Failed Y-calibration of a new CoreOne
Yesterday we've received our long awaited CoreOne printer.
It was a batch 2 printer and the assembly of the display was no problem (maybe the display cable was already a little bit longer than in first batch printers).
After linking the printer to our network the self calibration started. What should have been a routine task (especially for a pre assembled printer), became a big problem.
The calibration of the Y-axis failed with a red ERROR message:
PRECISE REFINEMENT FAILED
Consider adjusting belt tension.
More detail at prusa.io/31102
The given link 'prusa.io/31102' leads to nirvana;)...
I've ajusting the belt tension to exactly 85Hz but this didn't change anything.
I've recognized that on Y-movements the carriage touches the stop on the left side about 2-3mm before the stop on the right side would be touched. -> there is a gap of 2-3mm on the right hand side. The opposite gap shows up when the carriage is moved to the maximum Y-position.
Can't be sure if this gap is intented but it look strange to me. It also results in a reduction of the Y-travel by 2-3mm, possibly causing the calibration failure.
I've contacted prusa support (by eMail) 18 hours ago, but no reaction so far.
Maybe someone can confirm that the Y-axis should reach the hard stops on both sides simultaneously.
Thanks, Martin
RE: Failed Y-calibration of a new CoreOne
I have found that it is better to use the chat.
Any queries can be answered straight away.
It's also always quicker.
RE: Failed Y-calibration of a new CoreOne
@david-17 reports the same problem in this thread. He has tried quite a few things, but has not been able to resolve the matter yet. His latest update was that his printer will likely be sent back to Prusa for analysis and service.
RE: Failed Y-calibration of a new CoreOne
@david-17 reports the same problem in this thread. He has tried quite a few things, but has not been able to resolve the matter yet. His latest update was that his printer will likely be sent back to Prusa for analysis and service.
Thank you Jürgen!
Yes it's the same problem. Support got back to me yesterday and suggested to adjust the left and right belt tension go get the X-axis aligned. Yes, it's possible to close the gap on one side with excessive belt tension on this side. But in case of my printer this results in a resonance frequency of 95Hz on the right side and 80-82Hz on the left side.
If the belts are loose or tightened to a resonance frequency of 85Hz on both sides, there is this 2-3mm gap on the right side. Exactly as David shows on his printer.
The 90° angle of the X-axis (measured to the Y-rails) depend on the accuracy of the two 90° bent sheet metal braces, connecting the X-axis to the Y-axis bearings. If the bend angle of these braces are only off by 0.5°, a gap of 2.7mm (X-axis width * tan(0.5°)) apppears. Closing this gap by unequal belt tension may not only result in printing issues but generates static load on the Y-bearings, possibly causing excessive wear on these bearings.
Relying on the bending accuracy of 2 metal sheets for this critical alignment is - in my book - not a very good design decision.
Yesterday I reported my findings to the support, I'm waiting for further instructions from them.
Thanks again,
Martin
RE: Failed Y-calibration of a new CoreOne
In their instructions for tensioning belts on the Core One, they emphasize the importance of tensioning both with as little deviation as possible.
Can you post a picture of the part?
RE: Failed Y-calibration of a new CoreOne
Yes Rainer, I absolutely understand the importance of equal belt tension in a core x/y design.
And in this requirement there lies the problem of the design.
If there is only a tiny deviation of the bent sheet metal brackets, the required 90° angle of the x/y axis is skewed.
Here's an image of the right metal bracket with the critical 90° angle marked:
The angles of both brackets on my printer are obviously not equal, resulting in a slightly shifted angle of about 89.5° (instead of 90°).
If the angle of both brackets would differ equally from their target value of 90° (e.g. both are 89°), the resulting angle of the X-axis assembly would still be 90°. But this deviation would still cause static load to the bearings, which can't be a good thing! I think more printers may be affected by this issue than is obvious by now.
Support just got back to me and advised me to adjust the belts differently to get the angle aligned to 90°.
This results in a big difference of the resonance frequencies (80-82Hz on the left side; 95Hz on the right side). They advised me to live with this inbalance and just watch out for any print defects.
In my book this would be a poor 'solution' to accept for a new printer (not printed anything by now)...
RE: Failed Y-calibration of a new CoreOne
The 90° angle of the X-axis (measured to the Y-rails) depend on the accuracy of the two 90° bent sheet metal braces, connecting the X-axis to the Y-axis bearings. If the bend angle of these braces are only off by 0.5°, a gap of 2.7mm (X-axis width * tan(0.5°)) apppears. Closing this gap by unequal belt tension may not only result in printing issues but generates static load on the Y-bearings, possibly causing excessive wear on these bearings.
Relying on the bending accuracy of 2 metal sheets for this critical alignment is - in my book - not a very good design decision.
Hmm -- you may be onto something there. I was under the impression that Prusa had found a nice solution with the single-piece, stamped metal frame which carries the CoreXY module. That part should be pretty accurate, since its right angles depend exclusively on the stamped contour.
But you are referring to the brackets which connect the linear bearings (which ride on the Y rails) with the X gantry, right? (Lower left and right in the attached photo.) These do indeed seem to define the angle of the X gantry, and do so via their bending angles.
It's difficult to measure these in place, and reworking them would involve significant disassembly. So for a new printer under warranty, it might be a "send it back to Prusa for an overhaul" scenario. But it's definitely something I will double-check when I get my Core One kit -- thank you for the hint!
RE:
BINGO!
Get in line to order your Core One > Core Two upgrade today! Shipping starts in January!
RE: Failed Y-calibration of a new CoreOne
Let's wait and see. I would like to see photos of the whole construction. I could imagine that during assembly the gantry is pushed all the way forward and then the screws are tightened.
This may have shifted during transportation. Which of course should not happen.
The kit assembly instructions may provide more clarity. But that will take a few more weeks.
RE: Failed Y-calibration of a new CoreOne
Get in line to order your Core One > Core Two upgrade today! Shipping starts in January!
If these bent brackets are really the root cause of the skewed gantry, it should be easy for Prusa to tighten the tolerance on these parts and either correct or discard out-of-tolerance brackets in production. No design change needed, I think. But it's a somewhat invasive fix in an already shipped unit. Let's see what service comes back with!
I am wondering whether incorrect angles in these brackets could also be behind the VFAs (vertical ripple structures) observed by some users. What if only one of the bracket angles is off, or the two brackets deviate from 90° in opposite directions? There would be mechanical stress on the assembly of X gantry & Y rods then. Could that lead to asymmetrical tension on the belts, and hence maybe a more pronounced "signature" from their tooth pattern in the prints?
RE: Failed Y-calibration of a new CoreOne
I completely overlooked your post and the picture.Now it's clear exactly what you mean.
I would not accept such different belt tensions, as Pusa points out.
I would contact the support team again.
If you want, you could try to correct the angle with underlays.First loosen the bolts of the angle on the X axle. Then push the axle all the way forward to the stop.Then you should be able to see where you need to shim.
Whether you want to do this on a new device that is not quite cheap is up to you.
I would probably try it out of curiosity.You can still contact the support and insist on a repair.
Yes Rainer, I absolutely understand the importance of equal belt tension in a core x/y design.
And in this requirement there lies the problem of the design.
If there is only a tiny deviation of the bent sheet metal brackets, the required 90° angle of the x/y axis is skewed.
Here's an image of the right metal bracket with the critical 90° angle marked:
The angles of both brackets on my printer are obviously not equal, resulting in a slightly shifted angle of about 89.5° (instead of 90°).
If the angle of both brackets would differ equally from their target value of 90° (e.g. both are 89°), the resulting angle of the X-axis assembly would still be 90°. But this deviation would still cause static load to the bearings, which can't be a good thing! I think more printers may be affected by this issue than is obvious by now.
Support just got back to me and advised me to adjust the belts differently to get the angle aligned to 90°.
This results in a big difference of the resonance frequencies (80-82Hz on the left side; 95Hz on the right side). They advised me to live with this inbalance and just watch out for any print defects.
In my book this would be a poor 'solution' to accept for a new printer (not printed anything by now)...
RE: Failed Y-calibration of a new CoreOne
Rainer, you didn't overlook my post. It just wasn't visible. My posts are 'moderated'. Obviously it takes up to 10 hours until they are released. I hope the reason for this is that I'm a new member in this forum, not because I'm the bad guy here😀...
The support got silent after a few exchanges and my suggestions for solution. I'm waiting for a replay for 20 hours now. Our company does use Prusa printers (MK3s and hopefully the Core One in the future) for several years and I own several printers for private use (MK3s and MK4s). Never did need customer support but the experience so far isn't too exciting.
Thinking about returning this printer and moving on...
Thanks for your suggestions for adjusting the angle with underlays. I'm not going to tinker with this printer.
If you are lucky and have got a printer with exactly bent metal brackets you are fine. But you may have got a printer with two metal brackets with equally wrong bend angles (e.g. 89°). The angle of the x-axis will be perfectly fine (90°). But the misalignment causes permanent pressure on the Y rail bearings, eventually leading to excessive wear.
If you are less lucky (as I am) you have a printer with problematic Y calibration or differently tensioned belts, causing less than perfect prints.
Here is a picture of my printer with fully loosened belts (maybe you have to click into the photo to see it in it's full width):
Without any 'aligning help' from the belt tension there is a gap of ~4mm on the right side.
This is not up to the Prusa quality standard I know...
RE: Failed Y-calibration of a new CoreOne
The late appearance of your posts has nothing to do with you. It's just the way it is at times. The same goes for notifications of subscribed topics.
Have you used the chat?
I'm sure there will be a solution. It's always more difficult with completely new products.
In any case, I will pay special attention to this with my kit.
RE: Failed Y-calibration of a new CoreOne
The late appearance of your posts has nothing to do with you. It's just the way it is at times. The same goes for notifications of subscribed topics.
I understand the need for moderation of a new member in this forum. But the content of my posts should make it clear that I'm not a spammer but a customer, trying to solve a problem of a new item that I bought from them. Don't know how many posts I have to make until I'm a trustworthy forum member...
These delays (up to 10h) do - unnessesarily - kill the flow of a thread.
Support just came back to me (by eMail) and told me, that I should tighten up the belts again for closing the gap. This results in a high inbalance of the resonance frequencies (80-82Hz vs 95Hz). If a test print would show no visible print defects, I/we would have to live with this flawed printer.
I'm not sure if the support team understands the requirements for dynamic movement of a core x/y head. And what role belt tension plays for achieving best movements.
At least for me, this is NOT an acceptable solution. Sad about it, but now we have to consider cancellation of our purchase.
I wish you good luck for your kit!
RE: Failed Y-calibration of a new CoreOne
If there’s an uneven gap, there might be a slight issue with the Y-axis carriage assembly itself. Make sure the carriage is properly seated on both sides and that nothing is preventing it from moving evenly.
RE: Failed Y-calibration of a new CoreOne
My posts are 'moderated'. Obviously it takes up to 10 hours until they are released. I hope the reason for this is that I'm a new member in this forum, not because I'm the bad guy here😀...
[...]
Here is a picture of my printer with fully loosened belts (maybe you have to click into the photo to see it in it's full width):
Without any 'aligning help' from the belt tension there is a gap of ~4mm on the right side.
This is not up to the Prusa quality standard I know...
Right, posts by new users are manually reviewed before they go public on this forum. It's not a perfect system since it sometimes leads to bumpy discussions, but it seems to keep most of the spammers out. Now that you have more than 5 posts under your belt, I believe your posts should appear right away.
Many thanks for the photo showing the top view of the skewed gantry. It looks like the Bowden tube and the cable harness might put some strain onto the gantry when it is in the frontmost position. Can you rule out that this drag is pulling the gantry out of alignment?
RE: Failed Y-calibration of a new CoreOne
The low resistance should not play a role, but must of course be taken into account.
But the high difference in tension does not explain this.
As this is a new complete device, the support team is responsible for finding a solution, not the customer.
If the printer is set to the correct tension according to the instructions and you print a rectangle of maximum size, you should be able to recognize the deviation relative to the bed.
The sheet should lie absolutely straight.
I would confront the support with this.
RE: Failed Y-calibration of a new CoreOne
Right, posts by new users are manually reviewed before they go public on this forum. It's not a perfect system since it sometimes leads to bumpy discussions, but it seems to keep most of the spammers out. Now that you have more than 5 posts under your belt, I believe your posts should appear right away.
At the time of my writing, 6 of my posts have been 'published'. I think it's realtively easy to see that I'm not here to spam. I'm a long time customer of Prusa (don't remember when I've bought my first MK3).
It is always a risk to buy a newly introduced product. Since most of the parts are already used in the MK4s (which I also own one), I thought it was worth taking.
But I have to say, when I look at this - in my opinion - questionable design solution and experience the Prusa support so far it feels slightly disheartening.
They try not to solve the problem but play it down.
Many thanks for the photo showing the top view of the skewed gantry. It looks like the Bowden tube and the cable harness might put some strain onto the gantry when it is in the frontmost position. Can you rule out that this drag is pulling the gantry out of alignment?
Thank you for the idea about the bowden tube and the cable harness. I've checked right now. When I move the print head in all extreme positions (min/max x/y and the middle positions), the gap of ~4mm (when the belts are loose) is always the same. The potential stress caused by the bowden tube and cable harness seems too small to have an influence on the X-axis angle. So I think that this influence should not bother us.
I've also measured the force I have to apply to the right bracket for closing the gap.
A force of 8.1N is needed to push the x axis straight.
RE: Failed Y-calibration of a new CoreOne
If the printer is set to the correct tension according to the instructions and you print a rectangle of maximum size, you should be able to recognize the deviation relative to the bed.
The sheet should lie absolutely straight.
I would confront the support with this.
If the belt tension is setup up according to the instructions (resonance frequency of 85Hz on both belts), the printer fails to perform the calibration of the Y-axis. This was the situation when I started this new thread/topic. The printer misses the 2.5mm gap in the of the expected/required travel of the y-axis and aborts the calibration without any further message or hint.
Therefore no chance to print anything on the printer with equally tensioned belts. But if printing would start, a rectangle would be out of shape by about 0.5°.
Support doesn't question the gap of 2-3mm on this printer they have sent me (I've shown it with photos and a video). But they think it's good enough to close the gap by extensive belt tension on the right side. If there are no visible print defects, they suggest everything is fine...
Yes, thats really the solution you have to accept on a new - and not inexpensive - printer, isn't it?
RE: Failed Y-calibration of a new CoreOne
@martinf -- thank you for checking the (non-) effect of the bowden tube and cable harness. Makes sense that the force they exert is small; that's the way it should be. I just thought that they looked to have quite a sharp bend in your photo. Anyway, too bad that they do not get you close to a solution.
I can certainly relate to your frustration with your Core One, especially since Prusa has a reputation for solid engineering an great support and does not seem to be living up to either. Have you indicated to the support team that you are considering to return the printer? At least Prusa gives you 60 days to make that call (without the need to get into a quality/warranty debate).
In the meantime, I am spending too much time reading the threads here in preparation of receiving my Core One kit, and am having some doubts... With a kit, I can watch out for a few potential issues while putting things together, as long as the root causes are identified in time. On the other hand, I won't have the warranty for a fully functional printer (obviously).
Would I have a 60-day return window on the kit? Would that mean taking everything apart again, putting all parts in their repsective bags and sending them back? That appears to be what the support page says: "Pack the order down as it was received." ( https://www.prusa3d.com/page/refund-and-returns_939/ -- which seems to apply to kits as well?)