how’s it going, everyone? i’m tom andtoday 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 mostrequested topics, and instead of jamming everything into a single guide, i decided to break themout and cover each option in depth. so, let’s start out with # radial ball bearings,because they work in exactly the same way
cheap 3d printing service uk, as linear ones. the basic idea behind themis that, instead of supporting a motion by having two surfaces slide on each other, you’readding a rolling element between them, in this case, balls, but other bearings use needlepins 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 elsewhere you need to support a rotating element. now, radial bearings can support forces perpendicularto the shaft or, in a more limited way, also along the shaft. they can not support torsionalmoments, for example when you mount a pulley on a shaft and support it like this. whichis why stepper motors have two ball bearings, one on each end, to support these kind ofmoments. radial ball bearings are available in a hugevariety 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 innerdiameter and the 623 and 624 bearings with 3 and 4mm inner diameters. now, each of thesebearings is available in different configurations,
and the ones that are most often used arezz and rs types. zz means that the bearing will have metal dust caps on each side, guardingits balls from larger foreign objects, while rs types have an actual rubber seal on eachside, which both seal the bearings lubricant inside the bearing, but also keeps prettymuch everything, including liquids, from entering the bearing. both types are about the sameprice, so i’d recommend using sealed rs types wherever possible. and staying withthe 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 thebearings, which would shorten their usable service life, it doesn’t really make a differencewhich 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 metricscrew, and that does hold them in place, but won’t make for a super-snug fit since malemetric threads are always a bit smaller than the actual diameter they’re named after- a male m8 thread is only about 7.8mm in diameter on the outside. just something youshould keep in mind when using or designing for this kind of mount.now, the other type of ball bearing you’re typically seeing in 3d printers is the lineartype, which lets you guide things along a round shaft. now, because the balls of thosebearings directly ride on the shaft instead of a separate inner race, the quality of theshaft itself will # hugely influence the quality
of the linear motion you’ll get. first ofall, you will want at least a hardened shaft, preferably even a hardened # and chrome platedone, instead of a mild steel or plain stainless steel one. aluminum rods or tubes can absolutelynot be used with linear ball bearings. on shafts that are too soft, what will happenis that the balls will gradually form grooves in the shaft’s surface, which cause extrabacklash in the bearing. often that backlash is the cause for things like irregular layersor z-wobble, if the shafts of your z-axis are worn and have too much backlash. the otherreason why you’d want proper linear shafts is that those are made to tighter tolerancesthan other rods that # aren’t specifically made for linear motion. again, this wouldlead to backlash and a poorer, less regular
quality on your prints. rods with an g6 orh6 tolerance rating are the ones that work best with the lm uu style bearings. you cancheck how tight the bearing is on the shaft by rotating it, a good fit is when you canfeel some resistance when rotating the bearing around the shaft. if it’s loose and wobblyat all, you already have too much backlash, if it’s too tight, to a point where it’seven 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 areavailable 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 andshaft, you increase the rigidity of that axis,
which is especially important for the rodsof 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, andthen occasionally lubricating the rods they ride on to keep the bearings running smoothlyand to keep them from randomly jamming. they do have a rubber seal on each end, but thatusually isn’t tight enough to permanently keep all the grease in and dirt out, so alsokeep your linear shafts clean and dust-free at all times.linear ball bearings are also pretty sensitive to misalignment, which is why most carriagesonly use three bearings instead of four. if
you mount two bearings in a way where theyare not aligned or have no way of aligning themselves, one of the bearings will inevitablyrun noisier or even jam. so either use precise mounts or provide a way for the bearings toalign, for example by using only one zip tie per bearing.and just like radial bearings, linear bearings are also available in a couple of differentvarieties. for example, for the standard lm8uu size, which is the short type, you can alsoget an lm8 #l uu, which is same bearing, but twice as long. they are also available pre-fittedinto aluminum blocks as the # sc 8uu, or as a flange type as the lm # f 8uu. there’sa huge number of other variations available, but typically, you’ll only be using thestandard or long type.
now, just like radial bearings, you can buylinear ball bearings from high-end brands like skf or from your typical chinese ebayvendor, and even though the chinese linear bearings aren’t as quite good as their radialones, i’d still say go for the cheaper option here. you might get a couple of bearings thatare a bit too loose or too tight, so buy some spares, but considering that brand-name bearingscost about ten times as much as no-name ones, it’s still cheaper to throw out a coupleduds 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 preciseand 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 affordablebearings. as always, thank you for watching. pleaseshare and like this video if you found it helpful and subscribe if you want to stayupdated when i upload new videos. see you next week.
