X & Y Axis overhaul: Comprehensive parts list & steps available?  

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

Posted by: @bobstro

After 3 years of stalwart service, my Mk3 is finally showing signs of aging. The linear bearings on the X-axis appear to be failing, binding up and causing layer shifts even after lubrication. I'm preparing to do a full tear-down and replace all of the X and Y bearings. I don't really enjoy working on the printer, so I'd like to do this as efficiently as possible. I'm planning to replace:

• X axis linear bearings and smooth rods
• Y axis linear bearings and smooth rods

I think this might be a good time to replace some other high-wear parts:

• X & Y belts
• Bed thermistor and heater cabling

Cost isn't a primary driver, but I don't want to waste money either. A few questions for those who have done this before:

• I have seen many discussions recommending the Misumi linear bearings. I assume these in the Prusa shop are suitable. I recall recommendations to buy Misumi bearings and smooth rods together. Is this recommended? If so, is there a ready US-based source for Misumi bearings and rods sized for the Mk3? Are Misumi worth the extra cost?
• The Vesconite linear bearings come up often. Is there a consensus on whether these are worthwhile? Any caveats to using Vesconite linear bearings?
• My smooth rods seem fine. Is it recommended to replace them along with the linear bearings? This seems like a good "while you've got it all apart" step, but I can skip it if there's no real benefit.
• I'm going to follow the procedure for de-greasing the linear bearings, then packing with SuperLube. Any suggestions or cautions?

I'm expecting to order:

• LM8UU Linear bearings X 8 (6 + 2 spare - either Misumi or generic) from the Prusa store.
• X smooth rods X 2
• Y smooth rods X 2
• Heatbed thermistor
• Heatbed-Einsy power cable
• GT2 X-axis belt
• GT2 Y-axis belt

I'm going to investigate some of the prints that allow easier belt-tightening and other minor upgrades at the same time. Any recommendations?

If anybody has found a good online guide beyond the Prusa Mk3 kit assembly guide, a link would be appreciated.

Thanks!

 

 

 

 

I would just like to say something about the linear shafts and the linear bearings:
If there are no scratches or other signs of wear visible on the linear shafts, there is no need to change them. The new linear bearings, regardless of the brand, are usually provided with anti-corrosion agent in their original condition. For this reason, I would clean (fresh petroleum/kerosene) and grease them.
I have installed slide bearings on my printers (oil-soaked sintered bronze). They are actually undestroyable.

Changing belts and thermistors is certainly a good idea. For lubrication of the linear bearings I would recommend a very soft NLGI 1 or max. 2 grease (brand does not matter).

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

One of the things i wasn’t sure when i assembled my MK3s+ was the belt tension. I used this to Have a visual cue https://www.prusaprinters.org/prints/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

@bapski

I read on the German forum that a user was able to use it to find ideal belt tensions and eliminate his calibration errors.
I have no problems with the belt tensions but out of curiosity I will also print and test this.

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

I agree with Karl, if your rods are in good shape I can't think of a reason to replace them. I'll be rebuilding mine before to long and as of now I'm still going to stick with the LM8UU Bearings, I've not had any issues related to them to date, and I keep seeing folks having leaking issues with the Misumi bearings coming with their kits. Don't forget your Trapezoid Nuts & Bearing Housing 623h. I have not had any issues with the older U-bolts either but I had considered getting the new Clips and seeing how they do when it's time.

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

I replaced my bearings on the x axis when I rebuilt the extruder to use a geared Bunny/Buterworth version (I wanted to keep my mk3 sensor rather than the mk3s version).  I too just went with the standard ones but of course made sure to properly clean and repack them.  I've got a jar of some thin nlg1 grease too.  Not sure of the brand as I got it from a local factory, I asked about suppliers with one of the guys there and they just gave me some from their drum of it lol.

If / when I have to do it again I will certainly be using one of the x axis ends that has a nut pocket in there to allow you to push the rods out.  I recall seeing some on thingiverse.  This style https://www.thingiverse.com/thing:3606189    You should be familiar with the designer Bob 🙂

When I do the Y axis I will probably use the new style clips rather than the u bolts too.  Never did like them.

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

You can order directly from Misumi in the US.  It's suggested to match your rods and bearings. Shipping is probably a wash from WI or Prague. 

I updated to the Bear X-axis years ago.  Prusa has added a lot of the updates in it to their latest extruder.  But for tensioning, it's a must for me.  https://www.thingiverse.com/thing:4362586

edit: You might also want to order the mk3s filament sensor. It's required for any recent extruder updates. 

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

@karl-herbert

you could also rotate the smooth rods 22.5 degrees (if you oriented the bearings per instruction manual), this will ensure the bearing is contacting a different portion of the smooth rod to eliminate the possibility that there may be any wear effecting performance.  

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

My y-axis chattered during the first two hours of printing after I assembled the kit.  During assembly, I cleaned my bearings with IPA and used the rods to pack Lucas Oil brand White Lithium grease - NLGI #2.  I learned that the drag coefficient with grease is too high and the tiny balls bearings "stutter".   

To remedy the issue, I printed new linear bearing holders out of PETG, then cleaned out the grease from the linear bearings and replaced the grease with SUPER LUBE Multi-Purpose Synthetic Oil w/ Syncolon (PTFE).  It runs really smooth and quiet! 

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

So parts start wearing out about 2.5-3 years? My i3MK3S (upgraded to 3S+)  is 2.5 years old.

I noticed that one of my Y-axis rods has a long scratch and one of the bearing is not functioning like the others. Some of you replaced the stock rods with Misumi’s PSFJ8 while others chose the SJF8 series. Besides the look, which is better in terms of making better prints? Also, shall I use LMU8 or LM8UU?

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

Time out to edit. Is it recommended to buy LMU8 or LM8UU?

RE: X & Y Axis overhaul: Comprehensive parts list & steps available?

I'm also confused on which bearings to use - LMU8 (short) or LM8UU (long)?