How do they put the balls in bearings?

How do they get the ball bearings (or cylinder bearing thingies, any of the stuff that rolls) into the bearing?

I recently bought the machining textbook for my community college’s machining program (“manufacturing technologies”) in an effort to learn more about this art/skill I didn’t know about until recently, and loving to just schmooze through books like that, and also being skeptical of what skills I’d gain in engineering school vs. something like machinists’ school or welding school.

Very much like looking through it, and immediately learned a bunch of things I didn’t know about before. I was somewhat surprised to learn that ball bearing are loaded into a bearing by just pressing/squeezing them in there with an arbor press.

I mean… that’s what it seemed to say. So am I to understand that steel, even the more-rigid heat-hardened/carbeurized steels are… “springy” enough to be squeezed through a space/doorway they normally wouldn’t fit through if you just mash it with enough pressure?

What about the bearings where it doesn’t use ball bearings, but cylinders or oblong cylinders, like the conical bearings in most automotive/machinery/trailer axles? How do they mount those cylinders onto the axles in that inner ring that holds them? Or do they not each have axles, and that thing just provides spots/spaces for them to roll in?
How does the… gasket, that holds in that circle of little ball bearings or cylinder bearing get installed? They also just squeeze that in?

Also, if anybody knows, how do they manufacture those cylindrical or oblong cylindrical bearing? I could imagine a million ways ball bearings could be made, the properties of a sphere lend themselves well to intuitive manufacturing processes, though getting them perfectly spherical I’m sure is a bit harder. But how do they make the little cylinders, or the ones that are oblong cylinder shaped?

Anyway, I kind of went on there with the questions, I guess my main question is the squeezing thing. Is that all that it is, that steel is just springy enough that they can squeeze it into its place through the smaller-than-the-bearing opening?

IME, the ball or roller carriers are made of comparatively lightweight sheet metal. That’s what springs enough to allow the balls/rollers to be inserted into their carrier slots. Then the carrier is inserted between the two bearing halves, the inner and outer races. The races and balls/rollers don’t get compressed meaningfully in the installation process.

probably should have you-tubed it first. Apparently the whole pressing thing is to install the bearing onto a shaft. The bearings are pre-made (in factories by machines) and reasonably no machinist would be working on a bearing itself.

But I did find out that a lot of bearing and stuff are just forced onto shafts, and this is called an “interference fit”, and they even have little induction heaters you can heat up a part (bearing, usually) you want to fit so it expands, and then you put it on the shaft and let it cool.

As an aside,

doesn’t really work.

To quote the infallible Wikipedia on the matter, ‘schmooze’ means to converse informally, make small talk or chat (from Yiddish שמועסן shmuesn ‘converse’, from Hebrew שמועות shəmūʿōth ‘reports, gossip’).

So, unless you’re trying to chat up that book, better to use another verb.


These are a couple non pressed bearings.

Back when I rebuilt CV joints and Drive shafts. You grease the parts so they don’t fall all over the place as you put them back together.
Needle bearings in the drive shaft yoke.
Star/Cage/Balls in the CV.

They have C-clip retainers and rubber boots to keep grease in.


People seem to forget that springs are made from steel precisely because steel is springy. Drop a ball bearing on a thick piece of steel plate and you’ll be surprised at how high it bounces.

As for the shapes of the rolling elements, they all start as round bar and are machined and then ground and polished to final dimensions.

As you would expect, the balls are made in huge numbers at high speeds and they vary in size and depending on the application, bearings may be produced with a tighter or looser fit between the races. For example, electric motor bearings are on the loose side of the spectrum with a “C3” fit and so those bearings are using slightly smaller balls that allow more “play” between the inner and outer races.

wait, really?

Now that I’ve researched it, it seems I was mistaken. The bearings are pre-made, and even made without any squeezing, they just construct it one layer after another, all made by machines, actually. Most machinists may be replacing a bearing but not fixing it or altering it. This seems to be what the issue with presses and pulling things was

…then again, the book did mention something about specifically pushing ball bearings through holes, I think, from what I can remember (I’m not at my apartment so I can’t check on the book).
But surely there’s a limit on the size difference between the hole/opening and the size of the ball before you start deforming the hole? I mean, broaching is a method in machining that involves just pushing and that deforms/shapes the metal

Speaking of interference fit (the part inside is actually larger than the outside):

Can anyone confirm that the shafts connecting the turbines and generators in hydro-electric installations are actually interference fits? That the shaft is a few thousands on and inch larger in diameter than the holes in turbine and generator?
If so: how the hell do they cool a shaft that size enough to cause it to shrink?

:DShall we scare him with casting babbitt in place?

Now that the question’s been answered, can I point out that it might make a good catchphrase for a male exotic dancer who plays an auto mechanic character?

The use of this word as a transitive is a horrible, slimy corruption of a nice word.

**How do they put the balls in bearings? **

They read to them from something called Ulysses.

You mean the autobiography of Ulysses S Grant?

They heat the bearing with a bearing heater:

I would guess that for gargantuan bearings, there are equally huge heaters.

Looks like they’re preparing something huge. I have an old lathe from a bicycle repair shop with Babbit Bearings. It’s surprising how smoothly and freely the head turns.

I’ll mention that not all ball and roller bearing units are closed. Some have split bodies, others are an open frame type where a shaft becomes the inner race. There are also a number of mechanical means of seating bearings that don’t require joining with dissimilar temperatures.

I was installing a ball screw many years ago, 1st time for me. The bearing assembly comes with a cardboard cylinder installed, and you are supposed to thread the ball screw into it. I found out that you should thread the screw in, as you slowly remove the cardboard cylinder. Otherwise, you end up with 44 ball bearings rolling around the floor… I ended up using a heavy grease to hold all the balls in, while I put the cardboard cylinder back in.

Sometimes the opposite method is used - frequently, interference parts are packed in dry ice, and then inserted into the other part. Heating up large parts can be difficult, and can lead to heat distortion.

all this talk of insertion just adds to the mechanic-themed male stripper mentioned above.
Mention male and female fittings and you’ll really get the ladies going crazy