RE: Belt tension adjustment
Not everyone wants to screw on a new printer themselves.
I would try to loosen the belts and move the X axis all the way to the front.
Then I would slightly loosen the screw of the metal bracket on the X axis.
Now the X axis should be parallel to the frame.
I would gradually tighten the screws again and observe whether and when the gantry starts to warp again.
I would either try tightening only the screws that do not cause warping or try using shims.
Then bring to the recommended tension and check whether the gantry is still parallel.
This would at least allow you to narrow down the sources of error.
RE: Belt tension adjustment
I just got mine today and it has the exact same issue, only the gap is 2-3mm.
Ugh. I have the same issue. Are y’all opening tickets with Prusa?
RE: Belt tension adjustment
I'm waiting for my kit, and i've added then accelerometer as well in the order.
Is there a way to check the belt tension using the accelerometer? If not, shouldn't there be an option like this, especially for the Core One, seeing how important it is for them to be tightened the same?
RE: Belt tension adjustment
Is there a way to check the belt tension using the accelerometer? If not, shouldn't there be an option like this, especially for the Core One, seeing how important it is for them to be tightened the same?
Even better, there is a way to check the belt tension without the accelerometer. 😉 Just use Prusa's regular tuning app, which now includes instructions for the Core One and knows about the 85 Hz target frequency for its belts' resonance.
RE: Belt tension adjustment
I know about the app, but when i used it with my mini, it shows the belt as too tight, even though the PETG tool has it as being just right, sitting in the middle of the marks.
also, when i tried using the app, the reading kept changing. So its up to if you are strumming just right, holding the phone at just the right place, and your phone’s mic hole is gunk free ;). Even if it looks clean, lint and dust gathers.
With a built in accelerator, i guess it could start vibrating and then telling you “yeah, keep going, keep g… There!”
RE: Belt tension adjustment
Wouldn't there be a challenge in that the resonance frequency of the oscillating print head is affected by both belts in parallel? No matter whether you excite the motion via one or both motors at a time, both belts are always pulling at the print head and are hence contributing to a compound spring constant.
It might be impossible to distinguish two correctly tightened belts from one too tight, another too loose, via the accelerometer. Or is there some clever trick which other CoreXY printers use to tell the two contributions apart?
(I believe the Bambu Lab printers use the accelerometer to diagnose that "something is wrong" and instruct you to check the belt tension. But they then use their spring-loaded, semi-automatic tensioners to actually set the individual tension on the two belts.)
RE: Belt tension adjustment
Hm. Don’t know what bambu does to be honest. If only one motor is pulling at a time, it would still have the wrong readings you mean since its coupled with the other one.
RE: Belt tension adjustment
If only one motor is pulling at a time, it would still have the wrong readings you mean since its coupled with the other one.
Yes, that's what I would expect. Imagine a mass suspended from the ceiling on two springs which are arranged in parallel. If you wiggle one of the springs to excite a vertical oscillation of the mass, the other spring will still contribute to the total spring constant. (Which, together with the mass, determines the resonance frequency.)
RE: Belt tension adjustment
I had horrible luck with the belt tuner in the app, and ended up using the website version instead. That worked much better.
RE: Belt tension adjustment
There is no way to check belt tension with the accelerometer.
The only good ways to measure belt tension is via frequency (belt tuner) or by measuring flex.
RE: Belt tension adjustment
So update on my saga. My old printer was returned, new one sent, with the belts both at 85Hz using the tuner, there was a _slight_ angle to the X axis where it would not sit flush on the right side when the left side was flush. Prusa support ended up having me loosen the belt on the left side, in my case, prop something small in front of the left stop, and very gently pull on the right (I assume bending the brackets gradually), rinse and repeat multiple times, re-tightening the belts each time checking for skew.
I am not suggesting anybody else follow this procedure, but clearly Prusa support is aware of this issue. You have to be extraordinarily careful and apply only very light tension, and repeat multiple times. You can easily break the plastic parts if you use too much pressure, so I highly suggest engaging with Prusa support before doing anything. It's a lot of work, but I can now report my Core One has both belts at 85Hz and now sits flush against the end-stops at the front on both sides.
RE: Belt tension adjustment
So even after they have been made aware of the problem, they still ship printers where the gantries are not properly squared? And instead tell customers to bend things in the field, risking damage to the bearings? I am not impressed.
RE: Belt tension adjustment
Just a heads up: I had approximately 5mm space on one side which was kind of possible to compensate by different belt tensions on left and right side but calibration of the Y axis would fail. It turned out I did mount the X axis pulley the wrong side (teeth further from the motor instead of closer). After reversing it, it was aligned perfectly.
The step that needs to be double-checked is https://help.prusa3d.com/guide/5-corexy-assembly_835522#843284.
RE: Belt tension adjustment
Just to encourage everybody who is building his kit, conversion or preassebled.
maybe I was just lucky, but when building my conversion kit I took special care when installing the xy assembly. I had to unscrew the linear rail from the brackets several times, bend the brackets ever so lightly and test again. Eventually I got it square. ( wheel tilting the xy frame slightly the linear rail slides to the front and back without gap.
Upon finish I tensioned the belts with the tuner to 85—87 herz. Since adjusting one the other changes as well, so that took quite some time. In that phase I compared the belts by ear.
and I was very surprised, that the all calibrations successfully finished on the first run.
so it’s doable 😁
btw. I whited to install the vesonite bearings on y. But I found there where binding when tightening the linear rail on the brackets. Seems the normal bearings ar much more forgiving.
RE:
btw. I whited to install the vesonite bearings on y. But I found there where binding when tightening the linear rail on the brackets. Seems the normal bearings ar much more forgiving.
Did you adjust the distance and parallel alignment of the Y rods? The two rods over-constrain the movement of the X gantry, and I am surprised that Prusa's assembly instructions don't include this step. (Or at least they did not when I built my early kit.)
Loosen the screws which hold the mounting blocks for one of the Y rods, then push the X gantry all the way back and forward. This will nudge the Y rod into the correct position. Lightly tighten the mounting block screws, repeat the X gantry movement, then tighten the mounting blocks fully.
RE: Belt tension adjustment
Good advice. I will check .