Grooveless metal engineering (Electrical discharge machining)
by Rob Beschizza from on (#4C1HJ)
In this otherwise unsourced video (via Singaporean news site Mothership) we may enjoy seeing parts so finely engineered that when they are socketed together, they appear to become single blocks of metal.
UPDATE: Commenter for_SCIENCE pointed out that these are made using Electrical discharge machining, which Mark posted about here.
More from RandomDude:
"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."