Problem printing Benchy - raised section hits nozzle  

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Technical Ted
(@technical-ted)
Trusted Member

Finished up assembly of my Mk3S+, ran wizards, ran the first layer setups, etc. and everything was good to go. Printed the Prusa logo test and everything was fine. I attempted to print two Benchies... they both failed in exactly the same point. The arches over the doors and the rear window were raised where the bridging starts. The nozzle hit this raised area and popped the benchy free from the base. I feel I had good adhesion because you can hear a very crisp pop when they brake free and the skirt is hard to remove. They both printed fine until they hit this bridging section. Both sides are raised up and it's quite clear when you put something flat across the open section.

What could be causing this? How do I remedy?

Thanks,

Ted

 

Posted : 12/03/2021 10:00 pm
Technical Ted
(@technical-ted)
Trusted Member

Forgot to add I'm using the Prusa PLA filament that came with the printer and the default PLA settings. The g code is the code that comes standard with the SD card for the printer provided by Prusa.

Thanks,

Ted

 

Posted : 12/03/2021 10:12 pm
bobstro
(@bobstro)
Illustrious Member

I had a similar experience.

In my case, it turned out that my underlying issue was bed adhesion. The motion generated by Cura's gcode just so happened to trigger a bit of wobbling as the print lost adhesion, and it would move parts of the print up into the path of the nozzle where it would get knocked off.

Once I figured out bed adhesion (https://projects.ttlexceeded.com/3dprinting_mk3_bed_adhesion.htm l" target="true">notes here), the problem went away entirely. 

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...
Posted : 12/03/2021 10:27 pm
bobstro
(@bobstro)
Illustrious Member

Trying the link again.

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...
Posted : 12/03/2021 10:59 pm
GMoney
(@gmoney)
Active Member

That's really weird looking.  Maybe it's just the photo (or my old eyeballs) but the back half of the cabin looks lower than the front.  And why is the end of the arch higher than everything else?  Were you watching it print?

Posted : 12/03/2021 11:56 pm
Technical Ted
(@technical-ted)
Trusted Member

@gmoney

I watched both of mine print when they broke off. I even have one in a video and you can hear the nice "pop" when it snaps off the bed. The print looks fantastic except for where it raises up at the top of the door way arches and back window.

Ted

 

Posted : 13/03/2021 12:02 am
GMoney
(@gmoney)
Active Member

@technical-ted

Understood.  I'm a relative "noob" myself, only been doing this since last May as a hobby.  So I can't figure out what would cause your Z to go to one level and print, and then drop back down and cause some drama, which is what it looks like is happening.  It's not like it could be a belt that's loose or something on the Z axis.  Maybe it's over-extruding?  Or maybe one of your belts IS slipping on another axis and allowing it to extrude too much in one place and pile up?

I dunno.  That print just looks weird.

This post was modified 3 months ago 2 times by GMoney
Posted : 13/03/2021 12:24 am
Velvia
(@velvia)
Eminent Member
Posted by: @technical-ted

@gmoney

I watched both of mine print when they broke off. I even have one in a video and you can hear the nice "pop" when it snaps off the bed. The print looks fantastic except for where it raises up at the top of the door way arches and back window.

Ted

 

That looks like a cooling issue. The spot where it warped cooled quicker and therefore it raised up quicker. Although I cant tell you why that happens. Whats your ambient temperature and are there any drafts?

Posted : 13/03/2021 12:27 am
93fd3s and GMoney liked
Technical Ted
(@technical-ted)
Trusted Member

Room temperature is probably around 65 F and no drafts. Happened to two different attempts in the exact same spot. Print looks great except for this problem. Bottom looks fine. 

Thanks

Posted : 13/03/2021 12:32 am
Velvia
(@velvia)
Eminent Member
Posted by: @gmoney

@technical-ted

Understood.  I'm a relative "noob" myself, only been doing this since last May as a hobby.  So I can't figure out what would cause your Z to go to one level and print, and then drop back down and cause some drama, which is what it looks like is happening.  It's not like it could be a belt that's loose or something on the Z axis.  Maybe it's over-extruding?  Or maybe one of your belts IS slipping on another axis and allowing it to extrude too much in one place and pile up?

I dunno.  That print just looks weird.

I don't think its related to that. The benchy looks relatively spotless besides the arches where it curls up.

Z usually doesnt hops around, unless something goes badly wrong. The Z axes uses screws to lift and drop the extruder. If you watch carefully you can see them making very very small movements (watch the screws turn a few degrees as the extruder moves over the bed) which I think is related to compensate for bed leveling.

There is some minor ringing and stringing on the benchy but that looks pretty alright to me. I would be more curious to see its bottom. Although you say its adhering properly.

Posted : 13/03/2021 12:33 am
Velvia
(@velvia)
Eminent Member
Posted by: @technical-ted

Room temperature is probably around 65 F and no drafts. Happened to two different attempts in the exact same spot. Print looks great except for this problem. Bottom looks fine. 

Thanks

That equals to 18.3 degrees C. Pretty cool imho but it should still work.

 

How about re slicing the benchy yourself and having it print at a lower speed? The Prusa provided gcode on the SD can sometimes be a bit wonky. Just an idea to try out.

 

Edit: There are also new firmware versions out there for the mk3s. I havent updated my production machine to the latest because its running 24/7. I dont know what version your board was shipped and how it works with the provided gcode.

This post was modified 3 months ago by Velvia
Posted : 13/03/2021 12:36 am
GMoney
(@gmoney)
Active Member

@velvia

Yeah, as I typed that I was thinking if there were issue with any of the axes the rest of the print would be funky too.  And there's no kind of adjustment or anything you could screw up on your build for Z.

Posted : 13/03/2021 12:38 am
Velvia
(@velvia)
Eminent Member
Posted by: @gmoney

@velvia

Yeah, as I typed that I was thinking if there were issue with any of the axes the rest of the print would be funky too.  And there's no kind of adjustment or anything you could screw up on your build for Z.

Jup. Most likely curling due to a cooling issue. Makes sense since the little wedge isnt supported underneath and cools out much quicker. And 65 deg F is not exactly warm. My printroom is heated (albeit just a little) I don't know how to fix that one though. I would reslice the object and give it another try. Maybe try a higher layer height like 0.20mm. If I remember correctly, the SD provided gcode is 0.10mm. 

Posted : 13/03/2021 12:51 am
93fd3s liked
Diem
 Diem
(@diem)
Honorable Member
Posted by: @technical-ted

. The nozzle hit this raised area and popped the benchy free from the base. I feel I had good adhesion because you can hear a very crisp pop when they brake free and the skirt is hard to remove.

This is almost certain to be an adhesion problem.  You appear to have good basic adhesion so my first suspect is a fingerprint under one end of the model; that end lifts slightly and when the print is tall enough to allow leverage it starts to distort the print until some is in the way of the nozzle, then it flicks off.

Give the bed a thorough cleaning and try again.  If it fails, show us a picture of the bottom of the print.

Cheerio,

Posted : 13/03/2021 2:47 am
Technical Ted
(@technical-ted)
Trusted Member

@diem

Thanks. It's a brand new textured sheet. I have not touched either surfaces, only the edges. I cleaned it 3 times with 90% Isopropyl.

Here's the bottom of both Benchies. 

 

Posted : 13/03/2021 1:23 pm
Diem
 Diem
(@diem)
Honorable Member

OK, a pretty decent first layer.

Try moving the model to a different part of the print bed - see if it sticks better there.

Cheerio,

Posted : 13/03/2021 8:24 pm
Technical Ted
(@technical-ted)
Trusted Member

Based on the helpful feedback received from my post, I think I'll try two things:

1- Reslice a Benchy but also give it a brim to help hold it down to see if adhesion is the problem.

2- If #1 fails, make up a quick/dirty enclosure out of cardboard to  hold heat in to see if it is a cooling problem.

I'm also considering buying a smooth sheet from Prusa for PLA.

Thoughts?

Ted

This post was modified 3 months ago by Technical Ted
Posted : 13/03/2021 8:31 pm
Trimetric
(@trimetric)
Eminent Member

@technical-ted

I had the same exact problem with my Benchy on the textured sheet. The smooth sheet definitely works better for PLA unless the model has decent surface area. I'll bet if you printed it with PETG it would be fine on the textured sheet. You might try upping the bed temp just a bit to see if that helps with the adhesion.

I was also printing in my basement with about the same ambient temp as you and moved my printer upstairs. I could actually hear the PLA popping and cracking in the colder basement. An enclosure might help some but don't get it too hot for PLA.

Posted : 14/03/2021 3:57 am
Diem
 Diem
(@diem)
Honorable Member

@trimetric

'PLA popping and cracking' suggests your filament is damp.

Cheerio

Posted : 14/03/2021 6:45 am
Trimetric
(@trimetric)
Eminent Member

@diem

Yeah, that would make sense. But I had literally just opened the new sealed bag of filament. My basement was about 15C and I think the temp difference was just causing it to cool a little too quickly. I was able to print with the exact same settings and filament once I moved the printer upstairs. Could've just been bad luck the first time too. My testing wasn't exactly scientific method 😀 

Posted : 14/03/2021 11:47 am
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