Combing Z Seam Issue

[demonsgalore 0]

I ran into some weird z seam issues ending with some kind of underextrusion at the z seam. After calibrating my Lin Advance I still had this issue wherever I was using cura. It seems like Combing mode no matter if changing to not in skin causes this issue. 

 

I'd like to understand what's going on with this setting and hopefully someone may explain me what's causing this.

 

Combing set to not in skin:

Combing off:

Edited April 17, 2022 by demonsgalore
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[mprenter 0]

I'd like to bump this topic.  I'm having the same issue with an Ender 5 Plus.  It's small gaps at the seam of a perimeter, but it's not a Z seam.  For my object, which is very similar in shape to yours, it draws the perimeters from inside to outside, then after completing the outer most perimeter, it crosses back to the middle to do the infill.  It's like there is coasting or something turned on, but it's not.  Very frustrating and I have not been able to figure out a solution.  Most people seem to have a bulge at the seam, I have a dip.

[GregValiant 1,250]

With a model loaded in Cura and with the settings configured to get that dimple - use the "File | Save Project" command and post the 3mf file here.  Working just with photos isn't easy.

[mprenter 0]

Thanks for your help!!  I switched to version 5 of Cura and the little gaps (seams) are still there, only the locations have changed.

CE5P_Hose Connector.3mf

[GregValiant 1,250]

Did you calibrate the E-steps on the printer?  Having to run at 117% Flow sticks out.  

 

The Outer Wall Wipe distance of .5 is a lot.  That move is typically around 1/4 to 1/2 of the line width.  The move is at travel speed (200mm/sec in your file) and is supposed to carry over residual nozzle pressure and clean up the Z-seam.

 

Looking at the starts and ends of your Outer Wall extrusions, they match up exactly.  The Wipe move then runs past the Outer Wall start point.  That should be smearing the Z-seam, but it isn't.

 

So back to flow.  If there is little to no residual pressure in the nozzle then no material comes out during the Wipe move and there is no smearing at the seam.

When the Flow is calibrated then the volume required for an extrusion is the volume of filament that the E number is calculated for.  100% Flow should be at {Volume-In = Required Volume-Out}.  That calculation will be correct provided that the actual real filament diameter is entered into Cura, and the E-steps are correct in the printer.

 

So Flow (E-steps), Outer Wall Wipe Distance, and Travel Speed look to be the parameters that are involved.

Lowering the wipe distance to .15 and lowering the travel speed to 120 reduces print time by 1 minute.  Increasing the Travel Acceleration to 1000 may also help (you might have to add a line "M201 X1000 Y1000" to your startup gcode to increase the printers Max Accel setting).

 

Finally, round objects are tough because there are no corners to hide in.

[mprenter 0]

Thanks so much for replying.  I REALLY appreciate the technical input.  Your "lack of pressure in the nozzle" theory would make complete sense with the symptoms I am seeing.  I went back to my eSteps and I'm getting some odd results.  How repeatable should the extrusion be?  I'm extruding 100mm with the bowden disconnected so I'm just extruding into thin air.  Sometimes I get 99mm, sometimes I get 100.6mm.

[GregValiant 1,250]

Yes, bowden disconnected and extruding into air is correct.  That +/-1% difference you are seeing is fine and about what you can expect from plastic that's being squished between a roller and a hard place.  Consider that at .2 layer height and .4 line width 100mm of filament is 3006mm's of extrusion.

With the E-steps calibrated you can drop the flow to 100%.  The first layer is more dependent on the leveling, but succeeding skins, and especially top skins, can tell much about the flow and if it needs to be tweaked in Cura.  If you have a magnifying glass you can take a close look at a top skin.  When the adjacent extrusions are welded together and there is no ridge at the weld joint then you are good to go.  Walls really aren't any good as a flow indicator because they always look kinda good unless the machine is way off.

[mprenter 0]

Boy I seem to have nothing but trouble.  So I tried putting some black marker on my extruder gear and tensioner and while watching them extrude found that the tension pully was slipping.  I tried tighting the tension but ended up installing my stock (plastic) Creality extruder tensioner again.  Then I calibrated my esteps again, also extruding into thin air.  I get exactly 100mm now when I extrude 100mm.  So next I printed a cube with only 1 perimeter.  My understanding is that I should now be getting "close" to a 0.4mm line width, but I'm not.  I'm getting like 0.52mm.  So I would have to reduce the flow to like 77% which still seems wrong.

Edited May 22, 2022 by mprenter
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[GregValiant 1,250]

Right now, without waiting, without passing GO, and without collecting $200 - throw that single wall constipation cube as far as you can.  It has nothing to do with anything.

Once you have your E-steps calibrated you are done.

 

When you enter the line width and layer height into Cura it is an easy calculation to figure out the volume of an extrusion.  LineWidth x LayerHeight x Length.

You have entered the exact filament diameter into Cura (or Cura will use the default 1.75mm diameter) and it is an easy calculation to determine the volume of a length of filament.  PI x r² x Length.

You may notice that neither formula says anything about wall thickness.  It's "What volume of plastic is needed" to "The volume of plastic that is pushed".  When that ratio is 1:1 then flow is 100%.

[mprenter 0]

Thanks for all your input.  I think I'm better off now.  Instead of a gap between perimeters I now get a bulge like everyone else.  Now I can see about trying to reduce that.  🙂  Feels a bit like I'm trading one problem for another.  Thanks again!!!

[GregValiant 1,250]

Take a regular old simple calibration cube and scale it to X=100 Y=50 and Z=1.0 and slice it at 100% flow for everything (except maybe the "Initial Layer Flow").  Also change the Top/Bottom line directions to [0,90].

As it prints you can tune the Flow on the LCD every 50 or 60 lines of extrusion and watch it closely to see how they go down.  Make sure to change the flow rate across the top surface.

When it's done, take a look at the top skin with a magnifying glass (a microscope is best).  You may see how your changes in the flow are reflected in how each extrusion abuts with it's neighbors on either side.  There will often be some over-extrusion at the beginning and/or end of each nozzle run.  That's generally a function of the acceleration setting.  Lower acceleration will create more of that "look" than higher acceleration settings do.  There is a point where print accuracy can fall off if the Accel is too high for the mechanicals of your printer at your print speed.

[demonsgalore 0]

You talking about underextrusion but I can tell that I actually have overextrusion with my e-steps calibrated to Polyterra PLA and still get those ugly Z-Srams whenever I turn on combing.

 

Can somebody help?

Edited June 15, 2022 by demonsgalore
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