Curved Prints Have Chords
Folks, I need your help again.
I'm having trouble printing a Ring Pull Can Opener. As you can see from the picture, the print has several chords in the first layers. I've had the same problem with other prints. All of them involve curves of various shapes and sizes. Some, I was able to fix by enabling the "Avoid crossing perimeters" setting in PrusaSlicer. Some I have been unable to fix enabling the setting. I cannot think of any other slicer setting(s) that will solve my problem.
I've examined the files, both the ones I was able to print successfully and the ones I couldn't,
in the PrusaSlicer, before and after slicing. The chords did not show up in any of the files. I also examined some of the g-code files in a graphical g-code editor. Again, the chords were not there.
I am using version 2.2.0+win64 of the PrusaSlicer. I am slicing for 0.2mm quality. My printer is a factory assembled MK3S. It is using firmware version 3.8.1-2869. The filament is from Matterhackers. It is purple MH Build Series PLA.
I've also uploaded the original .stl file, the g-code created by the slicer and the .3mf file with the slicer settings.
Any help you can give me will be greatly appreciated.
RE: Curved Prints Have Chords
turn off avoid crossing perimeters, that isnt he problem and it slows slicing down massively.
Your problem is the bottom of that model is almost all overhangs, massively so, the layers as they are printing have nothing on the previous layer to attach to so they just get pulled along giving you what you call chords. Turn on Detect Bridging perimeters and slice it again. Now look at the preview once it completes, you will see all the perimeter above layer 1 to layer 13 is overhang (dark blue lines)
You should really enable support or alter the model to remove the overhangs by using a fillet rather than the curves.
For support settings, select support on print bed only, set the contact z distance to 0.2 or 0.25 (the default of 0.1 is too close and supports will stick too much). Also upping the x/y separation to 70-80% is usually a good idea.
That should allow a successful print but the side facing the bed wont be pretty as surfaces printed on supports almost never are. Thats why if it was an angled fillet at 45-55 degrees slope instead of a gradual curve it would print without support. But I'm guessing its a downloaded model ?
RE: Curved Prints Have Chords
Neophyl
Thanks for your help.
It is a downloaded model from Thingiverse. I printed a copy with supports using the settings you recommended. It was not pretty, but it did print without the chords. I'm going to try to clean up the print.
I don't understand what you mean by "if it was an angled fillet at 45-55 degrees slope instead of a gradual curve it would print without support". To me a fillet is a gentle curve added to a joint where 2 pieces meet at right angles. Where would you add the fillet? How would you orient the print?
RE: Curved Prints Have Chords
Csalber,
I think Neophyl "mis-spoke", I am certain he meant chamfer rather than fillet. The problem with fillets is that since they are curves in the horizontal dimension they are very "shallow" angles (with respect to the build plate) in the initial stages and so are essentially unsupported nearly flat overhang surfaces. In contrast a chamfer is a constant angle from the build plate and the printer can easily with angles up to around 45 degrees (note you can get shallower with manipulation of settings but 45 degree chamfers will print with default settings.
You can play with support settings to get better finishes but unless you go to soluble support materials which allow full contact support you will not achieve good results with larger fillets adjacent to the build plate (i.e. on the bottom of the model).
Regards,
Steve
RE: Curved Prints Have Chords
Sorry yeah, was getting my chamfers and fillets mixed up 😀. I find with a mk3 you can easily and safely do 60-65 degrees overhang even with normal settings.
if you can avoid it in your designs then shallow curves on both bottom and top is best, bottom due to the overhang problem and tops due to the stator step effect being much more noticeable, although using variable layer heights can help with that lots.
RE: Curved Prints Have Chords
Steve_g
Thank you for clearing up my confusion. You taught me another thing to consider when preparing a model for printing. I rotated the model by 90 degrees in the X-axis because I was having difficulty printing it. The interior arc at the top of the original orientation was not printing smoothly. I think it was because I tried printing it without supports.
Do you know of an .stl file editor I can use to edit the downloaded file?
Charlie
RE: Curved Prints Have Chords
neophyl
I've misspoke many times. I know how that feels.
Can you recommend an editor I can use to modify the .stl file?
Charlie
RE: Curved Prints Have Chords
Stl is generally not a good file format for editing. That being said I've edited a lot of them by now. Personally I use Blender. Like most programs its got a bit of a learning curve but its free, open source and works on windows/mac/linux and will do the job. Its also got LOTS of tutorials on YouTube and there are add on's etc that can help with various tasks. For example I use the 3dprint add on as its handy for checking for model issues. Version 2.8 onwards have a completely new user interface which is easier to get on with than earlier versions.
You could also try something like Meshmixer.
RE: Curved Prints Have Chords
neophyl
Thank you for your help.
I'll download Blender and Meshmixer to see which is a better fit for me.
Charlie