Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?  

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

Is it always at the same height can you get video and do the motors move down or does it slip

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

I have other examples as well  No consistent  height  

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

Posted by: @paul-beard

I have other examples as well  No consistent  height  

Ok print a small cube that's as tall as the printer can print then see if you can video when it does slip 

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

Two other examples of damaged workpieces. The height is not relevant, since all 3 pieces had reached a different Z-height before being knocked off the printbed. The white piece eventually printed successfully on a different machine so there is nothing wrong with the file itself. The red piece in the earlier post later printed successfully on the Prusa, in the same filament. 

Why did you start a new thread?

Plase show us the undersides of the prints above.

Cheero,

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

The undersides of the pieces are solid. The workpieces (another last night) were knocked off with force, they did not fall over due to lack of adhesion. The scorch marks on the pieces are right there to be seen and I have seen and heard the printhead knock a piece over. What I want to know if why the machine fails to follow the gcode up the Z-axis and knocks the pieces over. I assume this is a mechanical fault, since the same pieces have printed correctly on the same machine and another one. 

The undersides of the pieces are solid

Splendid.  Show us.

Cheerio,

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

Instead of perseverating about the base, take a look at the scorch marks and divots taken out by the impact of the print head on the obviously firmly adhered workpiece. Those would not happen if the piece was not firmly on the build plate. 

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

Posted by: @paul-beard

Instead of perseverating about the base, take a look at the scorch marks and divots taken out by the impact of the print head on the obviously firmly adhered workpiece. Those would not happen if the piece was not firmly on the build plate. 

We needs video of it doing it as I've already asked for 

take a look at the scorch marks and divots taken out by the impact of the print head

Not interested, those are probably just symptoms,

on the obviously firmly adhered workpiece.

Not obvious.

Cheerio,

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

I'm sure these errors can be attributed to bed adhesion or an unclean print bed. If only there was a video to prove this happened. 

I am more inclined to think this machine has some issues that can't be so easily blamed on the person trying to get useful work out of it. 

Thank you.

I'm sure these errors can be attributed to bed adhesion or an unclean print bed.

You are correct.

The white part is unclear but both the red and grey parts first layer's 'Z' calibration is too high, not enough squish.

The red part also shows fingerprint patterns and signs of a badly abraded print surface - I think you said elsewhere that this is a second hand school machine, and, also in another thread, you outlined a cleaning procedure that should have dealt with ordinary grease marks, these must be something else.  The print sheet used for that part is probably ruined.

The shape of the red part is liable to warp so bed adhesion is critical, the least bit of lifting will put it in the way of the nozzle.

The grey part *might* have been sliced at a slight angle to the bed, or the bed might need a levelling adjustment, which will not be clear until the first layer 'Z' offset is recalibrated.  If so this page might be useful: https://help.prusa3d.com/article/bed-level-correction_2267 - but calibrate first.

You appear to have more than one print sheet; remember that each will have a different calibration value, store them in the LCD menu and tell the machine when you switch sheets.

this machine has some issues that can't be so easily blamed on the person trying to get useful work out of it.

This is common when a machine is open for general use by poorly supervised newbies who's idea of maintenance planning is based around years out-of-date youtube videos.  It's recoverable, you're just the one who has to remedy the misuse.

Cheerio,

RE: Prusa Mk3S+ can't/won't advance in Z, hits workpieces and knocks them off printbed: why and how to fix?

Unless the grey first layer rectangle is printed properly, tying to try to print parts is a waste of time.

Do the lines in the single layer test stick together and form a solid plane if you pick it up? As @Diem already stated, it looks like you have to go further down with the nozzle (z-live more negative). What filament do you use, PLA, PETG, which brand? The plate is similar to the textured one by prusa but not the original one, right? I ask to get an idea about the squish you may need. The textured sheet is good for rather sticky filaments like PETG or FLEX, less so for PLA (see prusa materials). Nowadays I mostly use the satin sheet as a nice allrounder. On the textured sheet you have to squish the filament substantially deeper so that it does adhere not only to the "hills" of the texture but also to is "valleys". Otherwise the surface is too small to get enough adherence. Just do not go overboard. You are too deep when the upper surface starts to become rough or distortions ("zebra pattern") perpendicular to the filament lines occur. Your first layer is good when your single layer rectangle is smooth and when you fold it does not crack too easily.

Please do not place parts onto the sheet to make photos of them. I never touch the sheet with my fingers but let the sheet cool down and use paper kitchen towels to pick the parts. As a scraper I use one for ceran board for kitchen stoves, albeit degreased, only for the printer and with slightly rounded corners so that I do not damage the sheet. This way, once you have degreased the sheet with plain dish-soap, flushed with plenty of hot water and immediately dried with fresh paper towels, I can print many dozens of parts before I have to repeat this. I do use neither IPA nor Windex or alike. On the satin sheet, I occasionally use a very light touch of glue stick when I print FLEX, ASA or alike. Not to increase adhesion, but on the contrary rather to limit it.

On newer firmware versions, you can store the z-live offset for several sheets. Then you can select the stored offset for the sheet you put onto the printer instead of noting the z-live value down and readjust it every time you change the sheet. That's what @Diem ment by "telling the machine".

Happy printing!