Bearings going bad?  

RE: Bearings going bad?

I've been trying to track down an awful vibration that started up recently with my new MK3S. Just checked the x-axis rod and it's got some  scratches on the back that pretty clearly came from the bearings. Definitely seems like a common issue.

RE: Bearings going bad?

The black ring shows where the axis stops in most extended point ie. max points. My recently built MK3S has over 48 hours of printing.  Its where the lubrication within the supplied bearings deposits on the steel rods. Along with the lubrication already on the hardened steel rods.  My rods do not show signs of wear or scratching yet. 

RE: Bearings going bad?

What is the recommended lubricant for the bearings? Also printing in a dusty environment may affect bearings and rods. 

RE: Bearings going bad?

You can use either machine oil, however that requires relubricating often. So a better alternative is a semi-fluid lithium-soap based grease. The grease's consistency should be NLGI 0 or below, but if applied carefully in a small amount directly on the bearing balls, even the easier to find NLGI 2 will work. Grease will last longer than oil (6 months of print time). Do not use spray-can materials, like "White Lithium" or even "WD-40", none are suitable. Greases with particles (Moly - MoS₂ or Teflon - PTFE) are generally not recommended by linear bearing manufacturers, nevertheless people do report good results with SuperLube 21030 (which contains PTFE particles). 

RE: Bearings going bad?

Posted by: Vojtěch

I was super careful building my Mk3 when I got it in December. My LM8UU's from Prusa failed rather quickly, within a month or two. I replaced the bearings with Misumi LMU8's and matching rods from the Zaribo web shop. I'm now at 2047 hours print time total, most of it on the Misumis. I'm re-packing the bearings everytime I take the printer apart with Zeller+Gmelin Divinol Lithogrease 000/150. Meticulously made sure the printer is square and there is little load on the bearings across the whole length of the rods. So far no signs of wear at all, the printer is running precise and quiet.

The reasons I chose a NLGI 000 Lithium grease with a low-viscosity base oil (380 mm²/s) and without solid additives are both theoretical (it's what Misumi recommends plus what comes out of the equations when you plug in 3D printer loads) and practical (I used a NLGI 1-2 Mogul LVT 1-EP before and after thoroughly packing the bearings the balls simply didn't move at all, and were sliding on the rods, scoring them immediately).

At this point I have no plans to switch to bushings. If anything, I'm thinking about an upgrade to SKF LBBR8's. They have twice as many raceways compared to Misumi LMU8's, simply a different league yet.

Hello, I have a question. In this paragraph is a small contradiction. "Divinol Lithogrease 000/150" has a base oil viscosity of 150mm²/s.  And "Divinol Lithogrease 000" base oil viscosity of 380 mm²/s.  Which of these two products do you use? And are there any differences between these two for use in a linear guide? 

Many Thanks.

RE: Bearings going bad?

The closest grease I can find to this Zeller+Gmelin Divinol Lithogrease 000/150 is https://www.penriteoil.com.au/products/steering-box-lube

RE: Bearings going bad?

When I chatted with Misumi about what grease to use, the engineer was pretty clear that #2 is chosen for a reason.  But he added even motor oil is better than nothing.  Just buy while Lithium grease or Superlube ... comes in tubes at any hardware or auto parts store.

RE: Bearings going bad?

So I'm getting concerned about my printer now that I'm reading this thread...like I assume most people, I took the manual at face value when I assembled my MK3S a month ago and thought the bearings were greased already, even though it's sounding like they really weren't after all. Now granted I haven't noticed any scratches on my rods yet (and I've been printing pretty heavily, 2 day prints for lithos that I sell as a side gig, it's in operation at least 5/7 days of the week usually), and the black gunk I just assumed was sorta normal since I noticed it on the printer I had before, and it's usually mixed with varying amounts of cat hair floating around my house (I have 2 and no enclosure for my printer since I print primarily in PLA). However, I have noticed that it seems to be nosier than before, especially with long movements along the x axis I can hear it more audibly than compared to when I first built it. 

Should I give the rods a tear down and grease the bearings up some, then reassemble? I've greased the rods about twice now, but obviously that isn't reaching the bearings. I only have the grease tube included with the kit and some Superlube (with ptfe) that I had bought for my other printer previously, will they work? Any advice for how to lube up the bearings properly?

RE: Bearings going bad?

I use Superlube - it seems to work for me, and there are others here that agree.  In the mean time, try a few drops of light machine oil on the rods both sides of the bearings, 3-in-1 or sewing machine oil, work the extruder and bed back and forth to get it past the seals. You should feel the bearings loosen up and quiet down when the oil gets inside.  That will allow some time before you need to tear down. 

RE: Bearings going bad?

If using oil, you will hear some bearing noise as the balls are free to move about, with grease, the noise will be damped down, but you should be using minimal amounts of grease, if you have packed the bearings, they will not recirculate properly and may well end up sliding on the shaft.

If you try oil, then you will need to clean any old grease out from inside, wash them with a degreaser (IPA) and once dry, give the insides a few drops on each line of bearings before fitting the rods through. It may take a few moves along the rods before everything becomes nice and smooth as the oil runs round the channels with the bearings. The first time I did this, I oiled the bearings, slid them on the rods a few times, took them off again and oiled them again.

You will have to oil regularly though, just a drop before every print if long prints, but you only need to oil once if doing lots of small prints, and wipe off any excess pushed up to the ends of the rods at the end printing using a paper towel.

You will get the feel for it after some use, if you start to get drips accumulating especially at the ends of the rods, your over doing it, but you should always be able to wipe a clean finger just a cm along a rod and get oil on it, just a bit, but visible.

It does require some work, but you end up with a clean smooth running printer.

You can use grease, the thinner the better, but in all cases, only greasing the rods and then a thin film, anymore is simply a waste of grease as the seals at the end will just push it to the ends of the rods.

RE: Bearings going bad?

Posted by: Tim

I use Superlube - it seems to work for me, and there are others here that agree.  In the mean time, try a few drops of light machine oil on the rods both sides of the bearings, 3-in-1 or sewing machine oil, work the extruder and bed back and forth to get it past the seals. You should feel the bearings loosen up and quiet down when the oil gets inside.  That will allow some time before you need to tear down. 

I also have used this on a couple of printers.  Superlube works.  

RE: Bearings going bad?

Hi all again,

I’m trying to grease up my bearings, and I’m wondering what would be the easiest way to get the x axis off without having to disassemble everything? The main problem is the trail of wires sticking out of the extruder carriage it seems since that prevents me from just raising it off the z screw and rods.

So I’m trying to remember, how exactly is the carriage held in? I’ve unscrewed the back plate and I see the zip ties holding it onto the bearings; can I clip them and then would I be able to take the extruder carriage off? Or is there some other way I should go about doing this?

Thanks!

RE: Bearings going bad?

I just watched a youtube on this very thing, I think it was something like "mk3 damaged rods and bearings"- he cut the zip ties on the cable bundle which loosened them enough to lift off the top. I have to do this too - scratched X axis - not looking forward to it 😛

As far as I can tell, no way to do it without removing it, as you need to take the rods out of the holders on each side to replace. 🙁 

RE: Bearings going bad?

X-Axis has to be lifted off the Z-Axis rods and screws. Remove and reinstall the T-Nuts to the screws manually - then attach to the X-Axis.  Once the X-Axis is off the rods & screws, the ends can be slowly and very slightly twisted back and forth while pulling to separate an end.  Once an end is loose, the extruder bearings can slide off.