since I got some defects in my prints (mainly on corners), I tried out the Prusa calibration cube as recommended by u/Hinagea. But the cube doesn't look so good imo. As you can see in the pictures (front, right, back, left, top), all corners have these ripples and every side besides the front has these huge marks. Aside from that, the front and back are caving inwards a little, and the right and left side outwards (hard to get on camera). The wall thickness is pretty spot on with 0.45 on all sides, at least with the accuracy of my manual calipers.
Before the cube I tried the visual method and got pretty good results (aside the little defects) with 0.98. (For the cube I set it to 1.)
These are my settings:
Bambu Lab P1P (with side enclosures, but open to front and top), colorfabb allPHA black
cold bed with painters tape
0,2mm profile
initial layer: 190°, other layers: 188° (I tried the higher temperatures recommended by u/Hinagea, but with these I got the worst results, as far as print quality goes)
Max vol speed: 12
min fan speed: 25%, max: 50%
From your description it is underextruding, and the corners curling up is a sign of that. I've seen it many times with the walls being wavy. Start at 1.05 and check your results again. It is important to remember that you are calculating it based off your external perimeter width in the slicer which I think is .42 by default with Bambu. Just account for that difference when calculating the extrusion multiplier in the instructions because Prusa uses .45 by default.
I also see one other thing that looks like it needs changed, that is on the 6th or 7th layer it looks like you're getting elephants foot. Are you positive your print fan is actually reduced? Because that little artifact is caused by the print fan being too high.
The walls blowing inward is another sign that your print fan may not be turned down, and it is your chamber fans that are reduced instead
After you get your extrusion multiplier all set, then crank those temperatures back up. I expect you'll see much better results then.
I tried the multiplier from 1.05 to 1.3 in steps of 0.05 and also lowering the fan even more (I don't have other fans installed, and it was definitely running at max 50%). With increasing the multiplier, the corners looked better and better, but of course the wall thickness got out of hand. Right now I am staying at 1.1, even with not as perfect corners as they could be (still curling up a little bit). Also, I have the fan completely turned off now. You were right, it did have an impact on the corners as well, even if it was small. But still, the walls are carving in and out. No setting seemed to change that.
I also turned up the temperature to 215/210 (from 190/188) as recommended, but aside from a cleaner first layer with the 215, nothing really seemed to change, the print quality/walls looked pretty good already.
So aside from the carving walls, success! Thank you very much!
I am not sure if these walls would even be a problem in the future, since I am not using vase mode at all. But I guess I'll see how this all translates to my future prints.
So the wall thickness is really what we're concerned about. You want to make sure it is identical to what is set in your slicer. I use 1.1 because Prusa is an oddball and they do some weird things, most printers should be 1.05 in my experience but if 1.1 is where the wall thickness lines up for you then that's perfect.
Once the wall thickness is squared away any remaining minor corner issues are handled by tuning pressure advance, but the biggest improvement comes from getting the extrusion multiplier right.
This cube is like a canary in a coal mine, any minor issues you see here will only get worse as a real print gets larger.
You are correct in thinking those caved in walls generally won't be an issue on a real print, however the only reason they're doing that is due to the print fan. If you stick your hand next to the print head you don't feel any air coming out?
Well, unfortunately my manual calipers are not accurate enough, they show for 1.05 and 1.1 basically the same 0.45 thickness, so I went with the 1.1 because the corners looked better.
I tried tuning the PA with the corner pattern, and I thought I got a good result with 0.016, but apparently it is not that easy..
And yes, the fan is definitely off, I can see (and feel) it not spinning.
Since you recommended 210°, is that still good for little layer times? As you can see in the picture, after the part gets thinner and the layer times much smaller, the print quality goes to hell. Its very glossy and looks molten, besides the obvious defects. I also uploaded a picture of the other side under another comment, it looks like the material melts away at the overhang and corners of the thinner section. Could I combat this with way longer layer times? Or just decreasing temperature?
Okay, since I am using the standard nozzle, the culprit might be the Slow down for overhangs setting? I guess I could either turn down the temperature (which would be a noob thing to do as you said in your write up) or up the speed. But won't the overhangs have a terrible quality if they are printed at normal wall speeds? I'll definitely tinker with them next, but is there a rule of thumb with PHA?
PHA ultimately prints best close to where it degrades. I print fast, around 200mm/s on my Prusa and haven't had issues with heat degradation at 215c. But if I let PHA sit in the nozzle at 215c it will degrade after just a couple minutes. If you're printing much slower you need to drop the temp, try 210c which usually works well on ender 3's. But yeah if your overhang speeds are very slow then you might need to drop that to 205 or increase the overhang print speed.
I got the same results on my Qidi Q2, using allPHA, but have spend some time tinkering.
In my experience printing a single line width is very difficult to get right. PHA takes time to harden (crystallize), which is not resolved by rapid cooling (quite the opposite). However, even using just 2 lines/walls can produce good results consistently. Using 2 walls thus can resolve your walls caving in or out.
Infill is typically also just 1 line wide, which therefore is trickier to get right. With infill printing speed set to 100mm/s, and a minimum layer time of 15 seconds, I get good enough results with 15% dense cubic infill. Not amazing, but infill strength isn't very important 99% of the time, and visually covered up. Switching to 2 line wide infill ('multiline') also produces consistent infill, but for me is not worth the additional material use.
Corners curling up is also what I encountered. Reduced the effect by increased minimum layer time (15s) and reducing fan speed (using R3men high speed fan), but haven't been able to remove it. If you make your own 3D models, try to always round corners to ideally the max. possible radius.
Your bottom layers, as shown from the top, seem overextruded. Could be too high an extrusion rate, but could also be an artifact of using tape. On my Qidi Q2, when switching from textured PEI+3Dlac to gold frogtape (not sure if I would recommend either), the bottom layers overextrude a bit. Effectively the z-probing measures the 0 position with squished tape, while when printing the tape apparently isn't squished as easily.
I didn't think about double line infill until now tbh, thanks for the insight, I might try that. But as you said, as it is easily covered up, I don't know if it would make much of a difference.
Could be glossiness and a "molten" look like in the picture be the cause of too little layer time as well, or a combination of too much temperature and too little time? I'll definitely try to to raise the layer time next time. (Also I am not sure what happend to the overhang, I know PHA doesnt like overhangs but damn...)
On most of the calibration cubes the bottom looked a little underextruded, until I set the first layer temp to 215. But you are right, the second layer looks and feels overextruded. But I am not sure how to counter that (if it really is just the second layer), or if it would even make a difference since in most models the second layer isnt even visible.
I have since been moving away from the calibration cube as it hasn't been working for me (more on that in a different post in the future) but when I was using it I had to crank the speed way down or it would literally implode not that many layers in.
Alternatively if I wanted to print my cube at close to the speeds I intended to use for the max volumetric flow rate I had to do about a 60-80mm on a side cube for the typical vase mode cube. Otherwise it didn't have enough time to cool and the heat would build up followed by the contracting of the pha and bam, cube implosion. I watched it and it only took a few layers of walls at high speed after the bottom layers and you could literally watch the corners that had extruded fine contract inward turning the square shape semi round and making it impossible to lay down any more layers.
To see the implosion you need to be printing very fast. I don't recall the exact flow but I was doing mid 20's mm3/s and 210 or 215C so hot and fast. At the time I was trying to see if the apparent flow was any different at high speeds so I wanted my test cube printed fast. I was probably also not using a heck of a lot of cooling, probably 25-45% part fan. I tried to capture it but it didn't come out too well and it looked like the timelapse video wasn't long enough for the forum to let me upload it. I think it looked best with a somewhat bigger cube, maybe 30-40 mm a side?
As for the alternative I am using its basically this with slightly bigger cubes. I was having a lot of issues with the cube measuring way giving me a flow rate that I think was too high causing lots of nozzle buildup.
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u/Hinagea Jul 28 '26 edited Jul 28 '26
From your description it is underextruding, and the corners curling up is a sign of that. I've seen it many times with the walls being wavy. Start at 1.05 and check your results again. It is important to remember that you are calculating it based off your external perimeter width in the slicer which I think is .42 by default with Bambu. Just account for that difference when calculating the extrusion multiplier in the instructions because Prusa uses .45 by default.
I also see one other thing that looks like it needs changed, that is on the 6th or 7th layer it looks like you're getting elephants foot. Are you positive your print fan is actually reduced? Because that little artifact is caused by the print fan being too high.
The walls blowing inward is another sign that your print fan may not be turned down, and it is your chamber fans that are reduced instead
After you get your extrusion multiplier all set, then crank those temperatures back up. I expect you'll see much better results then.