Teach me about how tiny metal objects are manufactured

I think I have a basic understanding of how metal can be heated so hot that it melts, and then it is poured into a ceramic mold, to make all sorts of large objects. In addition, while it has not yet totally cooled and is soft, it can be pushed and pulled into various shapes (such as a blacksmith would do), or it can be put between rollers to make sheet metal or foil.

That’s about as far as my imagination will take me on this. But the finely detailed stuff, that’s what I can’t figure out. Here are two examples of what I mean: hollow needles such as are used in a hypodermic syringe, and the gears used in a wristwatch.

To my imagination, there are two ways to make a hollow needle: (1) Put molten metal into a tubular mold, but only enough molten metal to coat the inner walls of the mold, so that the resulting needle will be hollow. This sounds fine in theory, but I can’t imagine how to insure that even 20% of them really are hollow and that the walls have a consistent width. (2) Make a solid pin, and then drill a hole down the center. This too sounds fine in theory, but how can you make such a narrow drill bit and insure that it doesn’t bend or break?

The gears of a wristwatch are similarly tiny. I can imagine that they are stamped from sheet metal, but I can’t imagine how such a stamp would be made, and to the tolerances needed for clockwork.

My science-fiction imagination says that all these things could be manufactured very easily with lasers or similar heat-rays. But I really doubt that that’s what they actually do. And they certainly didn’t use lasers 200 years ago. But they did have such gears and needles way back then. So how were they manufactured?

Wikipedia says hypodermic needles are made by making a (smallish) tube and then stretching it until it’s thin enough.

Metal tubes in general are made by pushing molten metal through a hole with a pin sticking out through the middle of the hole. Often instead of the pin part being straight, it’s shaped more like a cone, and the center cone can be pushed out further to make the walls of the tube thinner (if you are having a hard time visualizing that, imagine with the point of the cone barely sticking out that the tube will be very thick, almost completely solid, where if the cone is pushed out so that it almost completely fills the hole then the resulting tube will have very thin walls).

Heracles already posted how they take one of these types of tubes and stretch it out to make it hypodermic needle sized.

Tiny gears are made in tiny molds. Since the molds are so small, the molten metal is usually forced into the mold under pressure. Tiny plastic parts are made using the same basic technique.

In the old days they would make small metal cylinders or tubes and would then cut the gear teeth with a very tiny lathe-like machine called a hob.

Super-duper incredibly tiny gears have been made using the same process that they use to make integrated circuits. Integrated circuits aren’t “made” so much as they are “grown”. If you’ve ever made sugar candy by filling up a glass with sugar saturated water, then put a string in it on a pencil and each day you turn the pencil as the sugar crystals attach to the string, it’s kinda the same thing for integrated circuits, except that it involves a lot of heat and nasty chemicals. But basically the silicon is a crystal that is grown into shape. When they make integrated circuits they “dope” the silicon crystals with particular impurities as they grow, which gives them their semiconductor properties. When making teeny tiny gears, they just grow pure silicon crystals.

Fineblanking and Swiss Screw Machines are more commonly used to create high volume, high precision metal products for industrial components like tiny gears and screws. This technology has been around for over 50 - 100 years and still produces the vast majority of small parts.

Not molten metal - and agree with the other parts. Here is a video of how a metal rod is converted to tube/pipe. Look from around 50s in the video to around 1:15.

That is true for a limited number of applications. More popular is the stamping process using sheet metal for small gears, gadgets, etc. Here is a video Sheet Metal Stamping Dies & Processes - YouTube

Sounds great on paper, but I’d love to see a video of how they can do it on such a tiny scale, and with consistent results to boot.

Thanks, but all I see is a hot glowing pipe being pushed from here to there with a rod going through it. My guess is that the central rod is actually a drill of some kind, but I don’t see it happening. And if it is indeed some kind of drill, I’m curious why the soft glowing pipe doesn’t get bent out of shape. If it isn’t a drill, but a “central cone” like engineer_comp_geek described, I’d expect that it needs something on the outside too, to maintain the shape. Perhaps that was towards the beginning of the video, and the pipe was hidden by the outside shaper?

Hypodermic needles (and other small tubes) are generally shaped and sized in the way wire is. Starting with an existing tube made in ways described above it is pulled through a series of dies with smaller and smaller apertures to reduce the size of the tube.

A friend worked for a hypodermic manufacturer, he said they could make them incredibly small, bend them into just about any shape, and taper the tube as well. Different finishing techniques were used for the point. They could be ground at an angle to form a simple penetrating point, or finished with special shapers to get blunt ends or even a side hole like the needles used to fill tires.

I think some watch gears are just stamped. There’s probably some minimal size where that’s no longer effective, and these days CNC machines probably shape them from stamped disks.

The central rod is a mandrel. Its not a drill - in the sense that no material is removed from the piece. Here is an ebook (pdf) that can answer all your questions and more.

Here’s avideofor you.

Sounds great on paper, but I’d love to see a video of how they can do it on such a tiny scale, and with consistent results to boot.

Imagine you have a block of metal with a tapered hole in it. The large end of the hole is the same size as the outside diameter of a garden hose and the small end of the hole is only 5% smaller, so not lot of “taper.” Now imagine you force the garden hose into the large end of the hole and then grab it with pliers as it comes out of the small end and pull. You can easily imagine how a flexible garden hose could do this.

It works the same way with a metal tube and as the tube goes through the die, they pull on it with so much force that as the metal compresses down to the smaller diameter, it is also stretched, so the wall thickness of the tube can be controlled by the amount of pulling force.

It’s like pulling on a plastic straw, the walls get thinner as you pull it harder.

Excellent, thank you! In particular, the diagram on the top of page 9 explains an awful lot of what I couldn’t see in that video. And Ornery Bob’d post confirms that I was understanding it correctly.

When people talk about stretching a tube, I could think only of pulling on the ends. But this mandrel is interesting. And I only need a small amount of “suspension of disbelief” to see it scaled down to hypodermic needles. Thanks again.

Just wanted to say that the TV shows “How it’s Made” and “How Do They Do It” are usually very interesting if you like that kind of thing. They leave out some details, but I still like them.

A lot of metal parts, including tubing, are made by “extrusion”. Here’s a very simple example of an extruding machine:


The center “hole” in the right-hand strip would produce a tube.

Keeve – You’ve left out one big way to make metal parts, which is just starting with a chunk of metal and grinding/milling away everything that you don’t want. Kind of like woodcarving or something, but it can be very very precise with big complicated computer-controlled milling machines. (Or could be a guy with a lathe and a hand-held tool).

Generally, this process would be called generally ‘machining’. I don’t know, but I’d guess the vast majority of, for instance female screw threads, are produced by machine cutting the threads (perhaps into a roughly-sized hole formed by casting).

This is what the Swiss Screw Machine that Si Amigo linked to is all about; I just thought it was worth being a little more explicit.

Then again, we can now make some metal parts by 3-D printing them: it’s fairly limited in the kinds of metals that can be printed, and in the size and shape of parts, and it’s way too expensive for mass-producing parts, but it is possible for many things.

Yes but the Swiss Screw Machine is not just a lathe, it’s for making productions level runs of very small precise parts. It’s capable of holding extremely tight tolerances on small dimensions. And it’s not just for screws.

I love threads like this!

For putting holes through big tubes, ejector drilling or trepanning is also used, it does turn a lot of potentially expensive material into chips on the floor though. The extrusion method shown making those pipes is somewhat limited on the wall thickness it can produce. So if you need thicker walled tubes sometimes you just have to bite the bullet and machine ( ejector or trepan) the bar. Machining also means yyou wont have to reheat treat the steel after the process.
A new system called flow forming basically takes effing great presses and can cold work 160ksi+ steels into fairy thick walled tubes. Would need to heat treat after the cold work, but an impressive new technology
see here
But that is all big stuff . For small fine parts electro discharge machining ( EDM, also wire EDM and Plunge EDM) can make extremely fine parts. you can also make really funky geometries on parts as well with EDM.

Here is a random website with some pic for some EDM parts

Click you way through the tabs on the left and se some really small holes and fine parts.

And while googling around these guys are comparing EDM to using a femtolaser to make parts, looks to be experimental rather than production though.


There are forms of casting that use sand or other materials that can are destroyed after casting and easily removed through a small opening. There’s also “acid” lithography which is used to make IC chips (e.g. CPU’s, the memory chips in flash drives, microcontrollers, etc.)

Did anyone else watch that video am77497 posted?? It seems preposterous that making 100 hypodermics at a time would take have that much human involvement and intervention at so many steps, only to ultimately be sold for pennies.

Is that true? Do they just show a more human-intensive process for the How It’s Made show?