RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Thickness of NLGI 0 and lower is appropriate for LMU8's because higher numbers (most greases are 2-4) will make the balls not move well in the recirculating raceways, increasing a risk of sliding instead of rolling
This makes a lot of sense. Is there any way to find out if the balls are rolling or sliding? Due to the total absence of noise while moving the bearing after greasing it, is suspect that they are sliding. If I increase the pressure, I can feel some mechanical motion inside the bearings, so I suspect that they start to roll under a little bit of pressure.
Yes, that's exactly it. If there is nothing, no sound and no vibration (the rods are not perfectly smooth, they're ground and so have tiny grooves), and that changes when you apply pressure, that's exactly when the grease is preventing rolling. If you don't have a thinner grease at hand, one way to combat this is to use very little grease, just to cover the surfaces, rather than packing the bearing with copious amounts.
You can also take a look when you're putting the bearing on the rod. When the rod is halfway in, you should see the balls circulating if you look down into the bearing.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
I'm myself using Zeller+Gmelin Divinol Lithogrease 000/150, specifically developed for linear guides. 2000+ hours on the printer with no wear at all and absolutely smooth movement on Misumi LMU8's with Misumi rods.
Where did you find this grease? I see a few eBay sources. the cheapest of which looks to be around $50 with shipping included.
I am planning on doing a Y-axis rebuild (new misumi bearings, new rods, printed bearing mounts) and would like to get the grease done right the first time. Picked up some superlube for it alright, but what I'm reading here suggests that would be a mistake.
Scott
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
I bought it at Öl Engel, from Germany. A minimum package of 1kg didn't make it particularly cheap, either. But don't get stuck on a particular brand, any low thickness low viscosity lithium grease should do a similarly good job.
I also can't say that SuperLube 21030 won't work - I haven't tested it myself. But it seems a little too thick (NLGI 2) and the addition of PTFE powder doesn't speak to its benefit for linear bearing applications. There are many people who swear by it, though.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Are those the Hilube or Superlube (pink) ones on the bed? I've got bed play as well with the latter, but I can't see any on the extruder where I have the Hilube (white) ones
I have not noticed an impact in print quality; I suspect the bed has enough weight on it that it doesn't lift up and down. spreading the rods slightly to pretension them would also help reduce play.
Great. I just ordered Superlubes but it seems that Hilubes are the better choice 😪
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Are those the Hilube or Superlube (pink) ones on the bed? I've got bed play as well with the latter, but I can't see any on the extruder where I have the Hilube (white) ones
Great. I just ordered Superlubes but it seems that Hilubes are the better choice 😪
How did you come to that conclusion? Maybe he got two different sets with different tolerances? Your result could be completely different.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
I moved the bearings a lot of times very fast along the rod and they lost a lot of grease every time. After a while, the transition point between sliding and rolling shifted to much lower radial forces. I then installed the extruder back cover and I could immediately feel the rolling inside the bearings. I guess that the unavoidable force of the extruder cover clamping down on the bearings adds the neccessary load.
Maybe this is something that should be taken into account in your calculation? The load on the bearings is not only the weight of the objects that are mounted, but also the force of the printed parts being screwed onto the bearings, as they are never perfectly straight and try to push the bearings out of alignment.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
I moved the bearings a lot of times very fast along the rod and they lost a lot of grease every time. After a while, the transition point between sliding and rolling shifted to much lower radial forces. I then installed the extruder back cover and I could immediately feel the rolling inside the bearings. I guess that the unavoidable force of the extruder cover clamping down on the bearings adds the neccessary load.
I've had the same observation after first purchasing and using a Mogul LVT 1 EP. I didn't want to have to make sure to get rid of the excess grease before installing, though, so I opted for a less thick grease that doesn't require force to make the balls roll. With that I can just pack, install, print and then possibly remove any excess grease from the rods.
Maybe this is something that should be taken into account in your calculation? The load on the bearings is not only the weight of the objects that are mounted, but also the force of the printed parts being screwed onto the bearings, as they are never perfectly straight and try to push the bearings out of alignment.
I'm not sure about that. The preload will only increase the pressure on one or two rows of balls, the remaining two or three will be lighter loaded instead. I prefer all four to roll.
Plus, I've had a rather bad experience with the amount of preload the original X carriage caused (the distance between rods was about 0.4mm less at the X carriage than at the X ends), so now I run a precision X carriage and X ends that don't preload the bearings at all.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Not neccessarily. If you try to tilt the axis of the bearing against the axis of the rod, you can bring all 4 rows of balls into contact. Two rows on the left and two rows on the right end of the bearing. An even, "non-tilted" loading would be much better of course, but it is unclear how the bearings is mounted since you can not look inside.
I agree with the rest you said and a lighter grease would be very beneficial.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Not neccessarily. If you try to tilt the axis of the bearing against the axis of the rod, you can bring all 4 rows of balls into contact. Two rows on the left and two rows on the right end of the bearing. An even, "non-tilted" loading would be much better of course, but it is unclear how the bearings is mounted since you can not look inside.
You're right. And it's probably a quite common occurence, too, otherwise companies like SKF wouldn't be developing self-aligning linear bearings.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
For the original Prusa rods you should use the white Hilube from Vesconite. NOT the Superlube!
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
For the original Prusa rods you should use the white Hilube from Vesconite. NOT the Superlube!
Where does that information come from?
Nadine from Vesconite recommended the pink ones for the original Prusa rods, I quote
"Also, I have quoted you both Vesconite Hilube (White) and Vesconite Superlube (Pink), the latter having the lowest coefficient friction and thus being the superior grade."
I have contacted Vesconite about my findings and asked them if they can provide any additional information or join this thread.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
For the original Prusa rods you should use the white Hilube from Vesconite. NOT the Superlube!
Where does that information come from?
Nadine from Vesconite recommended the pink ones for the original Prusa rods, I quote
"Also, I have quoted you both Vesconite Hilube (White) and Vesconite Superlube (Pink), the latter having the lowest coefficient friction and thus being the superior grade."
I have contacted Vesconite about my findings and asked them if they can provide any additional information or join this thread.
I have them both at home. It might be true that the Superlube ones have lower friction but their inner diameter is about 0,03mm greater than the Hilube ones. So they don't fit.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
It might be true that the Superlube ones have lower friction but their inner diameter is about 0,03mm greater than the Hilube ones.
This might be true for the ones you have, but it is not a general rule. I asked Juan from Vesconite about it and he replied with the following: (He gave me permission to post his answer)
"While there may be some discrepancies between the ID of the different bushings, both versions were designed to fit the stock rods without any noticeable differences. The difference in ID is due to the fact that every single bushing is individually manufactured on a CNC machine and checked against reference sizing. Measuring these can be tricky due to the fact that the material remains a polymer (not as easy to work with as steel / brass etc.)
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Is there anywhere an ID specification for the Vesconite bushings? What range is accepted?
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Is there anywhere an ID specification for the Vesconite bushings? What range is accepted?
The official spec for the pink ones is 0.05mm clearance over the nominal 8mm, so they should measure 8.05mm. Mine were bang on.
Based on the above message, the white ones should be the same.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
I measured all my 23 Vesconite (Superlube and Hilube) bushings. The inner diameter ranges from 7.99 to 8.04 mm. Thats really disappointing.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
I measured all my 23 Vesconite (Superlube and Hilube) bushings. The inner diameter ranges from 7.99 to 8.04 mm. Thats really disappointing.
What range of numbers do you get if you measure the exact same spot several times? Don't forget that at these scales human measurement error and technique also plays quite a role.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Is there anywhere an ID specification for the Vesconite bushings? What range is accepted?
The official spec for the pink ones is 0.05mm clearance over the nominal 8mm, so they should measure 8.05mm. Mine were bang on.
Based on the above message, the white ones should be the same.
8.05 means quite some (up to 0.064mm) slop on g6 rods, given that the printer steppers work with 0.01mm resolution. It's 5-6 microsteps.
The Misumi LMU8 bearings are 7.990-8.000 on 7.986-7.996 mm rods. So a wost case 0.014mm slop - a little more than 1 microstep, but the average case will be below a microstep.
Color me surprised, I'd have expected the plastic bushings to be very slightly smaller than the rods given that they're flexible and thus can stretch around the rod for a perfect fit.
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
Is there anywhere an ID specification for the Vesconite bushings? What range is accepted?
The official spec for the pink ones is 0.05mm clearance over the nominal 8mm, so they should measure 8.05mm. Mine were bang on.
Based on the above message, the white ones should be the same.
Can you give us a link on that please? Because I am surprised too.
I posted the same results on the Prusa Facebook group and most of them sad that I am too dumb to measure. I can only assure you that I know what I am doing but I will not start an internet discussion about something I am doing at work for over 10 years. 😏
RE: Comparison of original bearings, Misumi LMU8 and Vesconite polymer bushings
A link on the source of the spec? I do not have one, I'm afraid; this was verbatim from Juan in an email discussion I had on the y-axis play I was observing.