Re: Scratched rods from linear bearings
Thanks for the info sven! This is getting a bit off topic, but I'm wondering if those casings are really "only" printed without further tuning. A bit too much pressure and the bushings are ruined. I have mine in printed parts as well, but I always go through the hole with a precise h6 reamer. Definitely makes me wanna give it a try though... I still have some 15 mm stock flying around in the workshop. On the other hand I'm a bit worried about aligning the rods perfectly parallel. Maybe a project for the far future.
The THK stuff is indeed pretty impressive. I have a 20 pound linear unit with ball screw in my DLP printer because I got a used one fairly cheap. Would probably still have zero play if I ran it over with a tank.
Re: Scratched rods from linear bearings
Question for those that rotated the rods due to scratches: did you do it in place (by cutting zip ties and loosening everything) or did you dismantle the whole thing ?
Re: Scratched rods from linear bearings
Did you guys see CRT's video today? He had scratched/gouged rods and opened a support case with Prusa. They sent him new rods and bearings, and the replacement rods were a LOT harder. This was obvious after he did some (hardness) tests on both:
Re: Scratched rods from linear bearings
Same deal here, waiting to hear back from support..
Only a few hrs printing so far...
Re: Scratched rods from linear bearings
Question for the MEs reading this. I watched for about 10 minutes and it appeared he was replacing the bearings also. If that is the case, why? Wouldn't the scoring of the rods indicate that the bearings were much harder than the rods and therefore good?
Re: Scratched rods from linear bearings
Because Prusa told us to change the bearings as well - because you never know:-)
I received as well a set of new rods (which look indeed more blue in the reflection) and 10 bearings. I will keep some of the old bearings as potential replacements. I will see, when I have time to reassemble the printer
Great video by the way! Using a "file" (how to spell this?) to test the hardness was very clever and I learned a lot right there
Re: Scratched rods from linear bearings
Because Prusa told us to change the bearings as well - because you never know:-)
I received as well a set of new rods (which look indeed more blue in the reflection) and 10 bearings. I will keep some of the old bearings as potential replacements. I will see, when I have time to reassemble the printer
Great video by the way! Using a "file" (how to spell this?) to test the hardness was very clever and I learned a lot right there
If this kind of stuff interests you, have a watch of the videos by "AVE" (you will either love him or hate him)... He uses a special set of files to test hardness... You can buy a set which are different hardnesses, so when you want to check the hardness of a material you work you way up through the files until they stop "biting" and this will tell you a specific "value" of hardness.
Re: Scratched rods from linear bearings
If this kind of stuff interests you, have a watch of the videos by "AVE" (you will either love him or hate him)...
Love that guy (in a purely Platonic way!) Learned so much from his ramblings. Keep your stick on the ice 😆
Re: Scratched rods from linear bearings
I did this before assembly and have no problems.
Re: Scratched rods from linear bearings
Interesting approach! But this is not a greasing issue but a material issue. The scratched rods are not hardened - that is why Prusa replaces scratched rods with no questions asked.
And as we learned the replacement rods are way harder.
Re: Scratched rods from linear bearings
So are the "A LOT harder" rods getting swapped in on unshipped kits? Tempting to pre-emptively order a set of rods/bearings, but am hoping we can give some credit to the lovely folks in Prague that this is already taken care of.
Re: Scratched rods from linear bearings
so had contact to support some days ago because my rods are also scratched.
they wanted photos and even a video...
after the photos they told me that I got the MK2 rods instead of the MK3's and that they resolved the problem of accidentaly picking the wrong ones by seperating them in the inventory...
sounds pretty sketchy to me, I think they wanted to save some cash and chose poor quality and now it backfires ...
Re: Scratched rods from linear bearings
Why would they lie and say they confused their inventory when they could lie and say their vendor gave them bad product?
I'm not arguing what did or did not happen, I'm just saying if they are lying, this is a strange lie.
Re: Scratched rods from linear bearings
Question for the MEs reading this. I watched for about 10 minutes and it appeared he was replacing the bearings also. If that is the case, why? Wouldn't the scoring of the rods indicate that the bearings were much harder than the rods and therefore good?
You replace the bearings because they may be contaminated with material from the damaged rods. Another reason would be that it is cheap insurance in money and time compared to the risk of having the problem again just in case the bearing actually was the root cause of the failure starting.
Re: Scratched rods from linear bearings
Interesting approach! But this is not a greasing issue but a material issue. The scratched rods are not hardened - that is why Prusa replaces scratched rods with no questions asked.
And as we learned the replacement rods are way harder.
I retract what I said. I just checked and I do have bad scoring already after just a few days worth of printing. That is a problem with the rods. You are correct.
Re: Scratched rods from linear bearings
I still havn't built my MK3 yet (been ill all over Christmas).. Is there any way to check the rods before building?
I guess I could do the file test, but I have nothing to compare them too...
Re: Scratched rods from linear bearings
Well. They look different. The harder ones shimmer bluer. But without a direct comparison you have no chance to judge the color.
I heard in the YouTube video that the shamfer on the rod end is also different. Maybe someone could shoot some pics of the difference?!
Re: Scratched rods from linear bearings
Read some stuff here and just wanted to make a post to help out if I can
1. Dont use WD40. WD40 is really just a water displacer. It is not a lubricant. It contains very very small amounts of fish oil, but is mostly solvent. That also means don't get it on any of your plastic parts. It will act a lot like acetone or similar substances.
2. For degreasing, alcohol is not a good solution for the bearings. A citrus degreaser from the dollar store is a much better option. Alcohol works best as a final step for very small amounts of oil and grease buildup or can also be a good option to wipe rods.
3. Grease or oil will not help gouged rods but may help light scratching noises.
4. This is not likely a case of cheap bearings. What is most likely happening is the bearings are made of a harder material than the rods.
5. Do not mix oils and grease on the same application. e.g. oil on rods and grease on bearings.
6. For such a light duty application, especially with small motors and rapid movement, oil is better. For your understanding, grease is oil with a soap added which makes it thick. So general rule is the thinner the oil (including grease) the more often you have to apply. If you grease the bearings you very rarely need to apply. With a light machine oil (nyoil, 3 in 1, ptfe, silicone lube, etc) you should apply a very small amount once every two weeks or so. but never so much that there is buildup.
7. Even if there is no gouging, machine oil is a good thing for your bearings and threaded rods.
Re: Scratched rods from linear bearings
My reading leads me to believe the UU type bearings need lithium grease... See A-549 in linked document.
https://www.thk.com/sites/default/files/documents/us_pdf/products/generalA/en_A_523_lbearing.pdf
Re: Scratched rods from linear bearings
I decided to take a look at my rods (even thought they are still in the box) and they do not appear blue..
They also have more of a chamfer at the ends, which on the video looks like the old (soft) rods..... But as a final test, I took a file to the end, and with a light stroke easily removed material.
Clearly mine are not the "hard" versions and I am going to try and get Prusa to replace them before I start my build.. I am not in the mood to build it, wait for the scratches and then do a rebuild when it happens.
I am not convinced they will help, but atleast I was honest and told the truth, where as I could have just told them that mine were scratched and used someone elses photos...
Lets see what they say....
Jon
Edit: I just did a quick test and slid a bearing back and forth at the end of the shaft a handful of times.. You can already see marks on the rods... Very fine, but they are there and permanent..,