Scratched rods from linear bearings  

Re: Scratched rods from linear bearings

I like you built with gloves on, I then applied Anti Friction Dry PTFE Lubricant to the rods and have hammered the prints for nearly 3 weeks now and not a sign of any scratches.

Re: Scratched rods from linear bearings

Did you lubricate the bearings? I’m waffling between packing some sort of grease or using Nyoil II on mine. In any case lubrication is key.

Re: Scratched rods from linear bearings

I did not lubricate because the manual says it is not necessary. When the issues (failing self test for X axis length) started then I put some fine mechanical oil on the rods.

On the replacement bearings I definitely will put some "Super Lube" or similar grease before assembly.

Re: Scratched rods from linear bearings

I don’t have the printer yet but would struggle with leaving my bearings unlubricated. Will have to pick the motion industry rep’s brain when I get back to work.

Re: Scratched rods from linear bearings

Linear bearing info
http://reprap.org/wiki/Linear_bearing

Re: Scratched rods from linear bearings

Reading the wiki leads me to believe that the nyoil II we use on our fine electronic equipment will be adequate. Though the wiki does say “Not all Linear Bearings need lubrication” maybe Prusia uses pre lubed bearings???

Re: Scratched rods from linear bearings

The manual says they are pre lubricated! (And they are - but maybe not enough in my case?)

Regarding the manual: It says one could use "Super Lube" to grease the bearings AFTER a few hours of printing. So I ordered a Super Lube Tube from the US (am in Germany). But Super Lube contains PTFE, right? And the rep rap forum page that was just posted says to NOT use PTFE based grease on the bearings - so which one is it?!

Re: Scratched rods from linear bearings

Unfortunatly after only 2 hours and 32 minutes (14,77 m) of printing my rods are starting to create grooves.

I realised it on my left y-axis rod, where it is the most visible. But also the right one, x-axis rods and z-axis rods also already show visible scratches.

I also followed the manual carefully and didn't overtighten the bearings with the u-bolts (on the y-axis). I took enough time to aligne the y-axis bearings so that they run as smooth as they can.

Also didn't used lube on them, regarding the manual that they don't need to. Maybe I should have used some lube from Ballistol (without silicone and PTFE) which I use on my other printer.

Maybe the rods aren't hardened?

Re: Scratched rods from linear bearings

Oh that sound familiar. 😉

Have you contacted support already?

I got a UPS tracking number today for the replacement parts - I still do not know:
1. Should I apply grease on the bearings even though the manual says otherwise
2. Must I maybe wash the bearings in WD40 before greasing them - completely another thing that the manual says?
3. Which grease I should use? Is any lithium based grease fine? Or any multi purpose grease like the manual says? Or Super Lube (which the manual mentions) but which contains PTFE?

But if the quality is bad on the rods or on the bearings or both - no matter what I do it will not last long.
Maybe Prusa had to source some parts from suppliers who offer bad quality parts to be able to meet demand?

Well as long as Prusa replaces bad parts I am OK - but I want sometime in the near future get the feeling that my MK3 is finished and just works. Right now I am really not happy.

Re: Scratched rods from linear bearings

My X axis rods have the same problem and prusa have send me the replacement parts, i hope that the new one are better than the old rods.....

Re: Scratched rods from linear bearings

My X axis rods have the same problem and prusa have send me the replacement parts, i hope that the new one are better than the old rods.....

But did yours arrived already scratched? Or was it the bearings?

Re: Scratched rods from linear bearings

Yeah, just contacted support after I had posted here.

That's nice! Hope your new set will be okay. The support told me to rotate the bearings and rods on the y-axis for now and start again printing. Because if the other rods are getting more worse too, they would replace them also.

I also asked him about lubrication and some drops would be good. About what kind of lubrication he said: "we don't have reccomendation for lubes. generic oil for mechanical purposes will be ok"
Good question about WD-40. You want to wash the stock lube out of the bearings and fill it with the new lube, right?
I'm also asking me the same question which kind of lubrication would be the best. I have also some lithium based here, but I don't know if it's good for it.

Support said the rods are hardened. Maybe it was just the bearings? I'm also afraid it will just create grooves again. Just wondering why it already show marks after 2,5h.

Let's hope so, time will tell

Re: Scratched rods from linear bearings

Yeah, just contacted support after I had posted here.

That's nice! Hope your new set will be okay. The support told me to rotate the bearings and rods on the y-axis for now and start again printing. Because if the other rods are getting more worse too, they would replace them also.

I also asked him about lubrication and some drops would be good. About what kind of lubrication he said: "we don't have reccomendation for lubes. generic oil for mechanical purposes will be ok"
Good question about WD-40. You want to wash the stock lube out of the bearings and fill it with the new lube, right?
I'm also asking me the same question which kind of lubrication would be the best. I have also some lithium based here, but I don't know if it's good for it.

Support said the rods are hardened. Maybe it was just the bearings? I'm also afraid it will just create grooves again. Just wondering why it already show marks after 2,5h.

Let's hope so, time will tell

I use regular sew machine oil. Have been using for years with LM8UU bearings and havent had any issues yet =)

Re: Scratched rods from linear bearings

just use a lm grease don't wash out with wd40 its a water repellent anti seize just pack the bearings with lm grease all my printers are serviced with lm or 3in1 oil no oil in the bearings tho

Re: Scratched rods from linear bearings

Thin oils will not really help the dry ball bearings to be able to rotate in the races of the bearings. If you do not re-pack them before you install them, you will create groves as the balls slide along the rod instead of rolling like they need to to function correctly. And the seals on the ends will block most of any grease you try to place on the rods after the fact.

So the drier your bearing the faster you wear a small groove in the rod surface.

Re: Scratched rods from linear bearings

Lithium grease or sewing machine oil will be fine, the first would be the best option, plus a 500g of grease from the local hobby market (Obi, etc.) set's you back 3 bucks and will probably last a life time of printer greasing. If you have the bearings off add the lube to the inside of the bearing, not to the rods if possible. The bearings are more or less sealed, so you'll just move the stuff around on the rods.

If you want to degrease/wash your bearings just throw them into a cup of isopropyl alcohol over night, stir once in a while.
No WD-40 though! WD40 is great for getting stuff off, but not meant for permanent greasing, it's really just vaseline and solvents. Don't lubricate bearings with vaseline.

As for scratched rods: The bearings on my X-axis are utter crap, there's no nicer way to put this. During assembly it was already clear that they had too much friction, but since I didn't have any spare LMU8s at the time I put them on anyway. Took about 10 minutes of printing to run visibly and feelable, deep grooves into the rods. The lower X rod even got scored from only sliding one of the bearings on during assembly. I don't really blame Prusa. When I build a printer from scratch once in a while I always order twice the amount of cheap chinese bearings, find the best ones and throw the rest into the trash. Often times it's obvious that some of the balls in those bearings don't want to move properly. The bearings I got with my MK3 kit were 50% acceptable, 50% garbage as well. I understand that no one has the time to test every bearing though, so I didnt bother asking support for another hit or miss delivery and just ordered some proper ones from Misumi. And some new rods (g6 tolerance, hard chromed) as mine look like they have freaking olympic bobsleigh runs engraved in them.
If 3-5€ for Misumi bearings seems to expensive I'd suggest to just grab a bag of cheap ones (probably around 1€ per piece) on ebay/amazon and just throw out the bad ones.

Re: Scratched rods from linear bearings

If 3-5€ for Misumi bearings seems to expensive I'd suggest to just grab a bag of cheap ones (probably around 1€ per piece) on ebay/amazon and just throw out the bad ones.

Care to give some part numbers for the Misumi bearings/rods you are using!

Re: Scratched rods from linear bearings

If 3-5€ for Misumi bearings seems to expensive I'd suggest to just grab a bag of cheap ones (probably around 1€ per piece) on ebay/amazon and just throw out the bad ones.

Care to give some part numbers for the Misumi bearings/rods you are using!

Bearings are lmu8
https://us.misumi-ec.com/vona2/detail/110300026540/?HissuCode=LMU8

No idea about the rods.

Re: Scratched rods from linear bearings

If 3-5€ for Misumi bearings seems to expensive I'd suggest to just grab a bag of cheap ones (probably around 1€ per piece) on ebay/amazon and just throw out the bad ones.

Care to give some part numbers for the Misumi bearings/rods you are using!

PSSFJ8-370
(the 370 is for the length, X-axis)
https://de.misumi-ec.com/vona2/detail/110302634310/?HissuCode=PSSFJ8-370&PNSearch=PSSFJ8-370&KWSearch=PSSFJ8-370&searchFlow=results2type

I should add that chrome hardened surface is probably overkill. The original Prusa rods are pretty okay as long as they're not ruined by ultra cheap bearings 👿