Problem printing Benchy - raised section hits nozzle
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
RE: Problem printing Benchy - raised section hits nozzle
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
RE: Problem printing Benchy - raised section hits nozzle
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.
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RE: Problem printing Benchy - raised section hits nozzle
Trying the link again.
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Problem printing Benchy - raised section hits nozzle
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?
RE: Problem printing Benchy - raised section hits nozzle
@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
RE: Problem printing Benchy - raised section hits nozzle
@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.
RE: Problem printing Benchy - raised section hits nozzle
@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?
RE: Problem printing Benchy - raised section hits nozzle
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
RE: Problem printing Benchy - raised section hits nozzle
@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.
RE: Problem printing Benchy - raised section hits nozzle
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.
RE: Problem printing Benchy - raised section hits nozzle
@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.
RE: Problem printing Benchy - raised section hits nozzle
@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.
RE: Problem printing Benchy - raised section hits nozzle
. 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,
RE: Problem printing Benchy - raised section hits nozzle
@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. 
RE: Problem printing Benchy - raised section hits nozzle
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,
RE: Problem printing Benchy - raised section hits nozzle
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
RE: Problem printing Benchy - raised section hits nozzle
@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.
RE: Problem printing Benchy - raised section hits nozzle
@trimetric
'PLA popping and cracking' suggests your filament is damp.
Cheerio
RE: Problem printing Benchy - raised section hits nozzle
@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 😀