Witness lines in print, Prusa Slicer  

RE: Witness lines in print, Prusa Slicer

I am printing 205mm plus tall extrusions with a slot and bottom wall thickness...

The problem is that I get what look like layer shifts every time there is a detail... where there is an internal wall, I have to add a chamfer so that the ECHO of the feature is diminished across the part at that Z height.  If there is an insert (I use inserts as breakaway supports) there is a echo of the feature that looks like a layer shift, except that it is either a lower or raised surface all around the part (not a shift in one direction but all directions).  Also, as you can see from the images each part, although cut the same way, has a surface rash in different areas...

Using a .4mm nozzle the problems are evident, prints take 15 hours... using a .6 mm nozzle, problems are very large, but take 9 hours.

There is no indication of these "Offset" feature echoes in the Prusa Slicer 2.0.0. and yes I have seen this problem with other slicers...

RE: Witness lines in print, Prusa Slicer

You are doing something weird with your slice ... the surface quality shown in those images is not normal for a MK3. 

As for the bulge when an internal feature presents, you need to control perimeter print speeds to keep each layer printing at the same rate, and not slowing down for thin walled sections.  There are settings for Cooling that you need to change, as well as general perimeter print speeds.

RE: Witness lines in print, Prusa Slicer

Tim's got it. Depending on the part,an additional perimeter might help. If you've designed it, try bumping the wall thickness if feasible. Different extrusion widths may help.

There was a great community testing effort, sadly now lost to the search function of the new forums, that did a deep-dive on this very topic.

If you're the designer, tweak walls to facilitate 3D printing. If not, calibrate your extrusion multiplier and go slow on external perimeters. I use 25mm/s if appearance counts. 

RE: Witness lines in print, Prusa Slicer

Bob: Someone else found it in another thread...

Buldge when print reaches "solid" layers

RE: Witness lines in print, Prusa Slicer

The part is 4mm thick at the base and 3mm thick around the perimeter.  There is a large chamfer on the inside corner of the base of 3mm.

The extruded section is filled by two perimeter paths per side, and a central path... see image... filling the 3mm wall with material.

Thanks to all of you for your help and the link...to the other thread.

My intuition says that this issue is the result of a bead of material loading outside the path of the extruder, caused by start conditions and direction of the path of the perimeter.

It reminds me of CNC Machining, where programmers will use climb cutting vs conventional cutting to polish an edge... in fact they also ramp into a part in order to load the cutter with material in order to control the pressure on the cutter, "bending" it one direction or the other.  

This might be solved by programming the slicer to load the extrusion the same way.  But part design definitely has a great influence on this problem as it makes it highly complex.  There are CNC machining applications like SmartCam and MasterCam that defined all surfaces as lines, and you could connect the lines in a preferred direction in order to get the best surface.  (You could also control the offset of each line - scurf).

I think that this is one of the inherent flaws in FFF parts.

Another way to resolve the issue is to allow the programmer a way to "paint" the part line or startline for each layer.  I would paint the center rear of the part and want every path to start on the central or interior of the section and finish on the outside.  (this is done in applications for UV Mapping complex forms... faces of people etc.)

For now I am going to pursue the issue by tweaking parameters as I know I have been able to create this part with a .4mm nozzle... the .6mm nozzle really create the bulged layers, so there must be a few tricks to use to diminish the effects.  Perhaps this has something to do with the amount of materal, the size of the nozzle and the ironing effect related to the flow and distance to the next layer.  Since I am trying to increase my layer sizes, I am aggravating the issues.  My first test will be with a finer layer, longer print time.

I wish the slicer was wiser... say ai.

Regards,

Carter

RE: Witness lines in print, Prusa Slicer

Direction plays into the issue, but doesn't solve it; same with seam position, it helps, but not a cure (image2).  Whatever is happening in the worst of cases, it is a repeatable offset, not an ooze artifact. Walls actually make a step left or right (image1) - wall thickness stays the same, just moves one direction of the other, like  mechanical backlash, but not.  Last image is a selection of test results.  Strange behavior to say the least.

RE: Witness lines in print, Prusa Slicer

Had to chuckle when I saw your collection of test parts, Tim. I recently had to empty out my home office in preparation for new flooring, and finally dumped my table-top full of test prints. I'm sure to outsiders I look like some maniac trying to make a better Lego.

RE: Witness lines in print, Prusa Slicer

Is there a way to create my own layers in cad and get GCode from the slicer?

I am trying to cut a test piece with a single pass per layer... like a 40mm cube calibration piece...

But can't pass it through Prusa Slicer because it skips the hole.

RE: Witness lines in print, Prusa Slicer

Trying to make a test piece for the bulge... a 40mm cube with a hole in it... 

Q.  What should the width of a single pass be for a .6mm Nozzle in ABS?  at 25mm/s, 255C...

RE: Witness lines in print, Prusa Slicer

I solved the problem... I am now using Cura.  Same part in Prusa Slicer results in many bulged areas.  The part is a simple rounded rectangle extruded in Z with a few details, pocket, screw bosses.  Prusa Slicer is creating the bulges.

RE: Witness lines in print, Prusa Slicer

Posted by: carter.m2

I solved the problem... I am now using Cura.  Same part in Prusa Slicer results in many bulged areas.  The part is a simple rounded rectangle extruded in Z with a few details, pocket, screw bosses.  Prusa Slicer is creating the bulges.

PrusaSlicer with some settings will create the bulges, yes. Read the deep dive thread for info on preventing it with PrusaSlicer. There are some pics there that show the results with various slicers. The Prusa defaults are a bit aggressive for some surfaces, but can be tuned easily. Cura's a good slicer though, so use what works best for you. Here are the results I wound up with:

RE: Witness lines in print, Prusa Slicer

Thanks for the link... I had read this link before, and spent time diving into the problem.  As you can see in the image you provided, moving from slic3r to prusa slicer is a let down.  This is not an esoteric problem for the elite thinkers... it is a practical issue... I simply can't get prusa slicer to produce clean parts.  I was using sli3r, and will move back to it, but I have found Cura also does not create the bulges created when using prusa slicer... for now, prusa slicer is not usable... although I wish it were.

RE: Witness lines in print, Prusa Slicer

Posted by: carter.m2

[...]  for now, prusa slicer is not usable... although I wish it were.

You may have mis-interpreted my picture. That was taken shortly before the renaming from Slic3rPE to PrusaSlicer. The "Prusa Qual" print is using the prusa quality profile with the then-current version of Slic3rPE, the "S3r Mine" print shows my results using that exact same version of Slic3rPE with some tweaks. I think it compares well to all of the others, but I didn't spend much time tweaking Cura or Simplify 3D. (Will have to add ideaMaker to the mix sometime.)

I moved off Cura when I realized it doesn't have support for max. volumetric rate, so I was having to artificially constrain my speeds to meet worst-case conditions. I was also going insane with different profiles for each combination of nozzle size, filament and layer height. I tinker a lot of different hardware settings, so this aspect is really important to me. Each one has its strengths. Use what works best for you.

RE: Witness lines in print, Prusa Slicer

Thanks again for replying... I agree, moving to Cura has its drawbacks (I also have two printers with different size nozzles and materials), but Slic3r PE and Cura make clean parts (no bulges), the same parts in Prusa Slicer 2.0.0 look terrible.

Who do I contact for PrusaSlicer development issues?  Why isn't everyone pointing this issue out?

I have posted this issue before, recently, but it is treated like some type of research issue, like a rarely seen, difficult to diagnose fluke.  For me, it is simply an every print issue that is a  non starter for Prusa Slicer 2.0. (It does have a much better name, and I expect this will get fixed soon, I hope.)

RE: Witness lines in print, Prusa Slicer

https://github.com/prusa3d

RE: Witness lines in print, Prusa Slicer

Thanks.

RE: Witness lines in print, Prusa Slicer

You can reference my post here...

https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/witness-lines-in-print-prusa-slicer/

and look at this image attached for reference to the bulges... the PrusaSlicer part is on the left (also had severe warping that was fixed by adding a flat plate to the inside of the extrusion with .5mm offset.

I will post this on GitHub...thx.

RE: Witness lines in print, Prusa Slicer

adding image

RE: Witness lines in print, Prusa Slicer

Posted by: carter.m2

[...] and look at this image attached for reference to the bulges... the PrusaSlicer part is on the left (also had severe warping that was fixed by adding a flat plate to the inside of the extrusion with .5mm offset.

Can you provide a link to the STL? It is helpful to pull a print up in the slicer to see what's going on.