Grooveless metal engineering (Electrical discharge machining)

groovy :smiley:


On my desk they would soon be covered with dust and grime, which would probably spoil the seamless fit.


I’m having trouble finding evidence, but my memory of The Day the Earth Stood Still (1953) is that when the ship’s ramp is retracted the government inspects the surface and finds no seams to indicate where the mechanism and ship meet.



Watch out all you Right-to-Repair people!

“What the heck. Where’s the seam? How does this shit come apart?!”


Welcome to my world BB.

I run machines that do this daily for my living- EDM.

EDM is short for, as others mentioned, Electrical Discharge Machining. It is the only technology that makes specifically the kind of Parts you saw in that video possible. No other process can create perfect shapes that mesh so perfectly this way they appear seamless. I don’t care how good of a machinist you are it is physically impossible to do with traditional machining techniques what you saw. Maybe grinding for simple shapes, but none of these shapes apply (though there are 3d grinders, this was all electropolished EDM work).

There are two kinds of EDM- ram and wire. Wire cuts are exactly like an electrical cheese cutter using 0.005" or bigger wire- to slice perfect finished parts. But true sharp internal corners are impossible, due to a wire always having a radius. Ram EDM is what I run- no wire- just a 3D shape on a block of graphite or cuprotungsten, and it burns the shape into a block of conductive material.

You can make shapes otherwise impossible to cut with rotating tools, or machine things impossible to cut, like I do- superhardened die steel blocks turn into titanium forging dies for aerospace parts and artificial bones. Only thing is, material you burn must be conductive.

Other, ultra rare stuff, like LIGA and ultrasonic milling exists, but this kind of thing was definitely made with EDM. This is a level beyond what I work to- fits like this are tolerances of 0.00005" or so I’d guess. At most, I work to 0.0001-0.0002".

I love seeing parts fit so perfectly like this, so satisfying!


so the opposite of me reading decimal fractions of inches over and over in this thread, because a, while i can picture 0.5 or 0.1", anything less is unproportionately less… picturable to me, and b, inches and precision, man, inches are so… big and… odd :slight_smile:


Just as cabinetmakers refer to carpenters as “wood butchers”, at the grinding shop we referred to the traditional lathe machinists as “metal butchers”. Their tightest tolerances were generally our sloppy starting points. Of course when your parts are going out for secondary finishing, you waste zero time holding tolerances you don’t need to.


Cool! At our shop we precision ground custom screw threads on sets of electrodes for EDM machining of die molds. I learned a lot of trig figuring those threadforms out.


I actually find this deeply unsettling. Is there an opposite of trypophobia?


Oh I get that… from the digital perspective. When I see people don’t use magnetic alignment and they just drag their vertices in the general vincinity of other nodes - of course this is sub-sub-sub-sub-pixel and even sub-sub-sub-ink-dot, but still!

…but actually I was referring to my/our unfamiliartiy with Imperial units. (I’m aware that my feeling for 0.0001cm might be totally off, but i still find comfort in the illusion that)


I just looked at a nice demo of a fairly affordable DIY EDM setup- drilling, small scale- but still an actually useful application.


Call up your local EDM shop and see if they’ll whip up a sample. Make it clear you’re willing to pay and wouldn’t be a full run client and most can manage something.


As someone who learned manual machining a long time ago, those tolerances are already in the realm of mind-blowing. It must be fascinating work, although I suppose like anything you would get quite used to it.

Out of curiosity, those are just your print tolerances, right? Your precision is even higher, is my guess.

I run into this with my Chinese colleagues. They think of tolerances as accept/reject inspection limits and anything that is within tolerance is acceptable. When we get parts made in the USA, those are assumed to be statistical tolerances. So part deviation is less than 1/4 what we see made with the same print tolerances compared to parts made in China.

It’s one of the reasons we make critical parts in the USA.


Should have gone with Barry White for the soundtrack.


Not a bad idea, but I would guess I’d get a “fuck off” number. Which would be expected but you never know, I appreciate the suggestion

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Look for one that does prototyping. In my experience machine shops are used to weird requests and are often open to them if you are up front that it is a one off project and leave the time frame open.


Vacuum welding. It’s one of those underappreciated difficulties of spacecraft design. If you have two pieces of the same kind of metal that are supposed to slide over one another (like a hinge), it may turn into one piece in the vacuum of space.

It’s been described as the atoms sort of forgetting that they were supposed to be separate.


Yeah, I don’t think these parts would stay like that for long in the wild. The tiniest amount of dust on the mating surfaces, the slightest wear on the edges, or even fingerprints from handling the parts when separated, would be enough to make a visible seam. They’d still fit together really well, but not visibly more than you could achieve with ordinary milling.

That said, if someone took the time to make demonstration pieces like this with a decent jewellery milling machine, I think people might be surprised by the result.

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