Hi all
I have a pretty modified Monoprice maker select. Its running on a ramps board with the repetier firmware. I have been printing happily through many many spools of filament (mainly ABS).
I recently had some issues where my extruder would underextrude randomly through the print, mainly larger prints. After much faffing around, I replaced the whole hot end with a china special. Works well enough, after calibrating it etc, I can print a pretty good benchy:
I was messing with the flow rate, so ignore the under extruded section at the bottom 
The issue comes when I try and print a large round object (jack stand adapter). I have successfully printed this on the old hot end (before the issues). I attempted to re-print the exact same g code on this new hot end and I get odd issues. I get bobbly outer edges and bubbles showing, the print head ends up rumbling over these imperfections and it gets worse and worse until I cancel the print.
You can see where it starts off OK and then ends up mangling it self.
Top layer
Not quite sure where to go from here. This printer has printed this model perfectly before. Benchy printed on my normal settings straight off, without any changes.
Any thoughts are much appreciated.
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A few other examples of failed attempts:
Can you print a Benchy in the same filament you’re having trouble printing the disc in? Reason I ask is because when I had blobs and zits like that it ended up being the filament diameter. Different machine and one that uses 3.00mm filament so measuring was even more important. But the particular spool I was using required me to set the filament diameter to 3.05mm in the slicer and the problem was solved. Long story short looks like it could be some over extrusion. At least worth looking into.
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Thanks, yes I will give it a go.
I thought it might be a filemnt option (which is why there are 2 different colours in the failed prints pics) but they both behave in the same way.
Will do a Black benchy in a bit and post up.
It looks like over extrusion to me too, but when I reduce the flow rate I just end up getting classic underextrustion gaps etc, so makes no sense.
Only other thing could be Z axis isnt moving enough. I am currently printing a 40mm calibration cube to see what size it comes out to.
I thought about the z-axis as well and I think your idea of a calibration cube is spot on. Re the Benchy in black, I didn’t see the pic of the disc in the gold filament on my iPad for some reason (which is why I suggested doing a Benchy in black.) Curious to see how that turns out.
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Here’s the example Benchy I was talking about before making some adjustments to clean it up. This was on a Lulzbot Mini using eSUN 3.0mm HIPS. Played with a number of settings including the z-offset and the filament diameter.
Notice the similar blobs on the lower part of the hull that suddenly disappear (but then printing issues reappear higher up). Could be your z-offset is off as well? I note that because of the line across the hull of your Benchy at about the same location.
Following that is where you can see several more Benchys printed with a few different filaments (notice the white and green have the same line on the hull (printed in Cura with standard settings). Then I started playing with the HIPS and doing some tweaking. The middle Benchy and lower-left are the ones that turned out the best. but it shows that it looks like you might be in for some time testing settings. I ultimately used something smaller & quicker to print when changing settings as the Benchy takes too long then print the Benchy to see if I got them right.
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Aha I see! Yes. Just finished
40.5mm
40.1mm
41mm
So the dimensions are correct.
I did however have the same artifacts on the bottom of the print. I am going to try and print it again with different extrusion settings.
I think I have figured it out. The print bed has a bow in it, so it has a very slight bowl shape in the middle.
My benchy was printed to one side, if I offset my large model to one side, only half of it exhibits the problem!
As I am printing straight onto the ali print bed, I have ordered some glass and will snap that on top.
Will report back!
Update
Still having issues, so far I have tried:
New stepper drivers for Z and X/Y Axis
New glass build platform
New linear bearings everywhere.
Still the same issue. Prints this piece fine for the fist 1.5mm or so, then bubbles and ruins itself.
I can print a 30mm diameter, 40mm high solid cylinder without issues.
I can print a large flat calibration layer without issues.
Its not the filament.
I am stumped.
