Problem: X Axis can be homed only with an extremely loose X belt (with video)
 
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[Solved] Problem: X Axis can be homed only with an extremely loose X belt (with video)  

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eamp
 eamp
(@eamp)
New Member
Problem: X Axis can be homed only with an extremely loose X belt (with video)

After 3 days of tentatives, I've decided to ask for help for a problem I cannot figure it out.
I have a MK3S+ bought about 1 year ago, which has printed flawlessly since the beginning.
Two days ago, after a successful print, I started a second print and the X axis was not homed correctly: the extruder was homed almost at the full right, leading to a failure for the initial homing that is run at the beginning of every print.

After this failure, it has been impossible to start any print, and both the selftest and the Belt test fail on the X axis.

 

I can confirm the following points:

*) I have dismantled and lubricated all bearings, to ensure no sliding problem an linear bearings. The X axis without the belt slides with no effort at all.
*) The Settings -> Move Axis -> X works smoothly
*) There are no obstruction in the left and rear part of the extrusion block, and the block reaches easily both the leftmost and rightmost parts of the X axis. I have followed several forum posts on the "Selftest error! Please check : Axis length Axis X" error and I have re-checked all the hardware components involved, with no success. The fan cable, the rear clips, are all in the right position.
*) the pulley of the X axis motor is in the correct position, with a spacing of about 2.5mm from the stepper. The X belt looks centered on the pulley.

*) The belt test and the self test fail on the X axis. More precisely, these two test can work only if the X belt is extremely loose (with about 1mm backlash, so unusuable for 3D print). As soon as I try to tighten the X belt, the belt test registers an X axis of about 5/10mm length, independently of the initial position of the extruder on the X axis.

 

I have updated the firmware to the latest version, and the problem persists.
Even after a factory reset / all data, the situation remains unchanged. Any ideas about the possible reason?

I recorded a video to try to explain better the printer behaviour:

Best Answer by blauzahn:

my 2 cents: Please check, if the idler bearing is defective. It is a known weak point. The bearing of the idler can be changed. It is a regular roller bearing.

 

Does the fully assembled extruder move with ease as well? When you reassemble the x-carriage back plate, please verify the position of the linear bearing's zip ties and do tighten the 4 screws of  the cover only very ligthly.

 

For a test, I suggest to disassemble temporarily the pulley and try to pull the belt by hand. Pulling at the cables (please don't) does not yield the same loads on the bearings.

 

The linear bearings sound a bit noisy though. Maybe it is a good idea to get a set of spare rods and linear bearings. Just in case. A while ago, I had a groove in one of the rods and was very happy to have a spare one at hand.

 

Posted : 01/07/2021 6:52 pm
eamp
 eamp
(@eamp)
New Member
Topic starter answered:
RE: Problem: X Axis can be homed only with an extremely loose X belt (with video)

None has any idea or suggestion? Should I explain better the problem?
Do any of you think it could be a controller problem?
😭 😭 😭 

Posted : 04/07/2021 5:06 pm
Diem
 Diem
(@diem)
Noble Member
RE: Problem: X Axis can be homed only with an extremely loose X belt (with video)

Have you checked the X-idler?  If the bearing is failing it may allow the belt to slip when loose but jam when tight.

Cheerio,

Posted : 04/07/2021 5:34 pm
eamp
 eamp
(@eamp)
New Member
Topic starter answered:
RE: Problem: X Axis can be homed only with an extremely loose X belt (with video)

You mean the screws that fix the X motor and allow to tension the X belt?
As soon as I tension the X belt (even with a moderate tension), the homing procedure fails, like in the video.

Posted : 04/07/2021 5:42 pm
blauzahn
(@blauzahn)
Estimable Member
RE: Problem: X Axis can be homed only with an extremely loose X belt (with video)

my 2 cents: Please check, if the idler bearing is defective. It is a known weak point. The bearing of the idler can be changed. It is a regular roller bearing.

 

Does the fully assembled extruder move with ease as well? When you reassemble the x-carriage back plate, please verify the position of the linear bearing's zip ties and do tighten the 4 screws of  the cover only very ligthly.

 

For a test, I suggest to disassemble temporarily the pulley and try to pull the belt by hand. Pulling at the cables (please don't) does not yield the same loads on the bearings.

 

The linear bearings sound a bit noisy though. Maybe it is a good idea to get a set of spare rods and linear bearings. Just in case. A while ago, I had a groove in one of the rods and was very happy to have a spare one at hand.

 

Posted : 04/07/2021 5:49 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Problem: X Axis can be homed only with an extremely loose X belt (with video)

@eamp

The original Prusa x-idler pulleys are not a high quality product.

These bearing has also failed twice on my MK3 (and also the Mini) printer. I bought other pulleys (GT2 16t) and mounted 2 higher quality MR63 bearings. Since 3 years - silence.

MR63ZZ

wbr,

Karl

 

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 04/07/2021 5:54 pm
Diem
 Diem
(@diem)
Noble Member
RE: Problem: X Axis can be homed only with an extremely loose X belt (with video)
Posted by: @eamp

You mean the screws that fix the X motor and allow to tension the X belt?

No.  The other end of the belt.

Cheerio,

Posted : 04/07/2021 6:25 pm
eamp
 eamp
(@eamp)
New Member
Topic starter answered:
RE: Problem: X Axis can be homed only with an extremely loose X belt (with video)
Posted by: @blauzahn

my 2 cents: Please check, if the idler bearing is defective. It is a known weak point. The bearing of the idler can be changed. It is a regular roller bearing.

....

For a test, I suggest to disassemble temporarily the pulley and try to pull the belt by hand. Pulling at the cables (please don't) does not yield the same loads on the bearings.

...

Yes, you are right. When I disassembled the X axis to lubricate the bearings, I wrongly tightened the screw on the idler too much, blocking it.
Now the mk3s+ is back to life, has passed the full calibration and is printing again.
Still I don't know what caused the failure at the beginning, but now it is solved.

Thank you!

Posted : 04/07/2021 7:27 pm
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