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Part breaks free at same place every time  

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CybrSage
(@cybrsage)
Honorable Member
Part breaks free at same place every time

I am printing a calibration cube and it breaks free from the printing surface (textured PEI) and fails at the same point every time, regardless of the layer height in which I slice it (tried 0.2, 0.15, and 0.1 - all done in PrusaSlic3r).  I have a picture of the height it reaches before it fails, as well as the bottom so you can see the first layer.  As you can see, it is not very tall at all, especially considering it is supposed to be a 20mm cube.

I did a full system reset and ran the Setup Wizard, all is good.  I did the first layer calibration until it could not be removed by my fingernail easily and felt like a nice squish.  And I sliced the part in several layer heights.  There are no blobs on my heat block (pretty clean and shiny, actually).  I cleaned the surface with alcohol, then washed with Dawn, dried, and cleaned with alcohol again.  Nothing changes the result.

I also sliced a completely different calibration cube and its pics are the last two, sliced in 0.3mm.  No change.  Even the skirt got moved when the block slide against it.

As an aside, anyone know how to get ABS marks off the textured PEI sheet?  You can lightly see four round circles on the sheet, where I printed glow in the dark abs ghosts for Halloween.

Any idea as to what may be going on?

Postato : 26/06/2019 4:05 pm
gnat
 gnat
(@gnat)
Noble Member
RE: Part breaks free at same place every time

Really sounds like an adhesion issue. Have you tried the other side of the plate? Maybe try printing in a different location of the plate? You mention ABS residue, that could be the issue if you are printing on top of it.

MMU tips and troubleshooting
Postato : 26/06/2019 4:12 pm
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CybrSage
(@cybrsage)
Honorable Member
Topic starter answered:
RE: Part breaks free at same place every time

I tried both sides of the plate, no difference.  I am flashing the firmware again, just to make sure everything went fine with the last update...cannot hurt.  I am also going to slice it in S3D and see if that makes a difference.

Postato : 26/06/2019 4:23 pm
muddymaker
(@muddymaker)
Estimable Member
RE: Part breaks free at same place every time

Judging by your photo it looks as though your first layer height is incorrect. It really does need to be perfect, especially on the pc sheet. There seems to be a lot of gaps between the layers. You think you have the perfect first layer but as soon as you use a different filament it can throw your first layer out or even just using a different colour from the same filament manufacturer can give you different results. Get this technique down pat and you you will never have an adhesion issue again.

Postato : 26/06/2019 4:57 pm
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stoofer
(@stoofer)
Estimable Member
RE: Part breaks free at same place every time

I can see the path the extruder took on the textured sheet.  On my own prints, this generally means my nozzle is a smidge too high.  I'd try dropping it slightly on Live Z.  I would also do what gnat suggested and try a spot on the bed that never/rarely gets used, to rule out wear.  When my bed simply wont stick no matter what I try, that's when the acetone comes out.

Postato : 26/06/2019 4:58 pm
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gnat
 gnat
(@gnat)
Noble Member
RE: Part breaks free at same place every time
Posted by: stuart.b4

I can see the path the extruder took on the textured sheet.  On my own prints, this generally means my nozzle is a smidge too high.  I'd try dropping it slightly on Live Z.  I would also do what gnat suggested and try a spot on the bed that never/rarely gets used, to rule out wear.  When my bed simply wont stick no matter what I try, that's when the acetone comes out.

Isn't acetone a big no-no on the PC sheets?

MMU tips and troubleshooting
Postato : 26/06/2019 5:05 pm
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stoofer
(@stoofer)
Estimable Member
RE: Part breaks free at same place every time
Posted by: gnat
Posted by: stuart.b4

I can see the path the extruder took on the textured sheet.  On my own prints, this generally means my nozzle is a smidge too high.  I'd try dropping it slightly on Live Z.  I would also do what gnat suggested and try a spot on the bed that never/rarely gets used, to rule out wear.  When my bed simply wont stick no matter what I try, that's when the acetone comes out.

Isn't acetone a big no-no on the PC sheets?

Supposedly.  🙂  I use it as a weapon of last resort and it works.  I've only used it maybe 10 times, though.

Postato : 26/06/2019 5:18 pm
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CybrSage
(@cybrsage)
Honorable Member
Topic starter answered:
RE: Part breaks free at same place every time

I am trying a print sliced with S3D right now, then try a new location, then clean with acetone.

 

Postato : 26/06/2019 5:47 pm
bobstro
(@bobstro)
Illustrious Member
RE: Part breaks free at same place every time

Anything that breaks away points to adhesion. Sounds like you're doing the cleaning steps. One last thought is that it might be mechanical. Is it breaking free while printing infill? If you're over-extruding, that can cause the infill printed at high speed to not adhere well to the previous layer, stick up, and eventually snag the fast-moving nozzle, ripping the part loose.

Things to try:

  1. Have you tried a brim?
  2. Different infill or percentage of infill?
  3. Reduce extrusion multiplier (calibrate for each filament)?
  4. Slow down to 50% and see if it completes?

 

My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Postato : 26/06/2019 6:33 pm
CybrSage
(@cybrsage)
Honorable Member
Topic starter answered:
RE: Part breaks free at same place every time
Posted by: bobstro

Anything that breaks away points to adhesion. Sounds like you're doing the cleaning steps. One last thought is that it might be mechanical. Is it breaking free while printing infill? If you're over-extruding, that can cause the infill printed at high speed to not adhere well to the previous layer, stick up, and eventually snag the fast-moving nozzle, ripping the part loose.

Things to try:

  1. Have you tried a brim?
  2. Different infill or percentage of infill?
  3. Reduce extrusion multiplier (calibrate for each filament)?
  4. Slow down to 50% and see if it completes?

 

I have tried none of that yet, I will do this after my next set of prints where I use a different location.  I tried to lower the Z even more, but it went too low and started to have inconsistent extrusion (gaps, etc).  I raised it back up some and got a good first layer (I think).

The print from S3D got to about 85% complete before it failed and they ALL have failed during printing infill.  I have not tried different infill amounts, unless the different PrusaSlic3r layer height profiles use different infill amounts - I am using the defaults from Prusa.

Postato : 26/06/2019 6:45 pm
muddymaker
(@muddymaker)
Estimable Member
RE: Part breaks free at same place every time

When tuning your live Z, especially on a Prusa powder coated sheet, use your printer for reference because Prusa prints all of their plastic parts on the same powder coated sheet you have. Then print the Prusa logo or something of similar size that prints fairly quickly and compare the bottom of your print to the printed parts of your machine, the X axis plastic parts or the Z stepper motor mounts for example. This exercise may take a number of prints until you get it right but when you find that sweet spot you will have a Eureka moment. A lot of people cannot get the first layer right so you're in good company with many people that experience this problem.

You will have to calibrate your live Z for both PLA and PETG as they will differ in squish slightly. A general rule of thumb that I use is when you have ascertained your live Z for PLA, PETG will generally be around 0.2mm positive difference, meaning you want the nozzle slightly higher from the bed to achieve the right squish. Now of course you might find that a slightly higher value or even a lower value works for you but that's something you have to play around with until you get it right because different filaments have a role to play in all of this as well.  

This is all assuming that you indeed have cleaned your sheet as specified by the great man himself Joseph Prusa, and you don't have an under extrusion issue due to a partially blocked nozzle. 

Just as a side note Prusa are now recommending you don't use acetone to clean your powder coated sheets as this will introduce hairline cracks in the coating over time.

Postato : 26/06/2019 8:50 pm
CybrSage
(@cybrsage)
Honorable Member
Topic starter answered:
RE: Part breaks free at same place every time
Posted by: tony.s8

When tuning your live Z, especially on a Prusa powder coated sheet, use your printer for reference because Prusa prints all of their plastic parts on the same powder coated sheet you have. Then print the Prusa logo or something of similar size that prints fairly quickly and compare the bottom of your print to the printed parts of your machine, the X axis plastic parts or the Z stepper motor mounts for example. This exercise may take a number of prints until you get it right but when you find that sweet spot you will have a Eureka moment. A lot of people cannot get the first layer right so you're in good company with many people that experience this problem.

Just as a side note Prusa are now recommending you don't use acetone to clean your powder coated sheets as this will introduce hairline cracks in the coating over time.

A little bothersome to change a recommendation from "do it" to "it will kill your sheet if you do it", but it is what it is.  🙂

Here is a picture of my first layer as compared to the top of the Z axis.  That is an amazingly good idea on how to check the first layer, thanks!  I am pretty sure my first layer is good, but take a peek and let me know what you think.  The sides of that cube are beveled, which is why they look different.  I need to work on my bridging, but that is for another time.  A completed print has priority.

Postato : 27/06/2019 1:10 pm
Dave Avery
(@dave-avery)
Honorable Member
RE: Part breaks free at same place every time

sort of looks like a bit too high still , it looks like you have  a tiny separation near the top end of the cube

Postato : 27/06/2019 3:32 pm
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muddymaker
(@muddymaker)
Estimable Member
RE: Part breaks free at same place every time

That's looking a lot better and your welcome. I take it your test cube is staying put now? Looking at that photo I would come down a little more to match up with the other part, but if it is staying put for the entire print then you could get away with the Live Z you have set for smaller prints like your test cube. Just keep in mind that the larger the foot print of your model the better the first layer as you want to minimise warping and/or bed adhesion issues in the future.

The beauty about this hobby is that when you master a technique through past mistakes it gives you the confidence and drive to tackle any other issues that may arise during your foray into this wonderful hobby. Happy printing. 

Postato : 27/06/2019 10:05 pm
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CybrSage
(@cybrsage)
Honorable Member
Topic starter answered:
RE: Part breaks free at same place every time

Yes it is, thank you all!

 

I think my extruder head is loose also, when I replace the bearings most likely a square nut fell out and now I have a screw that doesn't tighten properly.

Postato : 27/06/2019 10:10 pm
Peter M
(@peter-m)
Noble Member
RE: Part breaks free at same place every time

With petg printing, the nozzle can hit the infill, use honeycomb for infill with petg, then the hitting off the infill is less.

live-z adjust should be perfect, practice this very often.

Cleaning is very important.

Also a big brim attach to model will help, 4 or 6 lines. But with cube it should not be necessary.

Different filament?

Postato : 28/06/2019 8:15 am
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