Problem with print sliced with Cura

[newdeal99 2]

I am a newbie to printing, I am trying to print something that is circular and empty in the middle.  I have sent a good amount of time playing with settings but I am having a problem and I feel like there is likely one setting that I can change that would help me.  The problem is only with Cura, with Prusa slicer the prints are fine.  The problem that I am having is that there is a huge amount of stringing on the internal of the circle that I am printing.  There is NO TRAVEL through the middle of the circle.  The outside of the circle prints fine, around the circle is another circle which is the support ring and it also prints fine and without stringing.  Only the inside of my part is affected and the amount of stringing is huge.  Since there is no travel through there I am certain that the head is grabbing little tiny bits and dragging them as it travels around the circle until eventually it fuses to the other side and breaks free from the head.  Prusa doesn't so that at all but I would rather use Cura due to conical supports and coasting.  The prints with Prusa are nearly perfect other than huge support structures and larger Z seams.  The prints with basically the same settings on Cura are ruined by all the zits and stringing on that internal surface.  I have tried everything I can think of (changing the order of printing, changing temps, speeds, playing with settings etc).  This is on a Kobra 2 max with Elegy rapid PETG filament.  Both Prusa and Cura I am using variable layer thickness from 0.3mm to 0.1mm with 0.3 at the base and then tapering to 0.1 as it nears the top layers

[gr5 2,176]

I can't really comment on settings unless you post the project file.  Also a photo of your print showing the strings would help.  Please post your project file - do menu "file" "save project" and then post that here.

 

Also you should know that PETG needs to be kept dry or it will string quite a bit.  Wet PETG prints 10X better than wet nylon filament but PETG if left out in normal air will absorb water after a few days and then be "stringy".

 

If your printer has a heated bed, unwind enough for the next print, put that on the heated bed, put the spool on top of that (in other words no need to cut the filament).  Set the bed temp to below the softening temp.  So 55C should be safe.  Cover all that in a blanket/towel or box.  Let it sit for 2-8 hours like that.  Then print again and you should see a big improvement in stringing.

 

Store your PETG in a 2 gallon (6-8 liter) bag with 1 cup or 1/4 liter of color-changing desiccant. I recharge the desiccant when it starts changing colors or about once per month.

[newdeal99 2]

Here is the project file, sorry I didn't take photos of the strings and I brushed them all away so now it's just a poor surface and I reprinted it using the purse slicer. The roll was brand new and the same roll prints fine with the purse slicer file which seems to use basically the same settings.  I attached the project file and like I said there are no travels inside the part but yet a ton of strings.  I tried printing outside to inside and inside to outside and both were poor.  I tried grid infill and line infill and both were poor also.  

Cura outer flare.3mf

Edited April 1 by newdeal99

[Slashee_the_Cow 268]

Holy %*#!ing @!^). I don't care how fast your PETG says it is, you should not be printing PETG this fast. With other materials (I don't have any high speed PETG, but I have high speed TPU) I find the "high speed" version prints better at the same speed as the regular version. For PETG, that's 50-60mm/s, tops.

 

*Turns on acceleration control to see what the defaults are*

*faints*

 

And I'm sorry, but this one is bugging me:

You couldn't get a rounder model? I've made a table with more faces than that... and it was supposed to be square. Also the seam between those two parts is so obvious, you can actually see it in the preview:

Also the seam at the rim:

Cue the preview:

That is going to look... sub-optimal.

 

Okay, back to the speeds: Slower. Much. As I said, 50-60mm/s tops, I don't care what the filament says it can do. And turn on acceleration control and lower that to like 1000mm/s², tops. I'd go 500 myself, but I'm overly cautious. Don't forget to lower the travel acceleration while you're at it. PETG is a much stringier material than PLA: if you're going too fast, it's inclined to hold onto the nozzle and be pulled along by it before it has time to dry. My printer (Ender-3 V3 SE) has a top acceleration of 2500mm/s² and I've seen it pull PLA with it as it zooms off, warping that whole section of the print, let alone PETG (and you don't wanna know what it's like with TPU).

 

I'm thinking that's what's happening here: you're not getting strings, you're getting bits of filament which are supposed to be part of the model being taken for a ride because they don't have time to dry.

 

A couple of other things, though these can be personal preference or depend on the filament:

• I print PETG at about 245°. You may (or may not) get better results by increasing the temperature. Especially at the speed you have it set to, you'd need it hotter just so it gets hot enough as it zooms through the hot end at a ridiculous flow rate. But even at a lower speed... I still print a little hotter than you. You could print a temp tower to test it.
• Is 25mm/s the fastest you can retract? That would help explain the need for coasting.
• You're using a lot of filament printing skin where it's angled like this:
  
  I'd change Top/Bottom > Bottom Layers and Initial Bottom Layers, lower the former and maybe set the latter a bit higher. The initial bottom layers are what's touching the plate.
• I don't envy your job getting that support interface off.

Edited April 2 by Slashee_the_Cow

[newdeal99 2]

thanks for the input I will look into all of this.  The speed I just copied over from the Anycubic slicer.  Seems to print ok at this speed but I can always turn it down via software or in the interface of the printer switch from standard to stable which seems to cut the speed considerably. Yes the support removal isn't easy for sure.  Seems to come off ok by putting a knife into the interface all the way around the edge.  The reason that the part is so messed up is because it is generated in code from tinkercad codeblocks.  This is the smoothest I can get it because I want to enter 3 parameters, the inside dimension of the hole, the outside dimension of the hole, and the radius of the curve and have it generate the shape.  Unfortunately in code blocks you can't get custom shapes only shapes from a preselected list so no HD torus only the regular low def torus which is why the outside of the flare has fewer sides.  To get this to be even this clean while still being under the number of shapes allowable (200) I am generating 180 spheres instead of 1 low def torus, rotating them in an arc, generating a ring to cut out the underside and some cylinders, holes etc and merging them all together.  Thats why the inside of the flare has better definition than the outside.  The way I can get it cleaner is to take the entire thing (except the holes in the mounting lip) and rotating it like 12 times by 1 degree and merging that together but code blocks can't handle that many items because even after they are merged each rotation thinks it is another 196 objects and not 1 merged object and so it exceeds the thousands of objects very quickly.  Those seams are all generated because the rings have 64 sides, the torus has only 24 sides, and the flare has like 180 sides so the corners can't line up but in the final print it really isn't bad.  I do wish that code blocks could allow me to make it cleaner because the seams go away if I rotate it multiple times by 1 degree each time and merge them together.  I can manually do it in tinkercad after exporting from code blocks but this is all just in the testing phase currently so doing that isn't worth the time.  I would really like to know how to get rid of that scalloped edge of the print that you pointed out.  I expect it is because of the geometry of the object.  I believe I have retraction in Prusa set to 2.5mm at 80mm/s.  I don't mind wasting filament because I need it to be pretty strong but I hate wasting filament on the supports which is why conical supports is nice.

Edited April 2 by newdeal99

[newdeal99 2]

I will mention that Prusa is printing this ok with the same speed settings as that

[Slashee_the_Cow 268]

If you could upload a Prusa project file (if they have those) and the gcode generated by Prusa I'd be interested to see what's in them.

[newdeal99 2]

yeah they do here is the file.  

Prusa Outer Flare.3mf

[gr5 2,176]

@newdeal99 - have you heard of openSCAD?  It's free and open source.  It's a programmatic way of making things from parameters. I like it quite a bit but can be tedious for complicated shapes.  For your shape it shouldn't be too bad.  You have "for" loops and all primitive shapes have variable number of faces so you definitely won't have the resolution issue. Like tinkercad you can add and subtract (and other binary options) shapes.  There are also free libraries for things like threads.

 

As a bonus, if you upload your scad file to thingiverse, thingiverse will let users fill in the parameters and thingiverse will create customized STL files on the fly for people and they don't even have to know how it works.

 

[Slashee_the_Cow 268]

3 minutes ago, gr5 said:

@newdeal99 - have you heard of openSCAD?  It's free and open source.  It's a programmatic way of making things from parameters. I like it quite a bit but can be tedious for complicated shapes.  For your shape it shouldn't be too bad.  You have "for" loops and all primitive shapes have variable number of faces so you definitely won't have the resolution issue

You wouldn't need to worry about for loops or anything with a model like that (except maybe the holes in the rim if you CBF doing it yourself). If you've never done any computer coding then it can be a little intimidating at first but it's not really that hard (although when there's a problem with the code, the errors aren't always as helpful as they could be.

 

But your model I could probably do with a combination of adding and subtracting just cylinders and a sphere or two.

 

Mandatory pedantry (most people, ignore this part): squares (which can be rectangles) and cubes (which can be rectangular prisms) are a fixed number of lines/faces.

[GregValiant 1,254]

Hi folks.  I thought I'd throw in my 2 cents since it definitely is a CAD thing.

 

That particular model is made up of 25 separate pieces and they don't appear to have been properly merged prior to export from CAD.  In fact, 23 of the pieces have no volume at all, just 1 or 2 faces.  That's 23 non-watertight entities in the model.  (They are more like single cell organisms than printable models.)  The only two parts that are relevant are the "bell" and the "cylinder".  They should be designed as a single piece but merging two parts is fine when it's done correctly.

 

If that model was a simple "Revolve" with 8 holes in the flange then all the model problems go away.

 

Which leads to a much better slice.

 

I print a lot of PETG and my normal print speed is 50.  If I want nice shiny outer walls I drop those to 35.  Just sayin'.

 

[newdeal99 2]

how did you make my primitive model into that nice smooth surface?  Like I said I am a newbie and want to just make a program so that I can make these in any size that I can print and my code does that and I can make it much nicer in regular tinkercad than I can in code blocks but then it doesn't generate itself.  Even with tinkercad it still isn't as smooth as what you show by any means

[jaysenodell 13]

I didn’t make that but if it were me using freecad…

 

create new body with new sketch in the YZ. Create profile with two arcs constrained by

inner arc- distance from axis on end points. 
outer arc- distance from inner arc. 

Close profile with lines constrained by endpoints of arcs. close sketch. Revolve sketch around Z axis. Select flange face. Create new sketch  Place hole centers constrained on equal distance and angle. Close sketch. Open hole tool. Select hole size, counter bore. 
 

select mesh work bench. convert body to mesh. Export mesh to STL. Import mesh to cura. 
 

I might have missed a step but I’m pretty sure that’s all of it. 

[GregValiant 1,254]

It could be done with a couple of cylinders and fillets as well.  The key is to have a model that is a single solid and to set TinkerCAD (or whatever) to the highest resolution you can for the output file.  Lower resolution means less triangles and surfaces but easier slicing and smaller file size.  Higher resolution is a model that more closely follows curves so less faceting and smoother prints.  Extremely high resolution models go beyond a printers ability and take forever to slice.

In AutoCAD the setting is "FacetRes".  Other software might have something similar.  You can edit a model in apps like MS 3D Builder and lower the resolution, but once the file is exported from CAD you cannot increase the resolution.

[newdeal99 2]

I know nothing about coding but I got it made in OpenSCAD with a small amount of messing around by making a 2d shape and then doing a rotational extrusion.  Really it isn't very many lines but I am not quite sure how to get the 8 holes into it yet.

[GregValiant 1,254]

If you can do a thing called a "polar array" you can make a cylinder the size of the hole you want, put it where you want, and then do a Polar Array of the cylinder with 8 items and the centerline of the part as the axis.  It would copy the cylinder equidistant around the center of the part.  Then, subtract all the cylinders from the main part.

[Slashee_the_Cow 268]

1 hour ago, newdeal99 said:

I know nothing about coding but I got it made in OpenSCAD with a small amount of messing around by making a 2d shape and then doing a rotational extrusion.  Really it isn't very many lines but I am not quite sure how to get the 8 holes into it yet.

You want to use something like:

difference(){
  union(){
    // everything you already have
  }
  for(angle = [0 : (360/8) : 7*(360/8)])
    rotate([0, 0, angle))
    	translate([0, distance_from_centre, 0])
            cylinder(r = cylinder_radius);
}

[Slashee_the_Cow 268]

2 minutes ago, GregValiant said:

If you can do a thing called a "polar array" you can make a cylinder the size of the hole you want, put it where you want, and then do a Polar Array of the cylinder with 8 items and the centerline of the part as the axis.  It would copy the cylinder equidistant around the center of the part.  Then, subtract all the cylinders from the main part.

No polar arrays. Vectors, but those can't contain shapes.

[newdeal99 2]

here we go all fixed up

 

 

outer flare openscad.stl

[GregValiant 1,254]

Yeah baby!!!  That's what I'm talkin' about.  Smooth, and it slices very nice.

[newdeal99 2]

thanks for the help guys, not sure it will print without stringing though on the Cura slicer still.  I did some playing around with pursa and changed my extrusion multiplier to 0.95, temp to 245 and fan to 100 and it seemed to help print even better.  I think maybe I had the temp low because the fan was low and having the fan low was a problem for picking up still too soft material on the way over it.  I also changed the minimum layer height to 0.2 from 0.3 it didn't really seem to effect the print time going to the larger layer it seemed, not sure why.  Maybe I should try those settings with Cura and see if it helps.

[GregValiant 1,254]

It's PETG so the strings are hard to get rid of.  Hotter print temp gives you better layer adhesion but a greater chance of stringing.

For this model...

Set the "Combing" to "All".

Set the Z-Seam location to wherever you want and then look at the "Z seam X" and "Z Seam Y" and make a note of them.

Go to the Travel Settings and make the "Layer Start X" and "Layer Start Y" the same as the Z seam locations.  You won't get as much travel through the center of the print.

 

If I have a screw connection I know that it will loosen over time from "cold flow deformation".  That plastic wants to flow away from the pressure exerted by the screws.  Those three cheesy walls around the screw hole are going to crush.

In the MarketPlace is a plugin for Cylindrical Support Shapes.

Here I've added one to a bolt hole in the flange.  It's 12mm dia by 3.2 tall.  The bottom is at 0.8 (resting on the bottom skins) and it ends at the first top skin.  It is set as an Infill Mesh with 8 walls.  It's an example of something you can do to make a model stronger in one area rather than filling something with infill.

I just eyeball them into the XY position.  It isn't like anyone will know they are there.  X-ray view helps.

 

[newdeal99 2]

I will have to look in to doing that for sure.  Unfortunately I started a print last night to test and still had a lot of stringing compared to Pursa slicer so I cancelled the print part way through.  I could take photos of the bit of the part that did print this time if that would be helpful.  I had also changed some defaults to be closer to what Prusa has (changed the flow to 95%, changed line width to 0.45, set the temp to 245 and fan to 100)

[gr5 2,176]

I'm so glad you were successful with openSCAD.  Now you can change one variable value to make it a different inner diameter or qty of holes or whatever.

 

 

[gr5 2,176]

If you ever choose to post this on thingiverse - this one screenshot shows you what comments to put around variables you want in the customizer and in the faint background on the left you can see what those comments generate:

https://cdn.thingiverse.com/assets/da/03/ff/97/ff/Screenshot-02.jpg