why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?  

Clean your build sheet thoroughly.

What do your fail stats say about recent prints?

Cheerio,

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

The build sheet is/was clean. The work piece didn't fall off, it was hammered on by the extruder and finally broken loose. Fail stars reveal nothing, all zeros. 

The work piece didn't fall off, it was hammered on by the extruder and finally broken loose.

So the part was lifting off the print sheet at one end.  The commonest reasons for poor adhesion are poorly adjusted first layer 'Z' offset calibration and dirty print sheets.

Which filament are you printing on what type of print sheet?  [PLA is best on smooth or satin, PETG on textured or satin, Flex on smooth with glue]

Fail stars reveal nothing, all zeros.

OK, so the first recourse is general maintenance and lubrication:  Have you kept up with https://help.prusa3d.com/en/article/i3-printers-regular-maintenance_2072

and try a drastic sheet clean; rub neat dishwashing detergent[Dawn/Fairy] into the surface, wait ten minutes, then rinse clean with very HOT water, handle by the edges only.

Cheerio,

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

No, it was not lifting off the bed at one end. It was adhered very well, took quite a solid knock from the extruder to break it free after being burned by the extruder. You can see the burn marks in the attached image. I am running the same job now and it is almost complete. But this has been a problem on several recent jobs where the extruder does not change levels and hits the workpiece repeatedly, moving from left to right, burning the piece and eventually dislodging it from the printbed. Adhesion was good in this case, and perhaps in the others as well. The firmware update today seems to have resolved it (fingers crossed). I agree that soap and water is the best cleaner, and I have nitrile gloves by the machine to keep my fingers off off the build plate. 

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

Posted by: @paul-beard

No, it was not lifting off the bed at one end. It was adhered very well, took quite a solid knock from the extruder to break it free after being burned by the extruder. You can see the burn marks in the attached image. I am running the same job now and it is almost complete. But this has been a problem on several recent jobs where the extruder does not change levels and hits the workpiece repeatedly, moving from left to right, burning the piece and eventually dislodging it from the printbed. Adhesion was good in this case, and perhaps in the others as well. The firmware update today seems to have resolved it (fingers crossed). I agree that soap and water is the best cleaner, and I have nitrile gloves by the machine to keep my fingers off off the build plate. 

On the mini There was a firmware bug like this never heard of it on mk3( I presume you have mk3 since you posted in mk3 topic) if it happens again see if you can get a video 

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

I was on the verge of taking a video when it finally succeeded in knocking the piece off the bed. The still picture above tells some of the story, I think. I re-ran the job after the firmware update and it completed without issues. So who knows? It was somewhat confused from an earlier firmware update that I had to roll back, the screen displayed odd characters. So maybe that was part of it. 

Also, still wondering what else I can do to get the self-test to complete. This was a factory-built machine but the wire bundle was still a bit too bulky. I have done all I can to move it away from the ends of travel but it still fails sometimes. 

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

Posted by: @paul-beard

I was on the verge of taking a video when it finally succeeded in knocking the piece off the bed. The still picture above tells some of the story, I think. I re-ran the job after the firmware update and it completed without issues. So who knows? It was somewhat confused from an earlier firmware update that I had to roll back, the screen displayed odd characters. So maybe that was part of it. 

Also, still wondering what else I can do to get the self-test to complete. This was a factory-built machine but the wire bundle was still a bit too bulky. I have done all I can to move it away from the ends of travel but it still fails sometimes. 

 

If you can take a video of the self test insuring we can see the lcd and print head that could help

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

Sorry, I have done a factory reset/calibration and a bit of overdue maintenance since I posted. It's not my machine so I have no idea when this was all done last. Canned air through the chassis and fans, a little white grease on the rods, and all seems well. Still not printing well but that's a while different thing. I don't think much of the eyeball method of setting Z: a sheet of paper seems to work better and faster. 

Please show us the underside of one of the failed prints.

Cheerio,

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

The underside isn't that interesting, it's the top layer turning to spaghetti or being dragged off the bed that's annoying. There is no reason I can find, the machine did fine yesterday after the firmware update, ran the same job it had failed on the day before. Today? Several adhesion failures, until I broke down and did a full reset/calibration. The printbed gets cleaned w soap and water between attempts so I can't work out where it's going wrong. It's doing fine now, a couple of hours into a 9 or so hour job but it has taken all day to get here. 

The underside isn't that interesting,

Just assume the underside is interesting to us.

Cheerio,

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

Two samples, top and bottom: 

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

Posted by: @paul-beard

Two samples, top and bottom: 

 

 502e8564-img_8513.JPG

Ok print a square the size of the bed 1 layer thick as soon as it finishes take a photo and share it

I think you've spotted it @hello - but I'd like to take a different tack.

@paul-beard, please save your project as a .3mf file - load it, slice it but don't bother with the gcode.

Then:

Files > Save Project as

Zip the .3mf and post it here. It will contain both your part and your settings for us to diagnose.

Cheerio,

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

Posted by: @diem

I think you've spotted it @hello - but I'd like to take a different tack.

@paul-beard, please save your project as a .3mf file - load it, slice it but don't bother with the gcode.

Then:

Files > Save Project as

Zip the .3mf and post it here. It will contain both your part and your settings for us to diagnose.

Cheerio,

Yeach looks like the bed isint level but I also like the way your going so please do both @paul-beard

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

OK, hold up…if the bed isn't level how am I only finding this out now? What is that 9 step mesh leveling process doing? I suspect there are some heating problems as well, inconsistent heat across the surface but haven't dug into that. First, explain this level issue. 

FWIW, I got a large workpiece off the bed this morning, 10 hours in the making, and it looks fine, the bottom is smooth and even. 

Nothing is yet certain.  Just supply a .3mf project file from one of the prints that fails repeatedly.

Cheerio,

RE: why does my machine stop on the Z axis and scorch prints before knocking them off the printbed?

Posted by: @paul-beard

OK, hold up…if the bed isn't level how am I only finding this out now? What is that 9 step mesh leveling process doing? I suspect there are some heating problems as well, inconsistent heat across the surface but haven't dug into that. First, explain this level issue. 

FWIW, I got a large workpiece off the bed this morning, 10 hours in the making, and it looks fine, the bottom is smooth and even. 

LIke diem says nothing Is certin only suspect so please provide 3mf file and print a 1 layer square that fills the bed and then show us a picture 

RE:

3mf file, two images of the aborted job, stopped when it started peeling from the corner.