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Layer Shifting/X Axis alignment Issue  

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Tango
(@tango)
Estimable Member
Layer Shifting/X Axis alignment Issue

Using an MKS3+ on this.

It took me a while to work out what my issue is and it boils down to the X axis, either the belt or the stepper motor. 

I had trouble, at first, with print head alignment and, at the time, thought it was a sensor issue. Basically I'd get a message about a forced Z axis recalibration. That was because the printhead would slide all the way to the right, then slide about halfway back instead of going all the way back. So, during the pre-print bed leveling, the head would never go back to 0 on the X axis. As I said, I thought it was a sensor issue, but I found out it was the belt. So I tightened it and it worked fine for a few prints. Then I started having trouble again.

I figured the belt was not as tight as it should be, so I opened up the back of the print head, took the X axis stepper off, cut off a notch on the belt and re-installed it, so it'd be tighter. I re-adjusted the screw that positions the X stepper motor, then re-attached the motor. (Which took a bit of effort because the belt was tighter now.) I recalibrated and things looked fine while I was printing my test squares (a 5x5 grid that covers most of the print bed). I didn't see any issues with the X axis or control. So I started a print and left it. Then I checked on it with OctoPrint and my webcam a couple hours later and had a nice start than a bowl of spaghetti. I looked at the webcam video. Here's a screenshot after it messed up:

I stopped it and the next print was okay. Then, after that, I got this on a similar part:

And then, a little later:

Basically, the print head was not returning to 0 on the X Axis, it was only going halfway back. Later screenshots indicate that at some point it did start returning to 0 on the X Axis.

I found this page about the belts on the MKS3 and checked my belt status. It says the belt tightness should be between 260 and 290. I'm not clear if that's for both X and Y axis, or just one of them. So here's a shot of the status:

It appears both my belts are too tight. I haven't had an problems with the Y axis, but that's not too far off. But, clearly, the X is off. I'm surprised I'm getting this issue with too tight a belt, since I would think a tight belt would keep it from slipping. Or is the belt so tight it might create a problem with the shaft on the motor?

Questions:

1) Is this so tight it's a serious issue? (I'm guessing it is.)
2) Could this be damaging the motor itself? Or could it be stretching the belt?
3) Could the tight belt be causing the problem with the printhead not returning all the way to the left, at X=0?
4) Is the Y axis belt an issue at 240 (since it's below 260?)

I like keeping some parts in stock, so, while looking over this, I've ordered replacement belts and steppers. For now, I'm going to readjust the X belt so I can get a number closer to the specified range. Any additional insight and advice on this is appreciated.

Posted : 24/02/2024 12:33 am
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Layer Shifting/X Axis alignment Issue

I went ahead and adjusted both X and Y belts. I was sure the X belt was loose because when I had problems earlier, I felt it and it was rather loose and very easy to pinch the parts together. That's why I tightened things up and it was after making the X belt as tight as I could that I got the 163 reading. It occurred to me I might be wrong, so I experimented and found I was right - the tighter the belt the lower the number.

As I kept adjusting the belts, I found that if I made them loose enough so the belt test showed anywhere near the specified range of 260-290, the belts were extremely loose - floppy, even.

I would love clarification on this, since if I loosen the belts to put the readings in the specified range, the belts are extremely loose. Am I using the wrong numbers?

Posted : 24/02/2024 4:02 am
Robin
(@robin)
Prominent Member
RE: Layer Shifting/X Axis alignment Issue

The firmware mesurment of the belt tension is not the most accurate thing. Are you aware of this thing: https://www.printables.com/model/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus , it is easy to use and works nicely.

If at first you don't succeed, skydiving is not for you.

Posted : 24/02/2024 10:57 am
Tango
(@tango)
Estimable Member
Topic starter answered:
RE: Layer Shifting/X Axis alignment Issue

The firmware mesurment of the belt tension is not the most accurate thing.

Good to know. When I got the belts to what looked like and felt like it would give me good and consistent tension on the stepper motors and the print head or print bed, the numbers were nowhere near the specified range. (I forgot to take a photo of the stats - it was late at night.)

Are you aware of this thing: https://www.printables.com/model/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus , it is easy to use and works nicely.

I wasn't aware of it. I'll have to order some Prusament PETG to print it. (Although I would think that while other filaments might not be as exact as what the creator wants with that, I would guess they'd be rather close.

Posted : 24/02/2024 5:02 pm
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