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battincld
(@battincld)
Active Member
new printer crashes

I have a question about crashes....

I have two MK3S printers.  One has never had a crash in the 2 months I've had it.  The other is only a week old and has had 28 crashes between 2 prints.  16 of them on one print, 12 on another.  Everything else has printed fine.   The two prints that had crashes printed fine on the other MK3S.  Can crashes be print-job specific?

Posted : 15/04/2020 9:21 pm
Neophyl
(@neophyl)
Illustrious Member
RE: new printer crashes

Not usually.  A crash is detected by the firmware due to an increase of stepper motor current past the threshold set in firmware.  Its usually an indication of friction in the bearings.  Either through improper assembly from over tightening or more likely because the Prusa assembly instructions are woefully inadequate in telling people that the bearings come pre-lubricated. 

They are not. 

They are shipped with an anti rust packing grease.  This can last a few months or it can last less than a week.  When assembling it is always best to clean out the bearings of this packing grease and use a proper bearing grease.  This results in many many months of trouble free use. 

In the short term you can apply some thin oil such as sewing machine oil or similar to the rods and work the bearings back and forth and then wipe off the excess oil.  The bearings have a black seal which is designed to keep dust and debris out and the grease in but a thin oil will work its way under to lubricate inside.  However this will only last awhile before you have to apply more.  Its an OK stopgap measure until you decide to disassemble and do a proper job of greasing the bearings (which has to be done periodically anyway).

Posted : 15/04/2020 10:25 pm
Agkirk
(@agkirk)
Estimable Member
RE: new printer crashes

I used synthetic bearing oil sold by skateboard shops.  Seems to work fine for the last month.  

Posted : 16/04/2020 12:02 am
battincld
(@battincld)
Active Member
Topic starter answered:
RE: new printer crashes

@neophyl

I should have mentioned, I bought it pre-assembled.  Should I assume the bearings were adequately lubricated?  I have the little white tube of lubricant that came with the printer but isn't that just for the rods?   Thanks for the info btw

Posted : 16/04/2020 1:48 am
Neophyl
(@neophyl)
Illustrious Member
RE: new printer crashes

@battincd

I'm not privy to the Prusa assembly method, however given their build manual instructions you take a guess.

The little tube of synthetic grease is a very recent addition to the kitting list sent out with the printer, so they know there have been issues.  Sticky bearings down to poor lubrication make up probably 25-50% the problem threads on this forum. It causes anything from homing issues, layer shifts, unable to calibrate etc. 

The bearings run on the rods, the lubrication needs to be inside the bearings to be effective.  You can apply the grease to the rods but its too thick to get much past the seals on the bearings (unless they are shot too).  So while it will work it will be less effective than a thin machine oil.  Also you don't want excess oil or grease on the rods as they will attract dirt which sticks to the oil/grease which is why cleaning the excess off once you have worked an axis back and forth over the oil is important. 

That grease in the little tube needs to go inside the bearings which unfortunately means disassembly to do a proper job.   Once you decide to go that far then getting some decent bearing grease in a bigger tube and printing off one of the bearing grease applicator nozzles on thingiverse makes the process much easier and less messy.

On the first printer I built from the kit I followed the instructions and didn't lubricate.  I got about 2 months printing before running into issues (I was lucky).  I then ran with adding a bit of oil every 3-4 prints for several months before I got so annoyed with having to do it.  By that point I'd decided to do some modifications to the printer anyway so took it as an opportunity to do things in one go.  Stripped it down, greased the bearings and inspected the rods (as dry bearings can score the rods making new ones necessary), did all my parts upgrades and in the 8 months since I haven't had a single problem related to bearings.

Posted : 16/04/2020 6:08 am
towlerg
(@towlerg)
Noble Member
RE: new printer crashes

@neophyl

Silly question but if the bearings are sealed, how do you get the grease into them? You mentioned a bearing grease applicator, does that in some way "break" the seal to allow the grease in or is it just pressure?

This post was modified 5 years ago by towlerg
Posted : 16/04/2020 12:27 pm
Neophyl
(@neophyl)
Illustrious Member
RE: new printer crashes

@towlerg

The bearings work by having lots of really tiny steel balls that run in 'races' inside, think little race tracks.  To properly lubricate them you must remove them from the rods which then allows access to the races and steel balls.  This is then where the grease goes in, although not too much as you dont want excessive grease actually slowing things down.  The black seals on the end are there to keep dirt out and grease in. The only 'seal' against the rod.  Its why you have to be very carefull when inserting the rods as you can dislodge the balls and that can ruin your bearing.  While its possible to reinsert them (if you can find them) it is a royal pain in the rear.  I speak from experience, you only do it once 🙂
They say a picture is worth a thousands words.

 

Posted : 16/04/2020 2:43 pm
towlerg
(@towlerg)
Noble Member
RE: new printer crashes

Thanks for the info (especially the picture, worth a thousand words etc.). Just to confirm, you can remove the bearings from the rods and all the balls will not fall out.

Posted : 17/04/2020 12:45 pm
Neophyl
(@neophyl)
Illustrious Member
RE: new printer crashes

@towlerg

Not on their own no, they don’t fall out. It’s when inserting the rods if you aren’t square you risk pushing them out. 

Posted : 17/04/2020 3:49 pm
Tyler
(@tyler)
New Member
RE: new printer crashes

What axis is the printer crashing in? It might be helpful to see if it's a specific axis to troubleshoot. I was getting a lot of crashes in my Y axis and traced it down to the belt pulley rubbing on the motor housing.

This post was modified 5 years ago by Tyler
Posted : 18/04/2020 10:45 pm
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