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Y-axis bearing bolt touching bed from below  

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Ratman
(@ratman)
Active Member
Y-axis bearing bolt touching bed from below

Hi all,

I just finished building my first mk3S+ printer and everything works fine except for the fact that the screws are touching the bed from below. I triple checked everything and cant find anything i did wrong. I also contacted Prusa and they confirm its assembled correctly, but agree the screws shouldn't stick out like that.

What i've tested:
Bolt length should be 12mm, it is
Frame thickness is 6mm, thats normal

bearing clip is 0.7mm thick, thats normal too

The 6x6x3t space is only 5,5mm high, which is normal according to prusa

The bolts in the manual look way shorter (~10mm) So maybe they changed something?

I have fixed it now with some m3 washers added to the spacers.  It works fine like this, but i have to assemble 5 more and i really want to make sure i did not make a mistake somewhere. 

Does anyone know what is going on?

Thanks!

 

Some pictures for illustration:

bolts touching bed:

 

Assembled bearing:

 

Bolts not touching anymore because I added washers:

Bolts in manual looking way shorter??

Publié : 08/12/2022 11:05 am
Tim Weston
(@tim-weston)
Estimable Member
RE: Y-axis bearing bolt touching bed from below

Out of interest, I just checked my printer for this. I also assembled it from the kit.

The final installation looks the same as yours with the bolts protruding from the nuts. However the bolts do not (quite) touch the heated bed - I can get a piece of paper between the bolt-end and the bed.

Logically, that would be right as 12-6-0.7 = 5.3 which is 0.2mm less than the 5.5mm spacer.

Other than bad luck with tolerances, I can offer no definitive reason for why you are seeing this.

That said, the pictures in the manual would definitely suggest that shorter (10mm?) bolts are being used for that illustration.

Cheers,

Tim

 

Publié : 08/12/2022 6:28 pm
RandyM9
(@randym9)
Honorable Member
RE: Y-axis bearing bolt touching bed from below

Try flipping the bolts ‘upside-down.’ It looks like you might have enough clearance in that orientation. At least until you an get some shorter screws. 

Publié : 08/12/2022 11:14 pm
Ratman
(@ratman)
Active Member
Topic starter answered:
RE: Y-axis bearing bolt touching bed from below

Thank you for checking, i guess it's just how it is
I think 0.2mm is not enough margin, frankly. So i will be adding spacers anyway.

Publié : 10/12/2022 8:59 am
Ratman
(@ratman)
Active Member
Topic starter answered:
RE: Y-axis bearing bolt touching bed from below

I tried the bolt upside down, but the nut is too big and doesn't fit in the bracket. I will try the shorter bolts (10mm), but i think they dont reach the nylon part of the nut. In that case the nuts can vibrate loose, so thats no good.

Publié : 10/12/2022 9:03 am
RandyM9
(@randym9)
Honorable Member
RE: Y-axis bearing bolt touching bed from below

Did you put the washers under the brackets? Not seeing them in your pic.

Publié : 11/12/2022 4:26 am
Ratman
(@ratman)
Active Member
Topic starter answered:
RE:

The washers are underneath the 6x6x3 spacers. So the bed sits slightly higher and won't touch the bolts from the y-axis.

Publié : 12/12/2022 8:28 am
Netpackrat
(@netpackrat)
Reputable Member
RE: Y-axis bearing bolt touching bed from below

It's possible that will be enough of a height increase to induce a Z calibration error.  Far better to shorten the screws slightly.

Publié : 12/12/2022 10:01 pm
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