spencyg
Posts: 13
Joined: Sun Feb 01, 2015 7:05 am

Perimeter layer gaps, not connected

Tue Jul 07, 2015 9:14 am

I've been an S3D user for about 8 months now and have been generally happy with the program. I have been having an issue lately which I can't seem to find an answer to using the search function of this forum.

I've got perimeter layer gaps. The gaps aren't consistent around the perimeter and seem to be worse in curves. I have calibrated my extruder with thin wall cubes and am getting a consistent 0.50 wall thickness with a 0.50 extrusion width setting within S3D. The layers look good otherwise, but the individual perimeter shell layers (looking down at the part during the printing process) are often disconnected. It seems to greatly improve in straight line sections, and some curve sections are also fine. I'm sure there is a setting somewhere that I'm missing but I can't seem to remidy this problem. The issue seems to also be .STL file specific as some prints don't exhibit any problems while others are really bad. Any thoughts would be greatly appreciated.

Image

Image

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KeyboardWarrior
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Re: Perimeter layer gaps, not connected

Tue Jul 07, 2015 11:45 am

My thoughts would be to increase your Extrusion Multiplier. Pushing out a bit more plastic should close up a lot of these gaps and give a nice smoother looking surface.

spencyg
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Re: Perimeter layer gaps, not connected

Tue Jul 07, 2015 11:52 am

I've tried that with limited success. Everything I've read suggests that once you have the extruder laying down the exact width that is set within the line width setting in S3D than this should't happen. To start adding back material via the multiplier just leads to extruding a line that is wider than what S3D thinks it is laying down. Just as an FYI, the part printed in the posted images was at a 0.5mm line width and 0.2mm layer height. Nozzle diameter 0.4mm. Material is ABS. Hot end temp 220, bed temp 110. After I made this part I did some line width measurements and the 0.5mm line width setting was extruding a line that was 0.54mm. I've since tuned it back to be printing an exact 0.5mm line width and of course my gap problem is worse but the vertical wall layer consistency is very good. It seems like there should be a setting within S3D that allows some sort of perimeter line overlap percentage where you could squeeze the perimeter lines together without compromising your actual line width. I don't feel like I'm asking too much of the 3D printing process here....this is basic stuff.

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jimc
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Re: Perimeter layer gaps, not connected

Tue Jul 07, 2015 2:20 pm

there is an outline overlap setting in the advanced tab. this is when the printer needs to squeeze multiple extrusions into a narrower section. the real question is the model. if i had to guess i would say the wall width in the radius is ever so slightly wider so the lines are spaced out a little more. remember that in a mesh there are no circles. its just a series of flats so on a bend there is no real consistent width. when we are talking about these micro fine spaces between your layers like in the pic i would say the model width there is ever so slightly wider than the straight wall sections. if your multiplier is spot on then just increase your extrusion width .01 at a time. you should be able to tell just in the print preview if the extrusions get closer together.

spencyg
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Re: Perimeter layer gaps, not connected

Tue Jul 07, 2015 3:02 pm

I just tried using the outline overlap percentage setting on the infill tab. It doesn't appear to affect the perimeter shell at all, only the overlap between the inner most shell and the mating infill geometry. As I go wider on extrusion width the print preview window basically just shows the lines getting wider as a group, not getting closer together which is what I'm trying to have happen. It seems S3D doesn't allow tweaking of the overlap BETWEEN the mating shell lines. I come from a machining background and setting a tool overlap for each path is a critical component in CNC machining. I see it being as critical here as well.

JoeJ
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Re: Perimeter layer gaps, not connected

Tue Jul 07, 2015 6:28 pm

+1 on increasing extrusion multiplier. If you have gaps between your perimeter outlines, then you aren't extruding enough regardless of what you are measuring

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jimc
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Re: Perimeter layer gaps, not connected

Tue Jul 07, 2015 8:09 pm

yes when i look at the red print it looks like you are slightly underextruding. if it was my print the first thing i would have done is increase the multiplier. if you come from a machining background you have to remember that is a completely different process. you really want to avoid overlap. if you overlap then youll have too much plastic extruded for a given space then the nozzle will start to drag on the part and cause sloppy top layers and skipped steps. you just want the extrusions to touch which is all controlled by filament diameter and multiplier. you can widen the extrusion width on a print like the red one as well. if your extrusions are to spec and you have gaps in your corners then your extrusions arent wide enough to evenly fit "x" number of extrusions in that space so they have small gaps between. concerning the overlap setting. that only kicks in if the total of all the extrusion widths are too wide to fit in a given space. they are then allowed to overlap up to the percentage you have specified.

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dkightley
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Re: Perimeter layer gaps, not connected

Wed Jul 08, 2015 5:41 am

I'd also reduce the number of perimeter shells down to give the infill a little more wiggle-room. It looks as if you have it set at either 3 or 4 and at one point there's the the perimeter extrusions and not enough space between them for the infill to fit at least two extrusions...and allow the overlap processing to squeeze in sufficient extrusions to fill the gap.

You may also find that there's an air gap lower down in the model where there may not be any connecting structure. Reducing the perimeter shells would probably ensure there's internal connection between the inside and outside surfaces.
Doug Kightley
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Railway modeller and webmaster at http://www.talkingtgauge.net

MichaelHerron
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Re: Perimeter layer gaps, not connected

Wed Jul 08, 2015 3:41 pm

Most of these guys have been printing much longer than i, but if it were me, i would ease back on the extrusion width. If you have a .4mm nozzle and a .2mm layer height, keep your extrusion width at .4 and dial it in from there. I know it makes theoretical sense that since the extruder is orthogonal to the motion path, it shouldn't matter--the reality is that the plastic has viscosity and extruding over your nozzle width will always result in "pulling or squishing" effects which are difficult to control.

I would agree that the prints appear to be under-extruded and increasing your extrusion multiplier is an easy first step, but i would first decrease your extrusion width.

Looking more closely at your prints, you may just want to decrease your "Minimum Infill Length" to something very small. The hollow curves indicate that this may be your only problem. If you are getting separation between outlines or infill, then decrease extrusion width/increase multiplier. If curves are your only issue, then reduce this Minimum Infill Length.

Rebekah_harper
Posts: 263
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Re: Perimeter layer gaps, not connected

Wed Jul 08, 2015 6:45 pm

I would tend to agree.

2 perimeter shells. Width to 0.4. But I'd have 4 or 5 top layers. The bend looks like they aren't suported underneath.

Is this 100% infill?

My understanding is that the extrusion width dictates the paths it takes. Setting it lower but higher multiplier might also be the way forward.

It will work, just needs tweaking of the settings.

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