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Hesitation in X and Y axis in positive direction only  

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Gravity
(@gravity)
New Member
Hesitation in X and Y axis in positive direction only

Hey all, I've been having a blast with my printer, but ran into a bit of an issue lately...

To start, I've ended up with a scratched top x-axis rod that Prusa is replacing under warranty (probably the best customer service experience I've had ever...) but as I've continued to use my printer a bit I noticed something:

About halfway through the axis, traveling in the POSITIVE direction ONLY, there is a slight hesitation like the bearings hang up on the rods for a split second. This is happening on both the X and Y axes and is particularly noticeable during the self test when you can see smooth motion for a while, then the hiccup, then continued smooth motion, and then a completely smooth return to 0 from the axis upper limit.

Does anyone else experience this? I feel like I see it while printing as well. Is this likely an issue with the rods being scratched and I now likely have a damaged Y-axis rod/bearing? I'm a little bummed, as I only have about 75 hours of printing on the printer at this point. Prusa really should direct us to clean and properly lube the bearings and rods in the assembly instructions. I personally know that the rust-preventative oil is NOT meant to lubricate, but still decided to follow the instructions as written. Kicking myself a bit now...

Responses are appreciated! Thanks!

Posted : 21/05/2021 6:38 pm
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(@)
Illustrious Member
RE: Hesitation in X and Y axis in positive direction only

This time around, clean and grease the bearings before you install them.

Bearings seizing is exactly what damaged the rods in the first place, and seizing causes the axes to stall.

Posted : 22/05/2021 12:26 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Hesitation in X and Y axis in positive direction only

@Gravity did you lubricate?

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Chuck H
3D Printer Review Blog...
Posted : 22/05/2021 12:28 am
Gravity
(@gravity)
New Member
Topic starter answered:
RE: Hesitation in X and Y axis in positive direction only

I understand that the bearings seizing scratches the rods, but was hoping there would be some weird alternative answer to why there might be a little hesitation in the travel. 😩 So it sounds like I can expect a scratch somewhere on the Y axis rods when I get the printer disassembled... That's a bummer.

I DEFINITELY plan to clean and regrease them before installation. Like I said I knew better when I first assembled, but followed the assembly instructions with some faith that maybe Prusa knew something I didn't. This is my first time dealing with linear bearings, so I thought maybe I just didn't know something different about them. Live and learn, I suppose.

Painful to take apart the printer, though. It was (and still is) performing quite well. Looks like I'll stop using it until I can verify if those Y axis rods are okay, though. Thanks!

Posted : 22/05/2021 11:34 am
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(@)
Illustrious Member
RE: Hesitation in X and Y axis in positive direction only

@gravity

I can't understand why Prusa continues to propagate this lie they ship greased bearings. They finally have a note about cleaning and greasing the bearings in their Mini guide ... but still say those same bearings don't need grease in the Mk3 guide. I just don't get it.

And yes, the Y will have the same issues. But you might be lucky. X has a different stressor than the Y axis. The rods on X can be squeezed together if the support bracket rod spacings aren't printed to the same precise size of the extruder bearing spacing. So the bearings are bending the rods as the extruder moves along. First sign of this is dark rubber abrading from the grease seals showing up on the rods. If there is oil or grease, the rubber dust is collected in the film ridge formed at either end of the rod.

Regarding the stutter.  There are a few things that can cause the printer to stop mid path, all bad. An SD card read error, the filament sensor forcing an interrupt, the heating system pausing for temps to recover, etc. But a quick check of the crash history will probably show the cause is seizing (assuming you are running in normal mode). 

 

As a suggestion, get some PETG and print spare X-Axis supports. Removing the rods has cost more than one person a lot of down time when they crack the supports in the process and have to wait for spares from the Czech Republic. They print easily and quickly. I made two sets, just in case... lol.

Posted : 22/05/2021 3:39 pm
Gravity
(@gravity)
New Member
Topic starter answered:
RE: Hesitation in X and Y axis in positive direction only

Yeah, definitely. Given that the X and Z axes will be apart I was going to do a color swap but the color of PETG I wanted is out of stock! Such is life. Definitely will print spares anyway. Is there an easy way to check the crash history? Just plug in a computer with the proper drivers, I assume? I'll have to give it a try. Is there any warning from the printer when a "crash" is detected, cause all prints have been relatively smooth and the selftest passes no problem. I've never seen the printer stop in the middle of a print due to a crash and I watch my prints reasonably closely.

If it's just the "Fail stats" my lifetime fail stats are all 0. No failures in anything that seems to be tracked. Unless there is a more advanced version of the crash history, I'm not sure where else to look.

This post was modified 2 months ago by Gravity
Posted : 22/05/2021 4:20 pm
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(@)
Illustrious Member
RE: Hesitation in X and Y axis in positive direction only

If you run in stealth, crashes aren't logged.

Posted : 22/05/2021 5:04 pm
Gravity
(@gravity)
New Member
Topic starter answered:
RE: Hesitation in X and Y axis in positive direction only

Ah, well, I've only ever run one print in stealth mode to my knowledge. Every other time I've made sure it is all normal and my crash detection is on.

Posted : 22/05/2021 5:35 pm
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