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Rail Wear Using LM8UU Bearings
#1
Reviewing some of the new hot end carriages I remember coming across a comment from another user that the use of LM8UU bearings as opposed to the bronze bushings used on the stock carriage was causing grooves to develop on the X rails after only a short periods of use. This would indicate that maybe the stock rails are not hardened.

I'm curious if others have found this to be an issue or if this users experience may have simply been caused by poor quality LM8UU bearings or improper ball orientation when installing the bearings.
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#2
I did notice that I was getting the grooves in my rails from the bearings and I can confirm that the rails are not hardened as well. I had a nick in one of my bushings when I converted back and that has since worn a grove in the rails. This wouldn't be the case if these were good quality hardened steel. I may do a hardness test after I replace my rails (going to do some wicked mods here shortly) and see how they rate in comparison to some of the products out there for repraps and such.
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#3
Wear is more likely to happen with cheap bearings, especially if they are not installed correctly. The weight of the carriage should be on two sets of the small balls, not one.

So orienting them like a"+" would increase wear while "x" would minimize.

When you slide the bearing on the shaft they may have a tendency to want to spin. I'm of the opinion all bearings on a particular rail should be trying to spin the same direction.

also, if you grease the balls they may not actually roll. You should use a light oil.

I have only the slightest wear at this point, and that's after hundreds of hours printing since changing the carriage.

In reality, this wear probably won't hurt anything.

I suggest if the wear is an issue you might print a lm8 bearing.

Kieth
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#4
I had mine setup like Keith is describing. I think that my bearings were bad, but that being said unless you are paying +$10 per bearing they will be all of questionable quality...

I guess my real question is why switch in the first place?

Bronze bushings are:
-Quieter
-Tighter
-and if properly lubricated have just as low friction
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#5
My question was coming from much of the same thinking as Keith detailed. If the bearings are installed properly and of reasonable quality even unhardened rails should have a reasonable amount of wear ability. As for using something other than the bushings I think one could argue either side. I think in reality the LM8's have slightly less friction but the friction can actually be good thing in this application in reducing oscillations since it's belt driven.

I raised the question to gather the experiences since I could accommodate either implementation in a new carriage. I appreciate the discussion so far.
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#6
I am designing a direct drive conversion for the printer now and I think I may stick with oilite brass bushings, but I may still decide to drop the cash on some decent linear bearings but we will see.
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#7
Quote:I am designing a direct drive conversion for the printer now and I think I may stick with oilite brass bushings, but I may still decide to drop the cash on some decent linear bearings but we will see.

Please keep us in the loop for this, I'm very interested!
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#8
It isnt going to be the faint of heart really Idk if I am going to take the time to do a write up even basically would take my printer and turn it into something that uses a davinci brain and box but that's it...
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#9
I appreciate this is an old thread but it may be worth revisiting.
I have a stock of Igus RJ4JP-01-08 plastic bearings, which are a drop in replacement for the LM8UU metal ones.
I have fitted them to my i3 and cut them down to fit my Makerbot clone. I like them very much. I am now eyeing up my 1.0A for a similar update.
I have found STLs for an extruder carriage and for one side of the x axis that incorporate the LM8UU bearings. But one side is missing.
I presume that the project was abandoned because the LM8UUs were found to wear grooves in the rods. As plastic bearings will not cause this wear and have other advantages over the LM8UUs, this might be a project worth reviving.
I have zero skills when it comes to CAD. Modelling a LEGO brick seems beyond me. lol I would gladly give someone a set of Rj4JP-01-08 bearings for the Da Vinci (by my reckoning 8 bearings) or even 2 sets to someone who would design replacement carriages, that will take LM8UU bearings., for me.
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