel it would take more than machining, there would have to be endless polishing involved as well...

Thoughts?

They'll never fuse just by being placed in proximity without a lot of pressure and heat A chemical bond needs to be created between adjacent crystals to form new ones, so energy must be added to create those bonds.

Two parts that are shrink fitted together are in very close proximity, more than you can achieve by slapping two lapped surfaces together. But, the shrink fit joint can always come apart if a proper heat differential can be achieved.
 
.....

But I've heard myths and urban legends that speak of people creating surfaces so perfect, that parts can actually "fuse" together....

Yes, and there are Dragons and Fairies all around us.
Tenths are hard, microns are worse, tenths of microns are very hard, pass this and ........
But its easy to "fuse" parts together. Press fit. One makes the other conform.
Two flats will "wring" together so maybe some see this as fused but neither will be at the molecular level.
Everyone wants to make precision, dead on parts. Often the actual number will be very much larger simply due to the fact that you can't measure it decently.
Now drag your atomic force microscope out of the closet and ...........
Bob
 
what the heck you mean by fusing??
the guys speaking of wringing gage blocks
that isn't fusing
its 2 true surfaces mated
the 2 aspects of fusing I can think of
sonic welding on plastics
and
friction welding
where 2 different materials
are driven together
to the point of melting together
to me that's a fusion fit
but then
what do I know
 
They used to make the 3 layered silver/copper/silver metal for making U.S. coinage by fusing them with an explosive layer that was applied to the outer layers of silver and detonated together. Or,was the outer layer silver? I know it isn't any more. But,in the beginning of the down grading of U.S. coinage,I think it was.

Maybe I am wrong about this explosive fusing? It's been a while.

There was a female artist who used this process to blast copper sheets against things laid beneath it. It was amazing the detail she could get. Even leaves were impressed cleanly against the copper. Of course,this was not fuzing.

Of course,nothing to do with precision,but the OP did include fusing.
 
Gage blocks wring together almost as if they were magnetic. But,pure gold is the only metal I know of that will actually fuse together when hammered or rubbed. An example of this is gilding. Overlapping sheets of gold are easily fused together when rubbed with a burnisher usually made of agate. I have done this many times.
i would like to try that. i just don't have any gold
 

On page 3 of that reference Johansson (Jo-blocks) demonstrated wringing forces 33 times atmospheric pressure---due to van der Waals forces. I did not know that such great forces could be seen in gage blocks. Such strong adhesion might look very much like "welding" to someone working with the gage blocks.

Starrett also coments on wringing gage blocks:
"Wringing requires two smooth, flat surfaces with surface finishes of 1 microinch AA or better.[SIZE=-1] For gage blocks, it becomes difficult to wring surfaces if the flatness starts to exceed 5[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] microinches. The sources of the forces holding gage blocks together are thought to come[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] from: [/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] 1. Air pressure from the surrounding environment as the air is squeezed out when the[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] blocks are slid together.[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] 2. Surface tension from oil that remains on the gage blocks or water vapor from the air acts[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] as a glue to hold them together.[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] 3. When two very flat surfaces are brought into such close contact with each other, this[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] allows an interchange of electrons between the atoms of the separate blocks, which[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] creates an attractive molecular force. (This force will remain even in a vacuum or if no oil[/SIZE][SIZE=-1]
[/SIZE][SIZE=-1] or water is present on the blocks.)[/SIZE][SIZE=-1]

[/SIZE]The last two sources are thought to be the most significant[SIZE=-1]."

Denis[/SIZE]
 
Two metals of the same composition can definitely fuse together if they have a clean joint and a good contact patch. This is very easily demonstrated by putting together several clean stainless nuts and bolts of the same alloy and letting them sit for a while. The one in the least accessible location will have its threads welded together. Stainless is self-passivating, forming chromium (or nickel?) oxides on the surface to protect the iron underneath very rapidly. When assembling, it is easy to wear off this oxide layer and allow the iron underneath to come in contact, and it can fuse (I believe similar to how two ice cubes will melt and refreeze under pressure). For this reason, as per Mil-Spec, all of our hardware that was seaworthy required stainless fasteners of differing alloys, passivated, and coated in anti-sieze compound.

There is definitely such a this as explosive welding. https://www.youtube.com/watch?v=2pr94Lk5a5k Always wanted to try to build an anvil this way.

And I think this is the kind of precision you are looking for. http://www.practicalmachinist.com/vb/general/video-dan-gilbert-micron-accuracy-lathe-grinder-300302/
 
Two metals of the same composition can definitely fuse together if they have a clean joint and a good contact patch. This is very easily demonstrated by putting together several clean stainless nuts and bolts of the same alloy and letting them sit for a while. The one in the least accessible location will have its threads welded together. Stainless is self-passivating, forming chromium (or nickel?) oxides on the surface to protect the iron underneath very rapidly. When assembling, it is easy to wear off this oxide layer and allow the iron underneath to come in contact, and it can fuse (I believe similar to how two ice cubes will melt and refreeze under pressure). For this reason, as per Mil-Spec, all of our hardware that was seaworthy required stainless fasteners of differing alloys, passivated, and coated in anti-sieze compound.

But, this cold welding (I call it galling) is not due to the precision fit of the threads. Now if you set a SS nut on a sheet of SS and a few minutes later, it was fused to the surface, then that would be fusion :D

Even ice has to undergo a phase change to freeze two ice cubes together. Learned this the hard way when I put an ice door in my ice door jamb in my igloo. ;)
 
I did a lot of research into Jo blocks (and certain super flat gage blocks) wringing. I think it's pretty neat that in this day and age scientists still aren't sure how it works.
 








 
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