RE:
Hey All!
Prusa support got back to me, (I had actually shared this thread with them in a note that I sent). This is the procedure that they are recommending:
Thank you for reaching out to us and choosing our products.
It looks like you're experiencing layer shifting in your prints.
To fix this, we first need to ensure that the frequency (tension) of both belts is close to 85 Hz.
Please measure them following the instructions in the next link and share the results with me: https://help.prusa3d.com/es/article/adjusting-belt-tension-core-one_845048
Once you have the results, please send me a photo similar to the following:
To take a photo similar to the previous one, please remove the top acrylic panel as follows:
Remove the four rivets from the top panel.
The previous photo is to determine whether the gantry (X-axis) is properly aligned with the printer frame.
If it is aligned, you will notice that both sides of the X-axis are fully tight against the front end. However, if you find a gap on either side, it indicates that it is not parallel, so you should follow the procedure below to adjust it:
- Loosen the belts almost completely. Carefully, as the square nuts can fall off the plastic parts when removed completely.
- Check which side sits against the front end (tight side) and which one has to be pushed towards it to touch it (loose side)
- Put an uniwrench or something that is at least 5mm thick between the tight side and the front end and slightly push on the loose side to correct the skew. Video showcase
- Check the alignment again and repeat if needed. In case the tight and loose sides switched, use something thinner and try to balance it out. Tighten the belts again
After making the previous adjustments, you can repeat the print that was experiencing layer shifts and let me know if the issue was resolved.
We will continue to follow up on your case until it is fully resolved.
I just tried this on my printer, which was quite considerably off (~10mm) on the right, and it worked. It took a few iterations of gently bending and moving the head around to try and balance it, but once it was sitting square on both sides I tightened both belts to 85Hz and its still square!
I didn't like doing it, but it seemed to work, just take your time
Time to rerun calibrations to check and run an input shaper calibration and hopefully I will see some VFA improvements.
RE: Failed Y-calibration of a new CoreOne
They are magnetic, so some kind of steel.
Thank you for checking and letting us know, that the brackets are mode from steel!
Therefore (re)bending the brackets in an assembled printer is a very risky task. The Y-bearings may get damaged by the applied forces.
And by just applying the bending forces when both brackets are attached, you will not be able to get the misangled back to 90°. The chance is much higher that the better angled bracket is getting off in the opposite direction, compensating the misalignent of the bad bracket. The x-carriage may now be right angled, but by this unspecific bending you created static forces to the y-bearings. If you choose to take the risk of (re)bending the brackets in an assembled printer, you should do it only after loosening the screws of one bracket (disconnecting the bracket from the x-carrage). In this way you can specifically adjust the angle of the mis-angled bracket.
But I would suggest to not apply this (re)bending on your assembled printer at all!
At least Prusa made a small into the right direction. They decided to not cover up the problem anymore by telling their customers to pull the x-carriage straight by different belt tension.
And hope remains that they will come up with a real solution. One day...
RE: Failed Y-calibration of a new CoreOne
If I was to bend metal I would definitely want to take them off the printer, once the kit comes along with an assembly instructions we know if that is easy or if removing the bracket have unexpected consequences, until then the procedure using shims feels safer. With a feeler gauge it is even possible to measure the gap.
the good part is that the problem now seems to be recognized by support implying they could try to improve quality assurance of the parts involved, that is the real fix to the problem.
/Anders
RE: Failed Y-calibration of a new CoreOne
Prusa support came back to me today and confirmed that the brackets are made of steel and their new official suggestion is bending the brackets as described in one of the above messages.
Since it does explain my concerns about this suggestion, I post my replay here too:
Hello xxxxx,
and thank you for confirming that they are steel brackets. I think their thickness is about 1mm (+ powder coating).
In my opinion there are two problems/dangers with your new, officially suggested approach:
1. The needed forces for bending the steel brackets are not only acting on the brackets, but at the same time on the bearings of the Y axis too. And these forces, acting on the short levers of the Y bearings, are quite high. I would fear to hurt them. At least they may loose some of their precision.
2. When you apply the bending forces while both brackets are attached, the forces are acting on both brackets and you eventually change the bending angle of both brackets by a similar amount. Yes, as a result the X-axis will stand in the 90° angle to the Y axis, but the result still isn’t good.
I try to explain why:
When you start the bending action, the angles of both brackets are different – if not, your X axis would be straight. Lets say for example left bracket +0.8°, right bracket -0.2° (these are approximately the numbers of our printer), resulting in a angle misalignment of 0.6°. The right bracket is pulling the left bracket a little bit straight by 0.2°.
When you apply the bending forces in the way Prusa does now officially suggest to get the x axis straight, the result for the straightened X-axis may be:
left bracket: +0.5°
right bracket -0.5°
You have corrected both brackets by -0.3°. The now equally misaligned brackets (both are off now by 0.5°) pull each other straight. The end result for the X axis is good, but the permanent pulling of each bracket creates everlasting load to the bearings of the Y axis.
In my opinion it’s important to adjust the bracket’s angles separately. You have to loose the mounting screws on one bracket and adjust the angle on the other bracket. Then vise versa. Only by doing so, you can be sure that both brackets are straight.
English is not my native tongue, but I hope I was able to explain the problem with understandable words.
I fully understand that every owner is free to do to his printer what he thinks is right, but I just want to tell, that the results of these official suggestions will give you a printer with a straightened X axis but print quality may be affected by the possibly overloaded bearings (by the bending forces) and by the constant (ever lasting) load you create by this unspecific rebending. Not to mention the wear this static pressure on the bearings may cause.
RE: Failed Y-calibration of a new CoreOne
Since I have adjusted my left bracket with a shim, I have started a couple of prints in PETG and ASA. From early testing I got the impression that the XY-homing head-banging was worse when the chamber is at higher temperatures. Now every print starts with the same number of impacts in the front right corner. My guess is around 10. Then it continues with nozzle cleaing (still an issue with PETG, fine with ASA) and print.
As I see it at the moment, aligning the gantry with a shim made my homing procedure repeatable and "ok" . My hope is that the next firmware update will reduce the homing impacts to 2 or 4 and do something with the nozzle cleaning procedure. Oh, and a reduced time on the "absorbing heat" stage would also be nice. For a small print, the time between sending a file and actual start of the print should be <5min in my mind.
RE: Failed Y-calibration of a new CoreOne
Has anyone been able to fix this issue using Prusa's instructions? I've tried so many times that I'm about to give up. The gantry looks aligned, and I've adjusted the belt tensions dozens of times, but I still can't get it to pass the homing test.
RE: Failed Y-calibration of a new CoreOne
Has anyone been able to fix this issue using Prusa's instructions? I've tried so many times that I'm about to give up. The gantry looks aligned, and I've adjusted the belt tensions dozens of times, but I still can't get it to pass the homing test.
If the gantry is right angled (left and right side of the gantry hits the end stops simultaneously with no gap on either side), the calibration of the Y-axis should succeed.
I think there's a software bug, causing the homing of a good aligned printer to sometimes (randomly) take 'forever'. Guess this will be solved with the next firmware release for the Core One.
The question remains: does your printer pass the Y-calibration and 'just' has homing problems?
Hint: sometimes homing passes without any issues after you abort an endless ongoing homing with a reset.
RE: Failed Y-calibration of a new CoreOne
Mine fails both the Y-axis test and homing. Here are pictures of the left and right sides. I've tried different belt tensions. The Y-axis test passed with the "factory setup," but at that time, the left belt was much tighter than the right, and the print quality was terrible. Now, if I set the belts back to those tensions, it no longer passes.
RE: Failed Y-calibration of a new CoreOne
Mine fails both the Y-axis test and homing. Here are pictures of the left and right sides. I've tried different belt tensions. The Y-axis test passed with the "factory setup," but at that time, the left belt was much tighter than the right, and the print quality was terrible. Now, if I set the belts back to those tensions, it no longer passes.
Check out MartinF procedure on the previous pages using shims, trying to use belt tension to compensate for faulty brackets is not going to be a good solution but it looks like some in the assembly line still use it as a trick to make the printer pass.
/Anders
RE: Failed Y-calibration of a new CoreOne
Hey All!
Prusa support got back to me, (I had actually shared this thread with them in a note that I sent). This is the procedure that they are recommending:
Thank you for reaching out to us and choosing our products.
It looks like you're experiencing layer shifting in your prints.
To fix this, we first need to ensure that the frequency (tension) of both belts is close to 85 Hz.
Please measure them following the instructions in the next link and share the results with me: https://help.prusa3d.com/es/article/adjusting-belt-tension-core-one_845048
Once you have the results, please send me a photo similar to the following:
To take a photo similar to the previous one, please remove the top acrylic panel as follows:
Remove the four rivets from the top panel.
The previous photo is to determine whether the gantry (X-axis) is properly aligned with the printer frame.
If it is aligned, you will notice that both sides of the X-axis are fully tight against the front end. However, if you find a gap on either side, it indicates that it is not parallel, so you should follow the procedure below to adjust it:
- Loosen the belts almost completely. Carefully, as the square nuts can fall off the plastic parts when removed completely.
- Check which side sits against the front end (tight side) and which one has to be pushed towards it to touch it (loose side)
- Put an uniwrench or something that is at least 5mm thick between the tight side and the front end and slightly push on the loose side to correct the skew. Video showcase
- Check the alignment again and repeat if needed. In case the tight and loose sides switched, use something thinner and try to balance it out. Tighten the belts again
After making the previous adjustments, you can repeat the print that was experiencing layer shifts and let me know if the issue was resolved.
We will continue to follow up on your case until it is fully resolved.
Thank you for this! This fixed same issue I was having.
Now everything is square, I was able to get the belts tuned to 85hz, and Y-Calibration is working
RE: Failed Y-calibration of a new CoreOne
Check out MartinF procedure on the previous pages using shims, trying to use belt tension to compensate for faulty brackets is not going to be a good solution but it looks like some in the assembly line still use it as a trick to make the printer pass.
Thanks for the suggestion! But I already straightened the gantry following the instructions from support, so it's too late for me to use shims. Also, support has not answered me for a week, so I'm not very happy with this purchase.
RE: Failed Y-calibration of a new CoreOne
Thanks for the suggestion! But I already straightened the gantry following the instructions from support, so it's too late for me to use shims. Also, support has not answered me for a week, so I'm not very happy with this purchase.
I'm not quite clear what the actual problem with your printer is.
If you successfully straightened the gantry by following the instructions from support, the printer should be able to succeed with the Y axis calibration.
Question: does your printer pass the Y axis test successfully when you start it manually from the menu (Control\Calibration and tests\Y axis test)?
Homing problems may have other reasons.
RE: Failed Y-calibration of a new CoreOne
Thanks for the suggestion! But I already straightened the gantry following the instructions from support, so it's too late for me to use shims. Also, support has not answered me for a week, so I'm not very happy with this purchase.
I'm not quite clear what the actual problem with your printer is.
If you successfully straightened the gantry by following the instructions from support, the printer should be able to succeed with the Y axis calibration.
Question: does your printer pass the Y axis test successfully when you start it manually from the menu (Control\Calibration and tests\Y axis test)?
Homing problems may have other reasons.
My printer fails the Y-calibration test after I straightened the gantry. Before straightening, I could pass the test by tightening the left belt 10Hz more than the right, but that caused horrible print quality. Now, with a straight gantry, I can't pass the calibration no matter how I adjust the belts.
RE: Failed Y-calibration of a new CoreOne
If you have followed the instructions from Prusa, you should now have a printer with a straight gantry (no gap on left or right side) and both belts tensioned to 85Hz.
Can you connfirm this state (no gaps, resonance frequency of 85Hz)?
If the printer still fails in the Y-calibration, there may be something wrong with the Y axis bearings.
How big was the gap before you began with the adjustments (when the belts were equally tensioned)?
Did you have to apply a lot of force for bending the brackets?
Can you upload a video of a failing Y-calibration?
RE: Failed Y-calibration of a new CoreOne
I'm trying to show that the gantry is straight from different angles. When I move the gantry, I push from the middle:
https://www.dropbox.com/scl/fi/3wdr7wvuw9bw83j1iznr0/IMG_3526.MOV?rlkey=x4kerw0efjprq1fy0ijxosmad&dl=0
https://www.dropbox.com/scl/fi/tl8tfaslnpyuo16ovugdi/IMG_3528.MOV?rlkey=3p43xy7hbpmrouwm6ek6nn4t2&dl=0
The gap was about 2 mm, but it's hard to tell if I used too much force to straighten it. I adjusted it multiple times, trying to use as little force as possible but enough to make a difference.
The belts should be at 85 Hz. I've used the belt tuner multiple times, tried tuning by ear, and even randomly set different belt tensions, but all attempts have failed.
y-axis test:
https://www.dropbox.com/scl/fi/n6biyyancr4hmxjjcxulp/IMG_3529.MOV?rlkey=oqt9u4h506f9wpe4oodttb4g4&dl=0
RE: Failed Y-calibration of a new CoreOne
Jukka, thanks for uploading the videos!
The grantry alignment looks good, but I'm not so sure about equal tension of the belts. In your first video, when you pluck the belts, the left does sound a bit tighter (more tension). But I may be wrong - it's hard to judge the tension by one pluck.
Calibration video: I think your printer has a problem by moving the head diagonally (45° angle). In one of the calibration trials (beginning at 0:55) you can hear that at the beginning the head does hit the stop of both axles alternatively. In subsequent movements the head moves away from one of the axes - it does only hit one stop in each cycle.
The printer does then starts a new calibration cycle (at 1:05) with the same result. I think there's more resistance in one axis than the other. The printer seems to loose steps in these diagonal calibration movements. I think the steps are lost in the Y-axis.
I do recommed to check the belt tension again (with the belt tensioner app).
When you already have read my recommandation in one of my previous steps, you know that it is important that BOTH brackets are aligned correctly (exact 90° angle). The gantry can be aligned well (like in your printer), but the individual bracket angles may still be off. You can check the situation with the following steps:
1.) loosen tension of both belts
2.) check if the gantry is still aligned perfectly (no gaps on either side)
3.) loosen the three mounting screws that attach the bracket to the X axis carriage on the left side.
4.) check if the gantry is still aligned perfectly (if it is not, the angle of the right bracket is off and can be corrected by shims of - if you are a brave man;) - by bending)
5.) re-tighten the left bracket and loosen the three mounting screws on the right bracket
6.) check if the gantry is still aligned perfectly (if it is not, the angle of the left bracket is off and can be corrected by shims of - if you are a brave man;) - by bending)
7.) re-tighten the screws on the right bracket and check if the gantry is still aligned perfectly
8.) re-tension the belts using the belt tensioner app
If the angles of the individual brackets are off, the resulting forces acting on the bearings of the Y-axis may cause friction and lost steps during calibration.
RE: Failed Y-calibration of a new CoreOne
Thanks for the detailed steps.
After loosening both belts the left side still had a small gap (the same side that had a 2 mm gap before). I fixed this by putting copper tape under the right bracket. Now it feels straight.
I did all the other steps too and it seems good to me. I set the belts to 85 Hz many times. I also tried other belt tensions just to be sure. But it always fails the Y-axis test the same way as in the video at 0:55.
RE: Failed Y-calibration of a new CoreOne
I just checked my belt tensions on a brand new pre-assembled printer using a professional belt frequency meter (Costs nearly as much as a new Mk4) which we use at work for setting belts on high precision machines and measures down to 0.1 Hz resolution.
What did I find, the belts were at 107.0 LH and 107.3 RH Both well above the recommended 85Hz
I have dropped them to 90.2 and 90.3 for now and going to run some tests including the skew test which is what made me question the belts tension in the first place.
My phone did not work to measure belt frequency.
Normal people believe that if it is not broke, do not fix it. Engineers believe that if it is not broke, it does not have enough features yet.
RE: Failed Y-calibration of a new CoreOne
What did I find, the belts were at 107.0 LH and 107.3 RH Both well above the recommended 85Hz
Seems strange that the two belts were so consistent with one another, but so far off the nominal value. Could it be a temperature effect -- was it very warm where you tested?
Alternatively, is there potentially a systematic deviation in the way the Prusa app measures frequency? It would be great if you could get the Prusa app to work and compare it with your high-end tuner. Maybe borrow a different phone, or take off the printer's lid to enable better placement of the microphone (as reported by @taubin here)?
RE: Failed Y-calibration of a new CoreOne
I just tested the phone and the frequency meter using an online tone generator and my headphones and the PRUSA app showed mostly 85 Hz but jumped between 83 and 85 whilst the ridiculously priced belt tester showed 85.1, 85.0 and 84.9 (Always take three readings and average them, well that's how we use these testers.
Must say, I'm impressed with the app's accuracy, but it still stands, the belts arrived at 107Hz and yes they did happen to be that close. Printer was showing 25 Deg C on the internal temperature gauge, room at 18 Deg C.
After a few tweaks, some lubrication manual levelling of the print bed (Adjusting each lead screw to get the level good), the printer is so far printing like a champ.
Although it looks like a heavy slab will need to be purchased to stop the table shaking.
Normal people believe that if it is not broke, do not fix it. Engineers believe that if it is not broke, it does not have enough features yet.