The parts need to be specially prepared so the that surfaces are flat to a molecular level -- and that's likely only possible if they're quite small.  But it's ultimately the same principle as forge welding; if the molecules get close enough together, they join to form one piece.  It can be done at low temperatures in space because there are no air molecules to get in the way, and no oxidation.

There have been a few discussions here on solid state welding. They would be hard to find as they were mostly in thread drift and sadly the person who knew a lot about such subjects, Thomas Powers, passed a while back ago. 

We keep our gauge blocks at work in a case separated from each other becuase there is a possibility they will weld together. You can clean off 2 of them and rub them together and they stick. I think the danger comes in time they are together. 

From what i understand in a vacuum such as space the surfaces do not have to be as close tolerance, just basically flat. 

 

While I have never been in space (I would go in a heart beat!)  I have worked with high vacuum systems and never experienced parts welding together.  The machines I worked on had vacuum chambers large enough that a person could be stuffed into one but were filled with precision components.  The chambers were made from steel and nickel plated to prevent rust.  Other internal components were non magnetic stainless steel, nickel plated aluminum or copper alloys all of which were machined to very high tolerances and flat where it was required.  The internal chamber pressures were similar to those experienced in low earth orbit and the chamber and parts were required to be meticulously clean and dry to achieve those pressures.  There were no bare steel parts as they can rust when exposed to room air (which was required during service of the internal components) and retain water vapor which is a large problem in vacuum chambers as are common organic oils and grease.  Even a finger print is a problem.  Gauge blocks wring together because there is no air between the very flat surfaces.  I imagine if you took two gauge blocks, placed them on an anvil and hit it with a sledge they would weld together.  I believe I read or watched something about welding dissimilar metals was discovered from artillery rounds striking an armored surface and welding together.

On 2/10/2026 at 9:07 AM, ILikeShinySteel said:

I know its somewhat old but to add to this, contrary to what most have said, machining is far superior in practicality's sake. You can make things you would never make with hammer and tongs. For example, a blacksmith might use a swage block which was machined to have perfectly round indents (i know they can be forged but it isnt nearly as precise). Perfectly flat and round surfaces can also be machined/ turned whereas they would never be hammered that way.

Personally I would be over the moon if I had my own lathe and milling machine, and intend on making one someday. But thats because I love making things and some things can only be made by machining. 

Obv blacksmithing takes the cake in terms of aesthetics and beauty but to me personally aesthetics are often second to practicality. 

Theres also no reason they have to be mutually exclusive, a Smith could forge a nice pleasant piece that needs specific tolerances to fit a certain application and those areas can be machined, leaving the rest of the piece nice to the eye.

I spent years collecting machinist's tools before I ever touched a 3D printer, and honestly thought printing was just for trinkets. Then a friend needed a replacement gear for an antique camera—impossible to find, too complex to cut by hand. We modeled it, printed it in nylon, and it's still running two years later. That shifted something. Now my lathe and printer sit side by side. The printer handles organic forms, lightweight brackets, prototypes I'd never waste stock on. Meanwhile I've printed fixtures to hold workpieces for milling, so they feed each other. What surprised me was finding sites, where people are selling files for massive articulated dragons or wearable game armor - cool things to 3d print for gamers that would take weeks to sculpt traditionally. It made me realize accessibility changes what gets made. You don't need a foundry to cast a prop sword anymore, just filament and patience. 

 

agree

Just to clarify, i did not think that my gauge blocks were welding when stacking. But that if we keep them separated because they may weld it would be them staying together for long periods of time.  

I am no expert on solid state welding, interesting subject though, i just go by the old guys i have worked with always said it could happen. Not will but could. 

I could be wrong but I always thought that to cold weld like that the surfaces had to be perfectly clean, which is why it happens is space. But if they're coated with any kind of lubricant or rust preventative like oil they wouldn't be able to weld due to a layer of oil/"contaminant" between the metal surfaces

As for welding in space, I’ve read that cold welding can happen naturally in a vacuum when two clean, flat metal surfaces come into contact because there’s no oxide layer or air to prevent the atoms from bonding.