Grooveless metal engineering (Electrical discharge machining)

Originally published at:


That stuff is so nice to see. I don’t know why it fascinates me.


I do, but I’m not allowed to tell you.


Some metals, if clean enough and in the right environment, will just fuse together when brought into contact.

If I’m not mistaken, that’s how the actual silicon in a cpu is wired with gold to the package with all the pins that we see. Touch two pieces of very pure gold together in a vacuum and instant cold weld.


Ive looked at buying something like these to keep at my desk and fiddle with, i’ve since forgotten what the process is called but as far as i know this is something that hasn’t really been commercialized. It’s usually done as a way to show what someone can do with particular equipment and that the tolerances are good.


Electrical discharge machining-it’s very precise, but slow, expensive and requires a fair bit of juice to run, usually industrial 3-phase. Wasn’t really fit for hobbyists or small-scale operations until pretty recently, and even then one pretty much has to build the machine from the ground up if you don’t have the cash for a commercial machine.


My gun smith friend showed two pics of a threaded barrel with a cap and with the cap screwed on you can’t see is even there. Seamless like these examples. Pretty sure he’s a witch.


I figured the cost of these would be very high. It was mostly curiosity on my part on what would these cost, and they’re not really a thing you can buy. I presume you’d have to know a guy.


I’d definitely love one of those sinking spiral things as a desk toy. Just beautiful.


Because it’s sorcery.



Many moons ago I worked for a precision grinding company. Most run-of-the-mill work had us hold tolerances of +/-.003”, which was usually easy to hold all day long. This was on old WW2-era centerless grinders.

We very occasionally would grind parts to a tolerance of +.0000”/-.0001”. The boss rarely took on jobs like that, and when he did, it was obvious that he priced them to be worth the risk and effort. It took our most senior guy to do them, and it’d take him all day to get the machine set up just perfectly. But it was possible.

These parts look like they’re at least that precise, and if they were machined to that mirror finish without a secondary grinding or polishing operation, you can color me a deep, rich shade of impressed.


Used commercial rigs seem to be mostly ~$40k to $100k, some even below $20k, curious why some are that low. Maybe parts are hard to find or something.


I see the makings of a pretty cool jigsaw puzzle.


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: