GregValiant

Easy part first... An outer wall is any wall with air on one side. They are "red" in the Cura preview. An inner wall has model on both sides and they are green in the Cura preview. Anything that is part of a skin is "yellow" in the preview. That would include any extra skin walls. The "Extra Skin Wall" is the border around any skin area. I was playing with the "Skin Overlap Percentage" and if there is a Skin Wall present it moves the Skin Wall closer to the inner wall (or if a negative number then farther from the inner wall). What I noticed is that if the "Extra Skin Wall Count" is 0 then the "Skin Overlap Percentage" will act directly on the skins. Setting the "Skin Overlap Percentage" to 50% (with the "Extra Skin Wall Count" = 0) might help. It looks like it makes a difference in the preview, but there is no shrinkage in the preview. This is with no skin wall and a Skin Overlap Percentage of -50% just to show what it does. This sort of looks like what is going on with your prints. But set to +50% you get this. The Skin lines are mashed into the inner wall lines. Maybe that has some value but you would need to do a couple of tests both with and without the Extra Skin Wall.

The "Gaps" thing. This comes up occasionally on this forum and I tend to agree with other people on this that the root cause is a shrinkage issue that transcends the slicer being used. This might not be what's going on in your specific case, but it is my take on the behavior. If enough time passes between each curved wall extrusion being laid down then shrinkage will occur and the next perimeter doesn't connect to the previous one. This is really hard to fix but making sure your filament is dry can go a long way. If you have a very good layer cooling system and you are running it hard when these extrusions go down (particularly Inner Walls around a small hole) then that can make the condition worse. Most filament comes in a sealed bag with a desiccant pack. That guarantees nothing. I've opened new rolls of filament and they were, well, not sopping wet, but pretty darn close. That is not a popular problem, but it can certainly happen. I have experienced the gap problem myself. I started paying more attention and it usually occurs with rolls of filament that I've left out, or that have just sat on the shelf for too long. I see you have an S5 so the "Flow" should be correct. There are a couple of other things you can try without requiring that the slicer be re-written. Hole Horizontal Expansion - The smaller the diameter of a hole, the more likely that the "Snot Factor" will come into play. That condition happens because the extrusion wants to get dragged in towards the center of the circle rather than stay on the periphery where it belongs. The extrusion WANTS to follow the nozzle and not form an arc. The gap can occur because the inner wall extrusion isn't where it's supposed to be. This is often why small holes don't come out at the design diameter. I did a test and if the hole diameter is over about 30mm then the Snot Factor falls to zero and no HHE is required. Inner Wall Flow - By kicking this up you can force more squish which should tend to keep the inner walls where they belong. Maybe you've thought of those before. Because I haven't experienced the problem lately myself - maybe I'm just out of touch.

@Peter_E6 In addition to Obewan's suggestion you have settings that simply don't apply: Avoid Printed Parts (impossible on this model), Avoid supports (none on this model), and combing set to Not In Skin (there isn't any on this model). Those are going to cause retractions because they affect other settings. "It seems like nothing can stop Cura regularly retracting the filament for no explicable reason" Any printer is a 4 axis (at least) robot. It has to be programmed to go and do what it's supposed to do. Any slicer has to be set up so that the generated gcode does what the user requires. This is the user's responsibility because in the end, the retractions and other things that the printer does is dependent on the input of the user. There is always a reason for any retraction and that is because that's how the software was set up. Now if there is a bug in the software then that is a different story. I do see problems with your settings. I don't see a bug. With your settings there are 182 retractions between ";LAYER:0" and the end of the file. Since the model is 260 layers that is somewhat less than one retraction per layer. Turn off Avoid Printed Parts, Avoid Supports, Retract Before Outer Wall, set Combing to "ALL", and set Retraction Minimum Travel to 10.0. With those changes there are 5 retractions between ";LAYER:0" and the end of the file. That's about 3% of what you are getting with your settings. I hope I made some sense. GV_MicroscopeOccular.3mf

When Cura adds the polka-dot pattern to a model it means the model has errors. That can happen for a number of reasons. In this case I think the 37 separate parts that make up the model assembly have gaps between some of the sub-parts, and the main body. Scaling the model up likely opened up the gaps to the point where Cura can notice them. The result is that if this does slice it will probably be "iffy" to print. Here I fixed a copy of the model using MS 3D Builder. It's pretty obvious which one was repaired. This is the repaired model sliced. The original model sliced after I rotated it on the build plate. There are bug reports regarding that behavior, but in this instance I think it is a model problem.

"I want to add say 2, or 3 or even 5 extra walls (perimeter) lines on every alternate layer, ..... on every Nth layer...?" There are no settings to do something like that. You can alternate a single extra wall I think that thought behind that is to trap the infill at the walls. "...apply only to inner walls, while just leaving a fixed wall count on outer perimeter walls." I'm not sure I understand that one. I'd say that because the answer to the first question is no, that this one doesn't come into play. Wouldn't 5 extra walls every 10th layer result in those extra wall extrusions being printed over air? You would need pretty high infill density to hold them up.

About 3 years ago there was a poster here who built a big pellet machine and he was using Cura. I tried to message him a while ago and didn't get a response. This is the post.

With the Custom setting button turned on and the Setting Visibility turned to All then in the Travel Section you will find "Layer Start X" and "Layer Start Y". There is no such setting for the infill. It will often be as you want it (start near the z seam or layer start point) but for different types of infill patterns it may be different and if you change the Infill Line Directions it may be different.

This is just an FYI... Depending on the "repeatability" of the end stop switches - it is generally not a good idea to home any axis during a print. The switches are going to vary at least a little bit every time you ask for homing. The "0" position this time will likely not be exactly the same as the "0" position last time. When the X and/or Y are involved during a print you can get a minor but noticeable layer shift. When it happens with the Z you can get an over-extruded layer (the new Z0 is a bit too low), or an under-extruded layer (the new Z0 is a bit too high).

There are a couple of bug reports about this on GitHub. Whether "Union Over-Lapping volumes" is turned on or off - they don't union but simply stay separate resulting in what you have there.. Union Over-Lapping Volumes = Off Union Over-Lapping Volumes = ON with Remove Mesh Intersection off Union Over-Lapping Volumes = ON with Remove Mesh Intersection on. This looks like one block is acting as a cutting mesh. There are still interior walls where I would have expected none.

"Incompatible Version" so I can't open the DWG file. I'm working with AutoCad 2000 and Mechanical Desktop 4.0 so you would need to do a Save-As in one of those formats, or put a DXF together.

After adding the shell and the first 2 excluded faces you can spin the model, then edit the shell and add the third face. You need to turn on supports in Cura or the horizontal parts will fail.

I'm an AutoCad guy. Pass me the .dwg file as an ACAD 2000 file (parametric if you can) and I'll take a look (you might have to zip it to post it here). Sometimes when you get too fussy with the "fits" there will be openings that the slicer will notice even though the gap might be on the order of .000001mm. You have those gussets on the two end pieces and they look to have flats where they hit the radii of the tubes. That's the sort of spot that can cause trouble. If the tube is only touching tangentially to the flat then there will be a tiny gap on either side. The gusset should be buried by a mm or so to insure the union works correctly. You can check by putting a fillet there. If it's successful then the union is fine. Computers may be stoopid, then they are accurate.

It's always safe. It's a question of whether it will be acceptable. There are these spots on opposite sides of the print. (You can see it on the right of my previous screenshot.) I have no idea why the flow narrows down so much there. Is it a model feature? There are these divots on the outside of the model. They are going to show up in the print. So would it be safe? Yes. Would it be acceptable? You'll have to decide. For a first effort I would say yes. Those divots have resulted in a few bug reports on Github regarding 5.3.1. Cura 5.2.2 didn't have the problem. It's possible that some of what we see is being caused by the model. BTW does your layer cooling fan work OK? I see in the gcode that it is listed on circuit "1". Typically a single extruder printer will have the fan on circuit "0".

That's a poorly sliced model.

I use the Raise3D slicer occasionally for comparisons with Cura. With an N2 installed in IdeaMaker there are T0 commands in the startup so they are probably alright. My guess would be that the firmware is similar across their product line. That G92 E0 E1 command looks to be contradictory and so it's probably illegal. It's trying to set the extruder location to 0 and to 1 at the same time. Not good. This is the N2 StartUp Gcode from Ideamaker: M221 T0 S94.00 ;set the flow to 94% G21 ;metric M140 S60.00 ;Bed temperature M104 T0 S215.00 ;hot end temperature M109 T0 S215.00 ;wait for hot end T0 ;set the tool M190 S60.00 ;wait for the bed temp G21 ;metric units G90 ;absolute movement M82 ;absolute extrusion M107 ;fan off G28 X0 Y0 ;Home the X and Y if they need it G28 Z0 ;Home the Z if it needs it G1 Z15.0 F300 ;move the nozzle up G92 E0 ;reset the extruder G1 F140 E29 ;purge G1 X20 Y0 F140 E30 ;move while purging some more G92 E0 ;reset the extruder G1 F9000.0 ;set the feedrate M117 Printing... M1001 ;enables the power resume function. There should me an M1002 in the Ending Gcode. I made up the one below. First use the "File | Save Project" command to save your current StartUp Gcode. (If you were to open that new 3mf file in Cura it would bring in your original StartUp Gcode.) After backing up your current startup gcode in the 3mf project file, you can try this by copying and over-writing the current StartUp in the StartUp Gcode box in the Cura Machine Settings dialog. ; <<< StartUp >>> M221 S100 ;reset the flowrate M220 S100 ;reset the feedrate G21 ;metric units G90 ;absolute movement M82 ;absolute extrusion M140 S{material_bed_temperature_layer_0} ;start the bed M104 S{material_print_temperature_layer_0} ;start the hot end G28 X Y ;home the XY G28 Z ;home the Z G1 X0 Y0 Z15.0 F600 ;move the nozzle up so the purge has somewhere to go. M109 S{material_print_temperature_layer_0} ;wait for hot end M190 S{material_bed_temperature_layer_0} ;wait for the bed temp M107 ;fan off G92 E0 ;reset the extruder G1 F140 E29 ;purge G1 X20 Y0 F140 E30 ;move while purging 1mm more G92 E0 ;reset the extruder G1 F9000.0 ;set the feedrate M1001 ;enable power resume function M117 Printing... ; <<< End of StartUp >>>

On the menu bar select "Settings/Printers/Manage Printers" and then "Machine Settings". There is a box for "Origin at Center" and unless you have a delta printer or one or two other printers that setting should be turned off. Most rectangular (cartesian) printers have the origin at the left front corner.

(I set the screenshots up so the first skin is going down on just the top infill layer.) The top layer sags because there is insufficient support below. The speed is off because you are Ironing at 50mm/sec and everything else is at 75mm/sec. Here is the slice with your settings. Notice that the extrusions are going down into a gap in the Lightning infill. The ends of the Lightning infill are very thin. So the first layer of skin is going into a gap and it's also at Printing Temp so it's softening the skinny ends of the lightning bolts. The end result is sagging because there is either zero support, or the infill upper layers are softening and sagging along with the skin. This is with the Infill Density at 20% and all of the Lightning angles at 50° and I've changed the Top/Bottom Line Directions to [0,90] so the first skin doesn't fall into the gaps as much. This allows for better support for ALL the skins. The heat problem is still there but probably not as troublesome. This is good ole' Grid infill at 15% density. You can see that the first layer of skin is well supported. If you set the Infill Layer Thickness to 2X Layer Height then the infill only goes down every other layer. That decreases the time penalty (vs Lightning) to about 7 minutes. It also results in a much more robust part. You could try turning off the infill and enabling the Bridge settings. The part is only 2" diameter and bridging should work but it might be necessary to add another top layer.

"...the left was printed just before..." Yep, it ran when I parked it.

@RonS the 3mf file opened as a model file. Use the "File | Save Project" command to create a 3mf project file that will contain your settings and printer as well as the model. (When you "Export" from Cura an option is for a 3mf model only file ... no printer or settings.) With just the model to work with and using my settings I get this. Everything is at 75mm/sec except for the outer-wall because I have it set to 50 and that's what all the speeds in the gcode show.

"...but many-many times." I think it will be all about the material. If you pick the wrong one then "many-many" will become "just a few". Good Luck!!

Have you considered printing it with all Walls (set the Wall Count to 5 or 6)? That would avoid all those little back and forth movements that the skin causes. It gets the print time down to about 1:45 as well.

It looks like the print on the right developed a problem in the hot end. Those upper layers appear to be severely under-extruded. The left "wing" on the right model didn't really print at all. It can never hurt to do some PM on the printer. Once a month I pull my hot end apart and clean it out, trim the bowden back, check and clean all the trolley wheels and check the X-beam alignment. The machines run for hour upon hour and do need some attention now and then. BTW...what material is that?

That's nice. The last I heard they had vacated their offices and were out of business. As a hobbyist I have no reason to shell out $200 when Cura, PrusaSlicer and IdeaMaker are free.

Most direct drives I've seen have retraction distances in the range of 0.8 to 2.0. Are you sure you are retracting 8mm? I can't retract that much on my bowden setup or I have problems with clogging. I think the Noctua's are 12volt fans and require a buck converter to work with the 24v circuit. They are about 20% less CFM so yes, that could be a problem.

The hot end fan is there to remove the heat from the finned aluminum heat sink. If there was no fan then eventually the heat sink would get hot enough to severely impact printing. In that case it would cause more oozing as retractions wouldn't be as "crisp" because the filament up above is too soft and is stretching rather than pulling the melted material back from the nozzle. I went to a 4015 hot end fan on my Ender 3 Pro. That required a 3mm shim to move the hot end housing outboard. I printed a little baffle that fits into the housing. It aims the airflow at the heat sink.