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  • How’s it going, everyone? I’m Tom and today i’m going to talk a bit about ball

  • bearing - and not just about the radial type, but also about the linear type. A guide on

  • different linear slides was one of the most requested topics, and instead of jamming everything

  • into a single guide, i decided to break them out and cover each option in depth.

  • So, let’s start out with # radial ball bearings, because they work in exactly the same way

  • as linear ones. The basic idea behind them is that, instead of supporting a motion by

  • having two surfaces slide on each other, youre adding a rolling element between them, in

  • this case, balls, but other bearings use needle pins or cylinders. This reduces the friction

  • and increases the life span of the bearing. Radial ball bearings are usually use for belt

  • idlers, in stepper motors and everywhere else where you need to support a rotating element.

  • Now, radial bearings can support forces perpendicular to the shaft or, in a more limited way, also

  • along the shaft. They can not support torsional moments, for example when you mount a pulley

  • on a shaft and support it like this. Which is why stepper motors have two ball bearings,

  • one on each end, to support these kind of moments.

  • Radial ball bearings are available in a huge variety of sizes, the most common ones are

  • the 62x series or the lighter 6 #0 x ones, particularly the cheapest bearing of all,

  • the 608 skateboard bearing with an 8mm inner diameter and the 623 and 624 bearings with

  • 3 and 4mm inner diameters. Now, each of these bearings is available in different configurations,

  • and the ones that are most often used are ZZ and RS types. ZZ means that the bearing

  • will have metal dust caps on each side, guarding its balls from larger foreign objects, while

  • RS types have an actual rubber seal on each side, which both seal the bearings lubricant

  • inside the bearing, but also keeps pretty much everything, including liquids, from entering

  • the bearing. Both types are about the same price, so i’d recommend using sealed RS

  • types wherever possible. And staying with the subject of price, brand-name radial bearings

  • are a good bit more expensive than no-name, Chinese bearings, but since our 3D printers

  • usually don’t put enormous forces on the bearings, which would shorten their usable

  • service life, it doesn’t really make a difference which ones you use, since even the cheapest

  • bearings are still pretty decent. Now, these bearings typically are mounted

  • in our 3D printers by simply using a metric screw, and that does hold them in place, but

  • won’t make for a super-snug fit since male metric threads are always a bit smaller than

  • the actual diameter theyre named after - a male M8 thread is only about 7.8mm in

  • diameter on the outside. Just something you should keep in mind when using or designing

  • for this kind of mount. Now, the other type of ball bearing youre

  • typically seeing in 3D printers is the linear type, which lets you guide things along a

  • round shaft. Now, because the balls of those bearings directly ride on the shaft instead

  • of a separate inner race, the quality of the shaft itself will # hugely influence the quality

  • of the linear motion youll get. First of all, you will want at least a hardened shaft,

  • preferably even a hardened # and chrome plated one, instead of a mild steel or plain stainless

  • steel one. Aluminum rods or tubes can absolutely not be used with linear ball bearings. On

  • shafts that are too soft, what will happen is that the balls will gradually form grooves

  • in the shaft’s surface, which cause extra backlash in the bearing. Often that backlash

  • is the cause for things like irregular layers or z-wobble, if the shafts of your z-axis

  • are worn and have too much backlash. The other reason why you’d want proper linear shafts

  • is that those are made to tighter tolerances than other rods that # aren’t specifically

  • made for linear motion. Again, this would lead to backlash and a poorer, less regular

  • quality on your prints. Rods with an g6 or h6 tolerance rating are the ones that work

  • best with the LM UU style bearings. You can check how tight the bearing is on the shaft

  • by rotating it, a good fit is when you can feel some resistance when rotating the bearing

  • around the shaft. If it’s loose and wobbly at all, you already have too much backlash,

  • if it’s too tight, to a point where it’s even running rough along the axis, the bearing

  • might fail and jam prematurely. So the typical type used is the LM8UU bearing,

  • made for an 8mm shaft. But the bearings are available in sizes from the 4mm LM4UU to things

  • like a crazy large LM100UU, but typically, only the 8, 10 and 12mm sizes are used in

  • 3D printers. When using a larger bearing and shaft, you increase the rigidity of that axis,

  • which is especially important for the rods of the Z-axis, which usually have to deal

  • with the acceleration forces from the X-axis. Because these bearings are completely open

  • on the inside, lubrication is somewhat important. I’d recommend smearing some heavy grease

  • inside the bearing before mounting it, and then occasionally lubricating the rods they

  • ride on to keep the bearings running smoothly and to keep them from randomly jamming. They

  • do have a rubber seal on each end, but that usually isn’t tight enough to permanently

  • keep all the grease in and dirt out, so also keep your linear shafts clean and dust-free

  • at all times. Linear ball bearings are also pretty sensitive

  • to misalignment, which is why most carriages only use three bearings instead of four. If

  • you mount two bearings in a way where they are not aligned or have no way of aligning

  • themselves, one of the bearings will inevitably run noisier or even jam. So either use precise

  • mounts or provide a way for the bearings to align, for example by using only one zip tie

  • per bearing. And just like radial bearings, linear bearings

  • are also available in a couple of different varieties. For example, for the standard LM8UU

  • size, which is the short type, you can also get an LM8 #L UU, which is same bearing, but

  • twice as long. They are also available pre-fitted into aluminum blocks as the # SC 8UU, or as

  • a flange type as the LM # F 8UU. There’s a huge number of other variations available,

  • but typically, youll only be using the standard or long type.

  • Now, just like radial bearings, you can buy linear ball bearings from high-end brands

  • like SKF or from your typical Chinese ebay vendor, and even though the Chinese linear

  • bearings aren’t as quite good as their radial ones, i’d still say go for the cheaper option

  • here. You might get a couple of bearings that are a bit too loose or too tight, so buy some

  • spares, but considering that brand-name bearings cost about ten times as much as no-name ones,

  • it’s still cheaper to throw out a couple duds than paying so much more up front.

  • So to sum things up about the linear bearings, use precision shafts and keep them clean and

  • lubricated and you should have a very precise and reliable motion system.

  • I put a couple of ebay links in the description, just to give you a starting point what you

  • should look for when going shopping for affordable bearings.

  • As always, thank you for watching. Please share and like this video if you found it

  • helpful and subscribe if you want to stay updated when i upload new videos.

  • See you next week.

How’s it going, everyone? I’m Tom and today i’m going to talk a bit about ball

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