Hello, good afternoon.
I was printing some 8mm diameter, 30mm tall pins in PETG HF. The height was correct, but the diameter varies as the piece grows.
The inner diameter is 3.24mm and the outer diameter is 3.1mm, but I’m not worried about this diameter; I just needed a little more precision in the outer diameter.
Has anyone else experienced this?
Is there any calibration step I can do to improve the outer dimensions, or is it better to modify the Step file?
Do you think it has to do with an elephant’s foot? But the height was correct. If it were an elephant’s foot, wouldn’t it also have to be shorter in height?
You’re printing with 0.4mm nozzles, it has a line width of 0.42mm, but the nozzle itself has a “flat” surface that is much larger than 0.4mm. When it’s drawing a circle, that flat surface would drag over the molten filament.
See my post here for my hand drawn illustration lmao.
There are many other factors also affecting the hole/contour accuracy.
Since you’re using Bambu PETG-HF, the easiest way to get a kind of working solution to the issue is to enable “Auto Contour Hole Compensation”, otherwise you can also do it manually.
So basically this is what is happening. When we don’t apply any kind of compensation, due to the viscosity of the molten filament, when the nozzle is drawing a circle, the filament would tend to stay at the “inner” side. So while in a perfect scenario, the filament should be filling the dashed lines as well, but in reality no.
Which is why usually you get smaller holes and smaller outter diameters when printing small items.
The slicer has only very basic compensation methods, XY scaling, XY hole, and XY contour, and also the “automatic hole contour compensation”.
the last one is an all in one solution but that only works for a couple of bambu filaments, including petg hf. the accuracy is generally acceptable. It’s a mixature of many attempts.
Elephants foot happens when the weight of the print pushes down on lower levels. It does not affect the nozzle path though, so the upper material is still deposited where it should be. So in practice, there’ll be some increased proposity in layers above the elephant foot.
Thank you for your explanation, the elephant’s foot is 0.15mm by default in the software, but to obtain more correct dimensions you should change the elephant’s foot to 0.25mm, this would at least make the part closer to the diameter?
The number indicates by how much the lowest layer will be shrunk. So it really depends on the measurement location (tricky to spot in the pics).
Here"s a further explanation as to what it does: https://wiki.bambulab.com/en/software/bambu-studio/parameter/elephant-foot
However, elephant foot is not only a first layer problem. It may also help to lower the heat bed temp by 5° for layers 2+ and of course to keep the chamber warm. Bambu recommends 35-50°C in the TDS.
If 7.91mm of 8.00mm is too much of a discrepancy, you are also going to have to sort out the seam settings (time consuming). Also, +1 on the auto compensation that Hotellonely brought up since you are using PETG. Its not a guaranteed fix, but it may get you within your requirements.
Wouldn’t archane wall generation also help with this? I use archane+precise z-height on (almost) all of my prints, and I find tolerances on height/width to be within 0.05mm. Small ID holes are a different story, but that’s covered in depth in another thread, and not relevant to the current conversation.
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