Rail holders scraping against y axis
I noticed an issue with my CoreXY during build, though somehow managed to convince myself that the motors being on would resolve it and ended up building the whole thing... 😓
Anyway, it appears that the holders for the linear rail are too low, causing them to scrape against the XY frame. They are very hard to move, and the motors can't move them at all.
Is there something I need to adjust inside to get the assembly to float, perhaps?
RE: Rail holders scraping against y axis
In the top picture the lower belt is assembled wrong!
It should go behind the idler!
RE: Rail holders scraping against y axis
Oh yep, you're right!
I also saw that the screws holding the idlers are on the wrong side of the carriage, which would explain why they're scraping against the metal like that.
RE: Rail holders scraping against y axis
This is a good case to learn the troubleshooting process. First you want to determine which part is too low. Is it the 3d printed pieces themselves, or is it another part that is attached to them? Once you determine which part is too low revisit the assembly instructions to see what looks incorrect.
RE: Rail holders scraping against y axis
Also, in all the pictures we can see that you have installed the XY carriage blocks the wrong way round. The heads of the screws (which form the axes for the idler wheels) need to go into the recesses which Prusa has wisely designed into the blocks. You have swapped the carriage blocks and installed them the wrong way, so the screw heads now sit on the flat surface and protrude. That's why your carriage is scraping on the frame.
Please go back to section 5 of the assembly instructions and look at the pictures carefully. I'm afraid there is some major disassembly ahead for you.
RE: Rail holders scraping against y axis
@Jurgen I saw that too. I managed to fix that without much trouble by taking the XY carriages off the rails.
The CoreXY moves freely now. The problem I'm facing now is that the gantry isn't completely aligned, which is likely its own forum topic.
RE: Rail holders scraping against y axis
This is the 3rd time I've seen this in 4 months which means I wonder how many time Prusa support has seen this. If Prusa intends to stay in the kit business I suppose they should redesign these parts so they can only be attached in the correct orientation. That said, the assembly instructions (at least I thought) are quite clear.
RE: Rail holders scraping against y axis
Actually, looking at the pictures and my Core One again -- the carriage blocks are installed on the correct side and in the right orientation. It's just the screws (idler axles) which you put in from the wrong side, apparently all of them.
You will still have to remove the idler blocks to get to the screws which have their heads on the bottom side. Those are the critical ones which are scraping against the frame.
RE:
The first photo has the belt routed exactly the way Butters did it, i.e. on the wrong side of the pulley.
RE: Rail holders scraping against y axis
The first photo has the belt exactly the way Butters did it, i.e. on the wrong side of the pulley.
Yup, that's what @max-rabas referred to. There must be some deeply rooted fear to have the toothed side of the belt touch a smooth pulley. 😉
RE: Rail holders scraping against y axis
Rooted fear ?.. No, just common sense. On a CoreXY printer, only a clueless designer would make a gantry where the toothed side of the belt runs against a smooth idler ( or vice versa ) .. and I know what I'm talking about.
RE: Rail holders scraping against y axis
Rooted fear ?.. No, just common sense. On a CoreXY printer, only a clueless designer would make a gantry where the toothed side of the belt runs against a smooth idler ( or vice versa ) .. and I know what I'm talking about.
Many users have theorized that this is the cause of VFAs. Some have swapped the smooth idlers for toothed ones. Few have reported an improvement. So I am withholding judgement on the "clueless designer" bit.
But I would call "running low on clues" when someone decides to route the toothed belt around a plastic corner instead. 😉
RE: Rail holders scraping against y axis
There is a history of this going back to the MK4 (at least that's where I started with Prusa). When I built that kit I remember scratching my head over why the belt teeth go around the pulley like that and was almost convincing myself that "Prusa has it wrong" (which in hindsight is stupid to think that)
https://help.prusa3d.com/guide/3-x-axis-x-carriage-assembly_429986#431040
RE: Rail holders scraping against y axis
Why would it be foolish to consider something that even the belt manufacturer recommends to protect the belt teeth? It's simply cheaper to use a smooth idler, nothing more. The effects aren't significant enough to justify the higher price. Otherwise, we often see the phenomenon of "man + instructions = bad combination." "I can do it, I know it, I don't need it, I can do it better without it." As @Jürgen already mentioned, Poka-Yoke would work very well here. Although I don't believe Prusa uses a production system or has even heard of one.
RE: Rail holders scraping against y axis
If you think that I don't know what I'm talking about, check the belt routing of Voron printers.
BTW good quality belts won't wear faster because the teeth engage against a geared idler instead of smooth, rather on the contrary,. that I can witness myself, after using Core XY printers for several years.
The gantry design of the Core One is terrible. I'm not surprised of VFAs and other issues, I'm surprised that the printer works at all.. It's not only the smooth/geared idler thing, it's mixing linear rails in one axis and linear bearings in the other, it's the cheap frame,..
I think that Prusa makes excellent products ( filaments, printing plates ) and the MK3/4 series printers are sturdy reliable little machines, but the Core One .. OMG!
RE: Rail holders scraping against y axis
If you think that I don't know what I'm talking about, check the belt routing of Voron printers.
No need to feel personally attacked. But the fact that some printers do it differently does not imply that that's the only valid way to do it. Do you own a Core One? Have you swapped out the two relevant idlers, and what did you find as a result?
Since you brought it up -- could you explain why "mixing linear rails in one axis and linear bearings in the other" is supposedly terrible?
RE: Rail holders scraping against y axis
BTW good quality belts won't wear faster because the teeth engage against a geared idler instead of smooth, rather on the contrary,. that I can witness myself, after using Core XY printers for several years.
Okay, so Gates wrote nonsense about their timing belts in their documentation. And every machine manufacturer/automotive manufacturer that uses toothed idler pulleys in their timing belt drive is doing something wrong, or what?
If you think that I don't know what I'm talking about, check the belt routing of Voron printers.
No, I don't, and I never claimed to.